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Sample records for characterizing fractured rock

  1. Site characterization in fractured crystalline rock

    International Nuclear Information System (INIS)

    This report concerns a study which is part of the SKI performance assessment project SITE-94. SITE-94 is a performance assessment of a hypothetical repository at a real site. The main objective of the project is to determine how site specific data should be assimilated into the performance assessment process and to evaluate how uncertainties inherent in site characterization will influence performance assessment results. Other important elements of SITE-94 are the development of a practical and defensible methodology for defining, constructing and analyzing scenarios, the development of approaches for treatment of uncertainties, evaluation of canister integrity, and the development and application of an appropriate Quality Assurance plan for Performance Assessments. (111 refs.)

  2. Analog site for fractured rock characterization. Annual report FY 1995

    Energy Technology Data Exchange (ETDEWEB)

    Long, J.C.S.; Loughty, C.; Faybishenko, B. [and others

    1995-10-01

    This report describes the accomplishments of the Analog Site for Fracture Rock Characterization Project during fiscal year 1995. This project is designed to address the problem of characterizing contaminated fractured rock. In order to locate contaminant plumes, develop monitoring schemes, and predict future fate and transport, the project will address the following questions: What parts of the system control flow-geometry of a fracture network? What physical processes control flow and transport? What are the limits on measurements to determine the above? What instrumentation should be used? How should it be designed and implemented? How can field tests be designed to provide information for predicting behavior? What numerical models are good predictors of the behavior of the system? The answers to these question can be used to help plan drilling programs that are likely to intersect plumes and provide effective monitoring of plume movement. The work is done at an {open_quotes}analogue{close_quotes} site, i.e., a site that is not contaminated, but has similar geology to sites that are contaminated, in order to develop tools and techniques without the financial, time and legal burdens of a contaminated site. The idea is to develop conceptual models and investigations tools and methodology that will apply to the contaminated sites in the same geologic regimes. The Box Canyon site, chosen for most of this work represents a unique opportunity because the Canyon walls allow us to see a vertical plane through the rock. The work represents a collaboration between the Lawrence Berkeley National Laboratory (LBL), Stanford University (Stanford), Idaho National Engineering Laboratory (INEL) and Parsons Environmental Engineering (Parsons). LBL and Stanford bring extensive experience in research in fractured rock systems. INEL and Parsons bring significant experience with the contamination problem at INEL.

  3. Analog site for fractured rock characterization. Annual report FY 1995

    International Nuclear Information System (INIS)

    This report describes the accomplishments of the Analog Site for Fracture Rock Characterization Project during fiscal year 1995. This project is designed to address the problem of characterizing contaminated fractured rock. In order to locate contaminant plumes, develop monitoring schemes, and predict future fate and transport, the project will address the following questions: What parts of the system control flow-geometry of a fracture network? What physical processes control flow and transport? What are the limits on measurements to determine the above? What instrumentation should be used? How should it be designed and implemented? How can field tests be designed to provide information for predicting behavior? What numerical models are good predictors of the behavior of the system? The answers to these question can be used to help plan drilling programs that are likely to intersect plumes and provide effective monitoring of plume movement. The work is done at an open-quotes analogueclose quotes site, i.e., a site that is not contaminated, but has similar geology to sites that are contaminated, in order to develop tools and techniques without the financial, time and legal burdens of a contaminated site. The idea is to develop conceptual models and investigations tools and methodology that will apply to the contaminated sites in the same geologic regimes. The Box Canyon site, chosen for most of this work represents a unique opportunity because the Canyon walls allow us to see a vertical plane through the rock. The work represents a collaboration between the Lawrence Berkeley National Laboratory (LBL), Stanford University (Stanford), Idaho National Engineering Laboratory (INEL) and Parsons Environmental Engineering (Parsons). LBL and Stanford bring extensive experience in research in fractured rock systems. INEL and Parsons bring significant experience with the contamination problem at INEL

  4. Characterizing and Modelling Preferential Flow Path in Fractured Rock Aquifer: A Case Study at Shuangliou Fractured Rock Hydrogeology Research Site

    Science.gov (United States)

    Hsu, Shih-Meng; Ke, Chien-Chung; Lo, Hung-Chieh; Lin, Yen-Tsu; Huang, Chi-Chao

    2016-04-01

    On the basis of a relatively sparse data set, fractured aquifers are difficult to be characterized and modelled. The three-dimensional configuration of transmissive fractures and fracture zones is needed to be understood flow heterogeneity in the aquifer. Innovative technologies for the improved interpretation are necessary to facilitate the development of accurate predictive models of ground-water flow and solute transport or to precisely estimate groundwater potential. To this end, this paper presents a procedure for characterizing and modelling preferential flow path in the fractured rock aquifer carried out at Fractured Rock Hydrogeology Research Site in Shuangliou Forest Recreation Area, Pingtung County, Southern Taiwan. The Shuangliou well field is a 40 by 30-meter area consisting of 6 wells (one geological well, one pumping well and four hydrogeological testing wells). The bedrock at the site is mainly composed of slate and intercalated by meta-sandstone. The overburden consists of about 5.6 m of gravel deposits. Based on results of 100 m geological borehole with borehole televiewer logging, vertical flow logging and full-wave sonic logging, high transmissivity zones in the bedrock underlying the well field were identified. One of transmissivity zone (at the depths of 30~32 m) and its fracture orientation(N56/54) selected for devising a multiple well system with 4 boreholes (borehole depths :45m, 35m, 35m and 25m, respectively), which were utilized to perform cross-borehole flow velocity data under the ambient flow and pumped flow conditions to identify preferential flow paths. Results from the cross-borehole test show the preferential flow pathways are corresponding to the predicted ones. Subsequently, a 3-D discrete fracture network model based on outcrop data was generated by the FracMan code. A validation between observed and simulated data has proved that the present model can accurately predict the hydrogeological properties (e.g., number of fractures

  5. MULTI-ATTRIBUTE SEISMIC/ROCK PHYSICS APPROACH TO CHARACTERIZING FRACTURED RESERVOIRS

    Energy Technology Data Exchange (ETDEWEB)

    Gary Mavko

    2000-10-01

    This project consists of three key interrelated Phases, each focusing on the central issue of imaging and quantifying fractured reservoirs, through improved integration of the principles of rock physics, geology, and seismic wave propagation. This report summarizes the results of Phase I of the project. The key to successful development of low permeability reservoirs lies in reliably characterizing fractures. Fractures play a crucial role in controlling almost all of the fluid transport in tight reservoirs. Current seismic methods to characterize fractures depend on various anisotropic wave propagation signatures that can arise from aligned fractures. We are pursuing an integrated study that relates to high-resolution seismic images of natural fractures to the rock parameters that control the storage and mobility of fluids. Our goal is to go beyond the current state-of-the art to develop and demonstrate next generation methodologies for detecting and quantitatively characterizing fracture zones using seismic measurements. Our study incorporates 3 key elements: (1) Theoretical rock physics studies of the anisotropic viscoelastic signatures of fractured rocks, including up scaling analysis and rock-fluid interactions to define the factors relating fractures in the lab and in the field. (2) Modeling of optimal seismic attributes, including offset and azimuth dependence of travel time, amplitude, impedance and spectral signatures of anisotropic fractured rocks. We will quantify the information content of combinations of seismic attributes, and the impact of multi-attribute analyses in reducing uncertainty in fracture interpretations. (3) Integration and interpretation of seismic, well log, and laboratory data, incorporating field geologic fracture characterization and the theoretical results of items 1 and 2 above. The focal point for this project is the demonstration of these methodologies in the Marathon Oil Company Yates Field in West Texas.

  6. Characterizing Fractured Rock with Geo-structural and Micro-structural Models

    Science.gov (United States)

    Dershowitz, William

    2015-04-01

    Fracture spatial structure and hydro-mechanical properties are key to the understanding of fractured rock geomechanical stability, hydrodynamics, and solute transport. This paper presents a quantitative approach to fracture characterization to provide information useful for stability and flow analysis, and for coupled flow/geomechanics. The approach presented is based on the concept of geo-structural, hydro-mechanical, and microstructural models. This approach is applicable for data collected from exposed surfaces (mapping, LiDAR, aero-magnetics), boreholes (core, optical images, and images based on resistivity and geophysical methods), and three dimensional imaging (seismic attributes and microseismics). Examples are presented comparing the results of conventional fracture characterization procedures and the recommended procedure. Fracture characterization for geo-structural fracture models is based on the idea that the geologically based fracture spatial pattern is the key, rather than individual fracture statistics. For example, while fracture intensity statistics can useful, the three dimensional fracture pattern for a bedded sedimentary rock can be better reproduced from the combination of a mechanical bedding model and a correlation between fracture spacing and bed height. In a fracture geo-structural model, the fracture spatial pattern, orientation, and intensity should be characterized in a combination of global and local coordinate systems. While some fracture sets may be oriented relative to the regional tectonics (the global coordinate system), other fracture sets are oriented relative to bedding (a local coordinate system). Fracture hydro-mechanical models define the combination of (a) conductive fractures, (b) flow-barrier fractures, (c) fractures which provide storage porosity, (d) fractures of significance for kinematic stability, and (e) fractures of significance for rock mass strength and deformability. The hydromechanical fractures are a subset of

  7. A new device for characterizing fracture networks and measuring groundwater and contaminant fluxes in fractured rock aquifers

    Science.gov (United States)

    Klammler, Harald; Hatfield, Kirk; Newman, Mark A.; Cho, Jaehyun; Annable, Michael D.; Parker, Beth L.; Cherry, John A.; Perminova, Irina

    2016-07-01

    This paper presents the fundamental theory and laboratory test results on a new device that is deployed in boreholes in fractured rock aquifers to characterize vertical distributions of water and contaminant fluxes, aquifer hydraulic properties, and fracture network properties (e.g., active fracture density and orientation). The device, a fractured rock passive flux meter (FRPFM), consists of an inflatable core assembled with upper and lower packers that isolate the zone of interest from vertical gradients within the borehole. The outer layer of the core consists of an elastic fabric mesh equilibrated with a visible dye which is used to provide visual indications of active fractures and measures of fracture location, orientation, groundwater flux, and the direction of that flux. Beneath the outer layer is a permeable sorbent that is preloaded with known amounts of water soluble tracers which are eluted at rates proportional to groundwater flow. This sorbent also captures target contaminants present in intercepted groundwater. The mass of contaminant sorbed is used to quantify cumulative contaminant flux; whereas, the mass fractions of resident tracers lost are used to provide measures of water flux. In this paper, the FRPFM is bench tested over a range of fracture velocities (2-20 m/day) using a single fracture flow apparatus (fracture aperture = 0.5 mm). Test results show a discoloration in visible dye corresponding to the location of the active fracture. The geometry of the discoloration can be used to discern fracture orientation as well as direction and magnitude of flow in the fracture. Average contaminant fluxes were measured within 16% and water fluxes within 25% of known imposed fluxes.

  8. Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Gary Mavko

    2004-11-30

    Most current seismic methods to seismically characterize fractures in tight reservoirs depend on a few anisotropic wave propagation signatures that can arise from aligned fractures. While seismic anisotropy can be a powerful fracture diagnostic, a number of situations can lessen its usefulness or introduce interpretation ambiguities. Fortunately, laboratory and theoretical work in rock physics indicates that a much broader spectrum of fracture seismic signatures can occur, including a decrease in P- and S-wave velocities, a change in Poisson's ratio, an increase in velocity dispersion and wave attenuation, as well as well as indirect images of structural features that can control fracture occurrence. The goal of this project was to demonstrate a practical interpretation and integration strategy for detecting and characterizing natural fractures in rocks. The approach was to exploit as many sources of information as possible, and to use the principles of rock physics as the link among seismic, geologic, and log data. Since no single seismic attribute is a reliable fracture indicator in all situations, the focus was to develop a quantitative scheme for integrating the diverse sources of information. The integrated study incorporated three key elements: The first element was establishing prior constraints on fracture occurrence, based on laboratory data, previous field observations, and geologic patterns of fracturing. The geologic aspects include analysis of the stratigraphic, structural, and tectonic environments of the field sites. Field observations and geomechanical analysis indicates that fractures tend to occur in the more brittle facies, for example, in tight sands and carbonates. In contrast, strain in shale is more likely to be accommodated by ductile flow. Hence, prior knowledge of bed thickness and facies architecture, calibrated to outcrops, are powerful constraints on the interpreted fracture distribution. Another important constraint is that

  9. Advanced Characterization of Fractured Reservoirs in Carbonate Rocks: The Michigan Basin

    Energy Technology Data Exchange (ETDEWEB)

    Wood, James R.; Harrison, William B.

    2000-10-24

    The main objective of this project is for a university-industry consortium to develop a comprehensive model for fracture carbonate reservoirs based on the ''data cube'' concept using the Michigan Basin as a prototype. This project combined traditional historical data with 2D and 3D seismic data as well as data from modern logging tools in a novel way to produce a new methodology for characterizing fractured reservoirs in carbonate rocks. Advanced visualization software was used to fuse the data and to image it on a variety of scales, ranging from basin-scale to well-scales.

  10. Nano-iron Tracer Test for Characterizing Preferential Flow Path in Fractured Rock

    Science.gov (United States)

    Chia, Y.; Chuang, P. Y.

    2015-12-01

    Deterministic description of the discrete features interpreted from site characterization is desirable for developing a discrete fracture network conceptual model. It is often difficult, however, to delineate preferential flow path through a network of discrete fractures in the field. A preliminary cross-borehole nano-iron tracer test was conducted to characterize the preferential flow path in fractured shale bedrock at a hydrogeological research station. Prior to the test, heat-pulse flowmeter measurements were performed to detect permeable fracture zones at both the injection well and the observation well. While a few fracture zones are found permeable, most are not really permeable. Chemical reduction method was used to synthesize nano zero-valent iron particles with a diameter of 50~150 nm. The conductivity of nano-iron solution is about 3100 μs/cm. The recorded fluid conductivity shows the arrival of nano-iron solution in the observation well 11.5 minutes after it was released from the injection well. The magnetism of zero-valent iron enables it to be absorbed on magnet array designed to locate the depth of incoming tracer. We found nearly all of absorbed iron on the magnet array in the observation well were distributed near the most permeable fracture zone. The test results revealed a preferential flow path through a permeable fracture zone between the injection well and the observation well. The estimated hydraulic conductivity of the connected fracture is 2.2 × 10-3 m/s. This preliminary study indicated that nano-iron tracer test has the potential to characterize preferential flow path in fractured rock.

  11. Using radar tomography, tracer experiments and hydraulic data to characterize fractured rock flow systems

    Science.gov (United States)

    Day-Lewis, Frederick David

    Among the most pressing problems in hydrogeology is describing heterogeneity in fractured rock, where data are typically local and sparse, and permeability varies by orders of magnitude over short distances. This dissertation presents new approaches to characterize fractured rock groundwater flow systems using cross-well radar, tracer, and hydraulic experiments. The methods are demonstrated using data from the U.S. Geological Survey Fractured Rock Hydrology Research Site near Mirror Lake, New Hampshire. One underutilized source of information in characterization of fractured rock is hydraulic connection data. Wells connected by a high-permeability fracture zone tend to exhibit similar hydraulic responses during pumping or drilling. A simulated-annealing algorithm is presented to condition geostatistical simulations to inferred connections. The method is used to generate 3-D realizations of fracture-zone geometry at the Mirror Lake Site. Results indicate the likely extents of specific zones. Flow models based on realizations are calibrated to hydraulic data to estimate the hydraulic parameters of the fracture zones and surrounding bedrock. Another innovative source of information for characterization is time-lapse difference-attenuation radar tomography, which has been used to monitor the migration of electrically conductive saline tracers. A sequential-inversion methodology is presented and demonstrated for a synthetic example. The method uses space-time parameterization and regularization to account for changes in concentration that occur quickly relative to the collection of radar data. The time-lapse tomographic inversion method is applied to data from the Mirror Lake Site. Difference-attenuation tomography indicates the timing and spatial distribution of tracer transport in three planes that form a triangular prism. Tracer migration is focused along a preferential pathway. Comparison of the time-series of tomograms with the outlet tracer data suggests that much

  12. Innovations in the characterization of fractured rocks developed within the Stripa project

    International Nuclear Information System (INIS)

    This text deals with the hydrogeological work that has been carried out at Stripa Mine. First of all, the philosophy applied evolved through the years, and has finally been focused on a fractured rock approach. Second, it has been necessary to develop hydraulic testing methods - such as focused packer testing - and equipment; the key of the success of the equipment that was built, was that it was fully computer controlled and able to regulate water pressures quickly, reliably and accurately. In the end, the aim of the hydrogeological testing was to characterize both the small scale fracture network and the large scale major fracture zone which composed the site. (TEC). 13 refs., 5 figs

  13. Hydrogeloogic characterization of fractured rock formations: A guide for groundwater remediators

    International Nuclear Information System (INIS)

    A field site was developed in the foothills of the Sierra Nevada, California to develop and test a multi-disciplinary approach to the characterization of ground water flow and transport in fractured rocks. Nine boreholes were drilled into the granitic bedrock, and a wide variety of new and traditional subsurface characterization tools were implemented. The hydrogeologic structure and properties of the field site were deduced by integrating results from the various geologic, geophysical, hydrologic, and other investigative methods. The findings of this work are synthesized into this report, which is structured in a guidebook format. The applications of the new and traditional technologies, suggestions on how best to use, integrate, and analyze field data, and comparisons of the shortcoming and benefits of the different methods are presented

  14. Hydrogeloogic characterization of fractured rock formations: A guide for groundwater remediators

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, A.J.B.

    1995-10-01

    A field site was developed in the foothills of the Sierra Nevada, California to develop and test a multi-disciplinary approach to the characterization of ground water flow and transport in fractured rocks. Nine boreholes were drilled into the granitic bedrock, and a wide variety of new and traditional subsurface characterization tools were implemented. The hydrogeologic structure and properties of the field site were deduced by integrating results from the various geologic, geophysical, hydrologic, and other investigative methods. The findings of this work are synthesized into this report, which is structured in a guidebook format. The applications of the new and traditional technologies, suggestions on how best to use, integrate, and analyze field data, and comparisons of the shortcoming and benefits of the different methods are presented.

  15. Ssismic Methodologies Applied To The Characterization Of Fractured Rock Massifs: Case Studies

    Science.gov (United States)

    Marti, D.; Carbonell, R.; Flecha, I.; Palomeras, I.; Font-Capo, J.; Vazquez-Sune, E.; Perez-Estaun, A.

    2007-05-01

    The detailed characterization of fractured media in the shallow subsurface is becoming important. The detailed knowledge of the fracture network is mandatory in any hydrogeological model to constrain the potential pathways for water circulation. The geophysical methodolgies can provide a detailed image of the fractured rock and also the 3D distribution of physical properties. Two case studies are discussed in this work. The characterization of fractures in a waste disposal site and, the design and construction of a subway tunnel. In the first case, a multiseismic experiment was carried out in an old abandoned uranium mine. 2D and 3D seismic experiments including VSP, surface seismic reflection and travel time seismic tomography provided a 3D image of the internal structure of a granitic massif for hydrogeological studies of the preferred paths for the migration of contaminants. The tectonic stability of the site was also addressed by means of seismic measurements. The joint interpretation of all the available data enabled the interpretation of the low velocity anomalies in the 3D seismic tomography image as the fragile fractures and the alteration associated to them. A 3D image of the geometry of the heterogeneous weathered surface layer was also obtained. This surface is controlled by the complex network of faults and dykes observed in the area. The second case study involves 2D and 3D seismic experiments to aid the horizontal drilling of tunnels for a new subway line in Barcelona (Spain). Seismic data acquisition in a densely populated city is very difficult. The street layout determines the geometry of the acquisition experiments. The instrumentation can not always be located on the surface projection of the tunnel trace, therefore, pseudo 3D acquisition is required, deploying the instrumentation were it is possible. Furthermore, the shallow subsurface features extremely heterogeneous "weathered" layer of variable thickness (building fundations, sewage system

  16. Characterization of preferential flow paths between boreholes in fractured rock using a nanoscale zero-valent iron tracer test

    Science.gov (United States)

    Chuang, Po-Yu; Chia, Yeeping; Liou, Ya-Hsuan; Teng, Mao-Hua; Liu, Ching-Yi; Lee, Tsai-Ping

    2016-05-01

    Recent advances in borehole geophysical techniques have improved characterization of cross-hole fracture flow. The direct detection of preferential flow paths in fractured rock, however, remains to be resolved. In this study, a novel approach using nanoscale zero-valent iron (nZVI or `nano-iron') as a tracer was developed for detecting fracture flow paths directly. Generally, only a few rock fractures are permeable while most are much less permeable. A heat-pulse flowmeter can be used to detect changes in flow velocity for delineating permeable fracture zones in the borehole and providing the design basis for the tracer test. When nano-iron particles are released in an injection well, they can migrate through the connecting permeable fracture and be attracted to a magnet array when arriving in an observation well. Such an attraction of incoming iron nanoparticles by the magnet can provide quantitative information for locating the position of the tracer inlet. A series of field experiments were conducted in two wells in fractured rock at a hydrogeological research station in Taiwan, to test the cross-hole migration of the nano-iron tracer through permeable connected fractures. The fluid conductivity recorded in the observation well confirmed the arrival of the injected nano-iron slurry. All of the iron nanoparticles attracted to the magnet array in the observation well were found at the depth of a permeable fracture zone delineated by the flowmeter. This study has demonstrated that integrating the nano-iron tracer test with flowmeter measurement has the potential to characterize preferential flow paths in fractured rock.

  17. Sealing of fractured rock

    International Nuclear Information System (INIS)

    This paper consists of a presentation of the third phase of the Stripa Project. This phase was dedicated to fracture sealing. First of all it has been necessary to show that fine-grained grouts could effectively be injected in relatively fine cracks, and that the fluidity of bentonite could also be enhanced. The field tests comprised investigation of excavation-induced disturbance and attempts to seal disturbed rock, and, in separate tests, grouting of deposition holes and a natural fine-fracture zone. (TEC). 12 figs., 1 tab., 6 refs

  18. Fracture characteristics in Japanese rock

    International Nuclear Information System (INIS)

    It is crucial for the performance assessment of geosphere to evaluate the characteristics of fractures that can be dominant radionuclide migration pathways from a repository to biosphere. This report summarizes the characteristics of fractures obtained from broad literature surveys and the fields surveys at the Kamaishi mine in northern Japan and at outcrops and galleries throughout the country. The characteristics of fractures described in this report are fracture orientation, fracture shape, fracture frequency, fracture distribution in space, transmissivity of fracture, fracture aperture, fracture fillings, alteration halo along fracture, flow-wetted surface area in fracture, and the correlation among these characteristics. Since granitic rock is considered the archetype fractured media, a large amount of fracture data is available in literature. In addition, granitic rock has been treated as a potential host rock in many overseas programs, and has JNC performed a number of field observations and experiments in granodiorite at the Kamaishi mine. Therefore, the characteristics of fractures in granitic rock are qualitatively and quantitatively clarified to some extent in this report, while the characteristics of fractures in another rock types are not clarified. (author)

  19. Characterizing fractured plutonic rocks of the Canadian shield for deep geological disposal of Canada`s radioactive wastes

    Energy Technology Data Exchange (ETDEWEB)

    Lodha, G.S.; Davison, C.C.; Gascoyne, M. [Atomic Energy of Canada Ltd. , Pinawa, MB (Canada). Whiteshell Labs.

    1998-09-01

    Since 1978 AECL has been investigating plutonic rocks of the Canadian Shield as a potential medium for the disposal of Canada`s nuclear fuel waste. During the last two years this study has been continued as part of Ontario Hydro`s used fuel disposal program. Methods have been developed for characterizing the geotechnical conditions at the regional scale of the Canadian Shield as well as for characterizing conditions at the site scale and the very near-field scale needed for locating and designing disposal vault rooms and waste emplacement areas. The Whiteshell Research Area (WRA) and the Underground Research Laboratory (URL) in southeastern Manitoba have been extensively used to develop and demonstrate the different scales of characterization methods. At the regional scale, airborne magnetic and electromagnetic surveys combined with LANDSAT 5 and surface gravity survey data have been helpful in identifying boundaries of the plutonic rocks , overburden thicknesses, major lineaments that might be geological structures, lithological contacts and depths of the batholiths. Surface geological mapping of exposed rock outcrops, combined with surface VLF/EM, radar and seismic reflection surveys were useful in identifying the orientation and depth continuity of low-dipping fracture zones beneath rock outcrops to a depth of 500 to 1000 m. The surface time-domain EM method has provided encouraging results for identifying the depth of highly saline pore waters. The regional site scale investigations at the WRA included the drilling of twenty deep boreholes (> 500 m) at seven separate study areas. Geological core logging combined with borehole geophysical logging, TV/ATV logging, flowmeter logging and full waveform sonic logging in these boreholes helped to confirm the location of hydro geologically important fractures, orient cores and infer the relative permeability of some fracture zones. Single-hole radar and crosshole seismic tomography surveys were useful to establish the

  20. Hydraulic conductivity of rock fractures

    International Nuclear Information System (INIS)

    Yucca Mountain, Nevada contains numerous geological units that are highly fractured. A clear understanding of the hydraulic conductivity of fractures has been identified as an important scientific problem that must be addressed during the site characterization process. The problem of the flow of a single-phase fluid through a rough-walled rock fracture is discussed within the context of rigorous fluid mechanics. The derivation of the cubic law is given as the solution to the Navier-Stokes equations for flow between smooth, parallel plates, the only fracture geometry that is amenable to exact treatment. The various geometric and kinetic conditions that are necessary in order for the Navier-Stokes equations to be replaced by the more tractable lubrication or Hele-Shaw equations are studied and quantified. Various analytical and numerical results are reviewed pertaining to the problem of relating the effective hydraulic aperture to the statistics of the aperture distribution. These studies all lead to the conclusion that the effective hydraulic aperture is always less than the mean aperture, by a factor that depends on the ratio of the mean value of the aperture to its standard deviation. The tortuosity effect caused by regions where the rock walls are in contact with each other is studied using the Hele-Shaw equations, leading to a simple correction factor that depends on the area fraction occupied by the contact regions. Finally, the predicted hydraulic apertures are compared to measured values for eight data sets from the literature for which aperture and conductivity data were available on the same fracture. It is found that reasonably accurate predictions of hydraulic conductivity can be made based solely on the first two moments of the aperture distribution function, and the proportion of contact area. 68 refs

  1. Relative Permeability of Fractured Rock

    Energy Technology Data Exchange (ETDEWEB)

    Mark D. Habana

    2002-06-30

    Contemporary understanding of multiphase flow through fractures is limited. Different studies using synthetic fractures and various fluids have yielded different relative permeability-saturation relations. This study aimed to extend the understanding of multiphase flow by conducting nitrogen-water relative permeability experiments on a naturally-fractured rock from The Geysers geothermal field. The steady-state approach was used. However, steady state was achieved only at the endpoint saturations. Several difficulties were encountered that are attributed to phase interference and changes in fracture aperture and surface roughness, along with fracture propagation/initiation. Absolute permeabilities were determined using nitrogen and water. The permeability values obtained change with the number of load cycles. Determining the absolute permeability of a core is especially important in a fractured rock. The rock may change as asperities are destroyed and fractures propagate or st rain harden as the net stresses vary. Pressure spikes occurred in water a solute permeability experiments. Conceptual models of an elastic fracture network can explain the pressure spike behavior. At the endpoint saturations the water relative permeabilities obtained are much less than the nitrogen gas relative permeabilities. Saturations were determined by weighing and by resistivity calculations. The resistivity-saturation relationship developed for the core gave saturation values that differ by 5% from the value determined by weighing. Further work is required to complete the relative permeability curve. The steady-state experimental approach encountered difficulties due to phase interference and fracture change. Steady state may not be reached until an impractical length of time. Thus, unsteady-state methods should be pursued. In unsteady-state experiments the challenge will be in quantifying rock fracture change in addition to fluid flow changes.

  2. Characterization and evaluation of sites for deep geological disposal of radioactive waste in fractured rocks. Proceedings

    International Nuclear Information System (INIS)

    The third Aespoe International Seminar was organised by SKB to assess the state of the art in characterisation and evaluation of sites for deep geological disposal of radioactive waste in fractured rocks. Site characterisation and evaluation are important elements for determining the site suitability and long-term safety of a geological repository for radioactive waste disposal. Characterisation work also provides vital information for the design of the underground facility and the engineered barrier system that will contain the waste. The aim of the seminar was to provide a comprehensive assessment of the current know-how on this topic based on world-wide experience from more than 20 years of characterisation and evaluation work. The seminar, which was held at the Aespoe Hard Rock Laboratory was attended by 72 scientists from 10 different countries. The program was divided into four sessions of which two were run in parallel. A total of 38 oral and 5 poster presentations were given at the seminar. The presentations gave a comprehensive summary of recently completed and current work on site characterisation, modelling and application in performance assessments. The results presented at the seminar generally show that significant progress has been made in this field during the last decade. New characterisation techniques have become available, strategies for site investigations have developed further, and model concepts and codes have reached new levels of refinement. Data obtained from site characterisation have also successfully been applied in several site specific performance assessments. The seminar clearly showed that there is a solid scientific basis for assessing the suitability of sites for actual repositories based on currently available site characterisation technology and modelling capabilities. Separate abstracts have been prepared for 38 of the presentations

  3. Characterization and evaluation of sites for deep geological disposal of radioactive waste in fractured rocks. Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-09-01

    The third Aespoe International Seminar was organised by SKB to assess the state of the art in characterisation and evaluation of sites for deep geological disposal of radioactive waste in fractured rocks. Site characterisation and evaluation are important elements for determining the site suitability and long-term safety of a geological repository for radioactive waste disposal. Characterisation work also provides vital information for the design of the underground facility and the engineered barrier system that will contain the waste. The aim of the seminar was to provide a comprehensive assessment of the current know-how on this topic based on world-wide experience from more than 20 years of characterisation and evaluation work. The seminar, which was held at the Aespoe Hard Rock Laboratory was attended by 72 scientists from 10 different countries. The program was divided into four sessions of which two were run in parallel. A total of 38 oral and 5 poster presentations were given at the seminar. The presentations gave a comprehensive summary of recently completed and current work on site characterisation, modelling and application in performance assessments. The results presented at the seminar generally show that significant progress has been made in this field during the last decade. New characterisation techniques have become available, strategies for site investigations have developed further, and model concepts and codes have reached new levels of refinement. Data obtained from site characterisation have also successfully been applied in several site specific performance assessments. The seminar clearly showed that there is a solid scientific basis for assessing the suitability of sites for actual repositories based on currently available site characterisation technology and modelling capabilities. Separate abstracts have been prepared for 38 of the presentations

  4. Characterization of fractures and flow zones in a contaminated crystalline-rock aquifer in the Tylerville section of Haddam, Connecticut

    Science.gov (United States)

    Johnson, Carole D.; Kiel, Kristal F.; Joesten, Peter K.; Pappas, Katherine L.

    2016-10-04

    The U.S. Geological Survey, in cooperation with the Connecticut Department of Energy and Environmental Protection, investigated the characteristics of the bedrock aquifer in the Tylerville section of Haddam, Connecticut, from June to August 2014. As part of this investigation, geophysical logs were collected from six water-supply wells and were analyzed to (1) identify well construction, (2) determine the rock type and orientation of the foliation and layering of the rock, (3) characterize the depth and orientation of fractures, (4) evaluate fluid properties of the water in the well, and (5) determine the relative transmissivity and head of discrete fractures or fracture zones. The logs included the following: caliper, electromagnetic induction, gamma, acoustic and (or) optical televiewer, heat-pulse flowmeter under ambient and pumped conditions, hydraulic head data, fluid electrical conductivity and temperature under postpumping conditions, and borehole-radar reflection collected in single-hole mode. In a seventh borehole, a former water-supply well, only caliper, fluid electrical conductivty, and temperature logs were collected, because of a constriction in the borehole.This report includes a description of the methods used to collect and process the borehole geophysical data, the description of the data collected in each of the wells, and a comparison of the results collected in all of the wells. The data are presented in plots of the borehole geophysical logs, tables, and figures. Collectively these data provide valuable characterizations that can be used to improve or inform site conceptual models of groundwater flow in the study area.

  5. Sealing of rock fractures

    International Nuclear Information System (INIS)

    The major water-bearing fractures in granite usually from fairly regular sets but the extension and degree of connectivity is varying. This means that only a few fractures that are interconnected with the deposition holes and larger water-bearing structures in a HLW repository are expected and if they can be identified and cut off through sealing it would be possible to improve the isolation of waste packages very effectively. Nature's own fracture sealing mechanisms may be simulated and a survey of the involved processes actually suggests a number of possible filling methods and substances. Most of them require high temperature and pressure and correspondingly sophisticated techniques, but some are of potential interest for immediate application with rather moderate effort. Such a technique is to fill the fractures with clayey substances which stay flexible and low-permeable provided that they remain physically and chemically intact. It is demonstrated in the report that effective grouting requires a very low viscosity and shear strength of the substance and this can be achieved by mechanical agitation as demonstrated in this report. Thus, by superimposing static pressure and shear waves induced by percussion hammering at a suitable frequency, clays and fine-grained silts as well as cement can be driven into fractures with an average aperture as small as 0.1 mm. Experiments were made in the laboratory using concrete and steel plates, and a field pilot test was also conducted under realistic conditions on site in Stripa. They all demonstrated the practicality of the 'dynamic injection technique' and that the fluid condition of the grouts yielded complete filling of the injected space to a considerable distance from the injection point. The field test indicated a good sealing ability as well as a surprisingly high resistance to erosion and piping. (author)

  6. FRACTAL PROPERTIES OF ROCK FRACTURE SURFACES

    Institute of Scientific and Technical Information of China (English)

    王金安; 谢和平; MarekA.KWASNIEWSKI

    1996-01-01

    To give a better understanding of the morphological features of rock fracture surfaces within the framework of fractal geometry, the fractal characters of the rough surfaces in" rock are analyzed according to the variogram method. The study elaborates the significance of the geometric parameters-fractal dimension D and the intercept A on a log-log plot to the surface structure. Investigation extends to the anisotropy and heterogeneity of rock fracture surfaces, and the scale effect on the fractal estimation. The present study indicates that fractal dimension alone may not be sufficient to characterize the surface roughness of rock joints. A reliable estimation should take into account the combination of D and A.

  7. Unsaturated fractured rock characterization methods and data sets at the Apache Leap Tuff Site

    Energy Technology Data Exchange (ETDEWEB)

    Rasmussen, T.C.; Evans, D.D.; Sheets, P.J.; Blanford, J.H. [Arizona Univ., Tucson, AZ (USA). Dept. of Hydrology and Water Resources

    1990-08-01

    Performance assessment of high-level nuclear waste containment feasibility requires representative values of parameters as input, including parameter moments, distributional characteristics, and covariance structures between parameters. To meet this need, characterization methods and data sets for interstitial, hydraulic, pneumatic and thermal parameters for a slightly welded fractured tuff at the Apache Leap Tuff Site situated in central Arizona are reported in this document. The data sets include the influence of matric suction on measured parameters. Spatial variability is investigated by sampling along nine boreholes at regular distances. Laboratory parameter estimates for 105 core segments are provided, as well as field estimates centered on the intervals where the core segments were collected. Measurement uncertainty is estimated by repetitively testing control samples. 31 refs., 10 figs., 21 tabs.

  8. Unsaturated fractured rock characterization methods and data sets at the Apache Leap Tuff Site

    International Nuclear Information System (INIS)

    Performance assessment of high-level nuclear waste containment feasibility requires representative values of parameters as input, including parameter moments, distributional characteristics, and covariance structures between parameters. To meet this need, characterization methods and data sets for interstitial, hydraulic, pneumatic and thermal parameters for a slightly welded fractured tuff at the Apache Leap Tuff Site situated in central Arizona are reported in this document. The data sets include the influence of matric suction on measured parameters. Spatial variability is investigated by sampling along nine boreholes at regular distances. Laboratory parameter estimates for 105 core segments are provided, as well as field estimates centered on the intervals where the core segments were collected. Measurement uncertainty is estimated by repetitively testing control samples. 31 refs., 10 figs., 21 tabs

  9. Grouting design based on characterization of the fractured rock. Presentation and demonstration of a methodology

    International Nuclear Information System (INIS)

    The design methodology presented in this document is based on an approach that considers the individual fractures. The observations and analyses made during production enable the design to adapt to the encountered conditions. The document is based on previously published material and overview flow charts are used to show the different steps. Parts of or the full methodology has been applied for a number of tunneling experiments and projects. SKB projects in the Aespoe tunnel include a pillar experiment and pre-grouting of a 70 meter long tunnel (TASQ). Further, for Hallandsas railway tunnel (Skaane south Sweden), a field pre-grouting experiment and design and post-grouting of a section of 133 meters have been made. For the Nygard railway tunnel (north of Goeteborg, Sweden), design and grouting of a section of 86 meters (pre-grouting) and 60 meters (post-grouting) have been performed. Finally, grouting work at the Tornskog tunnel (Stockholm, Sweden) included design and grouting along a 100 meter long section of one of the two tunnel tubes. Of importance to consider when doing a design and evaluating the result are: - The identification of the extent of the grouting needed based on inflow requirements and estimates of tunnel inflow before grouting. - The selection of grout and performance of grouting materials including penetration ability and length. The penetration length is important for the fan geometry design. - The ungrouted compared to the grouted and excavated rock mass conditions: estimates of tunnel inflow and (if available) measured inflows after grouting and excavation. Identify if possible explanations for deviations. For the Hallandsas, Nygard and Tornskog tunnel sections, the use of a Pareto distribution and the estimate of tunnel inflow identified a need for sealing small aperture fractures (< 50 - 100 μm) to meet the inflow requirements. The tunneling projects show that using the hydraulic aperture as a basis for selection of grout is a good

  10. Experimental and Numerical Study on the Cracked Chevron Notched Semi-Circular Bend Method for Characterizing the Mode I Fracture Toughness of Rocks

    Science.gov (United States)

    Wei, Ming-Dong; Dai, Feng; Xu, Nu-Wen; Liu, Jian-Feng; Xu, Yuan

    2016-05-01

    The cracked chevron notched semi-circular bending (CCNSCB) method for measuring the mode I fracture toughness of rocks combines the merits (e.g., avoidance of tedious pre-cracking of notch tips, ease of sample preparation and loading accommodation) of both methods suggested by the International Society for Rock Mechanics, which are the cracked chevron notched Brazilian disc (CCNBD) method and the notched semi-circular bend (NSCB) method. However, the limited availability of the critical dimensionless stress intensity factor (SIF) values severely hinders the widespread usage of the CCNSCB method. In this study, the critical SIFs are determined for a wide range of CCNSCB specimen geometries via three-dimensional finite element analysis. A relatively large support span in the three point bending configuration was considered because the fracture of the CCNSCB specimen in that situation is finely restricted in the notch ligament, which has been commonly assumed for mode I fracture toughness measurements using chevron notched rock specimens. Both CCNSCB and NSCB tests were conducted to measure the fracture toughness of two different rock types; for each rock type, the two methods produce similar toughness values. Given the reported experimental results, the CCNSCB method can be reliable for characterizing the mode I fracture toughness of rocks.

  11. Deformations of fractured rock

    International Nuclear Information System (INIS)

    Results of the DBM and FEM analysis in this study indicate that a suitable rock mass for repository of radioactive waste should be moderately jointed (about 1 joint/m2) and surrounded by shear zones of the first order. This allowes for a gentle and flexible deformation under tectonic stresses and prevent the development of large cross-cutting failures in the repository area. (author)

  12. Verification and characterization of continuum behavior of fractured rock at AECL Underground Research Laboratory

    International Nuclear Information System (INIS)

    The purposes of this study are to determine when a fracture system behaves as a porous medium and what the corresponding permeability tensor is. A two-dimensional fracture system model is developed with density, size, orientation, and location of fractures in an impermeable matrix as random variables. Simulated flow tests through the models measure directional permeability, K/sub g/. Polar coordinate plots of 1/√K/sub g/, which are ellipses for equivalent anistropic homogeneous porous media, are graphed and best fit ellipses are calculated. Fracture length and areal density were varied such that fracture frequency was held constant. The examples showed the permeability increased with fracture length. The modeling techniques were applied to data from the Atomic Energy of Canada Ltd.'s Underground Research Laboratory facility in Manitoba, Canada by assuming the fracture pattern at the surface persists at depth. Well test data were used to estimate the aperture distribution by both correlating and not correlating the aperture with fracture length. The permeability of models with uncorrelated length and aperture were smaller than those for correlated models. A Monte Carlo type study showed that analysis of steady state packer tests consistently underestimate the mean aperture. Finally, a three-dimensional model in which fractures are discs randomly located in space, interactions between the fractures are line segments, and the solution of the steady state flow equations is based on image theory was discussed

  13. Semi-automatic characterization of fractured rock masses using 3D point clouds: discontinuity orientation, spacing and SMR geomechanical classification

    Science.gov (United States)

    Riquelme, Adrian; Tomas, Roberto; Abellan, Antonio; Cano, Miguel; Jaboyedoff, Michel

    2015-04-01

    Investigation of fractured rock masses for different geological applications (e.g. fractured reservoir exploitation, rock slope instability, rock engineering, etc.) requires a deep geometric understanding of the discontinuity sets affecting rock exposures. Recent advances in 3D data acquisition using photogrammetric and/or LiDAR techniques currently allow a quick and an accurate characterization of rock mass discontinuities. This contribution presents a methodology for: (a) use of 3D point clouds for the identification and analysis of planar surfaces outcropping in a rocky slope; (b) calculation of the spacing between different discontinuity sets; (c) semi-automatic calculation of the parameters that play a capital role in the Slope Mass Rating geomechanical classification. As for the part a) (discontinuity orientation), our proposal identifies and defines the algebraic equations of the different discontinuity sets of the rock slope surface by applying an analysis based on a neighbouring points coplanarity test. Additionally, the procedure finds principal orientations by Kernel Density Estimation and identifies clusters (Riquelme et al., 2014). As a result of this analysis, each point is classified with a discontinuity set and with an outcrop plane (cluster). Regarding the part b) (discontinuity spacing) our proposal utilises the previously classified point cloud to investigate how different outcropping planes are linked in space. Discontinuity spacing is calculated for each pair of linked clusters within the same discontinuity set, and then spacing values are analysed calculating their statistic values. Finally, as for the part c) the previous results are used to calculate parameters F_1, F2 and F3 of the Slope Mass Rating geomechanical classification. This analysis is carried out for each discontinuity set using their respective orientation extracted in part a). The open access tool SMRTool (Riquelme et al., 2014) is then used to calculate F1 to F3 correction

  14. Flow and Transport Through Unsaturated Fractured Rock

    Science.gov (United States)

    Evans, Daniel D.; Nicholson, Thomas J.; Rasmussen, Todd C.

    This monograph is an update and revision of the first edition, Geophysical Monograph 42, on ground-water flow and transport through unsaturated, fractured rock, published by AGU in 1987. The first edition evolved from a special symposium held during the American Geophysical Union fall meetings in San Francisco in December 1986. Invited and contributed papers at that AGU session, as well as panel presentations, focused on conceptualizing, measuring and modeling flow and transport through unsaturated fractured rock. As noted in the preface to the first edition, "the expanded interest in the topic (water flow and contaminant transport through unsaturated fractured rock) was initiated when the U.S. Geological Survey proposed that deep unsaturated zones in arid regions be considered in the site selection for the first high-level, commercially generated radioactive waste repository." Much of the research reported in that first edition was motivated by the U.S. Department of Energy's program to investigate Yucca Mountain at the Nevada Test Site as a possible geologic repository for commercially generated, high-level radioactive waste. As noted in the overview paper of the first edition, "characterization methods and modeling are in their developmental stage with the greatest lack of knowledge being the interaction between fracture and matrix flow and transport properties." Although the first edition of this monograph reflected the state-of-the science, laboratory and field experimental programs were novel and limited and, in general, followed from the principles and methods developed in the soil science community.

  15. Electromagnetic characterization of fractured rock for geological disposal studies of spent nuclear fuel

    Energy Technology Data Exchange (ETDEWEB)

    Eloranta, E. [Radiation and Nuclear Safety Authority, Helsinki (Finland); Ermutlu, M. [Nokia Research Center, Helsinki (Finland); Flykt, M.; Lindell, I.; Nikoskinen, K.; Sihvola, A. [Helsinki Univ. of Technology, Espoo (Finland). Electromagnetics Lab.

    1998-04-01

    In the report, the results of a joint research project carried out in 1991-1997 by the Finnish Radiation and Nuclear Safety Authority (STUK) and the Electromagnetics Laboratory of the Helsinki University of Technology are presented. The main purpose was to create computational models for electric potential responses when the medium is anisotropic and is bounded by a perfect magnetic conductor, a perfect electric conductor, and an anisotropic impedance surface. Furthermore, the geometry of two anisotropic half spaces and a layered medium were considered. The solutions of the problems were made using image theory. For modeling the electric potential in anisotropic medium with inhomogeneities, an integral equation was formulated. Also a wedge structure was treated as an extension to the traditional two parallel plate model of fracture geometry. The equivalentization of fracturing with anisotropy is a research area that still continues that still continues 46 refs. The publication contains also fourteen previous publications by authors

  16. Advanced Characterization of Fractured Reservoirs in Carbonate Rocks: The Michigan Basin

    Energy Technology Data Exchange (ETDEWEB)

    Wood, James R.; Harrison, William B.

    2002-12-02

    The purpose of the study was to collect and analyze existing data on the Michigan Basin for fracture patterns on scales ranging form thin section to basin. The data acquisition phase has been successfully concluded with the compilation of several large digital databases containing nearly all the existing information on formation tops, lithology and hydrocarbon production over the entire Michigan Basin. These databases represent the cumulative result of over 80 years of drilling and exploration.

  17. Properties of Flow Zones in Fractured Rock

    Science.gov (United States)

    Salve, R.

    2004-12-01

    Observations over the last 25 years from various field studies suggest that preferential flow is common in soils and rocks. Despite this realization, very little is known about the large-scale properties (e.g., structure, distribution, continuity) of such flow regimes. This information is important for predictive models, but it remains elusive, mainly because of the difficulties involved in characterizing flow that has substantial spatial (both vertical and horizontal) and temporal variability. To better understand preferential flow in fractured rock, we carried out an in situ field experiment in the Topopah Spring tuff found in Exploratory Studies Facility at Yucca Mountain, Nevada. This experiment involved the release of ~22 m3 of ponded water (at a pressure head of ~0.04 m) over a period of 7 months, directly onto a 12 m2 infiltration plot. As water was released, changes in moisture content were monitored along horizontal boreholes located in the formation ~19-22 m below. Distinct flow zones, with significant differences in flow velocity, size, and extent of lateral movement, intercepted the 6-9 m long monitoring boreholes. Further, in some flow zones saturation levels persisted for the time period in which water was released, while in others there were periodic fluctuations. There was also evidence of water being diverted above the ceiling of a cavity in the immediate vicinity of the monitoring boreholes. Observations from this field experiment suggested that inconsistencies exist in present conceptual models of flow in fractured rock. Particularly, these observations suggest that isolated conduits within the fractured rock formation encompass a large number of fractures to form preferential flow paths that persist if there is a continuous supply of water. It appears that in fractured welded tuffs, the propensity for vertical dispersion and fracture-matrix interactions may be significantly greater than suggested by existing conceptual models. These observations

  18. Rock fracture processes in chemically reactive environments

    Science.gov (United States)

    Eichhubl, P.

    2015-12-01

    Rock fracture is traditionally viewed as a brittle process involving damage nucleation and growth in a zone ahead of a larger fracture, resulting in fracture propagation once a threshold loading stress is exceeded. It is now increasingly recognized that coupled chemical-mechanical processes influence fracture growth in wide range of subsurface conditions that include igneous, metamorphic, and geothermal systems, and diagenetically reactive sedimentary systems with possible applications to hydrocarbon extraction and CO2 sequestration. Fracture processes aided or driven by chemical change can affect the onset of fracture, fracture shape and branching characteristics, and fracture network geometry, thus influencing mechanical strength and flow properties of rock systems. We are investigating two fundamental modes of chemical-mechanical interactions associated with fracture growth: 1. Fracture propagation may be aided by chemical dissolution or hydration reactions at the fracture tip allowing fracture propagation under subcritical stress loading conditions. We are evaluating effects of environmental conditions on critical (fracture toughness KIc) and subcritical (subcritical index) fracture properties using double torsion fracture mechanics tests on shale and sandstone. Depending on rock composition, the presence of reactive aqueous fluids can increase or decrease KIc and/or subcritical index. 2. Fracture may be concurrent with distributed dissolution-precipitation reactions in the hostrock beyond the immediate vicinity of the fracture tip. Reconstructing the fracture opening history recorded in crack-seal fracture cement of deeply buried sandstone we find that fracture length growth and fracture opening can be decoupled, with a phase of initial length growth followed by a phase of dominant fracture opening. This suggests that mechanical crack-tip failure processes, possibly aided by chemical crack-tip weakening, and distributed solution-precipitation creep in the

  19. Hydrogeophysical characterization of transport processes in fractured rock by combining push-pull and single-hole ground penetrating radar experiments

    Science.gov (United States)

    Shakas, Alexis; Linde, Niklas; Baron, Ludovic; Bochet, Olivier; Bour, Olivier; Le Borgne, Tanguy

    2016-02-01

    The in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes, such as dispersion, channeling, trapping, matrix diffusion, ambient and density driven flows. We attempted to reduce this uncertainty by coupling push-pull tracer experiments with single-hole ground penetrating radar (GPR) time-lapse imaging. The experiments involved different injection fractures, chaser volumes and resting times, and were performed at the fractured rock research site of Ploemeur in France (H+ network, hplus.ore.fr/en). For the GPR acquisitions, we used both fixed and moving antenna setups in a borehole that was isolated with a flexible liner. During the fixed-antenna experiment, time-varying GPR reflections allowed us to track the spatial and temporal dynamics of the tracer during the push-pull experiment. During the moving antenna experiments, we clearly imaged the dominant fractures in which tracer transport took place, fractures in which the tracer was trapped for longer time periods, and the spatial extent of the tracer distribution (up to 8 m) at different times. This demonstrated the existence of strongly channelized flow in the first few meters and radial flow at greater distances. By varying the resting time of a given experiment, we identified regions affected by density-driven and ambient flow. These experiments open up new perspectives for coupled hydrogeophysical inversion aimed at understanding transport phenomena in fractured rock formations.

  20. ADVANCED CHARACTERIZATION OF FRACTURED RESERVOIRS IN CARBONATE ROCKS: THE MICHIGAN BASIN

    Energy Technology Data Exchange (ETDEWEB)

    James R. Wood; William B. Harrison

    2000-04-01

    Progress in year 2 of this project is highlighted by the completing of the writing and testing of the project database, ''Atlas'', and populating it with all the project data gathered to date. This includes digitization of 17,000+ original Scout Tickets for the Michigan Basin. Work continues on the Driller's Reports, where they have scanned about 50,000 pages out of an estimated 300,000 pages. All of the scanned images have been attached to ''Atlas'', the visual database viewer developed for this project. A complete set of the 1/24,000 USGS DEM (Digital Elevation Models) for the State of Michigan has been downloaded from the USGS Web sites, decompressed and converted to ArcView Grid files. A large-scale map (48 inches x 84 inches) has been constructed by mosaicking of the high-resolution files. This map shows excellent ground surface detail and has drawn much comment and requests for copies at the venues where it has been displayed. Although it was generated for mapping of surface lineations the map has other uses, particularly analysis of the glacial drift in Michigan. It presents unusual problems due to its size and they are working with vendors on compression and display algorithms (e.g. MrSID{copyright}) in an attempt to make it available over the Internet, both for viewing and download. A set of aeromagnetic data for the Michigan Basin has been acquired and is being incorporated into the study. As reported previously, the general fracture picture in the Michigan Basin is a dominant NW-SE trend with a conjugate NE-SW trend. Subsurface, DEM and gravity data support the interpretation of a graben-type deep basement structural trend coincident with the Michigan Basin Gravity High. They plan to incorporate the aeromagnetic data into this interpretation as well.

  1. Impact of rock anisotropy on fracture development

    Institute of Scientific and Technical Information of China (English)

    Lianbo Zeng; Jiyong Zhao; Shengju Zhu; Weiliang Xiong; Yonghong He; Jianwen Chen

    2008-01-01

    Experiments on uniaxial and triaxial rock mechanics and rock acoustic emissions have been conducted for research on the impact of rock anisotropy on the development of the fractures of different directions by taking as an example the ultra-low-permeability sandstone reservoir in the Upper Triassic Yanchang Formation within the Ordos Basin. The experimental results prove the existence of anisotropy of the rock mechanical property in the different directions on the plane, which is the chief reason for the production of impacts on the development of different assemblages of fractures in the geological periods. The rock anisotropy usually restricts the development of one assemblage of conjugate shear fractures. The fractures in the Yanchang Formation within the Ordos Basin are mainly shear fractures that formed under two tectonic actions. Theoretically, here, four assemblages of shear fractures should have developed, but due to the effect of a strong rock anisotropy, in each period one assemblage of fractures chiefly developed. Thus, two assemblages of fractures are usually developed in every part at present.

  2. A multidimensional horizontal-loop controlled-source electromagnetic inversion method and its use to characterize heterogeneity in aquiferous fractured crystalline rocks

    Science.gov (United States)

    Sasaki, Yutaka; Meju, Max A.

    2006-07-01

    The controlled-source dual horizontal-loop harmonic electromagnetic (HLEM) profiling method is well suited to the problem of investigating fracture zones in crystalline rocks but there are still limitations in the way that experimental data are currently interpreted-the use of 1-D data inversion leads to inaccurate determination of geological structure. To allow accurate characterization of zones of fractured rock especially underneath heterogeneous overburden, we have developed an efficient 2.5-D regularized inversion method for reconstructing subsurface electrical resistivity distributions from multifrequency HLEM data, with the forward problem solved in 3-D using a staggered-grid finite-difference method. The inversion method is validated using a synthetic example and practical data sets from four borehole sites in a granitic terrain in northeast Brazil. An appraisal of our results for sites with boreholes sited using conventional data analysis procedures shows that we can distinguish between optimally located productive wells in fracture-zone lineaments and those with diminished yields in weathered layer with no major underlying fracture zones. We suggest that 2.5-D inversion can aid in developing better strategies for sustainable groundwater resource development in the basement terrains.

  3. Geostatistics for fracture characterization

    International Nuclear Information System (INIS)

    As the critical role of fractures has become more apparent in fluid flow and contaminant transport studies, the characterization of fracture networks has received considerable attention in a wide variety of applications such as nuclear waste repository design. The application of geostatistics to fracture characterization has traditionally involved modelling fractures as thin disks; assumptions about the frequency, orientation, length and width of these disks allow the construction of a 3D model of the fracture network. This paper examines alternatives whose statistical parameters are more relevant for contaminant transport studies and are also easier to infer and validate. A new algorithm for conditional simulation is presented, one that is able to honor multipoint statistics through annealing. By honoring statistics that capture with two-point spatial convariances, this algorithm offers an important new tool not only for the specific problem of fracture characterization but also for the more general problem of spatial simulation

  4. Application of geophysical methods for fracture characterization

    International Nuclear Information System (INIS)

    One of the most crucial needs in the design and implementation of an underground waste isolation facility is a reliable method for the detection and characterization of fractures in zones away from boreholes or subsurface workings. Geophysical methods may represent a solution to this problem. If fractures represent anomalies in the elastic properties or conductive properties of the rocks, then the seismic and electrical techniques may be useful in detecting and characterizing fracture properties. 7 refs., 3 figs

  5. The Behaviour of Fracture Growth in Sedimentary Rocks: A Numerical Study Based on Hydraulic Fracturing Processes

    Directory of Open Access Journals (Sweden)

    Lianchong Li

    2016-03-01

    Full Text Available To capture the hydraulic fractures in heterogeneous and layered rocks, a numerical code that can consider the coupled effects of fluid flow, damage, and stress field in rocks is presented. Based on the characteristics of a typical thin and inter-bedded sedimentary reservoir, China, a series of simulations on the hydraulic fracturing are performed. In the simulations, three points, i.e., (1 confining stresses, representing the effect of in situ stresses, (2 strength of the interfaces, and (3 material properties of the layers on either side of the interface, are crucial in fracturing across interfaces between two adjacent rock layers. Numerical results show that the hydrofracture propagation within a layered sequence of sedimentary rocks is controlled by changing in situ stresses, interface properties, and lithologies. The path of the hydraulic fracture is characterized by numerous deflections, branchings, and terminations. Four types of potential interaction, i.e., penetration, arrest, T-shaped branching, and offset, between a hydrofracture and an interface within the layered rocks are formed. Discontinuous composite fracture segments resulting from out-of-plane growth of fractures provide a less permeable path for fluids, gas, and oil than a continuous planar composite fracture, which are one of the sources of the high treating pressures and reduced fracture volume.

  6. Water flow characteristics of rock fractures

    International Nuclear Information System (INIS)

    This report has been worked out within the project 'Groundwater flow and dispersion processes in fractured rock' supported by the National Board for Spent Nuclear Fuel (SKN) in Sweden, dnr 96/85. This project is attached to the safety problems involved in the final disposal of spent nuclear fuel. The purpose of the report is to give a survey of the knowledge of fracture characteristics and to discuss this knowledge in relation to the modelling of flow and dispersion of radioactive substances in the fractures

  7. Mechanic behavior of unloading fractured rock mass

    Institute of Scientific and Technical Information of China (English)

    YIN Ke; ZHANG Yongxing; WU Hanhui

    2003-01-01

    Under tension and shear conditions related to unloading of rock mass, a jointed rock mass model of linear elastic fracture mechanics is established. According to the model, the equations of stresses, strains and displacements of the region influenced by the crack but relatively faraway the crack (the distance between the research point and the center of the crack is longer than the length of crack) are derived. They are important for evaluating the deformation of cracked rock. It is demonstrated by the comparison between computational results of these theoretical equations and the observed data from unloading test that they are applicable for actual engineering.

  8. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Krogsbøll, Anette; Jakobsen, Finn; Madsen, Lena

    1997-01-01

    The main objective of the project is to combine geological descriptions of fractures, chalk types and rock mechanical properties in order to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. This report deals with 1) geological descriptions of outcrop locality ...

  9. Fractures and Rock Mechanics, Phase 1

    DEFF Research Database (Denmark)

    Havmøller, Ole; Krogsbøll, Anette

    1997-01-01

    The main objectives of the project are to combine geological description of fractures, chalk types and rock mechanical properties, and to investigate whether the chosen outcrops can be used as analogues to reservoir chalks. Five chalk types, representing two outcrop localities: Stevns and...

  10. Rock fracture skeleton tracing by image processing and quantitative analysis by geometry features

    Science.gov (United States)

    Liang, Yanjie

    2016-06-01

    In rock engineering, fracture measurement is important for many applications. This paper proposes a novel method for rock fracture skeleton tracing and analyzing. As for skeleton localizing, the curvilinear fractures are multiscale enhanced based on a Hessian matrix, after image binarization, and clutters are post-processed by image analysis; subsequently, the fracture skeleton is extracted via ridge detection combined with a distance transform and thinning algorithm, after which gap sewing and burrs removal repair the skeleton. In regard to skeleton analyzing, the roughness and distribution of a fracture network are respectively described by the fractal dimensions D s and D b; the intersection and fragmentation of a fracture network are respectively characterized by the average number of ends and junctions per fracture N average and the average length per fracture L average. Three rock fracture surfaces are analyzed for experiments and the results verify that both the fracture tracing accuracy and the analysis feasibility are satisfactory using the new method.

  11. Flow dynamics and solute transport in unsaturated rock fractures

    Energy Technology Data Exchange (ETDEWEB)

    Su, G. W.

    1999-10-01

    Rock fractures play an important role in flow and contaminant transport in fractured aquifers, production of oil from petroleum reservoirs, and steam generation from geothermal reservoirs. In this dissertation, phenomenological aspects of flow in unsaturated fractures were studied in visualization experiments conducted on a transparent replica of a natural, rough-walled rock fracture for inlet conditions of constant pressure and flow rate over a range of angles of inclination. The experiments demonstrated that infiltrating liquid proceeds through unsaturated rock fractures along non-uniform, localized preferential flow paths. Even in the presence of constant boundary conditions, intermittent flow was a persistent flow feature observed, where portions of the flow channel underwent cycles of snapping and reforming. Two modes of intermittent flow were observed, the pulsating blob mode and the rivulet snapping mode. A conceptual model for the rivulet snapping mode was proposed and examined using idealized, variable-aperture fractures. The frequency of intermittent flow events was measured in several experiments and related to the capillary and Bond numbers to characterize this flow behavior.

  12. Image Segmentation for rock fractures based on ARMA model

    OpenAIRE

    P. Seetal,; N.Natarajan

    2010-01-01

    Rock fracture mapping is very important in many applications related to rock mechanics. The toughest task is the extraction of the fractures from the images of the rocks. Time series model has been used in this paper for segmentation of fractures from the rock images. The model is compared with orthodox edge detection algorithms. A first order autoregressive image model has been implemented. The model has been applied for both rough as well as smooth fractures. The model was observed to perfo...

  13. Geometry, mechanics and transmissivity of rock fractures

    International Nuclear Information System (INIS)

    This thesis work investigates methods and tools for characterising, testing and modelling the behaviour of rock fractures. Using a 3D-laser-scanning technique, the topography of the surfaces and their position with respect to one another are measured. From the fracture topography, fracture roughness, angularity and aperture are quantified; the major features used for characterisation. The standard deviations for the asperity heights, surface slopes and aperture are determined. These statistical parameters usually increase/decrease according to power laws of the sampling size, and sometimes reach a sill beyond which they become constant. Also the number of contact spots with a certain area decreases according to a power-law function of the area. These power-law relations reveal the self affine fractal nature of roughness and aperture. Roughness is 'persistent' while aperture varies between 'persistent' and 'anti-persistent' probably depending on the degree of match of the fracture walls. The fractal models for roughness, aperture and contact area are used to develop a constitutive model, based on contact mechanics, for describing the fracture normal and shear deformability. The experimental testing results of normal deformability are simulated well by the model whereas fracture shear deformability is not as well modelled. The model predicts well fracture dilation but is too stiff compared to rock samples. A mathematical description of the aperture pattern during shearing is also formulated. The mean value and covariance of the aperture in shearing is calculated and verifies reported observations. The aperture map of samples is inserted in a numerical program for flow calculation. The 'integral transform method' is used for solving the Reynolds' equation; it transforms the fracture transmissivity pattern into a frequency-based function. This closely resembles the power laws that describe fractals. This function can be described directly from the fractal properties of

  14. Research on fracture analysis, groundwater flow and sorption processes in fractured rocks

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dae Ha [Korea Institute of Geology Mining and Materials, Taejon (Korea)

    1998-12-01

    Due to increasing demand for numerous industrial facilities including nuclear power plants and waste repositories, the feasibility of rocks masses as sites for the facilities has been a geological issue of concern. Rock masses, in general, comprises systems of fractures which can provide pathways for groundwater flow and may also affect the stability of engineered structures. such properties of fractures stimulate a synthetic study on (1) analyses of fracture systems, and (2) characterization of groundwater flow and sorption processes in fractured rocks to establish a preliminary model for assessing suitable sites for industrial facilities. The analyses of fracture systems cover (1) reconstruction of the Cenozoic tectonic movements and estimation of frequency indices for the Holocene tectonic movements, (2) determination of distributions and block movements of the Quaternary marine terraces, (3) investigation of lithologic and geotechnical nature of study area, and (4) examination of the Cenozoic volcanic activities and determination of age of the dike swarms. Using data obtained from above mentioned analyses along with data related to earthquakes and active faults, probabilistic approach is performed to determine various potential hazards which may result from the Quaternary or the Holocene tectonic movements. In addition, stepwise and careful integration of various data obtained from field works and laboratory experiments are carried out to analyze groundwater flow in fractures rocks as follows; (1) investigation of geological feature of the site, (2) identification and characterization of fracture systems using core and televiewer logs, (3) determination of conductive fractures using electrical conductivity, temperature, and flow logs, (4) identification of hydraulic connections between fractures using televiewer logs with tracer tests within specific zones. The results obtained from these processes allow a qualitative interpretation of groundwater flow patterns

  15. FRACTURING FLUID CHARACTERIZATION FACILITY

    Energy Technology Data Exchange (ETDEWEB)

    Subhash Shah

    2000-08-01

    Hydraulic fracturing technology has been successfully applied for well stimulation of low and high permeability reservoirs for numerous years. Treatment optimization and improved economics have always been the key to the success and it is more so when the reservoirs under consideration are marginal. Fluids are widely used for the stimulation of wells. The Fracturing Fluid Characterization Facility (FFCF) has been established to provide the accurate prediction of the behavior of complex fracturing fluids under downhole conditions. The primary focus of the facility is to provide valuable insight into the various mechanisms that govern the flow of fracturing fluids and slurries through hydraulically created fractures. During the time between September 30, 1992, and March 31, 2000, the research efforts were devoted to the areas of fluid rheology, proppant transport, proppant flowback, dynamic fluid loss, perforation pressure losses, and frictional pressure losses. In this regard, a unique above-the-ground fracture simulator was designed and constructed at the FFCF, labeled ''The High Pressure Simulator'' (HPS). The FFCF is now available to industry for characterizing and understanding the behavior of complex fluid systems. To better reflect and encompass the broad spectrum of the petroleum industry, the FFCF now operates under a new name of ''The Well Construction Technology Center'' (WCTC). This report documents the summary of the activities performed during 1992-2000 at the FFCF.

  16. A fractured rock geophysical toolbox method selection tool

    Science.gov (United States)

    Day-Lewis, F. D.; Johnson, C.D.; Slater, L.D.; Robinson, J.L.; Williams, J.H.; Boyden, C.L.; Werkema, D.D.; Lane, J.W.

    2016-01-01

    Geophysical technologies have the potential to improve site characterization and monitoring in fractured rock, but the appropriate and effective application of geophysics at a particular site strongly depends on project goals (e.g., identifying discrete fractures) and site characteristics (e.g., lithology). No method works at every site or for every goal. New approaches are needed to identify a set of geophysical methods appropriate to specific project goals and site conditions while considering budget constraints. To this end, we present the Excel-based Fractured-Rock Geophysical Toolbox Method Selection Tool (FRGT-MST). We envision the FRGT-MST (1) equipping remediation professionals with a tool to understand what is likely to be realistic and cost-effective when contracting geophysical services, and (2) reducing applications of geophysics with unrealistic objectives or where methods are likely to fail.

  17. Determining the frequency dependence of elastic properties of fractured rocks

    Science.gov (United States)

    Ahrens, Benedikt; Renner, Jörg

    2016-04-01

    In the brittle crust, rocks often contain joints or faults on various length scales that have a profound effect on fluid flow and heat transport, as well as on the elastic properties of rocks. Improving the understanding of the effect of fractures and the role of stress state and heterogeneity along the fractures on elastic properties of rocks is potentially important for the characterization of deep geothermal reservoirs. Seismic surveys, typically covering a frequency range of about 1 to 1000 Hz, are a valuable tool to investigate fractured rocks but the extraction of fracture properties remains difficult. The elementary frequency-dependent interaction between fractured rock matrix and viscous pore fluids and the resulting effects on wave propagation require well-founded dispersion analyses of heterogeneous rocks. In this laboratory study, we investigate the stress dependence of the effective elastic properties of fractured reservoir rocks over a broad frequency range. To assess the effect of faults on the effective elastic properties, we performed cyclic axial loading tests on intact and fractured samples of Solnhofen limestone and Padang granodiorite. The samples contained an idealized fault, which was created by stacking two sample discs on top of each other that experienced various surface treatments to vary their roughness. The dynamic loading tests were conducted with frequencies up to 10 Hz and amplitudes reaching 10% of the statically applied stress. Simultaneously, P- and S-wave measurements were performed in the ultrasonic frequency range (above 100 kHz) with a total of 16 sensors, whose positioning above and below the samples guarantees a wide range of transmission and reflection angles. Preliminary results of static and dynamic elastic properties of intact Padang granodiorite show a pronounced increase in Young's moduli and Poisson's ratio with increasing axial stress. Stress relaxation is accompanied by a decrease of the modulus and the Poisson

  18. Use of fracture filling mineral assemblages for characterizing water-rock interactions during exhumation of an accretionary complex: An example from the Shimanto Belt, southern Kyushu Japan

    Science.gov (United States)

    Ono, Takuya; Yoshida, Hidekazu; Metcalfe, Richard

    2016-06-01

    Various fracture filling minerals and secondary minerals in fracture walls were formed by fluid-rock interaction during the exhumation of the Palaeogene Shimanto Belt of Kyushu, Japan, which is located in an accretionary complex. Each mineral formed under favourable geological conditions and can be used to estimate the conditions of accretion and formation of the related rock sequences. Petrographic observations, mineralogical and geochemical analyses were made on fracture filling minerals and secondary minerals from boreholes of ca. 140 m depth, drilled in the Shimanto Belt. Results reveal that the secondary minerals were formed in three major stages distinguished by the sequential textural relationships of the minerals and the interpreted environment of mineral formation. Filling mineral assemblages show that the studied rock formation has been subducted to a depth of several km and the temperature reached was ca. 200-300 °C. After the subduction, the rock formation was uplifted and surface acidic water penetrated up to 80 m beneath the present ground surface. The acid water dissolved calcite fracture filling minerals to form the present groundwater flow-paths, which allowed recent wall rock alteration to occur. The results shown here imply that filling mineral assemblages can be an effective tool to evaluate the environmental changes during exhumation of an accretionary complex.

  19. Radionuclide retardation in crystalline rock fractures

    Energy Technology Data Exchange (ETDEWEB)

    Hoelttae, P.; Hakanen, M.; Siitari-Kauppi, M. [Univ. of Helsinki (Finland). Dept. of Radiochemistry; Hautojaervi, A.

    1995-12-31

    Transport and retardation of slightly sorbing sodium was studied in Syyry area SY-KR7 mica gneiss and in altered porous tonalite. Experiments were performed using dynamic fracture and crushed rock column methods and the static batch method. Flow conditions in the column were determined using tritiated water and chloride as non-sorbing tracers. {sup 14}C-PMMA method was used to study the pore structure of matrices and the surface areas were determined by B.E.T. method. Sodium was retarded strongly in altered tonalite owing to homogeneous porous matrix structure and the composition of alteration minerals. An agreement between retardation values in batch and crushed rock column experiments as well as in fracture column experiments was good.

  20. Investigation of blast-induced fracture in rock mass using reversed vertical seismic profiling

    Science.gov (United States)

    Zou, D. H.; Wu, Y. K.

    2001-10-01

    The rock mass on quarry and pit wall surfaces is usually fractured during production blasting. Quantitative investigations of the fractured zones are needed for stabilization of the rock walls. In this study, the principle of reversed vertical seismic profiling (RVSP) was applied. A set of seismic geophones were arranged on the horizontal bench surface and seismic signals were generated along the vertical rock wall using a free-swinging hammer. The travel times of seismic rays were recorded and the P-wave velocities of the rock mass were analyzed using the Simultaneous Iterative Reconstruction Technique (SIRT). A series of site tests have been carried out on the rock walls at a granite quarry that are characterized by fractures. The fracture depth at various locations on the wall surface is thereby determined. The results indicate that RVSP provides an easy and reliable method to quantitatively evaluate the blasting-induced fractures in the rock mass.

  1. Study on mechanical parameters of fractured rock masses

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The equivalent strength parameters of fractured rock masses are prerequisite for stability analysis of geotechnical engineering projects constructed in fractured rock masses which are encountered frequently in western china.Based on generated mesh of fractured rock masses,combined with statistic damage constitutive model of intact rock and damage model of structural plane,progressive failure of fractured rock masses is studied using finite element method(FEM) .Furthermore,Scale effect and anisotropy of compressive strength of fractured rock masses are studied.Study results show that the strength decreases and tend towards stability rapidly from intact rock to fractured rock masses,and the anisotropy of strength of fractured rock masses is not significant.At last,based on numerical simulation conducted on 10 m scale rock masses under different confining pressures,the equivalent strength parameters of fractured rock masses are gained and the results are compared with Hoek-Brown criteria.The method developed is helpful for determination of strength parameters of fractured rock masses.

  2. Natural fracture characterization using passive seismic illumination

    Energy Technology Data Exchange (ETDEWEB)

    Nihei, K.T.

    2003-01-08

    The presence of natural fractures in reservoir rock can significantly enhance gas production, especially in tight gas formations. Any general knowledge of the existence, location, orientation, spatial density, and connectivity of natural fractures, as well as general reservoir structure, that can be obtained prior to active seismic acquisition and drilling can be exploited to identify key areas for subsequent higher resolution active seismic imaging. Current practices for estimating fracture properties before the acquisition of surface seismic data are usually based on the assumed geology and tectonics of the region, and empirical or fracture mechanics-based relationships between stratigraphic curvature and fracturing. The objective of this research is to investigate the potential of multicomponent surface sensor arrays, and passive seismic sources in the form of local earthquakes to identify and characterize potential fractured gas reservoirs located near seismically active regions. To assess the feasibility of passive seismic fracture detection and characterization, we have developed numerical codes for modeling elastic wave propagation in reservoir structures containing multiple, finite-length fractures. This article describes our efforts to determine the conditions for favorable excitation of fracture converted waves, and to develop an imaging method that can be used to locate and characterize fractures using multicomponent, passive seismic data recorded on a surface array.

  3. Nuclide migration analysis in fractured rock

    International Nuclear Information System (INIS)

    This paper describes the results of PA studies considering heterogeneous fracture characteristics, for the purpose of contributing for the performance assessment of the natural barrier system PA in H12 report (The second progress report on research and development for the Geological Disposal of HLW in Japan). In this study, 3-D discrete fracture network model (DFN) and 1-D multiple pathways model is applied for 100 m scale of rock block. Although nuclide release rate calculated by DFN are widely distributed among the realizations, it is shown that several tens realizations are enough number to understand the stochastic characteristics of the nuclide release. From the data uncertainty analysis, there are no significant effects for the nuclide retardation in fracture geometry parameters such as fracture radius, density and etc. 1-D multiple pathways model is developed with focusing on the heterogeneity of the transmissivity, which has a large effect to the nuclide retardation effects. The nuclide release rate calculated by using 1-D multiple pathways model approximates to the results of DFN. This result also shows that the relatively large fractures/faults that connects disposal tunnel and downstream faults have an important role for performance assessment in natural barrier system. (author)

  4. Groundwater flow and sorption processes in fractured rocks (I)

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Won Young; Woo, Nam Chul; Yum, Byoung Woo; Choi, Young Sub; Chae, Byoung Kon; Kim, Jung Yul; Kim, Yoo Sung; Hyun, Hye Ja; Lee, Kil Yong; Lee, Seung Gu; Youn, Youn Yul; Choon, Sang Ki [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)

    1996-12-01

    This study is objected to characterize groundwater flow and sorption processes of the contaminants (ground-water solutes) along the fractured crystalline rocks in Korea. Considering that crystalline rock mass is an essential condition for using underground space cannot be overemphasized the significance of the characterizing fractured crystalline rocks. the behavior of the groundwater contaminants is studied in related to the subsurface structure, and eventually a quantitative technique will be developed to evaluate the impacts of the contaminants on the subsurface environments. The study has been carried at the Samkwang mine area in the Chung-Nam Province. The site has Pre-Cambrian crystalline gneiss as a bedrock and the groundwater flow system through the bedrock fractures seemed to be understandable with the study on the subsurface geologic structure through the mining tunnels. Borehole tests included core logging, televiewer logging, constant pressure fixed interval length tests and tracer tests. The results is summarized as follows; 1) To determine the hydraulic parameters of the fractured rock, the transient flow analysis produce better results than the steady - state flow analysis. 2) Based on the relationship between fracture distribution and transmissivities measured, the shallow part of the system could be considered as a porous and continuous medium due to the well developed fractures and weathering. However, the deeper part shows flow characteristics of the fracture dominant system, satisfying the assumptions of the Cubic law. 3) Transmissivities from the FIL test were averaged to be 6.12 x 10{sup -7}{sub m}{sup 2}{sub /s}. 4) Tracer tests result indicates groundwater flow in the study area is controlled by the connection, extension and geometry of fractures in the bedrock. 5) Hydraulic conductivity of the tracer-test interval was in maximum of 7.2 x 10{sup -6}{sub m/sec}, and the effective porosity of 1.8 %. 6) Composition of the groundwater varies

  5. Fracture systems in normal fault zones crosscutting sedimentary rocks, Northwest German Basin

    Science.gov (United States)

    Reyer, Dorothea; Bauer, Johanna F.; Philipp, Sonja L.

    2012-12-01

    Field studies of fracture systems associated with 58 normal fault zones crosscutting sedimentary rocks were performed in the Northwest German Basin. Fracture orientations, densities, apertures and lengths, as well as fault zone structural indices, were analysed separately for fault damage zones and host rocks. The results show a pronounced difference between carbonate and clastic rocks: mainly in carbonate rocks we found presence of clear damage zones, characterized by higher fracture densities than in the host rocks. While the maximum aperture is similar for both units, the percentage of fractures with large apertures is much higher in the damage zones than in the host rocks. Based on laboratory measurements of Young's moduli and field measurements of fracture densities, we calculate effective stiffnesses Ee, that is the Young's moduli of the in situ rock masses, within the normal fault zones. Compared with carbonate rocks, Ee computed for clastic-rock damage zones decreases significantly less due to lower fracture densities. We conclude that normal fault zones in carbonate rocks have more profound effects on enhancing permeability in fluid reservoirs than those in clastic rocks. The results are of great importance for modelling the hydromechanical behaviour of normal fault zones in subsurface fluid reservoirs.

  6. Predicting hydrology of fractured rock masses from geology

    Science.gov (United States)

    La Pointe, Paul R.

    Fracture network connectivity often dominates movement rate, flow volume, and mass transport through rock masses. These networks influence the effectiveness of petroleum reservoir development, safe disposal of nuclear waste, delineation of water supply or establishment of well-head protection plans, recovery from geothermal reservoirs, solution mining, construction of underground openings, and the remediation of contaminated rock. Well tests can provide a great deal of useful information on the hydraulic properties of fracture systems, but they are often expensive or logistically infeasible. These tests also may not provide an accurate description of the hydrologic properties of the rock volume under consideration. Methods to model fractured rock can be improved by quantifying the relation between geologic parameters and the hydrologically conductive fractures. This study illustrates the application of four statistical and pattern recognition methods—evaluation of correlation coefficients, contingency table analysis, multivariate regression, and neural net analysis. The data for the study consist of borehole and well-test information from eight boreholes used for characterizing a proposed low-level radioactive waste repository in Wake County, North Carolina. The analyses show that high localized flow rates are related to the presence of increased fracture intensity, and that this intensity is controlled by a complex interplay of structural geology and lithology. Some of the initial hypotheses concerning the relation of geology to hydrology were not substantiated by the data, leading to a refined conceptual model that differed in significant ways from the initial model. Although the techniques used are of general applicability, the precise nature of the correlation between geology and hydrology is site dependent.

  7. Grouting Rock Fractures with Cement Grout

    Science.gov (United States)

    El Tani, Mohamed

    2012-07-01

    The radial flow rate of a cement grout in a rock fracture is obtained from Bingham's relation and the fact that the power expended by the injection mechanism is the energy dissipated by viscous effects. The energy balance reveals that the advance ratio is of fundamental importance in the grouting process and is inherently related to the rest and advance phases of a cement grout. This allows giving a precise definition of the zero flow path that divides the energy diagram into two distinct domains for advancing and non-advancing grout. The advance ratio and the zero flow path are used to explore the grouting of one or more fractures, analyze the GIN model in the context of the SL dispute, draw a terminal sequence considering the energy interval alternative, and reformulate the refusal criterion of the North American grouting method. Secondary grouting effects are also investigated.

  8. Research on fracture analysis, groundwater flow and sorption processes in fractured rocks

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Dae-Ha; Kim, Won-Young; Lee, Seung-Gu [Korea Institute of Geology Mining and Materials, Taejon (KR)] (and others)

    1999-12-01

    Due to increasing demand for numerous industrial facilities including nuclear power plants and waste repositories, the feasibility of rocks masses as sites for the facilities has been a geological issue of concern. Rock masses, in general, comprises systems of fractures which can provide pathways for groundwater flow and may also affect the stability of engineered structures. For the study of groundwater flow and sorption processes in fractured rocks, five boreholes were drilled. A stepwise and careful integration of various data obtained from field works and laboratory experiments were carried out to analyze groundwater flow in fractured rocks as follows; (1) investigation of geological feature of the site, (2) identification and characterization of fracture systems using core and televiewer logs, (3) determination of hydrogeological properties of fractured aquifers using geophysical borehole logging, pumping and slug tests, and continuous monitoring of groundwater level and quality, (4) evaluation of groundwater flow patterns using fluid flow modeling. The results obtained from these processes allow a qualitative interpretation of fractured aquifers in the study area. Column experiments of some reactive radionuclides were also performed to examine sorption processes of the radionuclides including retardation coefficients. In addition, analyses of fracture systems covered (1) reconstruction of the Cenozoic tectonic movements and estimation of frequency indices for the Holocene tectonic movements, (2) determination of distributions and block movements of the Quaternary marine terraces, (3) investigation of lithologic and geotechnical nature of study area, and (4) examination of the Cenozoic volcanic activities and determination of age of the dike swarms. Using data obtained from above mentioned analyses along with data related to earthquakes and active faults, probabilistic approach was performed to determine various potential hazards which may result from the

  9. Reaction-driven fracturing of porous rock

    Science.gov (United States)

    Ulven, O. I.; Jamtveit, B.; Malthe-Sørenssen, A.

    2014-10-01

    A 2-D computer model has been developed to investigate fluid-mediated transformation processes such as chemical weathering, mineral carbonation, and serpentinization that require transport of H2O and/or CO2 into reacting rock volumes. Hydration and carbonation cause local volume expansion, and the resulting nonuniform stresses may drive fracturing, which increases both the rate of transport and the accessible reactive surface area in the system and thus accelerates the rate of the transformation process. The model couples reactions, fracturing, and fluid transport for systems with a range of initial porosities, assumed constant throughout the process. With low initial porosity, a sharp reaction front between completely reacted material and unreacted material propagates into unaltered rock, while for high porosities, diffuse reaction fronts are formed in which a large fraction of the initial volume is partly reacted. When diffusive transport is rate limiting, the total reaction rate depends on porosity to a power N, where N is in the range 0.45-2. The exponent N increases as the reaction-generated expansion decreases. In high-porosity rocks, the total reaction rate is limited by reaction kinetics, and it is thus insensitive to porosity variations. As the volume increasing reaction proceeds, fracturing divides the unreacted porous material into subdomains, which may undergo further subdivision as they are consumed by the reaction. The total reaction rate and progress depend on the initial geometry of a reacting domain, and this significantly affects the weathering profiles for systems that evolve from an initial assembly of blocks with different sizes and shapes.

  10. Erosion of clay-based grouts in simulated rock fractures

    International Nuclear Information System (INIS)

    The paper presents a laboratory study on the erosion of clay-based grouts in a simulated rock fracture and in a simulated rock fracture network. The apparatus specially constructed for these experiments and the testing procedure are described. The testing results have shown that a partially eroded clay-based grout may still be effective in sealing rock fractures and that the addition of cement in a clay grout can minimize erosion

  11. Simulation of Seismic Scattering from Rock Fractures

    Science.gov (United States)

    Petrovitch, C.; Teasdale, N.; Pyrak-Nolte, L. J.; de Hoop, M. V.

    2010-12-01

    Accurate predictions of the hydraulic and mechanical properties of fractured subsurface reservoirs are hampered because the coupled processes among fluid properties, mechanical behavior, and seismic scattering are not well understood. A goal of laboratory experiments is to illuminate fundamental physical behavior that can be used on the laboratory scale and translated to the field scale. Our approach to understanding the interrelationship between the hydraulic and seismic properties of fractures is based on determining the relevant geometric length scales that define a fracture and affect fluid flow, as well as the length scales associated with seismic measurements that quantify physical changes in fractures. To achieve this goal, we use a combination of numerical simulation and laboratory measurements to obtain the necessary range of relevant scales. We performed computational seismic scattering simulations from rough fluid-filled (either gas or water-saturated) fractures and compared the simulations to laboratory measurements. Plane-wave compressional-mode source and receiver transducers (water-coupled, 1 MHz central frequency, piezoelectric) were used to measure wave propagation across a single rough fracture. The fracture sample was an acrylic replica of an induced fracture from a carbonate rock (Austin Chalk). An acrylic sample was used to visualize the fluid-saturation of the sample. Reflection and transmission full-waveform measurements were made in 1 mm increments over a 60 mm by 60 mm region of the fracture. The roughness of the fracture surfaces was measured using laser profilometry. The surface roughness data were used to create the computational domain, and the measured arrival times, peak-to-peak amplitudes and frequency content are compared to the simulation results. Many fracture scattering simulations are done by assuming the fracture lies in a 2Dl plane and employ the displacement-discontinuity boundary conditions at the fracture’s surface

  12. Modern Workflows for Fracture Rock Hydrogeology

    Science.gov (United States)

    Doe, T.

    2015-12-01

    Discrete Fracture Network (DFN) is a numerical simulation approach that represents a conducting fracture network using geologically realistic geometries and single-conductor hydraulic and transport properties. In terms of diffusion analogues, equivalent porous media derive from heat conduction in continuous media, while DFN simulation is more similar to electrical flow and diffusion in circuits with discrete pathways. DFN modeling grew out of pioneering work of David Snow in the late 1960s with additional impetus in the 1970's from the development of the development of stochastic approaches for describing of fracture geometric and hydrologic properties. Research in underground test facilities for radioactive waste disposal developed the necessary linkages between characterization technologies and simulation as well as bringing about a hybrid deterministic stochastic approach. Over the past 40 years DFN simulation and characterization methods have moved from the research environment into practical, commercial application. The key geologic, geophysical and hydrologic tools provide the required DFN inputs of conductive fracture intensity, orientation, and transmissivity. Flow logging either using downhole tool or by detailed packer testing identifies the locations of conducting features in boreholes, and image logging provides information on the geology and geometry of the conducting features. Multi-zone monitoring systems isolate the individual conductors, and with subsequent drilling and characterization perturbations help to recognize connectivity and compartmentalization in the fracture network. Tracer tests and core analysis provide critical information on the transport properties especially matrix diffusion unidentified conducting pathways. Well test analyses incorporating flow dimension boundary effects provide further constraint on the conducting geometry of the fracture network.

  13. Phase-field modeling of fracture propagation under hydraulic stimulation in pre-fractured rocks

    Science.gov (United States)

    Khisamitov, Ildar; Mohseni, Seyed Ali; Meschke, Guenther

    2016-04-01

    The presentation presents the numerical analysis of hydraulic fracturing within Griffith theory of brittle damage. The phase-field method [1] is employed to model brittle fracture propagation driven by pressurized fluids within fully saturated porous rocks. The phase-field equation is coupled with the Biot-theory using the effective stress concept. The porous rock is assumed as fully saturated with incompressible fluid and deforms within elasticity theory. The hydraulic fracturing propagates under mode I crack opening in quasi-static regime with slow fluid flow in porous matrix and fracture. The phase-field approach for the modelling of brittle fracture [2] coincides with the maximum energy release rate criterion in fracture mechanics theory. The phase-field equation is approximated over entire the domain and introduces new degree of freedom (damage variable). Crack surface is represented by a smooth regularized damage distribution over the fractured area. The presented numerical investigations are characterized by different scenarios of hydraulic stimulation and the interaction of a new fracture emanating from the bore hole with pre-existing cracks. The scenarios include predefined fractures with different oriented to specific angle and spatial distribution over the entire domain. The undamaged rock matrix is modeled as an isotropic elastic material with initial porosity and isotropic matrix permeability. The flow within the undamaged region is governed by Darcy's law while the fluid flow in fractures is approximated by cubic law with the crack opening computed from the displacement solution and the damage variable distribution [3]. Initial fractures are modeled by an initial distribution of the damage variable and by special zero-thickness interface finite elements. Adaptive algorithms in conjunction with appropriately chosen refinement criteria are utilized to reduce the computational costs. References [1] M.J. Borden "A phase-field description of dynamic

  14. Proceedings of the International Symposium on Dynamics of Fluids in Fractured Rocks: Concepts and Recent Advances

    Energy Technology Data Exchange (ETDEWEB)

    Faybishenko, B. (ed.)

    1999-02-01

    This publication contains extended abstracts of papers presented at the International Symposium ''Dynamics of Fluids in Fractured Rocks: Concepts and Recent Advances'' held at Ernest Orlando Lawrence Berkeley National Laboratory on February 10-12, 1999. This Symposium is organized in Honor of the 80th Birthday of Paul A. Witherspoon, who initiated some of the early investigations on flow and transport in fractured rocks at the University of California, Berkeley, and at Lawrence Berkeley National Laboratory. He is a key figure in the development of basic concepts, modeling, and field measurements of fluid flow and contaminant transport in fractured rock systems. The technical problems of assessing fluid flow, radionuclide transport, site characterization, modeling, and performance assessment in fractured rocks remain the most challenging aspects of subsurface flow and transport investigations. An understanding of these important aspects of hydrogeology is needed to assess disposal of nu clear wastes, development of geothermal resources, production of oil and gas resources, and remediation of contaminated sites. These Proceedings of more than 100 papers from 12 countries discuss recent scientific and practical developments and the status of our understanding of fluid flow and radionuclide transport in fractured rocks. The main topics of the papers are: Theoretical studies of fluid flow in fractured rocks; Multi-phase flow and reactive chemical transport in fractured rocks; Fracture/matrix interactions; Hydrogeological and transport testing; Fracture flow models; Vadose zone studies; Isotopic studies of flow in fractured systems; Fractures in geothermal systems; Remediation and colloid transport in fractured systems; and Nuclear waste disposal in fractured rocks.

  15. Laboratory Hydraulic Fracture Characterization Using Acoustic Emission

    Science.gov (United States)

    Gutierrez, M.

    2013-05-01

    For many years Acoustic Emission (AE) testing has aided in the understanding of fracture initiation and propagation in geologic materials. AEs occur when a material emits elastic waves caused by the sudden occurrence of fractures or frictional sliding along discontinuous surfaces and grain boundaries. One important application of AE is the monitoring of hydraulic fracturing of underground formations to create functional reservoirs at sites where the permeability of the rock is too limited to allow for cost effective fluid extraction. However, several challenges remain in the use of AE to locate and characterize fractures that are created hydraulically. Chief among these challenges is the often large scatter of the AE data that are generated during the fracturing process and the difficulty of interpreting the AE data so that hydraulic fractures can be reliably characterized. To improve the understanding of the link between AE and hydraulic fracturing, laboratory scale model testing of hydraulic fracturing were performed using a cubical true triaxial device. This device consist of a loading frame capable of loading a 30x30x30 cm3 rock sample with three independent principal stresses up to 13 MPa while simultaneously providing heating up to 180 degrees C. Several laboratory scale hydraulic fracture stimulation treatments were performed on granite and rock analogue fabricated using medium strength concrete. A six sensor acoustic emission (AE) array, using wideband piezoelectric transducers, is employed to monitor the fracturing process. AE monitoring of laboratory hydraulic fracturing experiments showed multiple phenomena including winged fracture growth from a borehole, cross-field well communication, fracture reorientation, borehole casing failure and much more. AE data analysis consisted of event source location determination, fracture surface generation and validation, source mechanism determination, and determining the overall effectiveness of the induced fracture

  16. Multi-scale approach to invasion percolation of rock fracture networks

    CERN Document Server

    Ebrahimi, Ali N; Araújo, Nuno A M; Herrmann, Hans J

    2014-01-01

    A multi-scale scheme for the invasion percolation of rock fracture networks with heterogeneous fracture aperture fields is proposed. Inside fractures, fluid transport is calculated on the finest scale and found to be localized in channels as a consequence of the aperture field. The channel network is characterized and reduced to a vectorized artificial channel network (ACN). Different realizations of ACNs are used to systematically calculate efficient apertures for fluid transport inside differently sized fractures as well as fracture intersection and entry properties. Typical situations in fracture networks are parameterized by fracture inclination, flow path length along the fracture and intersection lengths in the entrance and outlet zones of fractures. Using these scaling relations obtained from the finer scales, we simulate the invasion process of immiscible fluids into saturated discrete fracture networks, which were studied in previous works.

  17. Modelling stress-dependent permeability in fractured rock including effects of propagating and bending fractures

    NARCIS (Netherlands)

    Latham, J.P.; Xiang, J.; Belayneh, M.; Nick, H.M.; Tsang, C.F.; Blunt, M.J.

    2013-01-01

    The influence of in-situ stresses on flow processes in fractured rock is investigated using a novel modelling approach. The combined finite-discrete element method (FEMDEM) is used to model the deformation of a fractured rock mass. The fracture wall displacements and aperture changes are modelled in

  18. Study of deep fracturation of granitic rock mass. Documentary study

    International Nuclear Information System (INIS)

    This documentary study realized with the financial support of the European Communities and the CEA aims at the utilization of available data for the understanding of the evolution of natural fractures in granitic rocks from the surface to deep underground. The Mt Blanc road tunnel, the EDF's Arc-Isere gallerie, the Auriat deep borehole and the Pyrenean rock mass of Bassies are studied because detailed structural and geological studies have been realized these last 20 years. In this study are more particularly analyzed the relationship between small fractures and large faults, evolution with depth of fracture density and direction, consequences of rock decompression and relationship between fracturation and groundwater

  19. Rock mass characterization for Copenhagen Metro using face logs

    DEFF Research Database (Denmark)

    Hansen, Sanne Louise; Galsgaard, Jens; Foged, Niels Nielsen

    2015-01-01

    of relevant rock mass properties for tunnelling in Danian limestone has previously been difficult, as core logging shows a high degree of induced fracturing and core loss due to drilling disturbance, with an underestimation of the RQD values, and other rock mass properties, compared to face logging. However......, describing rock mass characteristics using detailed face logging with geological description and recording of induration and fracturing, giving a field RQD value during excavation, combined with televiewer logs, when available, has shown to be a valuable tool for rock mass characterization compared...

  20. Fracturing of viscoelastic geomaterials and application to sedimentary layered rocks

    OpenAIRE

    Nguyen, S T; Jeannin, L; Dormieux, Luc; Renard, Francois

    2013-01-01

    We study analytically the behavior of a viscoelastic brittle solid loaded in tension, in which fractures may grow or not depending on the amount of dissipation allowed by the viscous behavior. We highlight a threshold in extension rate, below which the solid will not be fractured. Applied to sedimentary rocks, this model shows how viscous effects can prevent fracture growth in geological formations.

  1. Microscopic characteristics of different fracture modes of brittle rock

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Three types of rock specimens, three-point bending specimen, anti-symmetric four-point bending specimen and direct shearing specimen, were used to achieve Mode Ⅰ , Mode Ⅱ and mixed mode Ⅰ - Ⅱ fracture, respectively . Microscopic characteristics of the three fracture modes of brittle rock were studied by SEM technique in order to analyze fracture behaviors and better understand fracture mechanisms of different fracture modes of brittle rock. Test results show that the microscopic characteristics of different fracture modes correspond to different fracture mechanisms. The surface of Mode Ⅰ fracture has a great number of sparse and steep slip-steps with few tearing ridges and shows strong brittleness. In the surface of Mode Ⅱ fracture there exist many tearing ridges and densely distributed parallel slip-steps and it is attributed to the action of shear stress.The co-action of tensile and shear stresses results in brittle cleavage planes mixed with streamline patterns and tearing ridges in the surface of mixed mode Ⅰ - Ⅱ fracture. The measured Mode Ⅱ fracture toughness K Ⅱ c and mixed mode Ⅰ -Ⅱ fracture toughness Kmc are larger than Mode Ⅰ fracture toughness KⅠc. KⅡc is about 3.5times KI c, and KmC is about 1.2 times K Ⅰ c.

  2. Prediction of grout penetration in fractured rocks by numerical simulation

    OpenAIRE

    Yang, MJ; Yue, ZQ; Lee, PKK; Su, B; Tham, LG

    2002-01-01

    As fractures in rock significantly reduce the strength as well as the stiffness of the rock mass, grouting may be required to improve the performance of the rock mass in engineering or mining projects. During grouting, mortar of cement or other materials is injected into the rock mass so that the fractures can be filled up and the rock mass can act as an integral unit. Unlike water, grouts are usually viscous and behave as non-Newtonian fluids. Therefore, the equations describing the flow of ...

  3. Numerical evaluation of strength and deformability of fractured rocks

    Institute of Scientific and Technical Information of China (English)

    Majid Noorian Bidgoli; Zhihong Zhao; Lanru Jing

    2013-01-01

    Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods (DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from field mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confining pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to fit the well-known Mohr-Coulomb (M-C) and Hoek-Brown (H-B) failure criteria, represented by equivalent material properties defining these two criteria. The results show

  4. Dynamic model of normal behavior of rock fractures

    Institute of Scientific and Technical Information of China (English)

    YANG Wen-yi; KONG Guang-ya; CAI Jun-gang

    2005-01-01

    Based on laboratory tests of artificial fractures in mortar material, established the dynamic constitutive model of normal behaviour of rock fracture,. The tests were systematically conducted under quasi-static and dynamic monotonic loading conditions. The fractures were of different numbers of asperities in contact and were subsequently of different initial contact areas, which imitated the natural rock fractures. The rate of compressive load applied normal to the fractures covers a wide range from 10-1 MPa/s (quasi-static) up to 103 MPa/s (highly dynamic). The normal stress-closure responses of fractures were measured for different loading rates. Based on the stress-closure relation curves measured, a nonlinear (hyperbolic) dynamic model of fracture, normal behaviour, termed as dynamic BB model, was proposed, which was modified from the existing BB model of static normal behaviour of fractures by taking into account the effect of loading rate.

  5. Subcritical fracture propagation in rocks: An examination using the methods of fracture mechanics and non-destructive testing. Ph.D. Thesis

    Science.gov (United States)

    Swanson, P. L.

    1984-01-01

    An experimental investigation of tensile rock fracture is presented with an emphasis on characterizing time dependent crack growth using the methods of fracture mechanics. Subcritical fracture experiments were performed in moist air on glass and five different rock types at crack velocities using the double torsion technique. The experimental results suggest that subcritical fracture resistance in polycrystals is dominated by microstructural effects. Evidence for gross violations of the assumptions of linear elastic fracture mechanics and double torsion theory was found in the tests on rocks. In an effort to obtain a better understanding of the physical breakdown processes associated with rock fracture, a series of nondestructive evaluation tests were performed during subcritical fracture experiments on glass and granite. Comparison of the observed process zone shape with that expected on the basis of a critical normal principal tensile stress criterion shows that the zone is much more elongated in the crack propagation direction than predicted by the continuum based microcracking model alone.

  6. Pre- and post-stimulation characterization of geothermal well GRT-1, Rittershoffen, France: insights from acoustic image logs of hard fractured rock

    Science.gov (United States)

    Vidal, Jeanne; Genter, Albert; Schmittbuhl, Jean

    2016-05-01

    Geothermal well GRT-1 (Rittershoffen, Alsace) was drilled in 2012. Its open-hole section (extending down to a depth of 2.6 km) penetrated fractured sandstones and granite. In 2013, the well was subjected to Thermal, Chemical and Hydraulic (TCH) stimulation, which improved the injectivity index five-fold. The goal of the study was to assess the impact of the stimulation by comparing pre- and post-stimulation logs and well-logging (temperature [T] log) and mud-logging data. This comparison revealed modifications of almost all the natural fractures. However, not all of these fractures are associated with permeability enhancement, and the post-stimulation T logs are important for characterizing this enhancement. Chemical alteration due to mechanical erosion at the tops and bottoms of the fractures was observed in the sandstones. These zones display indications of very small new permeability after the TCH stimulation. Because a major fault zone caved extensively where it crosses the borehole, it was not imaged in the acoustic logs. However, this originally permeable zone was enhanced as demonstrated by the T logs. Based on the natural injectivity of this fault zone, hydraulic erosion and thermal microcracking of its internal quartz veins are associated with this permeability enhancement. Although local changes in the borehole wall observed in the acoustic images cannot be directly linked to the improved injectivity index, the comparison of the acoustic image logs allows for identification of fracture zones impacted by the TCH stimulation.

  7. Pre- and post-stimulation characterization of geothermal well GRT-1, Rittershoffen, France: insights from acoustic image logs of hard fractured rock

    Science.gov (United States)

    Vidal, Jeanne; Genter, Albert; Schmittbuhl, Jean

    2016-08-01

    Geothermal well GRT-1 (Rittershoffen, Alsace) was drilled in 2012. Its open-hole section (extending down to a depth of 2.6 km) penetrated fractured sandstones and granite. In 2013, the well was subjected to Thermal, Chemical and Hydraulic (TCH) stimulation, which improved the injectivity index fivefold. The goal of the study was to assess the impact of the stimulation by comparing pre- and post-stimulation well-logging (acoustic and temperature [T] logs) and mud-logging data. This comparison revealed modifications of almost all the natural fractures. However, not all of these fractures are associated with permeability enhancement, and the post-stimulation T logs are important for characterizing this enhancement. Chemical alteration due to mechanical erosion at the tops and bottoms of the fractures was observed in the sandstones. These zones display indications of very small new permeability after the TCH stimulation. Because a major fault zone caved extensively where it crosses the borehole, it was not imaged in the acoustic logs. However, this originally permeable zone was enhanced as demonstrated by the T logs. Based on the natural injectivity of this fault zone, hydraulic erosion and thermal microcracking of its internal quartz veins are associated with this permeability enhancement. Although local changes in the borehole wall observed in the acoustic images cannot be directly linked to the improved injectivity index, the comparison of the acoustic image logs allows for identification of fracture zones impacted by the TCH stimulation.

  8. An XFEM Model for Hydraulic Fracturing in Partially Saturated Rocks

    Directory of Open Access Journals (Sweden)

    Salimzadeh Saeed

    2016-01-01

    Full Text Available Hydraulic fracturing is a complex multi-physics phenomenon. Numerous analytical and numerical models of hydraulic fracturing processes have been proposed. Analytical solutions commonly are able to model the growth of a single hydraulic fracture into an initially intact, homogeneous rock mass. Numerical models are able to analyse complex problems such as multiple hydraulic fractures and fracturing in heterogeneous media. However, majority of available models are restricted to single-phase flow through fracture and permeable porous rock. This is not compatible with actual field conditions where the injected fluid does not have similar properties as the host fluid. In this study we present a fully coupled hydro-poroelastic model which incorporates two fluids i.e. fracturing fluid and host fluid. Flow through fracture is defined based on lubrication assumption, while flow through matrix is defined as Darcy flow. The fracture discontinuity in the mechanical model is captured using eXtended Finite Element Method (XFEM while the fracture propagation criterion is defined through cohesive fracture model. The discontinuous matrix fluid velocity across fracture is modelled using leak-off loading which couples fracture flow and matrix flow. The proposed model has been discretised using standard Galerkin method, implemented in Matlab and verified against several published solutions. Multiple hydraulic fracturing simulations are performed to show the model robustness and to illustrate how problem parameters such as injection rate and rock permeability affect the hydraulic fracturing variables i.e. injection pressure, fracture aperture and fracture length. The results show the impact of partial saturation on leak-off and the fact that single-phase models may underestimate the leak-off.

  9. Linear Elastic and Cohesive Fracture Analysis to Model Hydraulic Fracture in Brittle and Ductile Rocks

    Science.gov (United States)

    Yao, Yao

    2012-05-01

    Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a Perkins-Kern-Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone

  10. Study on orientation fracture blasting with shaped charge in rock

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    On the basis of the theories of mechanics of explosive and rock fracture mechanics, the mechanism of crack initiation and its expansion of directional fracture controlled blasting with shaped charges in rock were studied, then the blasting parameters were designed and tested by a model test in laboratory and field experiment. The experimental and test results showed that the energy from blasting is directionally concentrated for the cumulative action. The directional expansion of cracks is satisfactory, the results of the model test and field test suggested that the orientation fracture blasting with shaped charge is a good means of excavating tunnels or cutting rock.

  11. Effects of fracture distribution and length scale on the equivalent continuum elastic compliance of fractured rock masses

    Institute of Scientific and Technical Information of China (English)

    Marte Gutierrez; Dong-Joon Youn

    2015-01-01

    Fracture systems have strong influence on the overall mechanical behavior of fractured rock masses due to their relatively lower stiffness and shear strength than those of the rock matrix. Understanding the effects of fracture geometrical distribution, such as length, spacing, persistence and orientation, is important for quantifying the mechanical behavior of fractured rock masses. The relation between fracture geometry and the mechanical characteristics of the fractured rock mass is complicated due to the fact that the fracture geometry and mechanical behaviors of fractured rock mass are strongly dependent on the length scale. In this paper, a comprehensive study was conducted to determine the effects of fracture distribution on the equivalent continuum elastic compliance of fractured rock masses over a wide range of fracture lengths. To account for the stochastic nature of fracture distributions, three different simulation techniques involving Oda’s elastic compliance tensor, Monte Carlo simulation (MCS), and suitable probability density functions (PDFs) were employed to represent the elastic compliance of fractured rock masses. To yield geologically realistic results, parameters for defining fracture distribu-tions were obtained from different geological fields. The influence of the key fracture parameters and their relations to the overall elastic behavior of the fractured rock mass were studied and discussed. A detailed study was also carried out to investigate the validity of the use of a representative element volume (REV) in the equivalent continuum representation of fractured rock masses. A criterion was also proposed to determine the appropriate REV given the fracture distribution of the rock mass.

  12. Effects of fracture distribution and length scale on the equivalent continuum elastic compliance of fractured rock masses

    Directory of Open Access Journals (Sweden)

    Marte Gutierrez

    2015-12-01

    Full Text Available Fracture systems have strong influence on the overall mechanical behavior of fractured rock masses due to their relatively lower stiffness and shear strength than those of the rock matrix. Understanding the effects of fracture geometrical distribution, such as length, spacing, persistence and orientation, is important for quantifying the mechanical behavior of fractured rock masses. The relation between fracture geometry and the mechanical characteristics of the fractured rock mass is complicated due to the fact that the fracture geometry and mechanical behaviors of fractured rock mass are strongly dependent on the length scale. In this paper, a comprehensive study was conducted to determine the effects of fracture distribution on the equivalent continuum elastic compliance of fractured rock masses over a wide range of fracture lengths. To account for the stochastic nature of fracture distributions, three different simulation techniques involving Oda's elastic compliance tensor, Monte Carlo simulation (MCS, and suitable probability density functions (PDFs were employed to represent the elastic compliance of fractured rock masses. To yield geologically realistic results, parameters for defining fracture distributions were obtained from different geological fields. The influence of the key fracture parameters and their relations to the overall elastic behavior of the fractured rock mass were studied and discussed. A detailed study was also carried out to investigate the validity of the use of a representative element volume (REV in the equivalent continuum representation of fractured rock masses. A criterion was also proposed to determine the appropriate REV given the fracture distribution of the rock mass.

  13. Radionuclide migration through fractured rock: Effects of multiple fractures and two-member decay chains

    International Nuclear Information System (INIS)

    This report presents the results of an analytical study of the hydrological transport of a radioactive contaminant through fractured, porous rock. The purpose is to evaluate the time-, and space-dependent concentration of the contaminant in the ground-water in the fractures and in the rock pores. We propose a simplified analytical method that superposes two single-fracture solutions for the concentration in the rock matrix with a system of parallel fractures. The exact solutions require multiple integrals and summation of an infinite series, which converges slowly because of its oscillating nature. The convergence of the series becomes slower for strongly-sorbing media, large spacing of two fractures, and early times. In summary, we made extension to the theory of radionuclide penetration into multiply fractured rock, and provided solutions for a two-member decay chain. 9 refs., 10 figs., 1 tab

  14. Experiment on Hydraulic Fracturing in Rock and Induced Earthquake

    Institute of Scientific and Technical Information of China (English)

    Yan Yuding; Li Yalin; Zhang Zhuan; Ouyang Lisheng; Xie Mingfu

    2005-01-01

    Experiment on rock hydraulic fracturing strength under different confining pressures was conducted on a series of test specimens with various pre-cracks prepared from 7 types of rock.Combining the data of an actual reservoir-induced earthquake with the experimental results of the contemporary tectonic stress field according to the theory of rock strength and the principle and method of rock fracture mechanics, the authors tentatively investigated the earthquakes induced by pore-water pressure in rock and obtained the initial results as follows: ( 1 ) One type of induced earthquake may occur in the case of larger tectonic stress on such weak planes that strike in similar orientation of principle tectonic compressional stress in the shallows of the rock mass; the pore-water pressure σp may generate tensile fracture on them and induce small earthquakes; (2) Two types of induced earthquake may occur in the case of larger tectonic stress, i.e., ① on such weakness planes that strike in similar orientation of principle tectonic compressioual stress, σ1, in the shallows of the rockmass, the pore-water pressure, σp, may generate tensile fracture on them and induce small earthquakes; ② When the tectonic stress approximates the shear strength of the fracture, the pore-water pressure σp may reduce the normal stress, σn, on the fracture face causing failure of the originally stable fracture,producing gliding fracture and thus inducing an earthquake. σp may also increase the fracture depth, leading to an induced earthquake with the magnitude larger than the previous potential magnitude; (3) There is a depth limit for each type of rock mass, and no induced earthquake will occur beyond this limit.

  15. Influence of Rock Fabric on Hydraulic Fracture Propagation: Laboratory Study

    Science.gov (United States)

    Stanchits, S. A.; Desroches, J.; Burghardt, J.; Surdi, A.; Whitney, N.

    2014-12-01

    Massive hydraulic fracturing is required for commercial gas production from unconventional reservoirs. These reservoirs are often highly fractured and heterogeneous, which may cause significant fracture complexity and also arrest propagation of hydraulic fractures, leading to production decrease. One of the goals of our study was to investigate the influence of rock fabric features on near-wellbore fracture geometry and complexity. We performed a series of laboratory tests on Niobrara outcrop shale blocks with dimensions of 30 x 30 x 36 inches in a true-triaxial loading frame. Acoustic Emission (AE) technique was applied to monitor hydraulic fracture initiation and dynamics of fracture propagation. After the tests, the shape of the created hydraulic fracture was mapped by goniometry technique. To estimate fracture aperture, particles of different sizes were injected with fracturing fluid. In all tests, AE analysis indicated hydraulic fracture initiation prior to breakdown or the maximum of wellbore pressure. In most tests, AE analysis revealed asymmetrical hydraulic fracture shapes. Post-test analysis demonstrated good correspondence of AE results with the actual 3D shape of the fracture surface map. AE analysis confirmed that in some of these tests, the hydraulic fracture approached one face of the block before the maximum wellbore pressure had been reached. We have found that in such cases the propagation of hydraulic fracture in the opposite direction was arrested by the presence of mineralized interfaces. Mapping the distribution of injected particles confirmed the creation of a narrow-width aperture in the vicinity of pre-existing interfaces, restricting fracture conductivity. Based on the results of our study, we concluded that the presence of planes of weakness, such as mineralized natural fractures, can result in the arrest of hydraulic fracture propagation, or in poor fracture geometries with limited aperture, that in turn could lead to high net pressure

  16. Fracture Characterization in the Astor Pass Geothermal Field, Nevada

    Science.gov (United States)

    Walsh, D. C.; Reeves, D. M.; Pohll, G.; Lyles, B. F.; Cooper, C. A.

    2011-12-01

    The Astor Pass geothermal field, near Pyramid Lake, NV, is under study as a site of potential geothermal energy production. Three wells have been completed in the graben of this typical Basin and Range geologic setting. Lithologies include a layer of unconsolidated sediment (basin fill) underlain by various tertiary volcanic units and granodiorite and metavolcanic basement rock. Characterization of fractures within the relatively impermeable rock matrix is being conducted for the three wells. Statistical analysis of fracture orientation, densities, and spacing obtained from borehole imaging logs is used to determine stress orientation and to generate a statistically equivalent Discrete Fracture Network (DFN) model. Fractures at depth are compared to fracture data collected in nearby outcrops of the same lithologic stratigraphy. Fracture geometry and density is correlated to mechanically discrete layers within the stratigraphy to test whether variations in fracturing can be attributed to variations in Young's modulus. Correlation of fracture geometry and densities with spinner flowmeter logs and distributed temperature sensor records are made in an effort to identify potential flowing fracture zones intersecting the borehole. Mean fracture aperture is obtained from open fracture counts and reservoir-scale transmissivity values (computed from a 30 day pump test) in the absence of readily available aperture data. The goal of this thorough fracture characterization is to create a physically relevant model which may be coupled with a multipurpose fluid flow and thermal simulator for investigation of geothermal reservoir behavior, particularly at the borehole scale.

  17. Analysis of compressive fracture in rock using statistical techniques

    Energy Technology Data Exchange (ETDEWEB)

    Blair, S.C.

    1994-12-01

    Fracture of rock in compression is analyzed using a field-theory model, and the processes of crack coalescence and fracture formation and the effect of grain-scale heterogeneities on macroscopic behavior of rock are studied. The model is based on observations of fracture in laboratory compression tests, and incorporates assumptions developed using fracture mechanics analysis of rock fracture. The model represents grains as discrete sites, and uses superposition of continuum and crack-interaction stresses to create cracks at these sites. The sites are also used to introduce local heterogeneity. Clusters of cracked sites can be analyzed using percolation theory. Stress-strain curves for simulated uniaxial tests were analyzed by studying the location of cracked sites, and partitioning of strain energy for selected intervals. Results show that the model implicitly predicts both development of shear-type fracture surfaces and a strength-vs-size relation that are similar to those observed for real rocks. Results of a parameter-sensitivity analysis indicate that heterogeneity in the local stresses, attributed to the shape and loading of individual grains, has a first-order effect on strength, and that increasing local stress heterogeneity lowers compressive strength following an inverse power law. Peak strength decreased with increasing lattice size and decreasing mean site strength, and was independent of site-strength distribution. A model for rock fracture based on a nearest-neighbor algorithm for stress redistribution is also presented and used to simulate laboratory compression tests, with promising results.

  18. The effect of friction on simulated dynamic fracturing of rocks

    International Nuclear Information System (INIS)

    During underground nuclear tests, rocks may fail by plastic yielding, which limits shear strength, or by tensile fracture, wherever maximum principal stress exceeds tensile strength. A third mode of failure exists due to friction along closed fractured surfaces. There, friction affects slipping and can thus limit stress. In this paper, we study the effect of friction on the simulated dynamic response of rocks to underground nuclear explosions. The coefficient of friction is the ratio of total shear stress applied to a closed fracture surface to normal applied compressive total stress. At low coefficients of friction, the evolving stress field tends to be weakened by frictional slip, which also eases closing of fractures. At high coefficients of friction, the stress field tends to be strengthened, where fractures have closed, but remains weak, where fractures are left open. 4 refs., 4 figs

  19. Influence of adsorption properties on radionuclide transport in fractured rock

    International Nuclear Information System (INIS)

    Most models predicting radionuclide transport in fractured rock include mechanisms of advection, dispersion, radioactive decay, and equilibrium adsorption between the solid and liquid phases. Recently, nonequilibrium adsorption has been given a great deal of attention. In this paper, the authors have successfully derived the analytical solutions to transport equations for a single fracture under various conditions covering no sorption, nonequilibrium adsorption, and equilibrium sorption

  20. Analysis of steady-state hydraulic tests in fractured rock

    International Nuclear Information System (INIS)

    A model for the analysis of steady-state hydraulic injection tests into single fractures of a rock-mass is presented, and solved analytically. It is used to obtain a probability distribution for the transmissivities of fractures in Cornish granite. (author)

  1. Fractures inside crystalline rocks. Effects of deformations on fluid circulations

    International Nuclear Information System (INIS)

    The modeling of fluid flows inside granite massifs is an important task for the evaluation of the feasibility of radioactive waste storage inside such formations. This document makes a synthesis of the works carried out since about 15 years, in particular by the French bureau of geological and mining research (BRGM), about the hydro-mechanical behaviour of a fracture and about the hydrodynamical characterization of fracture networks inside crystalline rocks: 1 - introduction; 2 - hydro-mechanical behaviour under normal stress: experimental results (hydro-mechanical behaviour, flow regimes, mechanical behaviour, test protocol, complementary tests, influence of samples size), geometrical interpretation of experimental results (relation with walls geometry, relation with voids geometry, relation with contacts geometry), hydro-mechanical modeling (hydraulic modeling, mechanical modeling); 3 - from the hydro-mechanical behaviour under normal stress to the coupling with heat transfers and chemistry: experiment for the study of the chemo-thermo-hydro-mechanical coupling (experimental results, relation with walls morphology), thermo-hydro-mechanical experiments, thermo-hydro-chemical experiments with fractures, conclusions; 4 - hydro-mechanical behaviour during shear: experimental results, geometrical interpretation (relation with the geometry of damaged zones, relation with voids geometry, relation with walls geometry), hydro-mechanical modeling (mechanical modeling, hydro-mechanical modeling of the behaviour during shear). (J.S.)

  2. Characterizing the influence of stress-induced microcracks on the laboratory strength and fracture development in brittle rocks using a finite-discrete element method-micro discrete fracture network FDEM-μDFN approach

    Directory of Open Access Journals (Sweden)

    Pooya Hamdi

    2015-12-01

    Full Text Available Heterogeneity is an inherent component of rock and may be present in different forms including mineral heterogeneity, geometrical heterogeneity, weak grain boundaries and micro-defects. Microcracks are usually observed in crystalline rocks in two forms: natural and stress-induced; the amount of stress-induced microcracking increases with depth and in-situ stress. Laboratory results indicate that the physical properties of rocks such as strength, deformability, P-wave velocity and permeability are influenced by increase in microcrack intensity. In this study, the finite-discrete element method (FDEM is used to model microcrack heterogeneity by introducing into a model sample sets of microcracks using the proposed micro discrete fracture network (μDFN approach. The characteristics of the microcracks required to create μDFN models are obtained through image analyses of thin sections of Lac du Bonnet granite adopted from published literature. A suite of two-dimensional laboratory tests including uniaxial, triaxial compression and Brazilian tests is simulated and the results are compared with laboratory data. The FDEM-μDFN models indicate that micro-heterogeneity has a profound influence on both the mechanical behavior and resultant fracture pattern. An increase in the microcrack intensity leads to a reduction in the strength of the sample and changes the character of the rock strength envelope. Spalling and axial splitting dominate the failure mode at low confinement while shear failure is the dominant failure mode at high confinement. Numerical results from simulated compression tests show that microcracking reduces the cohesive component of strength alone, and the frictional strength component remains unaffected. Results from simulated Brazilian tests show that the tensile strength is influenced by the presence of microcracks, with a reduction in tensile strength as microcrack intensity increases. The importance of microcrack heterogeneity in

  3. Design approaches for grouting of rock fractures; Theory and practice

    OpenAIRE

    Yaghoobi Rafi, Jalaleddin

    2013-01-01

    Currently, cement base grout is used widely for sealing of the rock fractures in order to decrease the permeability of rock mass. Grouting procedure is one of the main tasks in cycle of rock excavation. In addition, huge amount of grout should be used during dam construction in order to seal the bedding and embankment walls. Therefore, considering the effect of grouting in duration and cost of the project, improving the design methods seems essential. In successful grouting the goal is to ach...

  4. Quantitative Analysis Of Acoustic Emission From Rock Fracture Experiments

    Science.gov (United States)

    Goodfellow, Sebastian David

    This thesis aims to advance the methods of quantitative acoustic emission (AE) analysis by calibrating sensors, characterizing sources, and applying the results to solve engi- neering problems. In the first part of this thesis, we built a calibration apparatus and successfully calibrated two commercial AE sensors. The ErgoTech sensor was found to have broadband velocity sensitivity and the Panametrics V103 was sensitive to surface normal displacement. These calibration results were applied to two AE data sets from rock fracture experiments in order to characterize the sources of AE events. The first data set was from an in situ rock fracture experiment conducted at the Underground Research Laboratory (URL). The Mine-By experiment was a large scale excavation response test where both AE (10 kHz - 1 MHz) and microseismicity (MS) (1 Hz - 10 kHz) were monitored. Using the calibration information, magnitude, stress drop, dimension and energy were successfully estimated for 21 AE events recorded in the tensile region of the tunnel wall. Magnitudes were in the range -7.5 triaxial deformation experiment, where the objectives were to characterize laboratory AE sources and identify issues related to moving the analysis from ideal in situ conditions to more complex laboratory conditions in terms of the ability to conduct quantitative AE analysis. We found AE magnitudes in the range -7.8 limited knowledge of attenuation which we proved was continuously evolving, (2) the use of a narrow frequency band for acquisition, (3) the inability to identify P and S waves given the small sample size, and (4) acquisition using a narrow amplitude range given a low signal to noise ratio. Moving forward to the final stage of this thesis, with the ability to characterize the sources of AE, we applied our method to study an engineering problem. We chose hydraulic fracturing because of its obvious importance in the future of Canadian energy production. During a hydraulic fracture treatment

  5. Multiporosity Flow in Fractured Low-Permeability Rocks

    CERN Document Server

    Kuhlman, Kristopher L; Heath, Jason E

    2015-01-01

    A multiporosity extension of classical double and triple porosity fractured rock flow models for slightly compressible fluids is presented. The multiporosity model is an adaptation of the multirate solute transport model of Haggerty and Gorelick (1995) to viscous flow in fractured rock reservoirs. It is a generalization of both pseudo-steady-state and transient interporosity flow double porosity models. The model includes a fracture continuum and an overlapping distribution of multiple rock matrix continua, whose fracture-matrix exchange coefficients are specified through a discrete probability mass function. Semi-analytical cylindrically symmetric solutions to the multiporosity mathematical model are developed using the Laplace transform to illustrate its behavior. The multiporosity model presented here is conceptually simple, yet flexible enough to simulate common conceptualizations of double and triple porosity flow. This combination of generality and simplicity makes the multiporosity model a good choice ...

  6. A new approach for effectively determining fracture network connections in fractured rocks using R tree indexing

    Institute of Scientific and Technical Information of China (English)

    LIU Hua-mei; WANG Ming-yu; SONG Xian-feng

    2011-01-01

    Determinations of fracture network connections would help the investigators remove those “meaningless” no-flow-passing fractures,providing an updated and more effective fracture network that could considerably improve the computation efficiency in the pertinent numerical simulations of fluid flow and solute transport.The effective algorithms with higher computational efficiency are needed to accomplish this task in large-scale fractured rock masses.A new approach using R tree indexing was proposed for determining fracture connection in 3D stochastically distributed fracture network.By comparing with the traditional exhaustion algorithm,it was observed that from the simulation results,this approach was much more effective; and the more the fractures were investigated,the more obvious the advantages of the approach were.Furthermore,it was indicated that the runtime used for creating the R tree indexing has a major part in the total of the runtime used for calculating Minimum Bounding Rectangles(MBRs),creating the R tree indexing,precisely finding out fracture intersections,and identifying flow paths,which are four important steps to determine fracture connections.This proposed approach for the determination of fracture connections in three-dimensional fractured rocks are expected to provide efficient preprocessing and critical database for practically accomplishing numerical computation of fluid flow and solute transport in large-scale fractured rock masses.

  7. Scaling and Hierarchy of Models for Flow Processes in Unsaturated Fractured Rock

    Science.gov (United States)

    Faybishenko, B.; Bodvarsson, G. S.; Witherspoon, P. A.; Hinds, J.

    2002-12-01

    A key question facing soil scientists and hydrogeologists is whether, in analyzing flow processes within unsaturated fractured rock with geological discontinuities, the same measurements and models can be used regardless of scale. The goal of this presentation is to illustrate scaling concepts and suggest using a hierarchy of scales in describing the spatial-temporal behavior of unsaturated flow and transport in fractured rock. A conventional scaling approach is valid for liquid permeability of saturated media or air permeability of unsaturated fractured media. We will illustrate that multiscale spatial and temporal variations of flow and transport processes in unsaturated fractured rock are caused by a variety of processes (such as preferential and fast flow, funneling and divergence of flow paths, transient flow behavior, nonlinearity, unstable and chaotic flow, and fracture-matrix interaction). Small-scale intrafracture flow processes are neither physically nor geometrically analogous to large-scale fracture-network processes. As a consequence, scaling laws developed for unsaturated flow through porous media may fail for fractured rocks. To study unsaturated fractured rock, we utilize the concept of a hierarchy of scales: elemental, small, intermediate, and large scales. For each scale, the triadic hierarchical approach requires investigations one level above this scale to determine boundary conditions, and one level below to determine parameters of the equations. Thus, different conceptual approaches are needed for characterization and modeling at different scales. These theoretical concepts are illustrated using the results from field investigations of fractured basalt at the Snake River Plain, Idaho, and fractured tuff at Yucca Mountain, Nevada.

  8. Anisotropy of strength and deformability of fractured rocks

    Directory of Open Access Journals (Sweden)

    Majid Noorian Bidgoli

    2014-04-01

    Full Text Available Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue for design and stability assessments of rock engineering structures, due mainly to the non-uniform and non-regular geometries of the fracture systems. However, no adequate efforts have been made to study this issue due to the current practical impossibility of laboratory tests with samples of large volumes containing many fractures, and the difficulty for controlling reliable initial and boundary conditions for large-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy of fractured rock masses is needed. The objective of this study is to systematically investigate anisotropy of strength and deformability of fractured rocks, which has not been conducted in the past, using a numerical modeling method. A series of realistic two-dimensional (2D discrete fracture network (DFN models were established based on site investigation data, which were then loaded in different directions, using the code UDEC of discrete element method (DEM, with changing confining pressures. Numerical results show that strength envelopes and elastic deformability parameters of tested numerical models are significantly anisotropic, and vary with changing axial loading and confining pressures. The results indicate that for design and safety assessments of rock engineering projects, the directional variations of strength and deformability of the fractured rock mass concerned must be treated properly with respect to the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnels in association with principal stress directions only may not be adequate for safety requirements. Outstanding issues of the present study and suggestions for future study are also presented.

  9. Anisotropy of strength and deformability of fractured rocks

    Institute of Scientific and Technical Information of China (English)

    Majid Noorian Bidgoli; Lanru Jing

    2014-01-01

    Anisotropy of the strength and deformation behaviors of fractured rock masses is a crucial issue for design and stability assessments of rock engineering structures, due mainly to the non-uniform and non-regular geometries of the fracture systems. However, no adequate efforts have been made to study this issue due to the current practical impossibility of laboratory tests with samples of large volumes con-taining many fractures, and the difficulty for controlling reliable initial and boundary conditions for large-scale in situ tests. Therefore, a reliable numerical predicting approach for evaluating anisotropy of fractured rock masses is needed. The objective of this study is to systematically investigate anisotropy of strength and deformability of fractured rocks, which has not been conducted in the past, using a nu-merical modeling method. A series of realistic two-dimensional (2D) discrete fracture network (DFN) models were established based on site investigation data, which were then loaded in different directions, using the code UDEC of discrete element method (DEM), with changing confining pressures. Numerical results show that strength envelopes and elastic deformability parameters of tested numerical models are significantly anisotropic, and vary with changing axial loading and confining pressures. The results indicate that for design and safety assessments of rock engineering projects, the directional variations of strength and deformability of the fractured rock mass concerned must be treated properly with respect to the directions of in situ stresses. Traditional practice for simply positioning axial orientation of tunnels in association with principal stress directions only may not be adequate for safety requirements. Outstanding issues of the present study and suggestions for future study are also presented.

  10. DEM modeling of fracture propagation in veined rock

    Science.gov (United States)

    Virgo, S.; Abe, S.; Urai, J. L.

    2012-04-01

    One fundamental aspect of crack seal veins is that an existing vein can act as a heterogeneity in the rock which controls the localization of successive fracturing at unchanged mean stress orientations. Observations from crack-seal vein systems suggest that existing veins fundamentally influence the fracture behavior of a rock even in cases where the orientation of the stress field is highly incompatible with the orientation of the vein. We used a series of 3D Discrete Element Simulations to systematically investigate the influence of existing veins with varying orientation and mechanical properties on an approaching fracture. The models consist of a tabular heterogeneity within a bonded particle volume fractured under uniaxial tension. The parameters varied in the study are the orientation of the heterogeneity relative to the direction of uniaxial extension and therefore relative to the orientation of the favorable fracture plane as well as the fracture strength ratio between the matrix material, the vein material and the interface between vein and matrix material. The elastic parameters (e.g. Young's modulus) are kept homogeneous throughout the model. Thereby it is ensured that the results are not altered by stress field perturbation induced by stiffness contrasts. The model materials used were carefully tested and calibrated to ensure comparability with natural examples in terms of their fracture-mechanical properties. The simulations were repeated for several random particle packings to eliminate the effect of heterogeneities in the packing on the results. The results show a strong influence of the tabular heterogeneity on the fracture propagation for all orientations and at cohesion ratios within the range of natural systems. Besides curving and deflection of the fracture path associated with changes in fracture mode, bifurcation of fractures as well as arrest of propagation and nucleation of new fractures can be observed.

  11. Fracture toughness properties of rocks in Olkiluoto: Laboratory measurements 2008-2009

    Energy Technology Data Exchange (ETDEWEB)

    Siren, T.

    2012-05-15

    In Olkiluoto an underground rock characterization facility (ONKALO) for the final disposal site of spent nuclear fuel has been under thorough research many years, but further knowledge is needed on fracture toughness parameters. Fracture toughness parameters are important for example in fracture mechanics prediction for Posiva's Olkiluoto Spalling Experiment (POSE). This working report describes a laboratory campaign that was done between 2008 and 2009. The campaign aimed at determining the fracture mechanics parameters as well as density and ultrasonic velocities for Olkiluoto rocks. The specimens delivered were selected by Posiva; the core showed no damage and the quality of the delivered cores was good with varying sample diameter. Most of the test samples (9 out of 12) are gneissic rock. The Mode I fracture toughness was determined using two different methods to account for two different fracturing directions. The methods are the Chevron Bend (CB) test as proposed in the ISRM Suggested Method and a method based on the Brazilian Disk (BD) experiment. The Mode II fracture toughness was determined using the Punch-Through Shear with Confining Pressure experiment on the remaining pieces from the CB testing. The scatter in the results is very large, even within one piece of core sample. Usually the scatter of results is less than 5 %. The high scatter in the data at hand is believed to be due to the very inhomogeneous nature of the rock material. The magnitude of the determined Mode I fracture toughness compares well with available reported data for medium to coarse grained granitoide rocks. However the scatter of the mode II fracture toughness values is higher than experienced on other rock types, but the variability is reasonable for the inhomogeneous rock type. Distinguishing the fracture toughness values for different anisotropy directions would require more thorough testing with quality samples at different anisotropy directions. However since fracture

  12. Prediction of Fracture Behavior in Rock and Rock-like Materials Using Discrete Element Models

    Science.gov (United States)

    Katsaga, T.; Young, P.

    2009-05-01

    The study of fracture initiation and propagation in heterogeneous materials such as rock and rock-like materials are of principal interest in the field of rock mechanics and rock engineering. It is crucial to study and investigate failure prediction and safety measures in civil and mining structures. Our work offers a practical approach to predict fracture behaviour using discrete element models. In this approach, the microstructures of materials are presented through the combination of clusters of bonded particles with different inter-cluster particle and bond properties, and intra-cluster bond properties. The geometry of clusters is transferred from information available from thin sections, computed tomography (CT) images and other visual presentation of the modeled material using customized AutoCAD built-in dialog- based Visual Basic Application. Exact microstructures of the tested sample, including fractures, faults, inclusions and void spaces can be duplicated in the discrete element models. Although the microstructural fabrics of rocks and rock-like structures may have different scale, fracture formation and propagation through these materials are alike and will follow similar mechanics. Synthetic material provides an excellent condition for validating the modelling approaches, as fracture behaviours are known with the well-defined composite's properties. Calibration of the macro-properties of matrix material and inclusions (aggregates), were followed with the overall mechanical material responses calibration by adjusting the interfacial properties. The discrete element model predicted similar fracture propagation features and path as that of the real sample material. The path of the fractures and matrix-inclusion interaction was compared using computed tomography images. Initiation and fracture formation in the model and real material were compared using Acoustic Emission data. Analysing the temporal and spatial evolution of AE events, collected during the

  13. Mixing induced reactive transport in fractured crystalline rocks

    International Nuclear Information System (INIS)

    In this paper the solute retention properties of crystalline fractured rocks due to mixing-induced geochemical reactions are studied. While fractured media exhibit paths of fast flow and transport and thus short residence times for conservative solutes, at the same time they promote mixing and dilution due to strong heterogeneity, which leads to sharp concentration contrasts. Enhanced mixing and dilution have a double effect that favors crystalline fractured media as a possible host medium for nuclear waste disposal. Firstly, peak radionuclide concentrations are attenuated and, secondly, mixing-induced precipitation reactions are enhanced significantly, which leads to radionuclide immobilization. An integrated framework is presented for the effective modeling of these flow, transport and reaction phenomena, and the interaction between them. In a simple case study, the enhanced dilution and precipitation potential of fractured crystalline rocks are systematically studied and quantified and contrasted it to retention and attenuation in an equivalent homogeneous formation.

  14. Neutron Production from the Fracture of Piezoelectric Rocks

    CERN Document Server

    Widom, A; Srivastava, Y N

    2011-01-01

    A theoretical explanation is provided for the experimental evidence that fracturing piezoelectric rocks produces neutrons. The elastic energy micro-crack production ultimately yields the macroscopic fracture. The mechanical energy is converted by the piezoelectric effect into electric field energy. The electric field energy decays via radio frequency (microwave) electric field oscillations. The radio frequency electric fields accelerate the condensed matter electrons which then collide with protons producing neutrons and neutrinos.

  15. Ozone generation by rock fracture: Earthquake early warning?

    Energy Technology Data Exchange (ETDEWEB)

    Baragiola, Raul A.; Dukes, Catherine A.; Hedges, Dawn [Engineering Physics, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2011-11-14

    We report the production of up to 10 ppm ozone during crushing and grinding of typical terrestrial crust rocks in air, O{sub 2} and CO{sub 2} at atmospheric pressure, but not in helium or nitrogen. Ozone is formed by exoelectrons emitted by high electric fields, resulting from charge separation during fracture. The results suggest that ground level ozone produced by rock fracture, besides its potential health hazard, can be used for early warning in earthquakes and other catastrophes, such as landslides or land shifts in excavation tunnels and underground mines.

  16. Sealing of fractured rock: grout composition and group properties

    International Nuclear Information System (INIS)

    The properties of smectite-rich clay with additives of quartz filler and salt and the properties of cement with additives of silica fume and superplasticizer are tested with respect to their usefulness for sealing fractured rock. Laboratory tests of the viscous properties as well as the longevity of the materials are performed. A flow theory for the behaviour of the grouts at static and dynamic pressure has been developed and tested in laboratory injection tests. The results show, so far, that the grout materials and the dynamic injection technique are well suited for sealing rock with narrow fractures

  17. The Friction Factor in the Forchheimer Equation for Rock Fractures

    Science.gov (United States)

    Zhou, Jia-Qing; Hu, Shao-Hua; Chen, Yi-Feng; Wang, Min; Zhou, Chuang-Bing

    2016-08-01

    The friction factor is an important dimensionless parameter for fluid flow through rock fractures that relates pressure head loss to average flow velocity; it can be affected by both fracture geometry and flow regime. In this study, a theoretical formula form of the friction factor containing both viscous and inertial terms is formulated by incorporating the Forchheimer equation, and a new friction factor model is proposed based on a recent phenomenological relation for the Forchheimer coefficient. The viscous term in the proposed formula is inversely proportional to Reynolds number and represents the limiting case in Darcy flow regime when the inertial effects diminish, whereas the inertial term is a power function of the relative roughness and represents a limiting case in fully turbulent flow regime when the fracture roughness plays a dominant role. The proposed model is compared with existing friction factor models for fractures through parametric sensitivity analyses and using experimental data on granite fractures, showing that the proposed model has not only clearer physical significance, but also better predictive performance. By accepting proper percentages of nonlinear pressure drop to quantify the onset of Forchheimer flow and fully turbulent flow, a Moody-type diagram with explicitly defined flow regimes is created for rock fractures of varying roughness, indicating that rougher fractures have a large friction factor and are more prone to the Forchheimer flow and fully turbulent flow. These findings may prove useful in better understanding of the flow behaviors in rock fractures and improving the numerical modeling of non-Darcy flow in fractured aquifers.

  18. Analysis of styress heterogeneity in deep fractured chrystalline rock

    Science.gov (United States)

    Sahara, David; Kohl, Thomas

    2016-04-01

    The mechanical properties variation, the fracture characteristic and the inclination of the well might perturbed the development of wellbore failures and, hence, affect the estimation of the stress state in fractured rocks. A detailed analysis of 1221 and 827 compressional and tensional wellbore failures, respectively, in a 3.5 km crystalline rock observed in the GPK4 well in Soultz-sous-Forêts enables us to analyze the different pattern of stress heterogeneities which might be related to several factors. The inclination of the well affects the stress distribution by a few MPa which is found to have a significant effect of the development of wellbore, i.e. the limitation of tensile failures in part of the well which is inclined by less than 10°, and the delay of compressional failures occurrence by about 300 m in a 25° inclined well. Fractures and alteration reduced the compressional strength of the crystalline by approximately 30% and, hence, promoted the development of breakout at a smaller far-field stress. The orientation of wellbore failures in such fractured zones are found to be heterogeneously distributed, hence, lower the quality of the stress estimation. Furthermore, the first and second order of stress heterogeneities pattern in the vicinity of major and minor fractures, respectively, in a highly fractured zone at depth 4600 to 4850 m are observed. The numerical modeling of the development of breakouts that take into account the weak zone as a results of fracturing process developed in this study shows a systematic analysis of the variation of the breakout orientation and the reduction of the mechanical properties. In fractured rock, wellbore failures do not correlate to the principal stress only, but also to the variation of the mechanical properties and the properties of fractures. Hence, a long continuous section of wellbore failures is a must to have a sufficient stress-related failures data.

  19. Experimental studies of rock fracture behavior related to hydraulic fracture

    Science.gov (United States)

    Ma, Zifeng

    The objective of this experimental investigation stems from the uncontrollable of the hydraulic fracture shape in the oil and gas production field. A small-scale laboratory investigation of crack propagation in sandstone was first performed with the objective to simulate the field fracture growth. Test results showed that the fracture resistance increased with crack extension, assuming that there was an interaction between crack faces (bridging, interlocking, and friction). An acoustic emission test was conducted to examine the existence of the interaction by locating AE events and analyzing waveform. Furthermore, the effects of confining stress, loading rate, stress field, and strength heterogeneous on the tortuosity of the fracture surface were experimentally investigated in the study. Finally, a test was designed and conducted to investigate the crack propagation in a stratified media with permeability contrast. Crack was observed to arrested in an interface. The phenomenon of delamination along an interface between layers with permeability contrast was observed. The delamination was proposed to be the cause of crack arrest and crack jump in the saturated stratified materials under confinement test.

  20. Radionuclide dispersion from multiple patch sources into a rock fracture

    International Nuclear Information System (INIS)

    This report presents results of an analytical study on hydrological transport of a radionuclide released from sources of finite areal extent into a planar fracture. The purposes of this work are to predict the space-time-dependent concentrations of a radionuclide which is released from multiple-patch (or area) sources and transported by advection and transverse dispersion in a planar fracture and by molecular diffusion in rock matrix, and to investigate the effects of transverse dispersion in the fracture. 5 refs., 14 figs

  1. Rapid imbibition of water in fractures within unsaturated sedimentary rock

    Science.gov (United States)

    Cheng, C.-L.; Perfect, E.; Donnelly, B.; Bilheux, H. Z.; Tremsin, A. S.; McKay, L. D.; DiStefano, V. H.; Cai, J. C.; Santodonato, L. J.

    2015-03-01

    The spontaneous imbibition of water and other liquids into gas-filled fractures in variably-saturated porous media is important in a variety of engineering and geological contexts. However, surprisingly few studies have investigated this phenomenon. We present a theoretical framework for predicting the 1-dimensional movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over the rough surfaces of fracture faces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Quantitative data on spontaneous imbibition of water in unsaturated Berea sandstone cores were acquired to evaluate the proposed model. The cores with different permeability classes ranging from 50 to 500 mD and were fractured using the Brazilian method. Spontaneous imbibition in the fractured cores was measured by dynamic neutron radiography at the Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge National Laboratory. Water uptake into both the matrix and the fracture zone exhibited square-root-of-time behavior. The matrix sorptivities ranged from 2.9 to 4.6 mm s-0.5, and increased linearly as the permeability class increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 mm s-0.5, and increased linearly with increasing fracture aperture width. The dispersion coefficients ranged from 23.7 to 66.7 mm2 s-1 and increased linearly with increasing fracture aperture width and damage zone width. Both theory and observations indicate that fractures can significantly increase spontaneous imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increase the dispersion of the wetting front. Further research is needed to investigate this phenomenon in other natural and engineered porous media.

  2. Challenges and opportunities for fractured rock imaging using 3D cross-borehole electrical resistivity

    Energy Technology Data Exchange (ETDEWEB)

    Robinson, Judith; Johnson, Timothy C.; Slater, Lee D.

    2015-02-02

    There is an increasing need to characterize discrete fractures away from boreholes to better define fracture distributions and monitor solute transport. We performed a 3D evaluation of static and time-lapse cross-borehole electrical resistivity tomography (ERT) data sets from a limestone quarry in which flow and transport are controlled by a bedding-plane feature. Ten boreholes were discretized using an unstructured tetrahedral mesh, and 2D panel measurements were inverted for a 3D distribution of conductivity. We evaluated the benefits of 3D versus 2.5D inversion of ERT data in fractured rock while including the use of borehole regularization disconnects (BRDs) and borehole conductivity constraints. High-conductivity halos (inversion artifacts) surrounding boreholes were removed in static images when BRDs and borehole conductivity constraints were implemented. Furthermore, applying these constraints focused transient changes in conductivity resulting from solute transport on the bedding plane, providing a more physically reasonable model for conductivity changes associated with solute transport at this fractured rock site. Assuming bedding-plane continuity between fractures identified in borehole televiewer data, we discretized a planar region between six boreholes and applied a fracture regularization disconnect (FRD). Although the FRD appropriately focused conductivity changes on the bedding plane, the conductivity distribution within the discretized fracture was nonunique and dependent on the starting homogeneous model conductivity. Synthetic studies performed to better explain field observations showed that inaccurate electrode locations in boreholes resulted in low-conductivity halos surrounding borehole locations. These synthetic studies also showed that the recovery of the true conductivity within an FRD depended on the conductivity contrast between the host rock and fractures. Our findings revealed that the potential exists to improve imaging of fractured

  3. Experimental assessment of the sealing effectiveness of rock fracture grouting

    International Nuclear Information System (INIS)

    The objective of this investigation is to determine the effectiveness of cement grouts as sealants of fractures in rock. Laboratory experiments have been conducted on seven 15-cm granite cubes containing saw cuts, three 23-cm diameter andesite cores containing induced tension cracks, and one 15-cm diameter marble core containing a natural fracture. Prior to grouting, the hydraulic conductivity of the fractures is determined under a range of normal stresses, applied in loading and unloading cycles, from 0 to 14 MPa (2000 psi). Grout is injected through an axial borehole, at a pressure of 1.2 to 8.3 MPa (180 to 1200 psi), pressure selected to provide a likely groutable fracture aperture, while the fracture is stressed at a constant normal stress. The fracture permeability is measured after grouting. Flow tests on the ungrouted samples confirm the inverse relation between normal stress and fracture permeability. The equivalent aperture determined by these tests is a reliable indicator of groutability. Postgrouting permeability measurements as performed here, and frequently in practice, can be misleading, since incomplete grouting of fractures can result in major apparent reductions in permeability. The apparent permeability reduction is caused by grouting of a small area of a highly preferential flowpath directly adjacent to the hole used for grouting and for permeability testing. Experimental results confirm claims in the literature that ordinary portland cement inadequately penetrates fine fractures

  4. Streaming potential modeling in fractured rock: Insights into the identification of hydraulically active fractures

    CERN Document Server

    Roubinet, D; Jougnot, D; Irving, J

    2016-01-01

    Numerous field experiments suggest that the self-potential (SP) geophysical method may allow for the detection of hydraulically active fractures and provide information about fracture properties. However, a lack of suitable numerical tools for modeling streaming potentials in fractured media prevents quantitative interpretation and limits our understanding of how the SP method can be used in this regard. To address this issue, we present a highly efficient two-dimensional discrete-dual-porosity approach for solving the fluid flow and associated self-potential problems in fractured rock. Our approach is specifically designed for complex fracture networks that cannot be investigated using standard numerical methods. We then simulate SP signals associated with pumping conditions for a number of examples to show that (i) accounting for matrix fluid flow is essential for accurate SP modeling and (ii) the sensitivity of SP to hydraulically active fractures is intimately linked with fracture-matrix fluid interaction...

  5. Reactive-infiltration instabilities in rocks. Fracture dissolution

    CERN Document Server

    Szymczak, Piotr

    2012-01-01

    A reactive fluid dissolving the surface of a uniform fracture will trigger an instability in the dissolution front, leading to spontaneous formation of pronounced well-spaced channels in the surrounding rock matrix. Although the underlying mechanism is similar to the wormhole instability in porous rocks there are significant differences in the physics, due to the absence of a steadily propagating reaction front. In previous work we have described the geophysical implications of this instability in regard to the formation of long conduits in soluble rocks. Here we describe a more general linear stability analysis, including axial diffusion, transport limited dissolution, non-linear kinetics, and a finite length system.

  6. Mass transfer and transport of radionuclides in fractured porous rock

    International Nuclear Information System (INIS)

    Analytical studies are made to predict space-time dependent concentrations of radionuclides transported through water-saturated fractured porous rock. A basic model, which is expected to generate conservative results when used in long-term safety assessment of geologic repositories for radioactive waste, is established. Applicability and limitations of the model are investigated. 67 refs., 54 figs., 3 tabs

  7. Statistical fracture mechanics approach to the strength of brittle rock

    International Nuclear Information System (INIS)

    Statistical fracture mechanics concepts used in the past for rock are critically reviewed and modifications are proposed which are warranted by (1) increased understanding of fracture provided by modern fracture mechanics and (2) laboratory test data both from the literature and from this research. Over 600 direct and indirect tension tests have been performed on three different rock types; Stripa Granite, Sierra White Granite and Carrara Marble. In several instances assumptions which are common in the literature were found to be invalid. A three parameter statistical fracture mechanics model with Mode I critical strain energy release rate as the variant is presented. Methodologies for evaluating the parameters in this model as well as the more commonly employed two parameter models are discussed. The experimental results and analysis of this research indicate that surfacially distributed flaws, rather than volumetrically distributed flaws are responsible for rupture in many testing situations. For several of the rock types tested, anisotropy (both in apparent tensile strength and size effect) precludes the use of contemporary statistical fracture mechanics models

  8. Modelling water table drawdown and recovery during tunnel excavation in fractured rock: estimating environmental impacts and characterizing uncertainties in a heterogeneous domain

    Science.gov (United States)

    Sege, J.; Li, Y.; Chang, C. F.; Chen, J.; Chen, Z.; Rubin, Y.; Li, X.; Hehua, Z.; Wang, C.; Osorio-Murillo, C. A.

    2015-12-01

    This study will develop a numerical model to characterize the perturbation of local groundwater systems by underground tunnel construction. Tunnels and other underground spaces act as conduits that remove water from the surrounding aquifer, and may lead to drawdown of the water table. Significant declines in water table elevation can cause environmental impacts by altering root zone soil moisture and changing inflows to surface waters. Currently, it is common to use analytical solutions to estimate groundwater fluxes through tunnel walls. However, these solutions often neglect spatial and temporal heterogeneity in aquifer parameters and system stresses. Some heterogeneous parameters, such as fracture densities, can significantly affect tunnel inflows. This study will focus on numerical approaches that incorporate heterogeneity across a range of scales. Time-dependent simulations will be undertaken to compute drawdown at various stages of excavation, and to model water table recovery after low-conductivity liners are applied to the tunnel walls. This approach will assist planners in anticipating environmental impacts to local surface waters and vegetation, and in computing the amount of tunnel inflow reduction required to meet environmental targets. The authors will also focus on managing uncertainty in model parameters. For greater planning applicability, extremes of a priori parameter ranges will be explored in order to anticipate best- and worst-case scenarios. For calibration and verification purposes, the model will be applied to a completed tunnel project in Mount Mingtang, China, where tunnel inflows were recorded throughout the construction process.

  9. Rock fracture under anti-plane shear (Mode Ⅲ) loading

    Institute of Scientific and Technical Information of China (English)

    RAO Qiu-hua; LIAO Zhen-feng

    2005-01-01

    Anti-plane punch-through shear test and anti-planefour-point bending test are used to study the crack initiation and propagation under anti-plane shear (Mode Ⅲ) loading. The tensile and shear stresses at the crack tip are calculated by finite element method. The results show that under Mode Ⅲ loading the maximum principal stress σ1 at crack tip is smaller or a little larger than the maximum shear stress τmax. Since the tensile strength of brittle rock is much lower than its shear strength, σ1 is easy to reach its critical value before τmax reaches its critical value and thus results in Mode I fracture. The fracture trajectory is helicoid and the normal direction of tangential plane with the fractured helicoid is along the predicted direction of the maximum principal stress at the notch tip. It is further proved that Mode Ⅰ instead of Mode Ⅲ fracture occurs in brittle rock under Mode Ⅲ loading. The fracture mode depending on the fracture mechanism must be distinguished from the loading form.

  10. Effect of loading point position on fracture mode of rock

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Anti-symmetric four-point bending specimen with different loading point positions was used to study effect of loading point position on fracture mode of rock in order to explore a feasible method for achieving Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock, KⅡC. Numerical and experimental results show that the distance between the inner and outer loading points, L1+L2, has a great influence on stresses at notch tip and fracture mode. When L1+L2>0.5L or 0.1L<L1+L2<0.5L, maximum principal stress σ1 exceeds the tensile strength σt. The ratio of τmax/σ1 is relatively low or high and thus Mode Ⅰ or mixed mode fracture occurs. When L1+L2<0.1L, σ1 is smaller than σt and the ratio of τmax/σ1 is much higher, which facilitates the occurrence of Mode Ⅱ fracture.

  11. Quantifying Fracture Heterogeneity in Different Domains of Folded Carbonate Rocks to Improve Fractured Reservoir Analog Fluid Flow Models

    NARCIS (Netherlands)

    Bisdom, K.; Bertotti, G.; Gauthier, B.D.M.; Hardebol, N.J.

    2013-01-01

    Fluid flow in carbonate reservoirs is largely controlled by multiscale fracture networks. Significant variations of fracture network porosity and permeability are caused by the 3D heterogeneity of the fracture network characteristics, such as intensity, orientation and size. Characterizing fracture

  12. Dynamic injection tests of dense slurry into fine rock fractures

    International Nuclear Information System (INIS)

    Dynamic injection is the technology that efficiently injects with high dense slurry into small rock fractures. This technology may be expected for the improvement of fluidity and a penetration property of grout materials and the prevention of blockade phenomena. On this study, in order to make clear the effect of the dynamic injection method and the condition of pulsation pressure, injection tests with a fine model fractures and rheological tests under a proper vibration were made for high dense and viscosity grout materials. (author)

  13. Discrete fracture hydromechanical model for the disturbed rock zone in a clay rock

    Science.gov (United States)

    Asahina, D.; Houseworth, J. E.; Birkholzer, J. T.

    2013-12-01

    We have developed a coupled thermal-hydrological-mechanical (THM) fracture damage model, TOUGH-RBSN, to investigate the behavior of fracture generation and evolution in rock in the presence of perturbations to THM conditions. This model combines the capabilities of the TOUGH2 simulator to represent thermal-hydrological processes with a rigid-body-spring-network (RBSN) model, a type of discrete modeling, to treat geomechanical and fracture-damage processes. In particular, the development and evolution of fractures in the excavation damaged zone (EDZ) of a clay rock, with application to high-level nuclear waste disposal, is a focus for this model development. Previously, the TOUGH-RBSN approach has been used to model fracture damage under tensile conditions as a result of desiccation shrinkage. The next phase of model testing will be application to the HG-A test being conducted at the Mont Terri underground research laboratory (URL) near Saint-Ursanne, Switzerland. This test is being conducted in a 13-m long, 1-m diameter microtunnel in the Opalinus clay rock in which a test section at the far end of the microtunnel is isolated using a packer. The test is specifically targeted to observe how fluids injected into the test section penetrate into the rock, with particular emphasis on the EDZ. The HG-A microtunnel was excavated in 2005 and subsequent mapping of the tunnel surface shows preferential fracturing and tunnel breakouts along zones where bedding planes are tangential to the tunnel wall and where faults intercept the tunnel. It appears that the EDZ fracture damage can be attributed to both tensile and shear fracturing mechanisms. A series of injection tests with water and gas have been performed which also show preferential invasion of the fluid pressure along the observed damage zones, as well as fracture self-sealing over time. The TOUGH-RBSN approach has been successfully applied to modeling fracture driven by predominately tensile loading, whereas only

  14. Laboratory characterization of rock joints

    International Nuclear Information System (INIS)

    A laboratory characterization of the Apache Leap tuff joints under cyclic pseudostatic and dynamic loads has been undertaken to obtain a better understanding of dynamic joint shear behavior and to generate a complete data set that can be used for validation of existing rock-joint models. Study has indicated that available methods for determining joint roughness coefficient (JRC) significantly underestimate the roughness coefficient of the Apache Leap tuff joints, that will lead to an underestimation of the joint shear strength. The results of the direct shear tests have indicated that both under cyclic pseudostatic and dynamic loadings the joint resistance upon reverse shearing is smaller than that of forward shearing and the joint dilation resulting from forward shearing recovers during reverse shearing. Within the range of variation of shearing velocity used in these tests, the shearing velocity effect on rock-joint behavior seems to be minor, and no noticeable effect on the peak joint shear strength and the joint shear strength for the reverse shearing is observed

  15. Laboratory characterization of rock joints

    Energy Technology Data Exchange (ETDEWEB)

    Hsiung, S.M.; Kana, D.D.; Ahola, M.P.; Chowdhury, A.H.; Ghosh, A. [Southwest Research Inst., San Antonio, TX (United States). Center for Nuclear Waste Regulatory Analyses

    1994-05-01

    A laboratory characterization of the Apache Leap tuff joints under cyclic pseudostatic and dynamic loads has been undertaken to obtain a better understanding of dynamic joint shear behavior and to generate a complete data set that can be used for validation of existing rock-joint models. Study has indicated that available methods for determining joint roughness coefficient (JRC) significantly underestimate the roughness coefficient of the Apache Leap tuff joints, that will lead to an underestimation of the joint shear strength. The results of the direct shear tests have indicated that both under cyclic pseudostatic and dynamic loadings the joint resistance upon reverse shearing is smaller than that of forward shearing and the joint dilation resulting from forward shearing recovers during reverse shearing. Within the range of variation of shearing velocity used in these tests, the shearing velocity effect on rock-joint behavior seems to be minor, and no noticeable effect on the peak joint shear strength and the joint shear strength for the reverse shearing is observed.

  16. Fracture and Healing of Rock Salt Related to Salt Caverns

    Energy Technology Data Exchange (ETDEWEB)

    Chan, K.S.; Fossum, A.F.; Munson, D.E.

    1999-03-01

    In recent years, serious investigations of potential extension of the useful life of older caverns or of the use of abandoned caverns for waste disposal have been of interest to the technical community. All of the potential applications depend upon understanding the reamer in which older caverns and sealing systems can fail. Such an understanding will require a more detailed knowledge of the fracture of salt than has been necessary to date. Fortunately, the knowledge of the fracture and healing of salt has made significant advances in the last decade, and is in a position to yield meaningful insights to older cavern behavior. In particular, micromechanical mechanisms of fracture and the concept of a fracture mechanism map have been essential guides, as has the utilization of continuum damage mechanics. The Multimechanism Deformation Coupled Fracture (MDCF) model, which is summarized extensively in this work was developed specifically to treat both the creep and fracture of salt, and was later extended to incorporate the fracture healing process known to occur in rock salt. Fracture in salt is based on the formation and evolution of microfractures, which may take the form of wing tip cracks, either in the body or the boundary of the grain. This type of crack deforms under shear to produce a strain, and furthermore, the opening of the wing cracks produce volume strain or dilatancy. In the presence of a confining pressure, microcrack formation may be suppressed, as is often the case for triaxial compression tests or natural underground stress situations. However, if the confining pressure is insufficient to suppress fracture, then the fractures will evolve with time to give the characteristic tertiary creep response. Two first order kinetics processes, closure of cracks and healing of cracks, control the healing process. Significantly, volume strain produced by microfractures may lead to changes in the permeability of the salt, which can become a major concern in

  17. Characterization of Fractured Reservoirs Using a Combination of Downhole Pressure and Self-Potential Transient Data

    OpenAIRE

    Yuji Nishi; Tsuneo Ishido

    2012-01-01

    In order to appraise the utility of self-potential (SP) measurements to characterize fractured reservoirs, we carried out continuous SP monitoring using multi Ag-AgCl electrodes installed within two open holes at the Kamaishi Mine, Japan. The observed ratio of SP change to pressure change associated with fluid flow showed different behaviors between intact host rock and fractured rock regions. Characteristic behavior peculiar to fractured reservoirs, which is predicted from numerical simulati...

  18. Radionuclide transport and retardation in rock fracture and crushed rock column experiments

    Science.gov (United States)

    Höltä, P.; Siitari-Kauppi, M.; Hakanen, M.; Huitti, T.; Hautojärvi, A.; Lindberg, A.

    1997-04-01

    Transport and retardation of non-sorbing tritiated water and chloride and slightly sorbing sodium was studied in Syyry area SY-KR7 mica gneiss, in altered porous tonalite and in fresh tonalite. Experiments were performed using dynamic fracture and crushed rock column methods. Static batch method for sodium was introduced to compare retardation values from static and dynamic experiments. The 14C-PMMA method was used to study the pore structure of matrices. The pore aperture distribution was evaluated from Hg-porosimetry determinations and the surface areas were determined using the B.E.T. method. The flow characteristics and transport behavior of tracers were interpreted using a numerical compartment model for dispersion. The effect of matrix diffusion was calculated using an analytical solution to the advection-matrix diffusion problem in which surface retardation was taken into account. Radionuclide transport behavior in rock fractures was explained on the basis of rock structure.

  19. Groundwater degassing in fractured rock: Modelling and data comparison

    Energy Technology Data Exchange (ETDEWEB)

    Jarsjoe, J.; Destouni, G. [Royal Inst. of Tech., Stockholm (Sweden). Water Resources Engineering

    1998-11-01

    Dissolved gas may be released from deep groundwater in the vicinity of open boreholes and drifts, where the water pressures are relatively low. Degassing of groundwater may influence observations of hydraulic conditions made in drifts, interpretation of experiments performed close to drifts, and buffer mass and backfill performance, particularly during emplacement and repository closure. Under certain conditions, considerable fracture inflow and transmissivity reductions have been observed during degassing experiments in the field and in the laboratory; such reductions affect the outcome and interpretation of both hydraulic and tracer tests. We develop models for the estimation of the resulting degree of fracture gas saturation and the associated transmissivity reduction due to groundwater degassing in fractured rock. Derived expressions for bubble trapping probability show that fracture aperture variability and correlation length influence the conditions for capillary bubble trapping and gas accumulation. The laboratory observations of bubble trapping in an Aespoe fracture replica are consistent with the prediction of a relatively high probability of bubble trapping in this fracture. The prediction was based on the measured aperture distribution of the Aespoe fracture and the applied hydraulic gradient. Results also show that the conceptualisation of gas and water occupancy in a fracture greatly influences model predictions of gas saturation and relative transmissivity. Images from laboratory degassing experiments indicate that tight apertures are completely filled with water, whereas both gas and water exist in wider apertures under degassing conditions; implementation of this relation in our model resulted in the best agreement between predictions and laboratory observations. Model predictions for conditions similar to those prevailing in field for single fractures at great depths indicate that degassing effects in boreholes should generally be small, unless the

  20. Discrete fracture modelling of the Finnsjoen rock mass: Phase 2

    International Nuclear Information System (INIS)

    A discrete fracture network (DFN) model of the Finnsjoen site was derived from field data, and used to predict block-scale flow and transport properties. The DFN model was based on a compound Poisson process, with stochastic fracture zones, and individual fracture concentrated around the fracture zones. This formulation was used to represent the multitude of fracture zones at the site which could be observed on lineament maps and in boreholes, but were not the focus of detailed characterization efforts. Due to a shortage of data for fracture geometry at depth, distributions of fracture orientation and size were assumed to be uniform throughout the site. Transmissivity within individual fracture planes was assumed to vary according to a fractal model. Constant-head packer tests were simulated with the model, and the observed transient responses were compared with actual tests in terms of distributions of interpreted transmissivity and flow dimension, to partially validate the model. Both simulated and actual tests showed a range of flow dimension from sublinear to spherical, indicating local variations in the connectivity of the fracture population. A methodology was developed for estimation of an effective stochastic continuum from the DFN model, but this was only partly demonstrated. Directional conductivities for 40 m block were estimated using the DFN model. These show extremely poor correlation with results of multiple packer tests in the same blocks, indicating possible limitation of small-scale packer tests for predicting block-scale properties. Estimates are given of effective flow porosity and flow wetted surface, based on the block-scale flow fields calculated by the DFN model, and probabilistic models for the relationships among local fracture transmissivity, void space, and specific surface. The database for constructing these models is extremely limited. A review is given of the existing database for single fracture hydrologic properties. (127 refs

  1. Spatial statistics for predicting flow through a rock fracture

    Energy Technology Data Exchange (ETDEWEB)

    Coakley, K.J.

    1989-03-01

    Fluid flow through a single rock fracture depends on the shape of the space between the upper and lower pieces of rock which define the fracture. In this thesis, the normalized flow through a fracture, i.e. the equivalent permeability of a fracture, is predicted in terms of spatial statistics computed from the arrangement of voids, i.e. open spaces, and contact areas within the fracture. Patterns of voids and contact areas, with complexity typical of experimental data, are simulated by clipping a correlated Gaussian process defined on a N by N pixel square region. The voids have constant aperture; the distance between the upper and lower surfaces which define the fracture is either zero or a constant. Local flow is assumed to be proportional to local aperture cubed times local pressure gradient. The flow through a pattern of voids and contact areas is solved using a finite-difference method. After solving for the flow through simulated 10 by 10 by 30 pixel patterns of voids and contact areas, a model to predict equivalent permeability is developed. The first model is for patterns with 80% voids where all voids have the same aperture. The equivalent permeability of a pattern is predicted in terms of spatial statistics computed from the arrangement of voids and contact areas within the pattern. Four spatial statistics are examined. The change point statistic measures how often adjacent pixel alternate from void to contact area (or vice versa ) in the rows of the patterns which are parallel to the overall flow direction. 37 refs., 66 figs., 41 tabs.

  2. Low- and intermediate level radioactive waste from Risoe, Denmark. Location studies for potential disposal areas. Report no. 2. Characterization of low permeable and fractured sediments and rocks in Denmark

    International Nuclear Information System (INIS)

    The low and intermediate level radioactive waste from Risoe (the nuclear reactor buildings plus different types of material from the research periods) and radioactive waste from hospitals and research institutes have to be stored in a final disposal in Denmark for at least 300 years. In Denmark, many different kinds of fine-grained sediments and crystalline rocks occur from the ground surface down to 300 meters depth. Therefore, the possible geological situations include sediments and rocks of different composition and age. These situations are geographical distributed over large areas of Denmark. These sediments and rocks are shortly described based on existing information and include five different major types of sediments and rocks: 1: Crystalline granite and gneiss of Bornholm (because these rock types are host for waste disposals in many other countries). 2: Sandstone and shale from Bornholm (as these sediments are rela- tively homogeneous although they have fracture permeability). 3: Chalk and limestone (because these sediments may act as low permeable seals, but in most areas they act as groundwater reservoirs). 4: Fine-grained Tertiary clay deposits (as these sediments have a low permeability, are widely distributed and can reach large thicknesses). 5: Quaternary glacial, interglacial and Holocene clay deposits. These sediments are distributed all over Denmark. Following the descriptions of the geologic deposits, the areas below (including several possible locations for waste disposal sites) are selected for further investigation. The Precambrian basement rocks of Bornholm could be host rocks for the disposal. The rock types for further evaluation will be: Hammer Granite, Vang Granite, Roenne Granite, Bornholm gneiss, Paradisbakke Migmatite and Alminding Granite. In the Roskilde Fjord area around Risoe, a combination of Paleocene clays, meltwater clay and clayey till could be interesting. The area is partly included in the OSD area in North Sjaelland but

  3. Low- and intermediate level radioactive waste from Risoe, Denmark. Location studies for potential disposal areas. Report no. 2. Characterization of low permeable and fractured sediments and rocks in Denmark

    Energy Technology Data Exchange (ETDEWEB)

    Gravesen, P.; Nilsson, B.; Schack Pedersen, S.A.; Binderup, M.; Laier, T.

    2011-07-01

    The low and intermediate level radioactive waste from Risoe (the nuclear reactor buildings plus different types of material from the research periods) and radioactive waste from hospitals and research institutes have to be stored in a final disposal in Denmark for at least 300 years. In Denmark, many different kinds of fine-grained sediments and crystalline rocks occur from the ground surface down to 300 meters depth. Therefore, the possible geological situations include sediments and rocks of different composition and age. These situations are geographical distributed over large areas of Denmark. These sediments and rocks are shortly described based on existing information and include five different major types of sediments and rocks: 1: Crystalline granite and gneiss of Bornholm (because these rock types are host for waste disposals in many other countries). 2: Sandstone and shale from Bornholm (as these sediments are rela- tively homogeneous although they have fracture permeability). 3: Chalk and limestone (because these sediments may act as low permeable seals, but in most areas they act as groundwater reservoirs). 4: Fine-grained Tertiary clay deposits (as these sediments have a low permeability, are widely distributed and can reach large thicknesses). 5: Quaternary glacial, interglacial and Holocene clay deposits. These sediments are distributed all over Denmark. Following the descriptions of the geologic deposits, the areas below (including several possible locations for waste disposal sites) are selected for further investigation. The Precambrian basement rocks of Bornholm could be host rocks for the disposal. The rock types for further evaluation will be: Hammer Granite, Vang Granite, Roenne Granite, Bornholm gneiss, Paradisbakke Migmatite and Alminding Granite. In the Roskilde Fjord area around Risoe, a combination of Paleocene clays, meltwater clay and clayey till could be interesting. The area is partly included in the OSD area in North Sjaelland but

  4. Application of Stochastic Fracture Network with Numerical Fluid Flow Simulations to Groundwater Flow Modeling in Fractured Rocks

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The continuum approach in fluid flow modeling is generally applied to porous geological media,but has limitel applicability to fractured rocks. With the presence of a discrete fracture network relatively sparsely distributed in the matrix, it may be difficult or erroneous to use a porous medium fluid flow model with continuum assumptions to describe the fluid flow in fractured rocks at small or even large field scales. A discrete fracture fluid flow approach incorporating a stochastic fracture network with numerical fluid flow simulations could have the capability of capturing fluid flow behaviors such as inhomogeneity and anisotropy while reflecting the changes of hydraulic features at different scales.Moreover, this approach can be implemented to estimate the size of the representative elementary volume (REV) in order to find out the scales at which a porous medium flow model could be applied, and then to determine the hydraulic conductivity tensor for fractured rocks. The following topics are focused on in this study: (a) conceptual discrete fracture fluid flow modeling incorporating a stochastic fracture network with numerical flow simulations; (b) estimation of REVand hydraulic conductivity tensor for fractured rocks utilizing a stochastic fracture network with numerical fluid flow simulations; (c) investigation of the effect of fracture orientation and density on the hydraulic conductivity and REV by implementing a stochastic fracture network with numerical fluid flow simulations, and (d) fluid flow conceptual models accounting for major and minor fractures in the 2-D or 3-D flow fields incorporating a stochastic fracture network with numerical fluid flow simulations.``

  5. Mechanics, hydraulic and coupled hydromechanics of fractured rock mass investigated by numerical experiment

    International Nuclear Information System (INIS)

    The Discrete Fracture Network-Discrete Element Method (DFN-DEM) approach uses DFN as the geometry of fractured rock and DEM for the solution technique to simulate the hydraulic and mechanical behaviour of fractured rock. This overview paper intends to summarize the applications on fractured rock using the DFN-DEM approach with the focus upon the determination of mechanical and hydraulic properties of fractured rock and their stress dependencies. The establishment of methodologies and actual applications in a site considered for geological repository of nuclear waste are introduced. (author)

  6. Fracturing tests on reservoir rocks: Analysis of AE events and radial strain evolution

    CERN Document Server

    Pradhan, S; Fjær, E; Stenebråten, J; Lund, H K; Sønstebø, E F; Roy, S

    2015-01-01

    Fracturing in reservoir rocks is an important issue for the petroleum industry - as productivity can be enhanced by a controlled fracturing operation. Fracturing also has a big impact on CO2 storage, geothermal installation and gas production at and from the reservoir rocks. Therefore, understanding the fracturing behavior of different types of reservoir rocks is a basic need for planning field operations towards these activities. In our study, the fracturing of rock sample is monitored by Acoustic Emission (AE) and post-experiment Computer Tomography (CT) scans. The fracturing experiments have been performed on hollow cylinder cores of different rocks - sandstones and chalks. Our analysis show that the amplitudes and energies of acoustic events clearly indicate initiation and propagation of the main fractures. The amplitudes of AE events follow an exponential distribution while the energies follow a power law distribution. Time-evolution of the radial strain measured in the fracturing-test will later be comp...

  7. Structural controls on anomalous transport in fractured porous rock

    Science.gov (United States)

    Edery, Yaniv; Geiger, Sebastian; Berkowitz, Brian

    2016-07-01

    Anomalous transport is ubiquitous in a wide range of disordered systems, notably in fractured porous formations. We quantitatively identify the structural controls on anomalous tracer transport in a model of a real fractured geological formation that was mapped in an outcrop. The transport, determined by a continuum scale mathematical model, is characterized by breakthrough curves (BTCs) that document anomalous (or "non-Fickian") transport, which is accounted for by a power law distribution of local transition times ψ>(t>) within the framework of a continuous time random walk (CTRW). We show that the determination of ψ>(t>) is related to fractures aligned approximately with the macroscopic direction of flow. We establish the dominant role of fracture alignment and assess the statistics of these fractures by determining a concentration-visitation weighted residence time histogram. We then convert the histogram to a probability density function (pdf) that coincides with the CTRW ψ>(t>) and hence anomalous transport. We show that the permeability of the geological formation hosting the fracture network has a limited effect on the anomalous nature of the transport; rather, it is the fractures transverse to the flow direction that play the major role in forming the long BTC tail associated with anomalous transport. This is a remarkable result, given the complexity of the flow field statistics as captured by concentration transitions.

  8. Site characterization in densely fractured dolomite: Comparison of methods

    Science.gov (United States)

    Muldoon, M.; Bradbury, K.R.

    2005-01-01

    One of the challenges in characterizing fractured-rock aquifers is determining whether the equivalent porous medium approximation is valid at the problem scale. Detailed hydrogeologic characterization completed at a small study site in a densely fractured dolomite has yielded an extensive data set that was used to evaluate the utility of the continuum and discrete-fracture approaches to aquifer characterization. There are two near-vertical sets of fractures at the site; near-horizontal bedding-plane partings constitute a third fracture set. Eighteen boreholes, including five coreholes, were drilled to a depth of ???10.6 m. Borehole geophysical logs revealed several laterally extensive horizontal fractures and dissolution zones. Flowmeter and short-interval packer testing identified which of these features were hydraulically important. A monitoring system, consisting of short-interval piezometers and multilevel samplers, was designed to monitor four horizontal fractures and two dissolution zones. The resulting network consisted of >70 sampling points and allowed detailed monitoring of head distributions in three dimensions. Comparison of distributions of hydraulic head - and hydraulic conductivity determined by these two approaches suggests that even in a densely fractured-carbonate aquifer, a characterization approach using traditional long-interval monitoring wells is inadequate to characterize ground water movement for the purposes of regulatory monitoring or site remediation. In addition, traditional multiwell pumping tests yield an average or bulk hydraulic conductivity that is not adequate for predicting rapid ground water travel times through the fracture network, and the pumping test response does not appear to be an adequate tool for assessing whether the porous medium approximation is valid. Copyright ?? 2005 National Ground Water Association.

  9. Preliminary capillary hysteresis simulations in fractured rocks, Yucca Mountain, Nevada

    Science.gov (United States)

    Niemi, A.; Bodvarsson, G. S.

    1988-12-01

    Preliminary simulations have been carried out to address the question of how hysteretic (history-dependent) capillary pressure-liquid saturation relation may affect the flow and liquid saturation distribution in a fractured rock system. Using a hysteresis model modified from the theoretically based dependent domain model of Mualem (1984), a system consisting of discrete fractures and rock matrix parts was simulated under periodically occurring infiltration pulses. Comparisons were made between the hysteretic case and the non-hysteretic case using the main drying curve alone. Material properties used represent values reported for the densely welded tuffs at Yucca Mountain, Nevada. Since no actual hysteresis measurements were available for the welded tuffs, the necessary data was derived based on information available in the soils literature The strongly hysteretic behavior in the uppermost layer of the matrix along with the overall lower matrix capillary suctions, generated higher fracture flows and a more "smeared" matrix liquid saturation vs. depth distribution for the hysteretic case. While the actual amounts of water being absorbed into the matrix were very similar, the distributions of this absorbed water were different and the matrix was affected up to greater depths in the hysteretic case in comparison to the non-hysteretic case.

  10. Simulation of fluid flow in fractured rock: a probabilistic approach

    International Nuclear Information System (INIS)

    This report describes the results of a research project designed to investigate the influence of discontinuities on fluid flow through fractured rock masses. The aim has been to provide a rational basis for the assessment of prospective intermediate level radioactive waste repository sites. The results of this work are presented in the form of two groups of FORTRAN computer programs. The first of these is designed to process data obtained from exposed rock faces and thereby provide an unbiased estimate of discontinuity characteristics. The resulting data are input to the second group of programs which generate a two-dimensional random realisation of discontinuity geometry. When appropriate boundary conditions have been specified, the resulting network of channels is solved numerically to determine nodal potentials, flow quantities and equivalent permeabilities. A number of validation runs are presented, together with some parametric studies, to investigate the influence of excavation size and discontinuity geometry on fluid flow. A practical application is given in the form of a case study involving the prediction of fluid flow into a 2.8 m diameter tunnel in water bearing, fractured rock. Finally, the applications and limitations of the programs in site assessment for radioactive waste repositories are discussed. (author)

  11. Characterizing Hydraulic Properties and Ground-Water Chemistry in Fractured-Rock Aquifers: A User's Manual for the Multifunction Bedrock-Aquifer Transportable Testing Tool (BAT3)

    Science.gov (United States)

    Shapiro, Allen M.

    2007-01-01

    packers, the submersible pump, and other downhole components to land surface. Borehole geophysical logging must be conducted prior to deploying the Multifunction BAT3 in bedrock boreholes. In particular, it is important to identify the borehole diameter as a function of depth to avoid placing the packers over rough sections of the borehole, where they may be damaged during inflation. In addition, it is advantageous to identify the location of fractures intersecting the borehole wall, for example, using an acoustic televiewer log or a borehole camera. A knowledge of fracture locations is helpful in designing the length of the test interval and the locations where hydraulic tests and geochemical sampling are to be conducted. The Multifunction BAT3 is configured to conduct both fluid-injection and fluid-withdrawal tests. Fluid-injection tests are used to estimate the hydraulic properties of low-permeability fractures intersecting the borehole. The lower limit of the transmissivity that can be estimated using the configuration of the Multifunction BAT3 described in this report is approximately 10-3 square feet per day (ft2/d). Fluid-withdrawal tests are used to collect water samples for geochemical analyses and estimate the hydraulic properties of high-permeability fractures intersecting the borehole. The Multifunction BAT3 is configured with a submersible pump that can support pumping rates ranging from approximately 0.05 to 2.5 gallons per minute, and the upper limit of the of the transmissivity that can be estimated is approximately 104 ft2/d. The Multifunction BAT3 also can be used to measure the ambient hydraulic head of a section of a bedrock borehole, and to conduct single-hole tracer tests by injecting and later withdrawing a tracer solution.

  12. Hydrogeological discrete fracture modelling to support rock suitability classification

    International Nuclear Information System (INIS)

    This report presents hydrogeological discrete fracture network (Hydro-DFN) modelling in support of the testing and development of the Posiva's Rock Suitability Classification (RSC) system. The aims are to: quantify information on the fulfilment of the inflow and large fracture criteria in the deposition tunnels and deposition holes; provide information on likely properties adjacent to large fractures and deformation zones; and quantify saline water upconing to support definition of the respect distances to the fault zones and hydraulically active zones. The work presented is an update to a previous RSC study performed in 2010, making use of an updated Hydro-DFN model developed for the 2012 Site Descriptive Model (SDM) accounting for new data, in particular that acquired underground in the pilot holes drilled ahead of the ONKALO facility. The interpretation of the tunnel pilot holes has provided a lower detection limit on the specific capacity of hydraulic fractures resulting in a higher overall number of inflows to deposition holes being simulated than in the previous study, although these are small in magnitude, and simulated inflows above 1 L/min are now very rare. Out of the 5391 possible deposition hole positions considered in the modelling, of order 100 are above the RSC limit of 0.1 L/min. It is demonstrated that screening such positions generally avoids locations with the highest post-closure flow-rates. Screening of positions in direct contact with large hydraulic fractures (defined as connected open fractures with equivalent radius greater than 75 m and at least one intersect with a deposition tunnel) is also very effective in avoiding the majority of locations with relatively high predicted post-closure flow-rates. Total inflows to the c. 40 km of deposition and adjacent central tunnels after grouting are of order 100 L/min. (orig.)

  13. Hydrogeological discrete fracture modelling to support rock suitability classification

    Energy Technology Data Exchange (ETDEWEB)

    Hartley, L.; Hoek, J.; Swan, D.; Baxter, D.; Woollard, H. [AMEC, Oxford (United Kingdom)

    2014-01-15

    This report presents hydrogeological discrete fracture network (Hydro-DFN) modelling in support of the testing and development of the Posiva's Rock Suitability Classification (RSC) system. The aims are to: quantify information on the fulfilment of the inflow and large fracture criteria in the deposition tunnels and deposition holes; provide information on likely properties adjacent to large fractures and deformation zones; and quantify saline water upconing to support definition of the respect distances to the fault zones and hydraulically active zones. The work presented is an update to a previous RSC study performed in 2010, making use of an updated Hydro-DFN model developed for the 2012 Site Descriptive Model (SDM) accounting for new data, in particular that acquired underground in the pilot holes drilled ahead of the ONKALO facility. The interpretation of the tunnel pilot holes has provided a lower detection limit on the specific capacity of hydraulic fractures resulting in a higher overall number of inflows to deposition holes being simulated than in the previous study, although these are small in magnitude, and simulated inflows above 1 L/min are now very rare. Out of the 5391 possible deposition hole positions considered in the modelling, of order 100 are above the RSC limit of 0.1 L/min. It is demonstrated that screening such positions generally avoids locations with the highest post-closure flow-rates. Screening of positions in direct contact with large hydraulic fractures (defined as connected open fractures with equivalent radius greater than 75 m and at least one intersect with a deposition tunnel) is also very effective in avoiding the majority of locations with relatively high predicted post-closure flow-rates. Total inflows to the c. 40 km of deposition and adjacent central tunnels after grouting are of order 100 L/min. (orig.)

  14. Preliminary Rock Physics Characterization of Mississippian Carbonate Reservoir in Canada

    Science.gov (United States)

    Lee, M.; Keehm, Y.; Kim, H.

    2011-12-01

    The Mississippian formations in the Western Canada Sedimentary Basin are known to have large hydrocarbon resources. The Lodgepole formation is the most important reservoir for oil production in Daly and Virden fields. In this study, we performed preliminary reservoir characterization using rock physics modeling. We first delineated the Lodgepole formation by geological information, well-logs and core analysis data. Then, we conducted rock physics analyses such as GR-AI, DEM modeling, porosity-Vp, density-Vp, and porosity-permeability. We identified the Lodgepole formation has different porosity types, volume of shale, and the degree of fractures in difference intervals. In the upper part of the formation, we found that vuggy pores are well developed. Inter-particular porosity and fractures become significant as the depth increases. We found that the lower part can be divided into two groups by acoustic impedance. The prospective reservoir interval, one of the two groups, has higher fracture density, which can be identified by lower acoustic impedance. This result also implies that we could also use AVO analyses to delineate good reservoir intervals. In conclusion, rock physics modeling can be effectively applied to characterize the Lodgepole formation quantitatively with well-log and core analysis data. Acknowledgement: This work was supported by the Energy Resources R&D program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 2009201030001A).

  15. Development of fractures in soft rock surrounding a roadway and their control

    Institute of Scientific and Technical Information of China (English)

    Li Xuehua; Yao Qiangling; Man Jiankang; Chen Chaoqun; He Lihui

    2011-01-01

    As the excavation of roadway,new fractures will be formed and the pre-existing fractures extend with the redistribution of stress in surrounding rocks.Eventually,fracture zone and bed separation are formed in rocks because of the developed fractures.Therefore,mastering the fracture evolution of surrounding rocks is very important to maintain the stability of roadway.The surrounding rocks of main haulage roadway in a certain coal mine is so broken and loose that the supporting is very difficult.Based on comprehensive analysis of the engineering geological conditions,a sight instrument was used to observe the fractures of internal surrounding rocks.Four indices,i.e.,the width of fracture zone W,the number of fractures n,the width of fractures d and rock fracture designation RFD,are put forward to evaluate the fracture development.According to the evolution rules of the soft rock roadway from this paper,control principles by stages and by regions are presented through the research.At the same time,the best time of grouting reinforcement is determined on the basis of fracture saturation.Field practice shows that the roadway can satisfy normal production during service periods by suitable first support and grouting reinforcement.

  16. Rock fracture by ice segregation: linking laboratory modelling and rock slope erosion

    Science.gov (United States)

    Murton, J.

    2009-04-01

    It has been unclear until recently if ice can fracture intact bedrock subject to natural freezing regimes, or whether it simply enlarges existing fractures or does both. This question is important, because if ice segregation in bedrock permafrost is widespread, then there may be considerable potential for significantly increased rock slope instability as ice-cemented discontinuities warm and active layers thicken. Laboratory modelling has now begun to elucidate the process of ice segregation in bedrock. Laboratory experiments indicate that moist, porous rock behaves remarkably like moist, frost-susceptible soil, with both substrates experiencing ice enrichment and fracture / fissuring of near-surface permafrost. It appears that significant concentrations of segregated ice are most likely in the transition zone between the active layer and the permafrost, as a result of downward migration of water in summer and upward advance of freezing at the beginning of the winter. Laboratory modelling indicates that given adequate water supply, ice segregation produces a zone of ice-bonded fractured bedrock immediately below the permafrost table. In general, the importance of ice segregation relative to in situ volume expansion increases with decreasing thermal gradients and increasing duration of freezing. Recent theoretical developments suggest that the maximum possible disjointing pressure is governed by the temperature depression below the bulk-melting point, even in the absence of large temperature gradients, and therefore slow ice segregation in bedrock may be possible at greater depths where the frozen permeability of rock limits the actual amount of heave produced. Thus, over long timescales, ice segregation may be highly significant in frozen steep bedrock slopes where the presence of ice-rich fractured bedrock may be critically important in releasing rock falls and rock slides during climate-induced warming and permafrost degradation. With recent climate warming

  17. Upscaling of permeability field of fractured rock system: Numerical examples

    KAUST Repository

    Bao, K.

    2012-01-01

    When the permeability field of a given porous medium domain is heterogeneous by the existence of randomly distributed fractures such that numerical investigation becomes cumbersome, another level of upscaling may be required. That is such complex permeability field could be relaxed (i.e., smoothed) by constructing an effective permeability field. The effective permeability field is an approximation to the real permeability field that preserves certain quantities and provides an overall acceptable description of the flow field. In this work, the effective permeability for a fractured rock system is obtained for different coarsening scenarios starting from very coarse mesh all the way towards the fine mesh simulation. In all these scenarios, the effective permeability as well as the pressure at each cell is obtained. The total flux at the exit boundary is calculated in all these cases, and very good agreement is obtained.

  18. MATLOC, Transient Non Linear Deformation in Fractured Rock

    International Nuclear Information System (INIS)

    1 - Description of program or function: MATLOC is a nonlinear, transient, two-dimensional (planer and axisymmetric), thermal-stress, finite-element code designed to determine the deformation within a fractured rock mass. The mass is modeled as a nonlinear anisotropic elastic material which can exhibit stress-dependent bi-linear locking behavior. 2 - Method of solution: The numerical solution of the nonlinear equilibrium equations is performed using the incremental tangential stiffness method in which the material stiffness matrices are continually updated. 3 - Restrictions on the complexity of the problem: Three-dimensional deformations and discontinuous displacements across open fractures and faults cannot be modeled. MATLOC can solve a problem with of 400 elements with up to 1000 nodes, of which 200 may be fixed

  19. Characterization and flow simulations of discrete fracture networks

    OpenAIRE

    Zeeb, Conny

    2013-01-01

    Fractures, such as joints, faults and veins, strongly influence the transport of fluids through rocks by either enhancing or inhibiting flow. Especially in rocks with negligible permeability fractures can act as major for fluid conduits. Therefore, the contribution of fracture networks to the overall flow behavior is of high interest to, for example, the hydrocarbon industry, the power generation using deep geothermal systems, the sustainable management of fractured rock aquifers, the plannin...

  20. Seismic characterization of fracture properties

    International Nuclear Information System (INIS)

    The purpose of this paper is to show that there is a relationship, both empirical and theoretical, between the measured seismic response, the mechanical stiffness (also referred to as specific stiffness) of fractures and their hydraulic conductivity. Laboratory measurements of the mechanical stiffness, hydraulic conductivity and seismic properties of natural fractures are summarized. A theoretical model for the amplitude and group time delay for compressional and shear waves transmitted across a single fracture is presented. Predictions based on this model are compared with laboratory measurements. Finally, the results for a single fracture are extended to multiple parallel fractures. 13 refs., 6 figs

  1. Three-Dimensional Geostatistical Analysis of Rock Fracture Roughness and Its Degradation with Shearing

    Directory of Open Access Journals (Sweden)

    Nima Babanouri

    2013-12-01

    Full Text Available Three-dimensional surface geometry of rock discontinuities and its evolution with shearing are of great importance in understanding the deformability and hydro-mechanical behavior of rock masses. In the present research, surfaces of three natural rock fractures were digitized and studied before and after the direct shear test. The variography analysis of the surfaces indicated a strong non-linear trend in the data. Therefore, the spatial variability of rock fracture surfaces was decomposed to one deterministic component characterized by a base polynomial function, and one stochastic component described by the variogram of residuals. By using an image-processing technique, 343 damaged zones with different sizes, shapes, initial roughness characteristics, local stress fields, and asperity strength values were spatially located and clustered. In order to characterize the overall spatial structure of the degraded zones, the concept of ‘pseudo-zonal variogram’ was introduced. The results showed that the spatial continuity at the damage locations increased due to asperity degradation. The increase in the variogram range was anisotropic and tended to be higher in the shear direction; thus, the direction of maximum continuity rotated towards the shear direction. Finally, the regression-kriging method was used to reconstruct the morphology of the intact surfaces and degraded areas. The cross-validation error of interpolation for the damaged zones was found smaller than that obtained for the intact surface.

  2. Characterization of Unstable Rock Slopes Through Passive Seismic Measurements

    Science.gov (United States)

    Kleinbrod, U.; Burjanek, J.; Fäh, D.

    2014-12-01

    Catastrophic rock slope failures have high social impact, causing significant damage to infrastructure and many casualties throughout the world each year. Both detection and characterization of rock instabilities are therefore of key importance. An analysis of ambient vibrations of unstable rock slopes might be a new alternative to the already existing methods, e.g. geotechnical displacement measurements. Systematic measurements have been performed recently in Switzerland to study the seismic response of potential rockslides concerning a broad class of slope failure mechanisms and material conditions. Small aperture seismic arrays were deployed at sites of interest for a short period of time (several hours) in order to record ambient vibrations. Each measurement setup included a reference station, which was installed on a stable part close to the instability. Recorded ground motion is highly directional in the unstable parts of the rock slope, and significantly amplified with respect to stable areas. These effects are strongest at certain frequencies, which were identified as eigenfrequencies of the unstable rock mass. In most cases the directions of maximum amplification are perpendicular to open cracks and in good agreement with the deformation directions obtained by geodetic measurements. Such unique signatures might improve our understanding of slope structure and stability. Thus we link observed vibration characteristics with available results of detailed geological characterization. This is supported by numerical modeling of seismic wave propagation in fractured media with complex topography.For example, a potential relation between eigenfrequencies and unstable rock mass volume is investigated.

  3. Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

    OpenAIRE

    Xue-wei Liu; Quan-sheng Liu; Shi-bing Huang; Lai Wei; Guang-feng Lei

    2016-01-01

    This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C). On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the...

  4. Novel methods for 3-D semi-automatic mapping of fracture geometry at exposed rock faces

    OpenAIRE

    Feng, Quanhong

    2001-01-01

    To analyse the influence of fractures on hydraulic andmechanical behaviour of fractured rock masses, it is essentialto characterise fracture geometry at exposed rock faces. Thisthesis describes three semi-automatic methods for measuring andquantifying geometrical parameters of fractures, and aims tooffer a novel approach to the traditional mapping methods. Three techniques, i.e. geodetic total station, close-rangephotogrammetry and 3-D laser scanner, are used in this studyfor measurement of f...

  5. Trends, prospects and challenges in quantifying flow and transport through fractured rocks

    Science.gov (United States)

    Neuman, Shlomo P.

    2005-03-01

    Among the current problems that hydrogeologists face, perhaps there is none as challenging as the characterization of fractured rock (Faybishenko and Benson 2000). This paper discusses issues associated with the quantification of flow and transport through fractured rocks on scales not exceeding those typically associated with single- and multi-well pressure (or flow) and tracer tests. As much of the corresponding literature has focused on fractured crystalline rocks and hard sedimentary rocks such as sandstones, limestones (karst is excluded) and chalk, so by default does this paper. Direct quantification of flow and transport in such rocks is commonly done on the basis of fracture geometric data coupled with pressure (or flow) and tracer tests, which therefore form the main focus. Geological, geophysical and geochemical (including isotope) data are critical for the qualitative conceptualization of flow and transport in fractured rocks, and are being gradually incorporated in quantitative flow and transport models, in ways that this paper unfortunately cannot describe but in passing. The hydrogeology of fractured aquifers and other earth science aspects of fractured rock hydrology merit separate treatments. All evidence suggests that rarely can one model flow and transport in a fractured rock consistently by treating it as a uniform or mildly nonuniform isotropic continuum. Instead, one must generally account for the highly erratic heterogeneity, directional dependence, dual or multicomponent nature and multiscale behavior of fractured rocks. One way is to depict the rock as a network of discrete fractures (with permeable or impermeable matrix blocks) and another as a nonuniform (single, dual or multiple) continuum. A third way is to combine these into a hybrid model of a nonuniform continuum containing a relatively small number of discrete dominant features. In either case the description can be deterministic or stochastic. The paper contains a brief assessment

  6. Zonal disintegration of rocks around underground workings. Part II. Rock fracture simulated in equivalent materials

    Energy Technology Data Exchange (ETDEWEB)

    Shemyakin, E.I.; Fisenko, G.L.; Kurlenya, M.V.; Oparin, V.N.; Reva, V.N.; Glushikhin, F.P.; Rozenbaum, M.A.; Tropp, E.A.; Kuznetsov, Yu.S.

    1987-05-01

    For a detailed testing of the effects discovered in situ, analysis of the patterns and origination conditions of fractured rock zones inside the bed around workings, and ways explosions affect the surrounding rocks, a program and a method of study on models of equivalent materials have been developed. The method of simulation on two- and three-dimensional models involved building in a solid or fissured medium a tunnel of a circular or arched cross section. The tests were done for elongate adit-type workings. At the first stage, three models were tested with different working support systems: anchor supports, concrete-spray supports and no supports. Zone formation is shown and described. Tests were continued on two groups of three-dimensional models to bring the model closer to in situ conditions. The presence of gaping cracks and heavily fractured zones deep in the interior of the bed with a quasicylindrical symmetry indicates that the common views concerning the stressed-strained state of rocks around underground workings are at variance with the actual patterns of deformation and destruction of rocks near the workings in deep horizons.

  7. Characterization and behaviour of argillaceous rocks

    International Nuclear Information System (INIS)

    The main activities concerning characterization and behaviour of argillaceous rocks and their environment are presented. The studies are related to the technico-economic feasibility and the long-term safety of disposal of radioactive waste in argillaceous media. (author)

  8. Stress-Induced Fracturing of Reservoir Rocks: Acoustic Monitoring and μCT Image Analysis

    Science.gov (United States)

    Pradhan, Srutarshi; Stroisz, Anna M.; Fjær, Erling; Stenebråten, Jørn F.; Lund, Hans K.; Sønstebø, Eyvind F.

    2015-11-01

    Stress-induced fracturing in reservoir rocks is an important issue for the petroleum industry. While productivity can be enhanced by a controlled fracturing operation, it can trigger borehole instability problems by reactivating existing fractures/faults in a reservoir. However, safe fracturing can improve the quality of operations during CO2 storage, geothermal installation and gas production at and from the reservoir rocks. Therefore, understanding the fracturing behavior of different types of reservoir rocks is a basic need for planning field operations toward these activities. In our study, stress-induced fracturing of rock samples has been monitored by acoustic emission (AE) and post-experiment computer tomography (CT) scans. We have used hollow cylinder cores of sandstones and chalks, which are representatives of reservoir rocks. The fracture-triggering stress has been measured for different rocks and compared with theoretical estimates. The population of AE events shows the location of main fracture arms which is in a good agreement with post-test CT image analysis, and the fracture patterns inside the samples are visualized through 3D image reconstructions. The amplitudes and energies of acoustic events clearly indicate initiation and propagation of the main fractures. Time evolution of the radial strain measured in the fracturing tests will later be compared to model predictions of fracture size.

  9. A Rock Mechanics and Coupled Hydro mechanical Analysis of Geological Repository of High Level Nuclear Waste in Fractured Rocks

    International Nuclear Information System (INIS)

    This paper introduces a few case studies on fractured hard rock based on geological data from Sweden, Korea is one of a few countries where crystalline rock is the most promising rock formation as a candidate site of geological repository of high level nuclear waste. Despite the progress made in the area of rock mechanics and coupled hydro mechanics, extensive site specific study on multiple candidate sites is essential in order to choose the optimal site. For many countries concerned about the safe isolation of nuclear wastes from the biosphere, disposal in a deep geological formation is considered an attractive option. In geological repository, thermal loading continuously disturbs the repository system in addition to disturbances a recent development in rock mechanics and coupled hydro mechanical study using DFN(Discrete Fracture Network) - DEM(Discrete Element Method) approach mainly applied in hard, crystalline rock containing numerous fracture which are main sources of deformation and groundwater flow

  10. A coupled DEM-DFN approach to rock mass strength characterization

    Science.gov (United States)

    Harthong, Barthelemy; Scholtes, Luc; Donze, Frederic

    2013-04-01

    An enhanced version of the discrete element method (DEM) has been specifically developed for the analysis of fractured rock masses [Scholtes L, Donze F, 2012]. In addition to the discrete representation of the intact medium which enables the description of the localized stress-induced damage caused by heterogeneities inherent to rocks, structural defects can be explicitly taken into account in the modeling to represent pre-existing fractures or discontinuities of size typically larger than the discrete element size. From laboratory scale simulations to slope stability case studies, the capability of this approach to simulate the progressive failure mechanisms occurring in jointed rock are presented is assessed on the basis of referenced experiments and in situ observations. For instance, the challenging wing crack extension, typical of brittle material fracturing, can be successfully reproduced under both compressive and shear loading path, as a result of the progressive coalescence of micro-cracks induced by stress concentration at the tips of pre-existing fractures. In this study, the dedicated DEM is coupled to a discrete fracture network (DFN) model to assess the influence of DFN properties on the mechanical behavior of fractured rock masses where progressive failure can occur. The DFN model assumes the distribution of fractures barycentres to be fractal and the distribution of fracture sizes to follow a power-law distribution [Davy P, Le Goc P, Darcel C, Bour O, de Dreuzy JR, Munier R, 2010]. The proposed DEM/DFN model is used to characterize the influence of clustering and size distribution of pre-existing fractures on the strength of fractured rock masses. The results show that the mechanical behaviour of fractured rock masses is mainly dependent on the fracture intensity. However, for a given fracture intensity, the strength can exhibit a 50 per cent variability depending on the size distribution of the pre-existing fractures. This difference can be

  11. A review of discrete modeling techniques for fracturing processes in discontinuous rock masses

    OpenAIRE

    A. Lisjak; Grasselli, G

    2014-01-01

    The goal of this review paper is to provide a summary of selected discrete element and hybrid finite–discrete element modeling techniques that have emerged in the field of rock mechanics as simulation tools for fracturing processes in rocks and rock masses. The fundamental principles of each computer code are illustrated with particular emphasis on the approach specifically adopted to simulate fracture nucleation and propagation and to account for the presence of rock mass discontinuities. Th...

  12. Numerical Study on Crack Propagation in Brittle Jointed Rock Mass Influenced by Fracture Water Pressure

    OpenAIRE

    Yong Li; Hao Zhou; Weishen Zhu; Shucai Li; Jian Liu

    2015-01-01

    The initiation, propagation, coalescence and failure mode of brittle jointed rock mass influenced by fissure water pressure have always been studied as a hot issue in the society of rock mechanics and engineering. In order to analyze the damage evolution process of jointed rock mass under fracture water pressure, a novel numerical model on the basis of secondary development in fast Lagrangian analysis of continua (FLAC3D) is proposed to simulate the fracture development of jointed rock mass u...

  13. Effective media models for unsaturated fractured rock: A field experiment

    International Nuclear Information System (INIS)

    A thick unsaturated rock mass at Yucca Mountain is currently under consideration as a potential repository site for disposal of high level radioactive waste. In accordance with standard industry and scientific practices, abstract numerical models will be used to evaluate the potential for radionuclide release through the groundwater system. At this time, currently available conceptual models used to develop effective media properties are based primarily on simplistic considerations. The work presented here is part of an integrated effort to develop effective media models at the intermediate block scale (approximately 8-125m) through a combination of physical observations, numerical simulations and theoretical considerations. A multi-purpose field experiment designed and conducted as part of this integrated effort is described. Specific goals of this experimental investigation were to: (1) obtain fracture network data from Topopah Spring Tuff for use in block scale simulations; (2) identity positions of the network conducting flow under three different boundary conditions; (3) visualize preferential flow paths and small-scale flow structures; (4) collect samples for subsequent hydraulic testing and use in block-scale simulations; and (5) demonstrate the ability of Electrical Resistance Tomography (ERT) to delineate fluid distribution within fractured rock

  14. Experimental demonstration of contaminant removal from fractured rock by boiling.

    Science.gov (United States)

    Chen, Fei; Liu, Xiaoling; Falta, Ronald W; Murdoch, Lawrence C

    2010-08-15

    This study was conducted to experimentally demonstrate removal of a chlorinated volatile organic compound from fractured rock by boiling. A Berea sandstone core was contaminated by injecting water containing dissolved 1,2-DCA (253 mg/L) and sodium bromide (144 mg/L). During heating, the core was sealed except for one end, which was open to the atmosphere to simulate an open fracture. A temperature gradient toward the outlet was observed when boiling occurred in the core. This indicates that steam was generated and a pressure gradient developed toward the outlet, pushing steam vapor and liquid water toward the outlet. As boiling occurred, the concentration of 1,2-DCA in the condensed effluent peaked up to 6.1 times higher than the injected concentration. When 38% of the pore volume of condensate was produced, essentially 100% of the 1,2-DCA was recovered. Nonvolatile bromide concentration in the condensate was used as an indicator of the produced steam quality (vapor mass fraction) because it can only be removed as a solute, and not as a vapor. A higher produced steam quality corresponds to more concentrated 1,2-DCA removal from the core, demonstrating that the chlorinated volatile compound is primarily removed by partitioning into vapor phase flow. This study has experimentally demonstrated that boiling is an effective mechanism for CVOC removal from the rock matrix.

  15. Evaluation of regional fracture properties for groundwater development using hydrolithostructural domain approach in variably fractured hard rocks of Purulia district, West Bengal, India

    Indian Academy of Sciences (India)

    Tapas Acharya; Rajesh Prasad; S Chakrabarti

    2014-04-01

    Estimation of geohydrologic properties of fractured aquifers in hard crystalline and/or metamorphosed country rocks is a challenge due to the complex nature of secondary porosity that is caused by differential fracturing. Hydrologic potentiality of such aquifers may be assessed if the geological controls governing the spatial distribution of these fracture systems are computed using a software-based model. As an exemplar, the Precambrian metamorphics exposed in and around the Balarampur town of Purulia district, West Bengal (India) were studied to find out the spatial pattern and consistency of such fracture systems. Surfer and Statistica softwares were used to characterize these rock masses in terms of hydrological, structural and lithological domains. The technique is based on the use of hydraulically significant fracture properties to generate representative modal and coefficient of variance () of fracture datasets of each domain. The is interpreted to obtain the spatial variability of hydraulically significant fracture properties that, in turn, define and identify the corresponding hydrolithostructural domains. The groundwater flow estimated from such a technique is verified with the routine hydrological studies to validate the procedure. It is suggested that the hydrolithostructural domain approach is a useful alternative for evaluation of fracture properties and aquifer potentiality, and development of a regional groundwater model thereof.

  16. Mechanical rock properties, fracture propagation and permeability development in deep geothermal reservoirs

    Science.gov (United States)

    Leonie Philipp, Sonja; Reyer, Dorothea

    2010-05-01

    Deep geothermal reservoirs are rock units at depths greater than 400 m from which the internal heat can be extracted using water as a transport means in an economically efficient manner. In many geothermal reservoirs, fluid flow is largely, and may be almost entirely, controlled by the permeability of the fracture network. No flow, however, takes place along a particular fracture network unless the fractures are interconnected. For fluid flow to occur from one site to another there must be at least one interconnected cluster of fractures that links these sites, that is, the percolation threshold must be reached. In "hydrothermal systems", only the natural fracture system (extension and shear fractures) creates the rock or reservoir permeability that commonly exceeds the matrix permeability by far; in "petrothermal systems", by contrast, interconnected fracture systems are formed by creating hydraulic fractures and massive hydraulic stimulation of the existing fracture system in the host rock. Propagation (or termination, that is, arrest) of both natural extension and shear fractures as well as man-made hydraulic fractures is mainly controlled by the mechanical rock properties, particularly rock toughness, stiffness and strengths, of the host rock. Most reservoir rocks are heterogeneous and anisotropic, in particular they are layered. For many layered rocks, the mechanical properties, particularly their Young's moduli (stiffnesses), change between layers, that is, the rocks are mechanically layered. Mechanical layering may coincide with changes in grain size, mineral content, fracture frequencies, or facies. For example, in sedimentary rocks, stiff limestone or sandstone layers commonly alternate with soft shale layers. In geothermal reservoirs fracture termination is important because non-stratabound fractures, that is, fractures not affected by layering, are more likely to form an interconnected fracture network than stratabound fractures, confined to single rock

  17. Fractal characterization of fracture surfaces in concrete

    Science.gov (United States)

    Saouma, V.E.; Barton, C.C.; Gamaleldin, N.A.

    1990-01-01

    Fractal geometry is used to characterize the roughness of cracked concrete surfaces through a specially built profilometer, and the fractal dimension is subsequently correlated to the fracture toughness and direction of crack propagation. Preliminary results indicate that the fracture surface is indeed fractal over two orders of magnitudes with a dimension of approximately 1.20. ?? 1990.

  18. Fracture Toughness Determination of Cracked Chevron Notched Brazilian Disc Rock Specimen via Griffith Energy Criterion Incorporating Realistic Fracture Profiles

    Science.gov (United States)

    Xu, Yuan; Dai, Feng; Zhao, Tao; Xu, Nu-wen; Liu, Yi

    2016-08-01

    The cracked chevron notched Brazilian disc (CCNBD) specimen has been suggested by the International Society for Rock Mechanics to measure the mode I fracture toughness of rocks, and has been widely adopted in laboratory tests. Nevertheless, a certain discrepancy has been observed in results when compared with those derived from methods using straight through cracked specimens, which might be due to the fact that the fracture profiles of rock specimens cannot match the straight through crack front as assumed in the measuring principle. In this study, the progressive fracturing of the CCNBD specimen is numerically investigated using the discrete element method (DEM), aiming to evaluate the impact of the realistic cracking profiles on the mode I fracture toughness measurements. The obtained results validate the curved fracture fronts throughout the fracture process, as reported in the literature. The fracture toughness is subsequently determined via the proposed G-method originated from Griffith's energy theory, in which the evolution of the realistic fracture profile as well as the accumulated fracture energy is quantified by DEM simulation. A comparison between the numerical tests and the experimental results derived from both the CCNBD and the semi-circular bend (SCB) specimens verifies that the G-method incorporating realistic fracture profiles can contribute to narrowing down the gap between the fracture toughness values measured via the CCNBD and the SCB method.

  19. Fracture Detection in Geothermal Wells Drilled in Volcanic Rocks

    Energy Technology Data Exchange (ETDEWEB)

    Gonfalini, Mauro; Chelini, Walter; Cheruvier, Etienne; Suau, Jean; Klopf, Werner

    1987-01-20

    The Phlegrean Fields, close to Naples, are the site of important geothermal activity. The formations are volcanic and mostly tuffites. They are originally very tight but the geothermal alteration locally produces fractures with large increase in permeability. The lack of geological markers makes well-to-well correlation quite difficult. Thus the local detection of fractured zones in each well is very important for the evaluation of its potential. The Mofete 8 D well is a typical example. A rather complete logging program was run for fracture detection. Standard methods turned out to be disappointing. However several non-standard detectors were found to be very consistent and, later on, in excellent agreement with the analysis of cuttings. They are derived from the Dual Laterolog, the SP, the Temperature log and, most particularly, the Acoustic Waveforms from the Long Spacing Sonic. The Dual Laterolog and the Temperature Log indicate invasion by fresh and cold mud filtrate; the SP behaves as in a typical Sand-Shale sequence. Sonic Waveforms were first analyzed by a purely empirical method derived from consistent log patterns. A practical algorithm compares the total energy measured in each of the two fixed time windows located the one before, the other after the fluid arrivals. The altered zones (i.e. fractured and permeable) are clearly shown by a complete reversal of the relative energy of these two windows. A more scientific method was then applied to the Waveforms; it is based on both logging experiments and physical considerations. The energy carried by the tube wave is separated by a frequency discrimination: it correlates very well with formation alteration, thus also with the other indicators including the empirical Waveform method. It should have two advantages: – It should permit at least a semi quantitative permeability evaluation – It seems to be promising in other formations: non-volcanic geothermal wells and even hydrocarbon-bearing rocks. 10 refs

  20. Characterizing and modelling 'ghost-rock' weathered limestones

    Science.gov (United States)

    Dubois, Caroline; Goderniaux, Pascal; Deceuster, John; Poulain, Angélique; Kaufmann, Olivier

    2016-04-01

    'Ghost-rock' karst aquifer has recently been highlighted. In this particular type of aquifer, the karst is not expressed as open conduits but consists in zones where the limestone is weathered. The in-situ weathering of limestone leaves a soft porous material called 'alterite'. The hydro-mechanical properties of this material differs significantly from those of the host rock: the weathering enhances the storage capacity and the conductivity of the rock. This type of weathered karst aquifer has never been studied from a hydrogeological point of view. In this study, we present the hydraulic characterization of such weathered zones. We also present a modelling approach derived from the common Equivalent Porous Medium (EPM) approach, but including the spatial distribution of hydrogeological properties through the weathered features, from the hard rock to the alterite, according to a weathering index. Unlike the Discrete Fracture Network (DFN) approaches, which enable to take into account a limited number of fractures, this new approach allows creating models including thousands of weathered features. As the properties of the alterite have to be considered at a centimeter scale, it is necessary to upscale these properties to carry out simulations over large areas. Therefore, an upscaling method was developed, taking into account the anisotropy of the weathered features. Synthetic models are built, upscaled and different hydrogeological simulations are run to validate the method. This methodology is finally tested on a real case study: the modelling of the dewatering drainage flow of an exploited quarry in a weathered karst aquifer in Belgium.

  1. Rock mass mechanical property estimations for the Yucca Mountain Site Characterization Project

    International Nuclear Information System (INIS)

    Rock mass mechanical properties are important in the design of drifts and ramps. These properties are used in evaluations of the impacts of thermomechanical loading of potential host rock within the Yucca Mountain Site Characterization Project. Representative intact rock and joint mechanical properties were selected for welded and nonwelded tuffs from the currently available data sources. Rock mass qualities were then estimated using both the Norwegian Geotechnical Institute (Q) and Geomechanics Rating (RMR) systems. Rock mass mechanical properties were developed based on estimates of rock mass quality, the current knowledge of intact properties, and fracture/joint characteristics. Empirical relationships developed to correlate the rock mass quality indices and the rock mass mechanical properties were then used to estimate the range of rock mass mechanical properties

  2. Low- and intermediate level radioactive waste from Risoe, Denmark. Location studies for potential disposal areas. Report no. 2. Characterization of low permeable and fractured sediments and rocks in Denmark

    Energy Technology Data Exchange (ETDEWEB)

    Gravesen, P.; Nilsson, B.; Schack Pedersen, S.A.; Binderup, M.; Laier, T.

    2011-07-01

    The low and intermediate level radioactive waste from Risoe (the nuclear reactor buildings plus different types of material from the research periods) and radioactive waste from hospitals and research institutes have to be stored in a final disposal in Denmark for at least 300 years. In Denmark, many different kinds of fine-grained sediments and crystalline rocks occur from the ground surface down to 300 meters depth. Therefore, the possible geological situations include sediments and rocks of different composition and age. These situations are geographical distributed over large areas of Denmark. These sediments and rocks are shortly described based on existing information and include five different major types of sediments and rocks: 1: Crystalline granite and gneiss of Bornholm (because these rock types are host for waste disposals in many other countries). 2: Sandstone and shale from Bornholm (as these sediments are rela- tively homogeneous although they have fracture permeability). 3: Chalk and limestone (because these sediments may act as low permeable seals, but in most areas they act as groundwater reservoirs). 4: Fine-grained Tertiary clay deposits (as these sediments have a low permeability, are widely distributed and can reach large thicknesses). 5: Quaternary glacial, interglacial and Holocene clay deposits. These sediments are distributed all over Denmark. Following the descriptions of the geologic deposits, the areas below (including several possible locations for waste disposal sites) are selected for further investigation. The Precambrian basement rocks of Bornholm could be host rocks for the disposal. The rock types for further evaluation will be: Hammer Granite, Vang Granite, Roenne Granite, Bornholm gneiss, Paradisbakke Migmatite and Alminding Granite. In the Roskilde Fjord area around Risoe, a combination of Paleocene clays, meltwater clay and clayey till could be interesting. The area is partly included in the OSD area in North Sjaelland but

  3. Use of the Fracture Continuum Model for Numerical Modeling of Flow and Transport of Deep Geologic Disposal of Nuclear Waste in Crystalline Rock

    Science.gov (United States)

    Hadgu, T.; Kalinina, E.; Klise, K. A.; Wang, Y.

    2015-12-01

    Numerical modeling of disposal of nuclear waste in a deep geologic repository in fractured crystalline rock requires robust characterization of fractures. Various methods for fracture representation in granitic rocks exist. In this study we used the fracture continuum model (FCM) to characterize fractured rock for use in the simulation of flow and transport in the far field of a generic nuclear waste repository located at 500 m depth. The FCM approach is a stochastic method that maps the permeability of discrete fractures onto a regular grid. The method generates permeability fields using field observations of fracture sets. The original method described in McKenna and Reeves (2005) was designed for vertical fractures. The method has since then been extended to incorporate fully three-dimensional representations of anisotropic permeability, multiple independent fracture sets, and arbitrary fracture dips and orientations, and spatial correlation (Kalinina et al. 20012, 2014). For this study the numerical code PFLOTRAN (Lichtner et al., 2015) has been used to model flow and transport. PFLOTRAN solves a system of generally nonlinear partial differential equations describing multiphase, multicomponent and multiscale reactive flow and transport in porous materials. The code is designed to run on massively parallel computing architectures as well as workstations and laptops (e.g. Hammond et al., 2011). Benchmark tests were conducted to simulate flow and transport in a specified model domain. Distributions of fracture parameters were used to generate a selected number of realizations. For each realization, the FCM method was used to generate a permeability field of the fractured rock. The PFLOTRAN code was then used to simulate flow and transport in the domain. Simulation results and analysis are presented. The results indicate that the FCM approach is a viable method to model fractured crystalline rocks. The FCM is a computationally efficient way to generate realistic

  4. ModeⅠrock fracture toughness with different types of brazilian disc

    Institute of Scientific and Technical Information of China (English)

    YU Hai-yong; JIN Zhi-xin; JING Hai-he

    2004-01-01

    According to the results evaluated by researchers for mode Ⅰ rock fracture toughness measurement, a series of comparison tests with different types Brazilian discs were conducted in order to search for the simplest geometry specimens by which accurate,comparable and consistent mode Ⅰ rock fracture toughness could obtain.

  5. Altered crystalline rock distributed along groundwater conductive fractures and the retardation capacity in the orogenic field of Japan - 16332

    International Nuclear Information System (INIS)

    In the orogenic field Japanese islands, there are wide areas of crystalline rocks that inevitably contain groundwater conductive fractures associated with alteration zones. However, little attention has been given to the formation process and possible influence on the radionuclides migration from radioactive waste repository that might be sited within crystalline rock. In particular, the influences of alteration minerals and micro-fractures, due to chemical sorption and/or physical retardation are required to assess the realistic barrier function. In order to understand the alteration process and the retardation capacity, detailed mineralogical and physico-chemical characterization of altered crystalline rocks have been carried out. Mineralogical analysis reveals that the altered crystalline rocks have been formed through basically two stages of water-rock interaction during and after uplift. Physico-chemical characteristics including laboratory sorption experiments show that altered crystalline rock has a certain volume of accessible porosity, particularly in plagioclase grains, which would influence on nuclide retardation more than the accessible porosity in other minerals present, such as biotite. These results provide confidence that even altered and fractured parts of any crystalline rock that might be encountered in a site for the disposal of high-level radioactive waste may still play a role of barrier function. (authors)

  6. Validation studies for assessing unsaturated flow and transport through fractured rock

    International Nuclear Information System (INIS)

    *The objectives of this contract are to examine hypotheses and conceptual models concerning unsaturated flow and transport through heterogeneous fractured rock and to design and execute confirmatory field and laboratory experiments to test these hypotheses and conceptual models. Important new information is presented such as the application and evaluation of procedures for estimating hydraulic, pneumatic, and solute transport coefficients for a range of thermal regimes. A field heater experiment was designed that focused on identifying the suitability of existing monitoring equipment to obtain required data. A reliable method was developed for conducting and interpreting tests for air permeability using a straddle-packer arrangement. Detailed studies of fracture flow from Queen Creek into the Magina Copper Company ore haulage tunnel have been initiated. These studies will provide data on travel time for transport of water and solute in unsaturated tuff. The collection of rainfall runoff, and infiltration data at two small watersheds at the Apache Leap Tuff Site enabled us to evaluate the quantity and rate of water infiltrating into the subsurface via either fractures or matrix. Characterization methods for hydraulic parameters relevant to Weigh-level waste transport, including fracture apertures, transmissivity, matrix porosity, and fracture wetting front propagation velocities, were developed

  7. Study on the growth height of separation fracture of mining rock in Panxie area

    Energy Technology Data Exchange (ETDEWEB)

    Tu, M. [Anhui University of Science and Technology, Huainan (China)

    2004-12-01

    Based on the analysis of engineering geological petrofabric of overlying strata in Panxie mining area, the numerical model of mining rock mechanics was built. The fractures evolution rules of mining rock in different shear heights of coal seam under the large-thick unconsolidated rich aquiferous layers were analyzed, and the plastic scope of overlying strata and the growth height of mining separation fracture in different mining height was 74 m. The actually measured data of the growth height of separation fracture of mining rock was fitted by lEast squares methods to get the theoretical calculating formula of height of caving zone and fracture band. 6 refs., 5 figs., 5 tabs.

  8. Fracture Analysis of basement rock: A case example of the Eastern Part of the Peninsular Malaysia

    International Nuclear Information System (INIS)

    In general, reservoir rocks can be defined into carbonates, tight elastics and basement rocks. Basement rocks came to be highlighted as their characteristics are quite complicated and remained as a significant challenge in exploration and production area. Motivation of this research is to solve the problem in some area in the Malay Basin which consist fractured basement reservoirs. Thus, in order to increase understanding about their characteristic, a study was conducted in the Eastern part of the Peninsular Malaysia. The study includes the main rock types that resemble the offshore rocks and analysis on the factors that give some effect on fracture characteristic that influence fracture systems and fracture networks. This study will allow better fracture prediction which will be beneficial for future hydrocarbon prediction in this region

  9. Application of multiple tracer test for single fracture in sedimentary rock

    International Nuclear Information System (INIS)

    The evaluation of the advection-dispersion in the fracture and diffusion into the matrix from fracture is important to describe the mass transport processes in fractured porous media such as a sedimentary rock. However, it is often difficult to uniquely determine a number of parameters relevant to these phenomena, such as the fracture aperture, dispersivity coefficient, and matrix diffusion coefficient, from a data set of single tracer test. In this report, one-dimensional multiple tracer test for single fracture in a sedimentary rock block was conducted under the condition of injection rate for the unique parameter estimation suggested by authors. (author)

  10. Experimental study on water seepage constitutive law of fracture in rock under 3D stress

    Institute of Scientific and Technical Information of China (English)

    赵阳升; 杨栋; 郑少河; 胡耀青

    1999-01-01

    The test method and test result of water seepage constitutive law of fracture in rock under 3D stress are introduced. A permeability coefficient formula including the coefficient of fracture connection, normal stiffness, 3D stress, initial width of fracture and Poisson ratio is presented based on the analysis of the test theory and its result.

  11. Hydro-thermo-mechanical response of a fractured rock block

    International Nuclear Information System (INIS)

    Hydro-thermo-mechanical effects in fractured rocks are important in many engineering applications and geophysical processes. Modeling these effects is made difficult by the fact that the governing equations are nonlinear and coupled, and the problems to be solved are three dimensional. In this paper we describe a numerical code developed for this purpose. The code is finite element based to allow for complicated geometries, and the time differencing is implicit, allowing for large time steps. The use of state-of-the-art equation solvers has resulted in a practical code. The code is capable of fully three dimensional simulations, however, in this paper we consider only the case of two dimensional heat and mass flow coupled to one dimensional deformation. Partial verification of the code is obtained by comparison with published semianalytical results. Several examples are presented to demonstrate the effects of matrix expansion, due to pore pressure and heating, on fracture opening due to fluid injection. 16 refs., 11 figs

  12. Comments on chevron bend specimen for determining fracture toughness of rock

    Institute of Scientific and Technical Information of China (English)

    孙宗颀; 陈枫; 徐纪成

    2001-01-01

    Based on a number of tests on different rocks, Suggested Methods for Determining the Fracture Toughness of Rock (SMs) was reviewed. The advantages of SMs are obvious, but some problems are also discovered. A serious one is that the nonlinear corrected fracture toughness of chevron bend specimens, KCCB, is less than the uncorrected one, KCB, for hard rock like granite, marble and others. The reason is discussed and the proposal is given.

  13. Joint seismic, hydrogeological, and geomechanical investigations of a fracture zone in the Grimsel Rock Laboratory, Switzerland

    International Nuclear Information System (INIS)

    This report is one of a series documenting the results of the Nagra-DOE Cooperative (NDC-I) research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a rock mass as a geologic repository for nuclear waste. From 1987 to 1989 the United States Department of Energy (DOE) and the Swiss Cooperative for the Storage of Nuclear Waste (Nagra) participated in an agreement to carryout experiments for understanding the effect of fractures in the storage and disposal of nuclear waste. As part of this joint work field and laboratory experiments were conducted at a controlled site in the Nagra underground Grimsel test site in Switzerland. The primary goal of these experiments in this fractured granite was to determine the fundamental nature of the propagation of seismic waves in fractured media, and to relate the seismological parameters to the hydrological parameters. The work is ultimately aimed at the characterization and monitoring of subsurface sites for the storage of nuclear waste. The seismic experiments utilizes high frequency (1000 to 10,000 Hertz) signals in a cross-hole configuration at scales of several tens of meters. Two-, three-, and four-sided tomographic images of the fractures and geologic structure were produced from over 60,000 raypaths through a 10 by 21 meter region bounded by two nearly horizontal boreholes and two tunnels. Intersecting this region was a dominant fracture zone which was the target of the investigations. In addition to these controlled seismic imaging experiments, laboratory work using core from this region were studied for the relation between fracture content, saturation, and seismic velocity and attenuation. In-situ geomechanical and hydrologic tests were carried out to determine the mechanical stiffness and conductivity of the fractures. 20 refs., 90 figs., 6 tabs

  14. Estimating hydraulic conductivity of fractured rocks from high-pressure packer tests with an Izbash's law-based empirical model

    Science.gov (United States)

    Chen, Yi-Feng; Hu, Shao-Hua; Hu, Ran; Zhou, Chuang-Bing

    2015-04-01

    High-pressure packer test (HPPT) is an enhanced constant head packer test for characterizing the permeability of fractured rocks under high-pressure groundwater flow conditions. The interpretation of the HPPT data, however, remains difficult due to the transition of flow conditions in the conducting structures and the hydraulic fracturing-induced permeability enhancement in the tested rocks. In this study, a number of HPPTs were performed in the sedimentary and intrusive rocks located at 450 m depth in central Hainan Island. The obtained Q-P curves were divided into a laminar flow phase (I), a non-Darcy flow phase (II), and a hydraulic fracturing phase (III). The critical Reynolds number for the deviation of flow from linearity into phase II was 25-66. The flow of phase III occurred in sparsely to moderately fractured rocks, and was absent at the test intervals of perfect or poor intactness. The threshold fluid pressure between phases II and III was correlated with RQD and the confining stress. An Izbash's law-based analytical model was employed to calculate the hydraulic conductivity of the tested rocks in different flow conditions. It was demonstrated that the estimated hydraulic conductivity values in phases I and II are basically the same, and are weakly dependent on the injection fluid pressure, but it becomes strongly pressure dependent as a result of hydraulic fracturing in phase III. The hydraulic conductivity at different test intervals of a borehole is remarkably enhanced at highly fractured zone or contact zone, but within a rock unit of weak heterogeneity, it decreases with the increase of depth.

  15. Design of a meso-scale poly-axial testing device for examining the role of anisotropic stress on fluid flow in fractured rock

    Science.gov (United States)

    Gosselin, M. J.; Boutt, D. F.

    2005-12-01

    Fluid flow in the shallow crust (meters) is not typically sensitive to the low magnitude crustal stress conditions present. Fractured rocks, unlike porous sedimentary rocks, in this respect are unique since most un-cemented fractures are compliant at lower stress states and fracture apertures can be strongly influenced by the loading. As a result, fracture permeability of the rocks can be strongly dependent on depth and loading conditions (e.g. residual tectonic stresses). This has implications for depth of flow systems and connections between deeper and shallower systems. This paper presents the design of a poly-axial testing apparatus for testing the role of low magnitude (flow and transport properties of fractured rock on meso-scale samples of fractured rock. A "true-triaxial" stress state will allow a more accurate description of shallow crustal conditions and isolation of the role of these stresses on fluid flow. Previous investigations into stress induced anisotropic conditions in fractured rocks have used traditional triaxial stress conditions to simulate crustal conditions. We constructed a frame with 6 loading pistons, two on each axis, which will be capable of stressing a cubic sample in 3 independent directions, thus creating a more realistic 3D stress state in the rock. The frame allows access to the sample on all sides. Six separate platens isolate each face of the sample permitting the measurement of fluid pressure response to off axis loading. The platens are designed to transfer the loads to the sample while allowing fluid flow monitoring and sampling. Design considerations also include geophysical characterization of the sample through both ultrasonic and NMR testing. We hope to quantify the relationships between stress fields and fluid flow through the fractured rock for low crustal stresses. Specifically we expect to be able to more completely quantify the aperture reduction on a fractured surface when a stress is not applied normal to the

  16. AVAZ inversion for fracture weakness parameters based on the rock physics model

    International Nuclear Information System (INIS)

    Subsurface fractures within many carbonates and unconventional resources play an important role in the storage and movement of fluid. The more reliably the detection of fractures could be performed, the more finely the reservoir description could be made. In this paper, we aim to propose a method which uses two important tools, a fractured anisotropic rock physics effective model and AVAZ (amplitude versus incident and azimuthal angle) inversion, to predict fractures from azimuthal seismic data. We assume that the rock, which contains one or more sets of vertical or sub-vertical fractures, shows transverse isotropy with a horizontal axis of symmetry (HTI). Firstly, we develop one improved fractured anisotropic rock physics effective model. Using this model, we estimate P-wave velocity, S-wave velocity and fracture weaknesses from well-logging data. Then the method is proposed to predict fractures from azimuthal seismic data based on AVAZ inversion, and well A is used to verify the reliability of the improved rock physics effective model. Results show that the estimated results are consistent with the real log value, and the variation of fracture weaknesses may detect the locations of fractures. The damped least squares method, which uses the estimated results as initial constraints during the inversion, is more stable. Tests on synthetic data show that fracture weaknesses parameters are still estimated reasonably with moderate noise. A test on real data shows that the estimated results are in good agreement with the drilling. (paper)

  17. AVAZ inversion for fracture weakness parameters based on the rock physics model

    Science.gov (United States)

    Chen, Huaizhen; Yin, Xingyao; Qu, Shouli; Zhang, Guangzhi

    2014-12-01

    Subsurface fractures within many carbonates and unconventional resources play an important role in the storage and movement of fluid. The more reliably the detection of fractures could be performed, the more finely the reservoir description could be made. In this paper, we aim to propose a method which uses two important tools, a fractured anisotropic rock physics effective model and AVAZ (amplitude versus incident and azimuthal angle) inversion, to predict fractures from azimuthal seismic data. We assume that the rock, which contains one or more sets of vertical or sub-vertical fractures, shows transverse isotropy with a horizontal axis of symmetry (HTI). Firstly, we develop one improved fractured anisotropic rock physics effective model. Using this model, we estimate P-wave velocity, S-wave velocity and fracture weaknesses from well-logging data. Then the method is proposed to predict fractures from azimuthal seismic data based on AVAZ inversion, and well A is used to verify the reliability of the improved rock physics effective model. Results show that the estimated results are consistent with the real log value, and the variation of fracture weaknesses may detect the locations of fractures. The damped least squares method, which uses the estimated results as initial constraints during the inversion, is more stable. Tests on synthetic data show that fracture weaknesses parameters are still estimated reasonably with moderate noise. A test on real data shows that the estimated results are in good agreement with the drilling.

  18. Thermo-hydro-mechanical processes in fractured rock formations during glacial advance

    Science.gov (United States)

    Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, P. A.

    2014-11-01

    The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modeling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures that can modify the pore pressure generation within the entire rock mass.

  19. Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

    Science.gov (United States)

    Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, P. A.

    2015-07-01

    The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modelling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures in modifying the pore pressure generation within the entire rock mass.

  20. Seepage properties of a single rock fracture subjected to triaxial stresses

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Coupled properties of seepage and stress fields of rock fractures greatly influence the safety of geotechnical engineering work.Based on the closing defomation principle of a single rock fracture,equations describing relationships of aperture and triaxial stresses are developed,and coupled models of seepage and triaxial stresses are proposed.Seepage tests are conducted under triaxial stress conditions by adopting hard granite specimens with an artificial fracture.The results show that the normal stress,lateral stress and seepage pressure significantly affect the flow behavior of rock fractures,and that hydraulic conductivity decreases with increasing normal.stress,but increases with rising lateral stress or seepage pressure.In addition,an exponential function provides a good representation of the seepage characteristics of a single rock fracture subjected to triaxial stresses.

  1. Lineament mapping of vertical fractures of rock outcrops by remote sensing images

    Science.gov (United States)

    Matarrese, Raffaella; Masciopinto, Costantino

    2016-04-01

    The monitoring of hydrological processes within the vadose zone is usually difficult, especially in the presence of compact rock subsoil. The possibility of recognizing the trend of the structural lineaments in fractured systems has important fallout in the understanding water infiltration processes, especially when the groundwater flow is strongly affected by the presence of faults and fractures that constitute the preferred ways of water fluxes. This study aims to detect fracture lineaments on fractured rock formations from CASI hyperspectral airborne VNIR images, with a size of 60 cm of the spatial resolution, and collected during November 2014. Lineaments detected with such high resolution have been compared with the fracture lineaments detected by a Landsat 8 image acquired at the same time of the CASI acquisition. The method has processed several remote sensed images at different spatial resolution, and it has produced the visualization of numerous lineament maps, as result of the vertical and sub-vertical fractures of the investigated area. The study has been applied to the fractured limestone outcrop of the Murgia region (Southern Italy). Here the rock formation hosts a deep groundwater, which supplies freshwater for drinking and irrigation purposes. The number of the fractures allowed a rough estimation of the vertical average hydraulic conductivity of the rock outcrop. This value was compared with field saturated rock hydraulic conductivity measurements derived from large ring infiltrometer tests carried out on the same rock outcrop.

  2. Review: Mathematical expressions for estimating equivalent permeability of rock fracture networks

    Science.gov (United States)

    Liu, Richeng; Li, Bo; Jiang, Yujing; Huang, Na

    2016-06-01

    Fracture networks play a more significant role in conducting fluid flow and solute transport in fractured rock masses, comparing with that of the rock matrix. Accurate estimation of the permeability of fracture networks would help researchers and engineers better assess the performance of projects associated with fluid flow in fractured rock masses. This study provides a review of previous works that have focused on the estimation of equivalent permeability of two-dimensional (2-D) discrete fracture networks (DFNs) considering the influences of geometric properties of fractured rock masses. Mathematical expressions for the effects of nine important parameters that significantly impact on the equivalent permeability of DFNs are summarized, including (1) fracture-length distribution, (2) aperture distribution, (3) fracture surface roughness, (4) fracture dead-end, (5) number of intersections, (6) hydraulic gradient, (7) boundary stress, (8) anisotropy, and (9) scale. Recent developments of 3-D fracture networks are briefly reviewed to underline the importance of utilizing 3-D models in future research.

  3. Theoretical and laboratory investigations of flow through fractures in crystalline rock

    International Nuclear Information System (INIS)

    A theoretical model developed for flow through a deformable fracture subject to stresses was successfully tested against laboratory experiments. The model contains no arbitrary parameters and can be used to predict flow rates through a single fracture if the fractional fracture contact area can be estimated and if stress-deformation data are available. These data can be obtained from laboratory or in situ tests. The model has considerable potential for practical application. The permeability of ultralarge samples of fractured crystalline rock as a function of stresses was measured. Results from tests on a pervasively fractured 1-m-diameter specimen of granitic rock showed that drastically simplifying assumptions must be used to apply theoretical models to this type of rock mass. Simple models successfully reproduce the trend of reduced permeability as stress is applied in a direction normal to the fracture plane. The tests also demonstrated how fracture conductivity increases as a result of dilatancy associated with shear displacements. The effect of specimen size on the hydraulic properties of fractured rock was also investigated. Permeability tests were performed on specimens of charcoal black granite containing a single fracture subjected to normal stress. Results are presented for tests performed on a 0.914-m-diameter specimen and on the same specimen after it had been reduced to 0.764 m in diameter. The data show that fracture conductivity is sensitive to stress history and sample disturbance

  4. Determination of the location and connectivity of fractures in metamorphic rock with in-hole tracers

    International Nuclear Information System (INIS)

    In-hole tracer tests were used in a geohydrologic investigation of metamorphic rock at the Savannah River Plant near Aiken, SC to locate water-transmitting fractures and to determine the connectivity of these fractures between boreholes. Only after development of a conceptual model of the fracture occurrence and connection could the proper methods of analysis for the hydraulic parameters be selected. In-hole tracers were used to locate fractures in a borehole and supplemented other methods, such as core inspection, geophysical logs, borehole wall imaging techniques, dry drilling, and packer tests. The first three of these do not necessarily investigate fluid-transmitting fractures. In the study of the connectivity of fractures between boreholes, the in-hole tracer techniques supplemented determinations by the rapidity of hydraulic response and the use of between-well tracer tests. In hydraulically transmissive rock, fractures were located by changes in the velocity of the tracer pulse in response to adding fluid to the well. In virtually impermeable rock, the movement of the tracer pulse in the rock was normalized to the movement of another tracer pulse in the cased portion of the well because the movement was so slow that direct measurement was difficult. Connectivity of fractures between boreholes was determined by placing an in-hole tracer in one hole and measuring the movement induced by pumping a nearby borehole. From this test, it was determined that the fractures were interlacing, and single fractures did not extend from one borehole directly to the other

  5. Numerical Simulation of Rock Fracturing under Uniaxial Compression Using Virtual Internal Bond Model

    Institute of Scientific and Technical Information of China (English)

    KE Chang-ren; JIANG Jun-ling; GE Xiu-run

    2009-01-01

    A multi-scale virtual internal bond (VIB) model for the isotropic materials has been recently proposed to describe the material deformation and fracturing. During the simulation process of material fracturing using VIB, the fracture criterion is directly built into the constitutive formulation of the material using the cohesive force law. Enlightened by the similarity of the damage constitutive model of rock under uniaxial compression and the cohesive force law of VIB, a VIB density function of rock under uniaxial compression is suggested. The elastic modulus tensor is formulated on the basis of the density function. Thus the complete deformation process of rock under the uniaxial compression is simulated.

  6. Couple analyzing the acoustic emission characters from hard composite rock fracture

    Institute of Scientific and Technical Information of China (English)

    Xingping Lai; Linhai Wang; Meifeng Cai

    2004-01-01

    Rock mass is fractured media. Its fracture is a nonlinear process. The accumulation of acoustic emission (AE) is closely related to the degree of damage. The dynamics problem is simply described based on the non-equilibrium statistical theory of crack evolvement, trying to use the hybrid analysis of the statistical theory and scan electron microscopy (SEM), the characters of AE sig nals from rock damage in a mined-out area is synthetically analyzed and evaluated. These provide an evidence to reverse deduce and accurately infer the position of rock fracture for dynamical hazard control.

  7. Petrography and geochemistry of basaltic rocks from the Conrad fracture zone on the America-Antarctica Ridge

    Science.gov (United States)

    le Roex, Anton P.; Dick, Henry J. B.

    1981-06-01

    Intrusive and extrusive basaltic rocks have been dredged from the Conrad fracture zone (transecting the slow-spreading America-Antarctica Ridge). The majority of rocks recovered are holocrystalline with the dominant mineral assemblage being plagioclase plus clinopyroxene with or without minor Fe-Ti oxides (olivine occurs in only three samples) and many of the samples show evidence of extensive alteration. Secondary minerals include chlorite, actinolite, K- and Na-feldspar, analcite and epidote. In terms of bulk chemistry the rocks are characterized by their generally evolved and highly variable compositions (e.g. Mg *=0.65-0.35;TiO 2=0.7-3.6%;Zr=31-374ppm;Nb=differentiation observed in the Conrad fracture zone basalts implies some additional constraint other than spreading rate on the formation of ferrobasalt and reaffirms the importance of extensive crustal differentiation during the production of this basalt type.

  8. Fluid-dependent anisotropy and experimental measurements in synthetic porous rocks with controlled fracture parameters

    International Nuclear Information System (INIS)

    In this study, we analyse the influence of fluid on P- and S-wave anisotropy in a fractured medium. Equivalent medium theories are used to describe the relationship between the fluid properties and the rock physics characteristics in fractured rocks, and P-wave and S-wave velocities and anisotropy are considered to be influenced by fluid saturation. However, these theoretical predictions require experimental measurement results for calibration. A new construction method was used to create synthetic rock samples with controlled fracture parameters. The new construction process provides synthetic rocks that have a more realistic mineral composition, porous structure, cementation and pressure sensitivity than samples used in previous research on fractured media. The synthetic rock samples contain fractures which have a controlled distribution, diameter, thickness and fracture density. In this study, the fracture diameter was about 4 mm, the thickness of fractures was about 0.06 mm, and the fracture density in the two fractured rock samples was about 3.45%. SEM images show well-defined penny-shaped fractures of 4 mm in length and 0.06 mm in width. The rock samples were saturated with air, water and oil, and P- and S-wave velocities were measured in an ultrasonic measurement system. The laboratory measurement results show that the P-wave anisotropy is strongly influenced by saturated fluid, and the P-wave anisotropy parameter, ε, has a much larger value in air saturation than in water and oil saturations. The S-wave anisotropy decreases when the samples are saturated with oil, which can be caused by high fluid viscosity. In the direction perpendicular to the fractures (the 0° direction), shear-wave splitting is negligible, and is similar to the blank sample without fractures, as expected. In the direction parallel to the fractures (the 90° direction) shear-wave splitting is significant. The fractured rock samples show significant P- and S-wave anisotropy caused

  9. Effect of isolated fractures on accelerated flow in unsaturated porous rock

    Science.gov (United States)

    Su, G.W.; Nimmo, J.R.; Dragila, M.I.

    2003-01-01

    Fractures that begin and end in the unsaturated zone, or isolated fractures, have been ignored in previous studies because they were generally assumed to behave as capillary barriers and remain nonconductive. We conducted a series of experiments using Berea sandstone samples to examine the physical mechanisms controlling flow in a rock containing a single isolated fracture. The input fluxes and fracture orientation were varied in these experiments. Visualization experiments using dyed water in a thin vertical slab of rock were conducted to identify flow mechanisms occurring due to the presence of the isolated fracture. Two mechanisms occurred: (1) localized flow through the rock matrix in the vicinity of the isolated fracture and (2) pooling of water at the bottom of the fracture, indicating the occurrence of film flow along the isolated fracture wall. These mechanisms were observed at fracture angles of 20 and 60 degrees from the horizontal, but not at 90 degrees. Pooling along the bottom of the fracture was observed over a wider range of input fluxes for low-angled isolated fractures compared to high-angled ones. Measurements of matrix water pressures in the samples with the 20 and 60 degree fractures also demonstrated that preferential flow occurred through the matrix in the fracture vicinity, where higher pressures occurred in the regions where faster flow was observed in the visualization experiments. The pooling length at the terminus of a 20 degree isolated fracture was measured as a function of input flux. Calculations of the film flow rate along the fracture were made using these measurements and indicated that up to 22% of the flow occurred as film flow. These experiments, apparently the first to consider isolated fractures, demonstrate that such features can accelerate flow through the unsaturated zone and should be considered when developing conceptual models.

  10. The Dynamic Fracture Process in Rocks Under High-Voltage Pulse Fragmentation

    Science.gov (United States)

    Cho, Sang Ho; Cheong, Sang Sun; Yokota, Mitsuhiro; Kaneko, Katsuhiko

    2016-10-01

    High-voltage pulse technology has been applied to rock excavation, liberation of microfossils, drilling of rocks, oil and water stimulation, cleaning castings, and recycling products like concrete and electrical appliances. In the field of rock mechanics, research interest has focused on the use of high-voltage pulse technology for drilling and cutting rocks over the past several decades. In the use of high-voltage pulse technology for drilling and cutting rocks, it is important to understand the fragmentation mechanism in rocks subjected to high-voltage discharge pulses to improve the effectiveness of drilling and cutting technologies. The process of drilling rocks using high-voltage discharge is employed because it generates electrical breakdown inside the rocks between the anode and cathode. In this study, seven rock types and a cement paste were electrically fractured using high-voltage pulse discharge to investigate their dielectric breakdown properties. The dielectric breakdown strengths of the samples were compared with their physical and mechanical properties. The samples with dielectric fractured were scanned using a high-resolution X-ray computed tomography system to observe the fracture formation associated with mineral constituents. The fracture patterns of the rock samples were analyzed using numerical simulation for high-voltage pulse-induced fragmentation that adopts the surface traction and internal body force conditions.

  11. Geophysical characterization of fractured bedrock at Site 8, former Pease Air Force Base, Newington, New Hampshire

    Science.gov (United States)

    Mack, Thomas J.; Degnan, James R.

    2003-01-01

    Borehole-geophysical logs collected from eight wells and direct-current resistivity data from three survey lines were analyzed to characterize the fractured bedrock and identify transmissive fractures beneath the former Pease Air Force Base, Newington, N.H. The following logs were used: caliper, fluid temperature and conductivity, natural gamma radiation, electromagnetic conductivity, optical and acoustic televiewer, and heat-pulse flowmeter. The logs indicate several foliation and fracture trends in the bedrock. Two fracture-correlated lineaments trending 28? and 29?, identified with low-altitude aerial photography, are coincident with the dominant structural trend. The eight boreholes logged at Site 8 generally have few fractures and have yields ranging from 0 to 40 gallons per minute. The fractures that probably resulted in high well yields (20?40 gallons per minute) strike northeast-southwest or by the right hand rule, have an orientation of 215?, 47?, and 51?. Two-dimensional direct-current resistivity methods were used to collect detailed subsurface information about the overburden, bedrock-fracture zone depths, and apparent-dip directions. Analysis of data inversions from data collected with dipole-dipole and Schlumberger arrays indicated electrically conductive zones in the bedrock that are probably caused by fractured rock. These zones are coincident with extensions of fracture-correlated lineaments. The fracture-correlated lineaments and geophysical-survey results indicate a possible northeast-southwest anisotropy to the fractured rock.

  12. Impact of hydraulic perforation on fracture initiation and propagation in shale rocks

    Institute of Scientific and Technical Information of China (English)

    ZHAO Xi; JU Yang; YANG Yong; SU Sun; GONG WenBo

    2016-01-01

    To enhance the oil and gas recovery rate,hydraulic fracturing techniques have been widely adopted for stimulation of low-permeability reservoirs.Pioneering work indicates that hydraulic perforation and layout could significantly affect fracture initiation and propagation in low-permeability reservoir rocks subjected to complex in-situ stresses.This paper reports on a novel numerical method that incorporates fracture mechanics principles and the numerical tools FRANC3D and ANSYS to investigate the three-dimensional initiation and propagation behavior of hydro-fracturing cracks in shale rock.Considering the transverse isotropic property of shale rocks,the mechanical parameters of reservoir rocks attained from laboratory tests were adopted in the simulation.The influence of perforation layouts on the 3D initiation of hydro-fracturing fractures in reservoir rocks under geo-stresses was quantitatively illuminated.The propagation and growth of fractures in three dimensions in different perforating azimuth values were illustrated.The results indicate that:1) the optimal perforation direction should be parallel to the maximum horizontal principal stress,2) the crack plane gradually turns toward the direction of the maximum horizontal principal stress when they are not in parallel,3) compared with the linear and symmetric pattern,the staggered perforation is the optimal one,4) the proper perforation density is four to six holes per meter,5) the optimal perforation diameter in this model is 30 mm,and 6) the influence of the perforation depth on the fracture initiation pressure is low.

  13. Numerical simulation of Fluid-Rock coupling heat transfer in naturally fractured geothermal system

    International Nuclear Information System (INIS)

    Estimating heat extraction from naturally fractured geothermal systems is a challenging task. Most of the previous works in this area assumed an instantaneous local thermal equilibrium while simulating heat extraction from the fractured geothermal systems. This paper investigates the role of heat transfer between the rock matrix and circulating fluid on economic hot water production from fractured geothermal systems. For this purpose a numerical procedure is developed by coupling fluid flow with heat transfer. The novelty of this approach lies in its dynamic treatment of the characteristic properties (aperture, length and orientation) of individual fractures in simulating fluid flow and heat transfer between rock and circulating fluid. A naturally fractured geothermal system with a medium fracture density of 0.05 m-1 is chosen for a case study. The results of this study have shown that heat transfer between rock and fluid and fracture connectivity has a profound effect on the economic potential of a geothermal reservoir. - Highlights: → The results of this study have shown that heat transfer between rock and fluid has profound on the economic potential of the geothermal reservoir. → Estimation of heat extraction from naturally fractured geothermal systems is a challenging task. → A numerical procedure is developed by coupling the fluid flow model with heat transfer model. → The heat transfer coefficient value depends on the properties of the rock, circulating fluid and fluid velocity.

  14. Computational Modelling of Fracture Propagation in Rocks Using a Coupled Elastic-Plasticity-Damage Model

    Directory of Open Access Journals (Sweden)

    Isa Kolo

    2016-01-01

    Full Text Available A coupled elastic-plasticity-damage constitutive model, AK Model, is applied to predict fracture propagation in rocks. The quasi-brittle material model captures anisotropic effects and the distinct behavior of rocks in tension and compression. Calibration of the constitutive model is realized using experimental data for Carrara marble. Through the Weibull distribution function, heterogeneity effect is captured by spatially varying the elastic properties of the rock. Favorable comparison between model predictions and experiments for single-flawed specimens reveal that the AK Model is reliable and accurate for modelling fracture propagation in rocks.

  15. Experimental Hydromechanical Characterization and Numerical Modelling of a Fractured and Porous Sandstone

    Science.gov (United States)

    Souley, Mountaka; Lopez, Philippe; Boulon, Marc; Thoraval, Alain

    2015-05-01

    The experimental device previously used to study the hydromechanical behaviour of individual fractures on a laboratory scale, was adapted to make it possible to measure flow through porous rock mass samples in addition to fracture flows. A first series of tests was performed to characterize the hydromechanical behaviour of the fracture individually as well as the porous matrix (sandstone) comprising the fracture walls. A third test in this series was used to validate the experimental approach. These tests showed non-linear evolution of the contact area on the fracture walls with respect to effective normal stress. Consequently, a non-linear relationship was noted between the hydraulic aperture on the one hand, and the effective normal stress and mechanical opening on the other hand. The results of the three tests were then analysed by numerical modelling. The VIPLEF/HYDREF numerical codes used take into account the dual-porosity of the sample (fracture + rock matrix) and can be used to reproduce hydromechanical loading accurately. The analyses show that the relationship between the hydraulic aperture of the fracture and the mechanical closure has a significant effect on fracture flow rate predictions. By taking simultaneous measurements of flow in both fracture and rock matrix, we were able to carry out a global evaluation of the conceptual approach used.

  16. Fractured-rock permeability-versus-stress relationships from in situ experiments

    Science.gov (United States)

    Rutqvist, Jonny

    2016-04-01

    The purpose of this presentation is (1) to review field data on stress-induced permeability changes in fractured rock, (2) to describe back-analysis of fractured rock stress-versus-permeability relationships through model calibration against such field data, and (3) to discuss observations of chemically mediated fracture surface compaction and its effect on fractured rock permeability. Reviewed field data on stress-induced permeability changes, some of which are used for model calibration, includes in situ block experiments, borehole injection experiments, observations of depth dependent permeability, studies of excavation-induced changes in permeability around tunnels, and permeability changes associated with a large-scale rock mass heating experiment. It is suggested that model calibration of stress-versus-permeability relationships against field experiments involving simultaneously elevated stress and temperature may be strongly affected by additional temperature dependent fracture closure and fracture surface interlocking. This is a phenomenon that has been observed both in the lab and the field and has been described as thermal over-closure related to better fit of opposing fracture surfaces at high temperatures. The same phenomenon has also been described as chemically mediated fracture closure related to pressure solution of fracture surface asperities. The back-calculated stress-versus-permeability relationship may implicitly account for such effects, but the relative contribution of purely mechanical versus chemically mediated mechanical changes is difficult to isolate.

  17. On the Characteristics of Rheological Fracture of Rock%岩石的蠕变断裂特性分析

    Institute of Scientific and Technical Information of China (English)

    陈有亮; 秦爱芳; 金孝杰

    2000-01-01

    Based on the traditional theory of fracture, time-dependence of rock fracture is taken into account and the creep fracture criteria are given. The effect of the microcrack zone on fracture toughness is analyzed. Finally, a model for time prediction of rheological fracture is derived and its feasibility is proven.

  18. Characterization of Unstable Rock Slopes Through Passive Seismic Measurements

    Science.gov (United States)

    Kleinbrod, Ulrike; Burjánek, Jan; Fäh, Donat

    2014-05-01

    Catastrophic rock slope failures have high social impact, causing significant damage to infrastructure and many casualties throughout the world each year. Both detection and characterization of rock instabilities are therefore of key importance. Analysing unstable rock slopes by means of ambient vibrations might be a new alternative to the already existing methods as for example geotechnical displacement measurements. A systematic measurement campaign has been initiated recently in Switzerland in order to study the seismic response of potential rockslides concerning a broad class of slope failure mechanisms and material conditions. First results are presented in this contribution. Small aperture seismic arrays were deployed at sites of interest for a short period of time (several hours) in order to record ambient vibrations. During each measurement a reference station was installed on a stable part close to the instability. The total number of stations used varies from 16 down to 2, depending on the site scope and resource availability. Instable rock slopes show a highly directional ground motion which is significantly amplified with respect to stable areas. These effects are strongest at certain frequencies which are identified as eigenfrequencies of the unstable rock mass. The eigenfrequencies and predominant directions have been estimated by frequency dependent polarization analysis. Site-to-reference spectral ratios have been calculated as well in order to estimate the relative amplification of ground motion at unstable parts. The retrieved results were compared with independent in-situ observations and other available data. The directions of maximum amplification are in most cases perpendicular to open cracks mapped on the surface and in good agreement with the deformation directions obtained by geodetic measurements. The interpretation of the observed wave field is done through numerical modelling of seismic wave propagation in fractured media with complex

  19. Study on the theoretical evaluation of grouting area and effective porosity for fractured rock masses

    International Nuclear Information System (INIS)

    An accurate evaluation of the grouting area in fractured rock is very important for designing the grouting pitch in the field. In this study, a method of determining the effective porosity and the grouting area of a three-dimensional (3-D) fractured rock mass are described. To evaluate the validity of this method, constant injection rate experiments were carried out in the laboratory. First, an experiment was performed on a gravel ground model. Then, a second experiment was performed on an axisymmetric cubic block model with gaps between the blocks minicking fractures in rocks. The results obtained from the experiments agree well with proposed theory. The effect of gravity on high permeability fractured rock mass was also evaluated and the Hele-Shaw's seepage model was applied in explaining the laboratory results. (author)

  20. Development of grouting technologies for geological disposal of high level waste in Japan (6). Description method of rock fractures using borehole fractures column

    International Nuclear Information System (INIS)

    A visually descriptive method of identifying type, occurrence and distribution of rock fractures is proposed using a newly developed borehole fractures column (BFC) technique. The BFC is constructed from borehole TV and core sample observation and interpretation. The usefulness of this approach is best illustrated through a case study of core sample taken from the Grimsel Test Site (GTS) in Switzerland. In this case, each mm scale fracture could be identified as forming part of much larger fracture zones. Fracture descriptions based on the BFC can be used to interpolate fractures between boreholes and provide fundamental 'big picture' insights into the fracture field of a rock mass. (author)

  1. Determination of hydraulic conductivity of fractured rock masses: A case study for a rock cavern project in Singapore

    OpenAIRE

    Zhipeng Xu; Zhiye Zhao; Jianping Sun; Ming Lu

    2015-01-01

    In order to reduce the risk associated with water seepage in an underground rock cavern project in Singapore, a reliable hydro-geological model should be established based on the in situ investigation data. The key challenging issue in the hydro-geological model building is how to integrate limited geological and hydro-geological data to determine the hydraulic conductivity of the fractured rock masses. Based on the data obtained from different stages (feasibility investigation stage, constru...

  2. Experimental and Analytical Research on Fracture Processes in ROck

    Energy Technology Data Exchange (ETDEWEB)

    Herbert H.. Einstein; Jay Miller; Bruno Silva

    2009-02-27

    Experimental studies on fracture propagation and coalescence were conducted which together with previous tests by this group on gypsum and marble, provide information on fracturing. Specifically, different fracture geometries wsere tested, which together with the different material properties will provide the basis for analytical/numerical modeling. INitial steps on the models were made as were initial investigations on the effect of pressurized water on fracture coalescence.

  3. Identification of transport processes in Southern Indian fractured crystalline rock using forced-gradient tracer experiments

    Science.gov (United States)

    Guihéneuf, Nicolas; Bour, Olivier; Boisson, Alexandre; Le Borgne, Tanguy; Becker, Matthew R.; Nigon, Benoit; Wajiduddin, Mohammed; Ahmed, Shakeel; Maréchal, Jean-Christophe

    2015-04-01

    Understanding dominant transport processes is essential to improve prediction of contaminants transfer in fractured crystalline rocks. In such fractured media, solute transport is characterized by fast advection within open and connected fractures and sometimes by matrix diffusion that may be enhanced by chemical weathering. To investigate this phenomenon, we carried out radially convergent and push-pull tracer experiments in the fractured granite of the Experimental Hydrogeological Park of Choutuppal (Southern India). Tracer tests were performed in the same permeable fracture from few meters to several ten meters and from few hours to two weeks to check the consistency of the results at different spatial and temporal scales. These different types of forced gradient tracer experiments allow separation of the effects of advection and diffusion on transport. Breakthrough curves from radially convergent tracer tests display systematically a -2 power law slope on the late time behavior. This tailing can be adequately represented by a transport model that only takes into account heterogeneous advection caused by fluid flow channeling. The negligible impact of matrix diffusion was confirmed by the push-pull tracer tests, at least for the duration of experiments. A push-pull experiment carried out with a cocktail of two conservative tracers having different diffusion coefficients displayed similar breakthrough curves. Increasing the resting phase during the experiments did not lead to a significant decline of peak concentration. All these results suggest a negligible impact of matrix diffusion. However, increasing the scales of investigation during push-pull tracer tests led to a decrease of the power law slope on the late time behavior. This behavior that cannot be modeled with a transport model based on independent flow paths and indicate non-reversible heterogeneous advection. This process could be explained by the convergence of streamlines after a certain distance

  4. Seismic Waves in Rocks with Fluids and Fractures

    Energy Technology Data Exchange (ETDEWEB)

    Berryman, J G

    2006-02-06

    Seismic wave propagation through the earth is often strongly affected by the presence of fractures. When these fractures are filled with fluids (oil, gas, water, CO{sub 2}, etc.), the type and state of the fluid (liquid or gas) can make a large difference in the response of the seismic waves. This paper will summarize some early work of the author on methods of deconstructing the effects of fractures, and any fluids within these fractures, on seismic wave propagation as observed in reflection seismic data. Methods to be explored here include Thomsen's anisotropy parameters for wave moveout (since fractures often induce elastic anisotropy), and some very convenient fracture parameters introduced by Sayers and Kachanov that permit a relatively simple deconstruction of the elastic behavior in terms of fracture parameters (whenever this is appropriate).

  5. Analyzing unsaturated flow patterns in fractured rock using an integrated modeling approach

    Science.gov (United States)

    Wu, Yu-Shu; Lu, Guoping; Zhang, Keni; Pan, Lehua; Bodvarsson, Gudmundur S.

    2007-05-01

    Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies due to the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. An integrated modeling methodology has been developed for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada (USA), a proposed underground repository site for storing high-level radioactive waste. The approach integrates moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for analyses. It takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain’s highly heterogeneous, unsaturated fractured tuffs. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptualizations through analyzing flow patterns in the unsaturated zone. In particular, this model provides clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain’s flow system is demonstrated to provide a practical modeling tool for characterizing flow and transport processes in complex subsurface systems.

  6. Influence of shear and deviatoric stress on the evolution of permeability in fractured rock

    NARCIS (Netherlands)

    Faoro, Igor; Niemeijer, André; Marone, Chris; Elsworth, Derek

    2009-01-01

    The evolution of permeability in fractured rock as a function of effective normal stress, shear displacement, and damage remains a complex issue. In this contribution, we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress

  7. Detecting rupture precursors and determining the main fracture spread direction of rock with dynamic rock resistivity change anisotropy

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    @@ In the past, domestic and abroad scientific workers have done a large number of experiment researches on a great number of researches of experiment for the relationship between electrical resistivity change and the load stress on rock (Geoelectric Testing Group, Department of Geophysics, Peking University and Research Division, Seismological Brigade of Lanzhou, 1978; Zhang, 1981; Chen, et al, 1983; Zhao, et al, 1983; Zhang, Lu, 1983; Zhang, et al, 1985; Brace, Orange, 1968; Kurite, 1986; Teisseyre, 1989), such as imitating dynamic fracture of rock, frictional sliding course, and observing its resistivity change shape with a lot of experimental workssuch as simulating the dynamic course of crustal rocks fracturing and frictional slipping along the fracture surface, and observing its resistivity change shape with experiment. They found that, in the fracture process of rock under loading, not only its resistivity shape change notably, and its direction changes also very clearly, and therefore many scientific workers have shown strong interest in anisotropy of resistivity change, and have done some researches onfor it.

  8. Use of markers of paleo-circulations to characterize the porous network of fractured granite.

    Science.gov (United States)

    Bertrand, L.; LeGarzic, E.; Géraud, Y.; Diraison, M.

    2012-04-01

    Fractured reservoirs in crystalline rocks are well studied nowadays for their application in water resources, oil exploitation or geothermics. In this king of rock, the matrice has a very low permeability and the fluid flow is localized in the fracture pattern. Thus, the characterization and the modeling of such reservoirs require the good knowledge of the fractures, in particular the orientation, density or spatial distribution. In actual fractured reservoirs, the access on those parameters are with seismic and borehole data. The two prospection techniques are at different scale and dimensions, and correlations between them are difficult to make. In consequence, it is necessary to study field rocks analogues on the underground fractured reservoirs. Tamariu's granite, Catalunya, is one of those fields' analogues. Previous studies have highlighted a structuration of the granite in structural blocs of different sizes, separated by faults, and internal fracture patterns in each bloc. Markers of intense paleofluids circulations have been seen in the faults and fractures of those blocs. This study follows the structural characterization of the fracture pattern and as the aim to study the fluid circulation in those fractures. With precise fracture maps, we have analyzed the principal flow direction and the nature of the hydrothermal deposits. Aside from primary hydrothermal quartz, the main secondary minerals are calcite and dolomite, and a little part of iron oxides. This observation, combined on the fracture maps, has allowed us to try a semi-quantification of the usable volume by the fluid in the granite at the circulations time. The fracture pattern has been the host of fluids of around 3% of their volume. Therefore, we have identified a diffuse flow in the grain matrice and which creates primary minerals alteration. The volume of alteration represent around 0,1-0,3% of the rock. In consequence, this study highlights a double-porosity behavior of the granite. On one

  9. Time-lapse imaging of saline-tracer transport in fractured rock using difference-attenuation radar tomography

    Science.gov (United States)

    Day-Lewis, F. D.; Lane, J.W.; Harris, J.M.; Gorelick, S.M.

    2003-01-01

    Accurate characterization of fractured-rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater hydrology. We demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests. Cross-well difference-attenuation ground-penetrating radar was used to monitor saline-tracer migration in an experiment at the U.S. Geological Survey Fractured Rock Hydrology Research Site in Grafton County, New Hampshire. Radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests. An innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection. The inverse algorithm minimizes a combination of two functions. The first is the sum of weighted squared data residuals. Second is a measure of solution complexity based on an a priori space-time covariance function, subject to constraints that limit radar-attenuation changes to regions of the tomograms traversed by high difference-attenuation ray paths. The time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes; from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures. These results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site.

  10. Potentially Conductive Channels in Fracture Cements of Low Permeability Rocks

    Science.gov (United States)

    Wright, E.; Landry, C. J.; Eichhubl, P.

    2015-12-01

    Natural fractures in shale reservoirs are frequently filled with mineral cement that lacks any residual fracture porosity that is visible under the petrographic microscope. These fully cemented fractures are generally interpreted to be impermeable for fluid flow. Scanning electron microscopy of calcite, dolomite, and barite fracture cements from a variety of shale reservoirs, prepared using broad ion beam milling, provides evidence of open to partially healed elongate pores that are on the order of hundreds of nanometers in aperture. In calcite fracture cement, these pores have consistent apertures of about 100 nm. In dolomite and barite, apertures are up to 500 nm. These pores have been previously overlooked because traditional thin sectioning and polishing destroys sub-micron details of the fracture cement pore structure. Ion milling preserves these details with a minimum of sample damage during sample preparation. Electron backscatter diffraction shows that these pores occur along grain boundaries within the blocky or columnar fracture cement. While partially healed, these pores, arranged along grain boundaries, are frequently sufficiently well connected acting as channels for fluid flow along and across fully cemented natural fractures. In shale reservoirs of ultra-low matrix permeability, these grain boundary channels may thus provide fracture permeability significantly contributing to reservoir production where intersected or indirectly reactivated by hydraulic fractures.

  11. Permeability in fractured rocks from deep geothermal boreholes in the Upper Rhine Graben

    Science.gov (United States)

    Vidal, Jeanne; Whitechurch, Hubert; Genter, Albert; Schmittbuhl, Jean; Baujard, Clément

    2015-04-01

    Permeability in fractured rocks from deep geothermal boreholes in the Upper Rhine Graben Vidal J.1, Whitechurch H.1, Genter A.2, Schmittbuhl J.1, Baujard C.2 1 EOST, Université de Strasbourg 2 ES-Géothermie, Strasbourg The thermal regime of the Upper Rhine Graben (URG) is characterized by a series of geothermal anomalies on its French part near Soultz-sous-Forêts, Rittershoffen and in the surrounding area of Strasbourg. Sedimentary formations of these areas host oil field widely exploited in the past which exhibit exceptionally high temperature gradients. Thus, geothermal anomalies are superimposed to the oil fields which are interpreted as natural brine advection occurring inside a nearly vertical multi-scale fracture system cross-cutting both deep-seated Triassic sediments and Paleozoic crystalline basement. The sediments-basement interface is therefore very challenging for geothermal industry because most of the geothermal resource is trapped there within natural fractures. Several deep geothermal projects exploit local geothermal energy to use the heat or produce electricity and thus target permeable fractured rocks at this interface. In 1980, a geothermal exploration well was drilled close to Strasbourg down to the Permian sediments at 3220 m depth. Bottom hole temperature was estimated to 148°C but the natural flow rate was too low for an economic profitability (operation was planned and the project was abandoned. The Soultz-sous-Forêts project, initiated in 1986, explored during more than 30 years the experimental geothermal site by drilling five boreholes, three of which extend to 5 km depth. They identified a temperature of 200° C at 5 km depth in the granitic basement but with a variable flow rate. Hydraulic and chemical stimulation operations were applied in order to increase the initial low permeability by reactivating and dissolving sealed fractures in basement. The productivity was considerably improved and allows geothermal exploitation at 165

  12. Mesoscale modeling of grain fracturing in high porosity rocks using the strong discontinuity approach

    Science.gov (United States)

    Tjioe, M.; Choo, J.; Borja, R. I.

    2013-12-01

    In previous studies, it has been found that two dominant micro-mechanisms play important roles in the deformation of high-porosity rocks. They are grain fracturing and crystal plasticity. Grain fracturing is a phenomenon where larger grains cleave to their smaller constituents as they respond to the stress concentration exerted on them close to the open pore spaces. Specimen-scale modeling cannot reflect such mechanism so our investigation is carried out in the next smaller scale, namely the mesoscopic scale. We model a solid matrix microstructure using finite element in which displacement discontinuity is introduced in each element where the slip condition has been exceeded. Such discontinuity is termed strong discontinuity and is characterized by zero band thickness and localized strain in the band that reaches infinity. For grains under compression, this slip condition is the cohesive-frictional law governing the behavior on the surface of discontinuity. The strong discontinuity in the grain scale is modeled via an Assumed Enhanced Strain (AES) method formulated within the context of nonlinear finite elements. Through this method, we can model grain-splitting as well as halos of cataclastic damage that are usually observed before a macropore collapses. The overall stress-strain curve and plastic slip of the mesoscopic element are then obtained and comparison to the crystal plasticity behavior is made to show the differences between the two mechanisms. We demonstrate that the incorporation of grain-fracturing and crystal plasticity can shed light onto the pore-scale deformation of high-porosity rocks.

  13. Hidromechanical simulation in a fractured rock mass: the experimental site of Coaraze (Southern-Alps, France)

    OpenAIRE

    Corbera Gaju, Sergi

    2004-01-01

    Hydromechanical processes in large permeable jointed rock masses have been poorly studied due to the difficulties in determining boundary conditions in such large sites. To study this type of problems, in situ field experiments have been carried out since 1997 on a small fractured calcareous rock mass in Southern France, near Coaraze (limestone aquifer). The present work is intended to enhance understanding of hydromechanics in rock masses by testing the stress and strain state...

  14. Characterising rock fracture aperture-spacing relationships using power-law relationships: some considerations

    Science.gov (United States)

    Brook, Martin; Hebblewhite, Bruce; Mitra, Rudrajit

    2016-04-01

    The size-scaling of rock fractures is a well-studied problem in geology, especially for permeability quantification. The intensity of fractures may control the economic exploitation of fractured reservoirs because fracture intensity describes the abundance of fractures potentially available for fluid flow. Moreover, in geotechnical engineering, fractures are important for parameterisation of stress models and excavation design. As fracture data is often collected from widely-spaced boreholes where core recovery is often incomplete, accurate interpretation and representation of fracture aperture-frequency relationships from sparse datasets is important. Fracture intensity is the number of fractures encountered per unit length along a sample scanline oriented perpendicular to the fractures in a set. Cumulative frequency of fractures (F) is commonly related to fracture aperture (A) in the form of a power-law (F = aA‑b), with variations in the size of the a coefficient between sites interpreted to equate to fracture frequency for a given aperture (A). However, a common flaw in this approach is that even a small change in b can have a large effect on the response of the fracture frequency (F) parameter. We compare fracture data from the Late Permian Rangal Coal Measures from Australia's Bowen Basin, with fracture data from Jurassic carbonates from the Sierra Madre Oriental, northeastern Mexico. Both power-law coefficient a and exponent b control the fracture aperture-frequency relationship in conjunction with each other; that is, power-laws with relatively low a coefficients have relatively high b exponents and vice versa. Hence, any comparison of different power-laws must take both a and b into consideration. The corollary is that different sedimentary beds in the Sierra Madre carbonates do not show ˜8× the fracture frequency for a given fracture aperture, as based solely on the comparison of coefficient a. Rather, power-law "sensitivity factors" developed from

  15. Study on the physical meaning of seismic inhomogeneous degree by rock fracture experiments

    Institute of Scientific and Technical Information of China (English)

    LI Zhi-xiong; MA Sheng-li; LI Sheng-qiang; LI Min-feng; LU Peng; CHEN Hua-jing; WANG Song; WU Ting

    2005-01-01

    It is observed that the parameter of seismic inhomogeneous degree (GL value) calculated from the earthquake catalog shows obvious abnormal changes prior to strong earthquakes, indicating the state change of local seismic activity. This paper focuses on the mechanism for the abnormal changes of the GL values based on the sequences of acoustic emission for three types of rock samples containing macro-asperity fracture; compressional en-echelon fracture and model-III shear fracture. The results show that for the three types of rock samples, there are continuous abnormal changes of GL value (>1) just before the non-elastic deformation occurs or during the process of nucleation prior to the instability. Based on the experimental results, it seems that the process of creep sliding and resistance-uniformization along fault zone is the possible mechanism for the abnormal changes of GL value before rock fractures.

  16. Analysis for preliminary evaluation of discrete fracture flow and large-scale permeability in sedimentary rocks

    International Nuclear Information System (INIS)

    Conceptual models for sedimentary rock settings that could be used in future evaluation and suitability studies are being examined through the DOE Repository Technology Program. One area of concern for the hydrologic aspects of these models is discrete fracture flow analysis as related to the estimation of the size of the representative elementary volume, evaluation of the appropriateness of continuum assumptions and estimation of the large-scale permeabilities of sedimentary rocks. A basis for preliminary analysis of flow in fracture systems of the types that might be expected to occur in low permeability sedimentary rocks is presented. The approach used involves numerical modeling of discrete fracture flow for the configuration of a large-scale hydrologic field test directed at estimation of the size of the representative elementary volume and large-scale permeability. Analysis of fracture data on the basis of this configuration is expected to provide a preliminary indication of the scale at which continuum assumptions can be made

  17. Sustainability of Water Resources in the Fractured-Rock Area of Maryland

    Science.gov (United States)

    Bolton, David W.; Gerhart, James M.; Kasraei, Saeid

    2009-01-01

    The fractured-rock area of Maryland encompasses the region of the State west of the Fall Line, which is approximated by the Interstate 95 corridor. It includes the Piedmont, Blue Ridge, Ridge and Valley, and Appalachian Plateau Physiographic Provinces (fig. 1). Surface water and ground water are important and interconnected water sources in this area. Streamflow characteristics vary in response to different land use, geology, topography, soil, and other factors. Ground-water flow is quite localized, tending to be controlled by local watersheds. Water in this region moves down through the soil and decomposed rock (saprolite) and along joints, faults, and fractures in the underlying rock (fig. 2). Water availability depends upon the size of fractures as well as the interconnections between fractures.

  18. Stresses and Shear Fracture Zone of Jinshazhou Tunnel Surrounding Rock in Rich Water Region

    Institute of Scientific and Technical Information of China (English)

    ZHENG Jun-jie; LOU Xiao-ming

    2008-01-01

    Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided into three zones, including elastic zone, plastic damage zone and shear fracture zone fof assessing the stability of the tunnel surrounding rock. By local hydrogeology, the stresses of surrounding rock of Jinshazhou circular tunnel was analyzed and the stress solutions on the elastic and plastic damage zones were obtained by applying the theories of fluid-solid coupling and elasto-plastic damage mechanics. The shear fracture zone generated by joints was studied and its range was determined by using Mohr-Coulomb strength criterion. Finally, the correctness of the theoretical results was validated by comparing the scopes of shear fracture zones calculated in this paper with those from literature.

  19. Experimental investigation of the temperature effects on CO2 permeability of fractured coal rock

    Science.gov (United States)

    Ju, Yang; Wang, Huijie; Pathegama Gamage, Ranjith; Sun, Huafei

    2012-11-01

    Accurate prediction of gas permeability is of great significance for coalbed methane production and CO2 sequestration. The permeability of coal rock plays a key role in determining coalbed methane productivity in the application of simultaneous excavation of coal and gas in deep coal mines. The main objective of this study is to investigate the temperature effects on the permeability of fractured coal rock in deep coal seams. The CO2 permeability of the fractured coal samples obtained from Ping Ding Shan coalfield, China, was measured using high pressure undrained triaxial apparatus. To probe the temperature effects, four levels of temperatures (25-75^o) were tested with the injection pressures ranging from 7 to 11MPa and a confining pressure of 15MPa. It is shown that the CO2 permeability of the fractured coal rock rises apparently with an increasing temperature. The physical mechanism that governs the CO2 permeability of coal rock is discussed in this study.

  20. Photo-Disintegration of the Iron Nucleus in Fractured Magnetite Rocks with Magnetostriction

    CERN Document Server

    Widom, A; Srivastava, Y N

    2013-01-01

    There has been considerable interest in recent experiments on iron nuclear disintegrations observed when rocks containing such nuclei are crushed and fractured. The resulting nuclear transmutations are particularly strong for the case of magnetite rocks, i.e. loadstones. We argue that the fission of the iron nucleus is a consequence of photo-disintegration. The electro-strong coupling between electromagnetic fields and nuclear giant dipole resonances are central for producing observed nuclear reactions. The large electron energies produced during the fracture of piezomagnetic rocks are closely analogous to the previously discussed case of the fracture of piezoelectric rocks. In both cases electro-weak interactions can produce neutrons and neutrinos from energetic protons and electrons thus inducing nuclear transmutations. The electro-strong condensed matter coupling discussed herein represents new many body collective nuclear photo-disintegration effects.

  1. Modeling of Immiscible, Two-Phase Flows in a Natural Rock Fracture

    Energy Technology Data Exchange (ETDEWEB)

    Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H

    2009-01-01

    One potential method of geologically sequestering carbon dioxide (CO2) is to inject the gas into brine-filled, subsurface formations. Within these low-permeability rocks, fractures exist that can act as natural fluid conduits. Understanding how a less viscous fluid moves when injected into an initially saturated rock fracture is important for the prediction of CO2 transport within fractured rocks. Our study examined experimentally and numerically the motion of immiscible fluids as they were transported through models of a fracture in Berea sandstone. The natural fracture geometry was initially scanned using micro-computerized tomography (CT) at a fine volume-pixel (voxel) resolution by Karpyn et al. [1]. This CT scanned fracture was converted into a numerical mesh for two-phase flow calculations using the finite-volume solver FLUENT® and the volume-of-fluid method. Additionally, a translucent experimental model was constructed using stereolithography. The numerical model was shown to agree well with experiments for the case of a constant rate injection of air into the initially water-saturated fracture. The invading air moved intermittently, quickly invading large-aperture regions of the fracture. Relative permeability curves were developed to describe the fluid motion. These permeability curves can be used in reservoir-scale discrete fracture models for predictions of fluid motion within fractured geological formations. The numerical model was then changed to better mimic the subsurface conditions at which CO2 will move into brine saturated fractures. The different fluid properties of the modeled subsurface fluids were shown to increase the amount of volume the less-viscous invading gas would occupy while traversing the fracture.

  2. Fracture Propagation Characteristic and Micromechanism of Rock-Like Specimens under Uniaxial and Biaxial Compression

    Directory of Open Access Journals (Sweden)

    Xue-wei Liu

    2016-01-01

    Full Text Available This paper presents a set of uniaxial and biaxial compression tests on the rock-like material specimens with different fracture geometries through a rock mechanics servo-controlled testing system (RMT-150C. On the basis of experimental results, the characteristics of fracture propagation under different fracture geometries and loading conditions are firstly obtained. The newly formed fractures are observed propagating from or near the preexisting crack tips for different specimens, while the propagation paths are affected by the loading condition obviously. Then, by adopting acoustic emission (AE location technique, AE event localization characteristics in the process of loading are investigated. The locations of AE events are in good agreement with the macroscopic fracture propagation path. Finally, the micromechanism of macroscopic fracture propagation under uniaxial and biaxial compression conditions is analyzed, and the fracture propagation can be concluded as a result of microdamage accumulation inside the material. The results of this paper are helpful for theory and engineering design of the fractured rock mass.

  3. Mathematical modelling on transport of petroleum hydrocarbons in saturated fractured rocks

    Indian Academy of Sciences (India)

    G Suresh Kumar

    2014-10-01

    The present paper addresses critical issues that describe the dissolution mass transfer of petroleum hydrocarbons in a saturated subsurface system. The field procedure associated with the estimation of Light Non-Aqueous Phase Liquid (LNAPL) thickness in site monitor wells is revisited. A brief theory has been included on the composition and transport of petroleum hydrocarbons following an onshore oil spill in order to demonstrate the level of complexity associated with the LNAPL dissolution mass transfer even in a classical porous medium. However, such studies in saturated fractured rocks are highly complex and limited, and hence, deserve a special attention as the fate and transport of the petroleum hydrocarbons are not uncommon in saturated fractured rocks. In this context, an improved mathematical model has been proposed that will better describe the dissolution kinetics of petroleum hydrocarbons in saturated fractured rocks at the scale of a single fracture using dual-porosity concept. The lumped mass transfer coefficient in a classical porous medium proposed depends on mean grain size, while the same parameter has been replaced by an equivalent average thickness of fracture aperture that better describes the LNAPL dissolution rate in a coupled fracture-matrix system. A set of nonlinear coupled partial differential equations is deduced for a coupled fracture-matrix system in analogy with the differential equations of a classical porous medium. The proposed mathematical model may work well for the fracture aperture thicknesses varying between 100 and 500 microns with a relatively low Reynolds Number and initial NAPL saturation.

  4. Study of the fracture behavior of mortar and concretes with crushed rock or pebble aggregates

    Directory of Open Access Journals (Sweden)

    Sebastião Ribeiro

    2011-03-01

    Full Text Available The objective of this work was to compare the fracture energy of mortar and concretes produced with crushed rock and pebble aggregates using zero, 10, 20, 30 and 40% of aggregates mixed with standard mortar and applying the wedge splitting method to achieve stable crack propagation. The samples were cast in a special mold and cured for 28 days, after which they were subjected to crack propagation tests by the wedge splitting method to determine the fracture energies of the mortar and concrete. The concretes showed higher fracture energy than the mortar, and the concretes containing crushed rock showed higher resistance to crack propagation than all the compositions containing pebbles. The fracture energy varied from 38 to 55 J.m-2. A comparison of the number of aggregates that separated from the two concrete matrices with the highest fracture energies indicated that the concrete containing pebbles crumbled more easily and was therefore less resistant to crack propagation.

  5. Mode Ⅱ fracture mechanism of direct shearing specimen with guiding grooves of rock

    Institute of Scientific and Technical Information of China (English)

    饶秋华; 孙宗颀; 王桂尧; 徐纪成; 张静宜

    2001-01-01

    Fracture mechanism of direct shear specimen with guiding grooves of rock was investigated experimentally and numerically in order to explore a favorable stress condition for creating Mode Ⅱ fracture and guide design of specimen configuration for determining Mode Ⅱ fracture toughness of rock, KⅡC. The experimental and numerical results demonstrate that Mode Ⅱ fracture can be successfully achieved in the direct shearing specimen with guiding groove because the guiding grooves added in the notch plane can generate a favorable stress condition for Mode Ⅱ fracture, i.e. tensile stress at the notch tip is completely depressed and shear stress at the notch tip is very high in the notch plane. The optimum design of the specimen configuration for KⅡC testing should aim to reduce tensile stress to be compressive stress or be lower than tensile strength and greatly increase shear stress at crack tip.

  6. Analysis of a mesoscale infiltration and water seepage test in unsaturated fractured rock: Spatial variabilities and discrete fracture patterns

    Science.gov (United States)

    Zhou, Q.; Salve, R.; Liu, H.-H.; Wang, J.S.Y.; Hudson, D.

    2006-01-01

    A mesoscale (21??m in flow distance) infiltration and seepage test was recently conducted in a deep, unsaturated fractured rock system at the crossover point of two underground tunnels. Water was released from a 3??m ?? 4??m infiltration plot on the floor of an alcove in the upper tunnel, and seepage was collected from the ceiling of a niche in the lower tunnel. Significant temporal and (particularly) spatial variabilities were observed in both measured infiltration and seepage rates. To analyze the test results, a three-dimensional unsaturated flow model was used. A column-based scheme was developed to capture heterogeneous hydraulic properties reflected by these spatial variabilities observed. Fracture permeability and van Genuchten ?? parameter [van Genuchten, M.T., 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892-898] were calibrated for each rock column in the upper and lower hydrogeologic units in the test bed. The calibrated fracture properties for the infiltration and seepage zone enabled a good match between simulated and measured (spatially varying) seepage rates. The numerical model was also able to capture the general trend of the highly transient seepage processes through a discrete fracture network. The calibrated properties and measured infiltration/seepage rates were further compared with mapped discrete fracture patterns at the top and bottom boundaries. The measured infiltration rates and calibrated fracture permeability of the upper unit were found to be partially controlled by the fracture patterns on the infiltration plot (as indicated by their positive correlations with fracture density). However, no correlation could be established between measured seepage rates and density of fractures mapped on the niche ceiling. This lack of correlation indicates the complexity of (preferential) unsaturated flow within the discrete fracture network. This also indicates that continuum

  7. Influence of piezometer construction on groundwater sampling in fractured rock.

    Science.gov (United States)

    Kozuskanich, J; Novakowski, K S; Anderson, B C

    2012-01-01

    A numerical model for groundwater flow and solute transport was employed to examine the influence of the screen and sandpack on the collection of a representative geochemical sample from a piezometer monitoring well installation in a discretely fractured bedrock aquifer. The optimization of screen and sandpack combinations was explored for the potential to reduce purging times and volumes in practice. Simulations accounted for the location of the fractures along the well screen, fracture aperture, screen length, and the pumping rate. The variability in the required purging times (t(99)-the time required to achieve 99% fractional contribution from the formation to pump discharge) can be explained by: (1) the relative hydraulic conductivities of the components of the system (fracture, sandpack, and screen), (2) the truncation of the flow field from the fracture to the screen by the upper and/or lower boundary of the sandpack of the flow field from another fracture, and (3) time-dependent drawdown. During pumping, only a portion of the sandpack may actually become hydraulically active. The optimal configuration (shortest purging time) is achieved when the ratios of the screen, sandpack, and fracture hydraulic conductivities are close to 1:1:1. More importantly, the role of the fracture hydraulic conductivity in the ratios is not as crucial to reducing t(99) as having the hydraulic conductivities of the screen and sandpack as similar as possible. This study provides a better understanding of well dynamics during pumping for the purpose of obtaining representative groundwater samples. PMID:21797851

  8. Research program to develop and validate conceptual models for flow and transport through unsaturated, fractured rock

    International Nuclear Information System (INIS)

    As part of the Yucca Mountain Project, our research program to develop and validate conceptual models for flow and transport through unsaturated fractured rock integrates fundamental physical experimentation with conceptual model formulation and mathematical modeling. Our research is directed toward developing and validating macroscopic, continuum-based models and supporting effective property models because of their widespread utility within the context of this project. Success relative to the development and validation of effective property models is predicated on a firm understanding of the basic physics governing flow through fractured media, specifically in the areas of unsaturated flow and transport in a single fracture and fracture-matrix interaction. 43 refs

  9. Research program to develop and validate conceptual models for flow and transport through unsaturated, fractured rock

    International Nuclear Information System (INIS)

    As part of the Yucca Mountain Project, our research program to develop and validate conceptual models for flow and transport through unsaturated fractured rock integrates fundamental physical experimentation with conceptual model formulation and mathematical modeling. Our research is directed toward developing and validating macroscopic, continuum-based models and supporting effective property models because of their widespread utility within the context of this project. Success relative to the development and validation of effective property models is predicted on a firm understanding of the basic physics governing flow through fractured media, specifically in the areas of unsaturated flow and transport in a single fracture and fracture-matrix interaction

  10. Influence of mechanical rock properties and fracture healing rate on crustal fluid flow dynamics

    Science.gov (United States)

    Sachau, Till; Bons, Paul; Gomez-Rivas, Enrique; Koehn, Daniel; de Riese, Tamara

    2016-04-01

    Fluid flow in the Earth's crust is very slow over extended periods of time, during which it occurs within the connected pore space of rocks. If the fluid production rate exceeds a certain threshold, matrix permeability alone is insufficient to drain the fluid volume and fluid pressure builds up, thereby reducing the effective stress supported by the rock matrix. Hydraulic fractures form once the effective pressure exceeds the tensile strength of the rock matrix and act subsequently as highly effective fluid conduits. Once local fluid pressure is sufficiently low again, flow ceases and fractures begin to heal. Since fluid flow is controlled by the alternation of fracture permeability and matrix permeability, the flow rate in the system is strongly discontinuous and occurs in intermittent pulses. Resulting hydraulic fracture networks are largely self-organized: opening and subsequent healing of hydraulic fractures depends on the local fluid pressure and on the time-span between fluid pulses. We simulate this process with a computer model and describe the resulting dynamics statistically. Special interest is given to a) the spatially and temporally discontinuous formation and closure of fractures and fracture networks and b) the total flow rate over time. The computer model consists of a crustal-scale dual-porosity setup. Control parameters are the pressure- and time-dependent fracture healing rate, and the strength and the permeability of the intact rock. Statistical analysis involves determination of the multifractal properties and of the power spectral density of the temporal development of the total drainage rate and hydraulic fractures. References Bons, P. D. (2001). The formation of large quartz veins by rapid ascent of fluids in mobile hydrofractures. Tectonophysics, 336, 1-17. Miller, S. a., & Nur, A. (2000). Permeability as a toggle switch in fluid-controlled crustal processes. Earth and Planetary Science Letters, 183(1-2), 133-146. Sachau, T., Bons, P. D

  11. Modeling of thermally driven hydrological processes in partially saturated fractured rock

    Energy Technology Data Exchange (ETDEWEB)

    Tsang, Yvonne; Birkholzer, Jens; Mukhopadhyay, Sumit

    2009-03-15

    This paper is a review of the research that led to an in-depth understanding of flow and transport processes under strong heat stimulation in fractured, porous rock. It first describes the anticipated multiple processes that come into play in a partially saturated, fractured porous volcanic tuff geological formation, when it is subject to a heat source such as that originating from the decay of radionuclides. The rationale is then given for numerical modeling being a key element in the study of multiple processes that are coupled. The paper outlines how the conceptualization and the numerical modeling of the problem evolved, progressing from the simplified to the more realistic. Examples of numerical models are presented so as to illustrate the advancement and maturation of the research over the last two decades. The most recent model applied to in situ field thermal tests is characterized by (1) incorporation of a full set of thermal-hydrological processes into a numerical simulator, (2) realistic representation of the field test geometry, in three dimensions, and (3) use of site-specific characterization data for model inputs. Model predictions were carried out prior to initiation of data collection, and the model results were compared to diverse sets of measurements. The approach of close integration between modeling and field measurements has yielded a better understanding of how coupled thermal hydrological processes produce redistribution of moisture within the rock, which affects local permeability values and subsequently the flow of liquid and gases. The fluid flow in turn will change the temperature field. We end with a note on future research opportunities, specifically those incorporating chemical, mechanical, and microbiological factors into the study of thermal and hydrological processes.

  12. Impact of Micro-to Meso-scale Fractures on Sealing Behavior of Argillaceous Cap Rocks For CO2 Sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Evans, James [Utah State Univ., Logan, UT (United States)

    2016-08-22

    This multi-disciplinary project evaluated seal lithologies for the safety and security of long-term geosequestration of CO2. We used integrated studies to provide qualitative risk for potential seal failure; we integrated data sets from outcrop, core, geochemical analysis, rock failure properties from mechanical testing, geophysical wireline log analysis, and geomechanical modeling to understand the effects of lithologic heterogeneity and changing mechanical properties have on the mechanical properties of the seal. The objectives of this study were to characterize cap rock seals using natural field analogs, available drillhole logging data and whole-rock core, geochemical and isotopic analyses. Rock deformation experiments were carried out on collected samples to develop better models of risk estimation for potential cap rock seal failure. We also sampled variably faulted and fractured cap rocks to examine the impacts of mineralization and/or alteration on the mechanical properties. We compared CO2 reacted systems to non-CO2 reacted seal rock types to determine response of each to increased pore fluid pressures and potential for the creation of unintentional hydrofractures at depth.

  13. Seismic waves in rocks with fluids and fractures

    Energy Technology Data Exchange (ETDEWEB)

    Berryman, J.G.

    2007-05-14

    Seismic wave propagation through the earth is often stronglyaffected by the presence of fractures. When these fractures are filledwith fluids (oil, gas, water, CO2, etc.), the type and state of the fluid(liquid or gas) can make a large difference in the response of theseismic waves. This paper summarizes recent work on methods ofdeconstructing the effects of fractures, and any fluids within thesefractures, on seismic wave propagation as observed in reflection seismicdata. One method explored here is Thomsen's weak anisotropy approximationfor wave moveout (since fractures often induce elastic anisotropy due tononuniform crack-orientation statistics). Another method makes use ofsome very convenient fracture parameters introduced previously thatpermit a relatively simple deconstruction of the elastic and wavepropagation behavior in terms of a small number of fracture parameters(whenever this is appropriate, as is certainly the case for small crackdensities). Then, the quantitative effects of fluids on thesecrack-influence parameters are shown to be directly related to Skempton scoefficient B of undrained poroelasticity (where B typically ranges from0 to 1). In particular, the rigorous result obtained for the low crackdensity limit is that the crack-influence parameters are multiplied by afactor (1 ? B) for undrained systems. It is also shown how fractureanisotropy affects Rayleigh wave speed, and how measured Rayleigh wavespeeds can be used to infer shear wave speed of the fractured medium.Higher crack density results are also presented by incorporating recentsimulation data on such cracked systems.

  14. Transient of diffusion from a waste solid into fractured porous rock

    International Nuclear Information System (INIS)

    Previous analytical studies of the advective transport of dissolved contaminants through fractured rock have emphasized the effect of molecular diffusion in the rock matrix in affecting the space-time-dependent concentration of the contaminant as it moves along the fracture. Matrix diffusion only in the direction normal to the fracture surface was assumed. Contaminant sources were constant-concentration surfaces of width equal to the fracture aperture and of finite or infinite extent in the transverse direction. Such studies illustrate the far-field transport features of fractured media. To predict the time-dependent mass transfer from a long waste cylinder surrounded by porous rock and intersected by a fracture, the present study includes diffusion from the waste surface directly into porous rock, as well as the more realistic geometry. Here we present numerical results from Chambre's analytical solution for the time-dependent mass transfer from the cylinder, for the low-flow conditions wherein near-field mass transfer is expected to be controlled by molecular diffusion. 5 refs., 3 figs

  15. Use of fracture mechanics parameters to characterize comminution

    OpenAIRE

    Hao, Bin

    1996-01-01

    This report is to investigate the use of fracture mechanics parameters (fracture toughness, specific work of fracture) to characterize comminution process. Comminution is a very important industrial process and is extremely low in efficiency. Establishment of a crushing index based on fracture mechanics principles is of great significance for improved machine design and enhanced efficiency. Single particle fracture study has been reviewed because it is considered the most eleme...

  16. Hydraulic anisotropy characterization of pneumatic-fractured sediments using azimuthal self potential gradient

    Science.gov (United States)

    Wishart, DeBonne N.; Slater, Lee D.; Schnell, Deborah L.; Herman, Gregory C.

    2009-01-01

    The pneumatic fracturing technique is used to enhance the permeability and porosity of tight unconsolidated soils (e.g. clays), thereby improving the effectiveness of remediation treatments. Azimuthal self potential gradient (ASPG) surveys were performed on a compacted, unconsolidated clay block in order to evaluate their potential to delineate contaminant migration pathways in a mechanically-induced fracture network. Azimuthal resistivity (ARS) measurements were also made for comparative purposes. Following similar procedures to those used in the field, compressed kaolinite sediments were pneumatically fractured and the resulting fracture geometry characterized from strike analysis of visible fractures combined with strike data from optical borehole televiewer (BHTV) imaging. We subsequently injected a simulated treatment (electrolyte/dye) into the fractures. Both ASPG and ARS data exhibit anisotropic geoelectric signatures resulting from the fracturing. Self potentials observed during injection of electrolyte are consistent with electrokinetic theory and previous laboratory results on a fracture block model. Visual (polar plot) analysis and linear regression of cross plots show ASPG lobes are correlated with azimuths of high fracture strike density, evidence that the ASPG anisotropy is a proxy measure of hydraulic anisotropy created by the pneumatic fracturing. However, ARS data are uncorrelated with fracture strike maxima and resistivity anisotropy is probably dominated by enhanced surface conduction along azimuths of weak 'starter paths' formed from pulverization of the clay and increases in interfacial surface area. We find the magnitude of electrokinetic SP scales with the applied N 2 gas pressure gradient (Δ PN2) for any particular hydraulically-active fracture set and that the positive lobe of the ASPG anomaly indicates the flow direction within the fracture network. These findings demonstrate the use of ASPG in characterizing the effectiveness of (1

  17. Determination of hydraulic conductivity of fractured rock masses:A case study for a rock cavern project in Singapore

    Institute of Scientific and Technical Information of China (English)

    Zhipeng Xu; Zhiye Zhao; Jianping Sun; Ming Lu

    2015-01-01

    In order to reduce the risk associated with water seepage in an underground rock cavern project in Singapore, a reliable hydro-geological model should be established based on the in situ investigation data. The key challenging issue in the hydro-geological model building is how to integrate limited geological and hydro-geological data to determine the hydraulic conductivity of the fractured rock masses. Based on the data obtained from different stages (feasibility investigation stage, construction stage, and post-construction stage), suitable models and methods are proposed to determine the hy-draulic conductivities at different locations and depths, which will be used at other locations in the future.

  18. Field test of ethanol/bentonite slurry grouting into rock fracture

    International Nuclear Information System (INIS)

    Crystalline rocks have fractures which may cause unexpected routes of groundwater seepage. Cement grouting is one of the most effective methods to minimize seepage; however, cement materials may not be suitable for the purpose of extra-long durability, because cement is neutralized or degraded by chemical and physical influence of chemical reaction. Natural clay like bentonite is one of the most promising materials for seepage barrier; however, water/bentonite grout is so viscous that enough amount of bentonite can not be grouted into rock fractures. To increase bentonite content in grout with low viscosity, the utilization of ethanol as a mixing liquid was studied. Ethanol suppresses bentonite swelling, and more bentonite can be injected more than that of water/bentonite slurry. In this paper, grouting into in-situ rock mass fracture from the ground surface was tested to investigate the barrier performance and workability of ethanol/bentonite slurry as a grouting material. (author)

  19. NUMERICAL ANALYSIS OF SATURATED-UNSATURATED SEEPAGE FLOW IN FRACTURED ROCK MASS DUE TO SURFACE INFILTRATION

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Seepage flow in fractured rock mass due to surface infiltration is a saturated-unsaturated seepage process. Aimed at rock mass with large fracture density, which can be equivalent to continuum, a mathematical model for saturated-unsaturated seepage flow in fractured rock mass due to surface infiltration was established in this paper. The Galerkin finite element method was used in numerical simulation and a finite element program used to calculate saturated-unsaturated seepage flow due to surface infiltration was worked out. A model experiment was employed examine the reasonableness of the program. The results show that the proposed model and program are reasonable. The application of the analysis method in this paper in an engineering project shows that the method is reliable and feasible.

  20. Permeability Heterogeneity in a Fractured Sandstone-Mudstone Rock Mass in Xiaolangdi Dam Site, Central China

    Institute of Scientific and Technical Information of China (English)

    JIANG Xiaowei; WAN Li; WANG Xusheng; KANG Aibin; HUANG Jun; HUANG Guoxing

    2009-01-01

    Heterogeneity of permeability in fractured media is a hot research topic in hydrogeology.Numerous approaches have been proposed to characterize heterogeneity in the last several decades.However, little attention has been paid to correlate permeability heterogeneity with geological information. In the present study, several causes of permeability heterogeneity, that is, lithology,tectonism, and depth, are identified. The unit absorption values (denoted as ω), which are results obtained from the packer test, are employed to represent permeability. The variability of permeability in sandstone-mudstone is so significant that the value of unit absorptions span 3-4 orders of magnitude at any depth with several test sections. By declustering, it has been found that under a similar tectonic history, the means of permeability differ greatly at different formations as a result of different mudrock contents. It has also been found that in the same formation, permeability can he significantly increased as a result of faulting. The well-known phenomenon, the decrease in permeability with depth, is found to be caused by the fractures in the rock mass, and the relationship between permeability and depth can be established in the form of logω-logd. After subtracting the trend of ω with absolute depth, the mean of the residual value at each relative depth can be well correlated with the distribution of mudstone.The methods proposed in this paper can be utilized to research in similar study areas.

  1. Advective-diffusive mass transfer in fractured porous media with variable rock matrix block size.

    Science.gov (United States)

    Sharifi Haddad, Amin; Hassanzadeh, Hassan; Abedi, Jalal

    2012-05-15

    Traditional dual porosity models do not take into account the effect of matrix block size distribution on the mass transfer between matrix and fracture. In this study, we introduce the matrix block size distributions into an advective-diffusive solute transport model of a divergent radial system to evaluate the mass transfer shape factor, which is considered as a first-order exchange coefficient between the fracture and matrix. The results obtained lead to a better understanding of the advective-diffusive mass transport in fractured porous media by identifying two early and late time periods of mass transfer. Results show that fractured rock matrix block size distribution has a great impact on mass transfer during early time period. In addition, two dimensionless shape factors are obtained for the late time, which depend on the injection flow rate and the distance of the rock matrix from the injection point.

  2. A mathematical model for solid liquid and mass transfer coupling and numerical simulation for hydraulic fracture in rock salt

    Institute of Scientific and Technical Information of China (English)

    LIANG Weiguo; ZHAO Yangsheng

    2005-01-01

    The hydraulic fracture in rock salt is a complicated solid fluid and mass transfer coupling process. Through theoretical analysis, a solid fluid and mass transfer coupling mathematical model of hydraulic fracture in rock salt is established in this work, and numerical simulations are carried out with the model. The simulation results indicate that rock salt cracks in the typical way of wing-crack(or tensile crack) during the fracture, and the relation of fracture aperture (w) with expanding distance (x) and fracture time (t) is w =(0. 0034 + 0. 0006t )e(0.0007+00018t)x. Furthermore, it has been found that boththe water pressure in the crack and the expanding velocity of the crack decrease gradually as a result of the influence of salt dissolving during fracturing. These numerical simulations well illustrate the process of hydraulic fracture in rock salt and are significantly meaningful in engineering practice.

  3. Fracture Mechanics Characterization of an AnisotropicGeomaterial

    OpenAIRE

    Cravero, Masantonio; Iabichino, Giorgio; Valente, Silvio; Fidelibus, Corrado; Barpi, Fabrizio

    2012-01-01

    Argillites are considered worldwide as potential host rock for high level radioactive waste given the low permeability and strong adsorption potential. However, the excavation of the galleries of a repository would produce a disturbed zone around the boundaries rich of new fractures which may enhance the conductivity of the rock along the gallery axis. Several mine-by experiments have been performed in underground rock labs to investi- gate the features of the disturbed zone. In Mont Terri UR...

  4. Radon (222Rn) in ground water of fractured rocks: A diffusion/ion exchange model

    Science.gov (United States)

    Wood, W.W.; Kraemer, T.F.; Shapiro, A.

    2004-01-01

    Ground waters from fractured igneous and high-grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water-transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half-life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion- exchange model. A dipole-brine injection/withdrawal experiment conducted between bedrock boreholes in the high-grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42??56???N, 71??43???W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion-exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion-exchange model.

  5. Processes controlling the migration and biodegradation of non-aqueous phase liquids (NAPLs) within fractured rocks in the vadose zone. FY96 annual report

    Energy Technology Data Exchange (ETDEWEB)

    Geller, J.T.; Holman, H.Y.; Conrad, M.; Pruess, K.; Hunter-Cevera, J.C. [Lawrence Berkeley National Lab., CA (United States). Earth Sciences Div.; Su, G. [Univ. of California, Berkeley, CA (United States). Dept. of Civil Engineering

    1997-02-01

    This project investigates both flow dynamics and microbial processes affecting NAPLs in fractured rock in a closely coupled, integrated manner. The objective is to develop a qualitative and quantitative understanding of the behavior of two and three immiscible fluid phases, microbial transformation and/or degradation, and to provide a scientific basis for field investigations, site characterization, and remedial action for NAPL contamination in fractured rocks. To achieve this, the program combines laboratory and theoretical investigations, coupled with the evaluation of conditions at relevant field sites. This report summarizes the work accomplished since inception of the project in April 1996.

  6. A numerical model of hydro-thermo-mechanical coupling in a fractured rock mass

    Energy Technology Data Exchange (ETDEWEB)

    Bower, K.M.

    1996-06-01

    Coupled hydro-thermo-mechanical codes with the ability to model fractured materials are used for predicting groundwater flow behavior in fractured aquifers containing thermal sources. The potential applications of such a code include the analysis of groundwater behavior within a geothermal reservoir. The capability of modeling hydro-thermo systems with a dual porosity, fracture flow model has been previously developed in the finite element code, FEHM. FEHM has been modified to include stress coupling with the dual porosity feature. FEHM has been further developed to implicitly couple the dependence of fracture hydraulic conductivity on effective stress within two dimensional, saturated aquifers containing fracture systems. The cubic law for flow between parallel plates was used to model fracture permeability. The Bartin-Bandis relationship was used to determine the fracture aperture within the cubic law. The code used a Newton Raphson iteration to implicitly solve for six unknowns at each node. Results from a model of heat flow from a reservoir to the moving fluid in a single fracture compared well with analytic results. Results of a model showing the increase in fracture flow due to a single fracture opening under fluid pressure compared well with analytic results. A hot dry rock, geothermal reservoir was modeled with realistic time steps indicating that the modified FEHM code does successfully model coupled flow problems with no convergence problems.

  7. Rock Springs Site 12 hydraulic/explosive true in situ oil shale fracturing experiment

    Energy Technology Data Exchange (ETDEWEB)

    Parrish, R.L.; Boade, R.R.; Stevens, A.L.; Long, A. Jr.; Turner, T.F.

    1980-06-01

    The experiment plan involved the creation and characterization of three horizontal hydraulic fractures, followed by the insertion and simultaneous detonation of slurry explosive in the two lower fractures. Core analyses, wellbore logging, and airflow and /sup 85/Kr tracer tests were used for site characterization and assessment of the hydraulic and explosive fracturing. Tiltmeters, wellhead pressure and flow gages, and in-formation pressure, flow and crack-opening sensors were used to monitor hydrofracture creation and explosive insertion. Explosive detonation diagnostic data were taken with stress and time-of-arrival gages and surface and in-formation accelerometers. The post-fracturing assessments indicated that: (1) hydrofracture creation and explosive insertion and detonation were accomplished essentially as planned; (2) induced fractures were randomly distributed through the shale with no extensively fractured regions or dislocation of shale; and (3) enhancement of permeability was limited to enlargement of the explosive-filled fractures.

  8. Long-range spatial dependence in fractured rock. Empirical evidence and implications for tracer transport

    International Nuclear Information System (INIS)

    Nonclassical stochastic continuum models incorporating long-range spatial dependence are evaluated as models for fractured crystalline rock. Open fractures and fracture zones are not modeled explicitly in this approach. The fracture zones and intact rock are modeled as a single stochastic continuum. The large contrasts between the fracture zones and unfractured rock are accounted for by making use of random field models specifically designed for highly variable systems. Hydraulic conductivity data derived from packer tests in the vicinity of the Aespoe Hard Rock Laboratory form the basis for the evaluation. The Aespoe log K data were found to be consistent with a fractal scaling model based on bounded fractional Levy motion (bfLm), a model that has been used previously to model highly variable sedimentary formations. However, the data are not sufficient to choose between this model, a fractional Brownian motion model for the normal-score transform of log K, and a conventional geostatistical model. Stochastic simulations conditioned by the Aespoe data coupled with flow and tracer transport calculations demonstrate that the models with long-range dependence predict earlier arrival times for contaminants. This demonstrates the need to evaluate this class of models when assessing the performance of proposed waste repositories. The relationship between intermediate-scale and large-scale transport properties in media with long-range dependence is also addressed. A new Monte Carlo method for stochastic upscaling of intermediate-scale field data is proposed

  9. Parameter estimation from flowing fluid temperature logging data in unsaturated fractured rock using multiphase inverse modeling

    Energy Technology Data Exchange (ETDEWEB)

    Mukhopadhyay, S.; Tsang, Y.; Finsterle, S.

    2009-01-15

    A simple conceptual model has been recently developed for analyzing pressure and temperature data from flowing fluid temperature logging (FFTL) in unsaturated fractured rock. Using this conceptual model, we developed an analytical solution for FFTL pressure response, and a semianalytical solution for FFTL temperature response. We also proposed a method for estimating fracture permeability from FFTL temperature data. The conceptual model was based on some simplifying assumptions, particularly that a single-phase airflow model was used. In this paper, we develop a more comprehensive numerical model of multiphase flow and heat transfer associated with FFTL. Using this numerical model, we perform a number of forward simulations to determine the parameters that have the strongest influence on the pressure and temperature response from FFTL. We then use the iTOUGH2 optimization code to estimate these most sensitive parameters through inverse modeling and to quantify the uncertainties associated with these estimated parameters. We conclude that FFTL can be utilized to determine permeability, porosity, and thermal conductivity of the fracture rock. Two other parameters, which are not properties of the fractured rock, have strong influence on FFTL response. These are pressure and temperature in the borehole that were at equilibrium with the fractured rock formation at the beginning of FFTL. We illustrate how these parameters can also be estimated from FFTL data.

  10. Self-potential measurements to determine preferred waterflow in fractured rocks

    Science.gov (United States)

    Hötzl, H.; Merkler, G.-P.

    The determination of the permeability behaviour of fractured rocks is of essential importance for the judgement of necessary grouting measures. Geoelectrical self-potential measurements in connection with water pressure tests and grouting experiments in rock masses were carried out to determine preferred flow paths of water or cement in relation to the joint system. The self-potential measurements proved to be closely related to the amount of water or cement absorption in the pressure-gauge borehole. The differences between the self-potential measuring values, calculated for various pressure/water or cement absorption proportions in the pressure-gauge boreholes, indicate an anisotropic system of water or cement pathways, especially in the statistical evaluation of the directions of self potential isolines. Use of this method may help to define the main water paths in fractured rocks and to determine the anisotropy of rock permeability.

  11. Sensors for hydraulic-induced fracturing characterization

    Science.gov (United States)

    Mireles, Jose, Jr.; Estrada, Horacio; Ambrosio, Roberto C.

    2011-06-01

    Hydraulic induced fracturing (HIF) in oil wells is used to increase oil productivity by making the subterranean terrain more deep and permeable. In some cases HIF connects multiple oil pockets to the main well. Currently there is a need to understand and control with a high degree of precision the geometry, direction, and the physical properties of fractures. By knowing these characteristics (the specifications of fractures), other drill well locations and set-ups of wells can be designed to increase the probability of connection of the oil pockets to main well(s), thus, increasing productivity. The current state of the art of HIF characterization does not meet the requirements of the oil industry. In Mexico, the SENER-CONACyT funding program recently supported a three party collaborative effort between the Mexican Petroleum Institute, Schlumberger Dowell Mexico, and the Autonomous University of Juarez to develop a sensing scheme to measure physical parameters of a HIF like, but not limited to pressure, temperature, density and viscosity. We present in this paper a review of HIF process, its challenges and the progress of sensing development for down hole measurement parameters of wells for the Chicontepec region of Mexico.

  12. A NEW HIGH RESOLUTION OPTICAL METHOD FOR OBTAINING THE TOPOGRAPHY OF FRACTURE SURFACES IN ROCKS

    Directory of Open Access Journals (Sweden)

    Steven Ogilvie

    2011-05-01

    Full Text Available Surface roughness plays a major role in the movement of fluids through fracture systems. Fracture surface profiling is necessary to tune the properties of numerical fractures required in fluid flow modelling to those of real rock fractures. This is achieved using a variety of (i mechanical and (ii optical techniques. Stylus profilometry is a popularly used mechanical method and can measure surface heights with high precision, but only gives a good horizontal resolution in one direction on the fracture plane. This method is also expensive and simultaneous coverage of the surface is not possible. Here, we describe the development of an optical method which images cast copies of rough rock fractures using in-house developed hardware and image analysis software (OptiProf™ that incorporates image improvement and noise suppression features. This technique images at high resolutions, 15-200 μm for imaged areas of 10 × 7.5 mm and 100 × 133 mm, respectively and a similar vertical resolution (15 μm for a maximum topography of 4 mm. It uses in-house developed hardware and image analysis (OptiProf™ software and is cheap and non-destructive, providing continuous coverage of the fracture surface. The fracture models are covered with dye and fluid thicknesses above the rough surfaces converted into topographies using the Lambert-Beer Law. The dye is calibrated using 2 devices with accurately known thickness; (i a polycarbonate tile with wells of different depths and (ii a wedge-shaped vial made from silica glass. The data from each of the two surfaces can be combined to provide an aperture map of the fracture for the scenario where the surfaces touch at a single point or any greater mean aperture. The topography and aperture maps are used to provide data for the generation of synthetic fractures, tuned to the original fracture and used in numerical flow modelling.

  13. Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance

    OpenAIRE

    Selvadurai, A. P. S.; Suvorov, A. P.; Selvadurai, P. A.

    2015-01-01

    The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-...

  14. Rock mechanics issues and research needs in the disposal of wastes in hydraulic fractures

    Energy Technology Data Exchange (ETDEWEB)

    Doe, T.W.; McClain, W.C.

    1984-07-01

    The proposed rock mechanics studies outlined in this document are designed to answer the basic questions concerning hydraulic fracturing for waste disposal. These questions are: (1) how can containment be assured for Oak Ridge or other sites; and (2) what is the capacity of a site. The suggested rock mechanics program consists of four major tasks: (1) numerical modeling, (2) laboratory testing, (3) field testing, and (4) monitoring. These tasks are described.

  15. Micromechanical Study of Rock Fracture and Fragmentation under Dynamic Loads using Discrete Element Method

    OpenAIRE

    Kazerani, Tohid

    2011-01-01

    The study presented in this thesis aims to numerically explore the micro-mechanisms underlying rock fracture and fragmentation under dynamic loading. The approach adopted is based on the Discrete Element Method (DEM) coupled to the Cohesive Process Zone (CPZ) theory. It assumes rock material as assemblage of irregular-sized deformable fragments joining together at their cohesive boundaries. The simulation, which is referred to as Cohesive Fragment Mod...

  16. Mechanical and hydraulic performance of sludge-mixed cement grout in rock fractures

    OpenAIRE

    Khomkrit Wetchasat; Kittitep Fuenkajorn

    2014-01-01

    The objective is to assess the performance of sludge mixed with commercial grade Portland cement type I for use in minimizing the permeability of fractured rock mass. The fractures were artificially made by applying a line load to sandstone block specimens. The sludge comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C) of 1:10, 3:10, 5:10 with water:cement ratio of 1:1 by weight are suitable for fracture gr...

  17. Simulation of water seepage through a vadose zone in fractured rock

    International Nuclear Information System (INIS)

    In order to improve our understanding of the vadose zone in fractured rock, obtaining useful tools to simulate, predict and prevent subsurface contamination, a three-dimensional model has been developed from the base of recent two-dimensional codes. Fracture systems are simulated by means of a dynamical evolution of a random-fuse network model, and the multiphase expression of Richards equation is used to describe fluid displacements. Physical situations presented here emphasized the importance of fracture connectivity and spatial variability on the seepage evolution through the vadose zone, and confirm the existence of dendritic patterns along localized preferential paths. (author)

  18. Evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions: An experimental study

    Science.gov (United States)

    Farough, Aida; Moore, Diane E.; Lockner, David A.; Lowell, R. P.

    2016-01-01

    We performed flow-through laboratory experiments on five cylindrically cored samples of ultramafic rocks, in which we generated a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at a confining pressure of 50 MPa, pore pressure of 20 MPa, and temperature of 260°C, simulating a depth of 2 km under hydrostatic conditions. A pore pressure difference of up to 2 MPa was imposed across the ends of the sample. Fracture permeability decreased by 1–2 orders of magnitude during the 200–330 h experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferro-magnesian minerals. By comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types, we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of tectonic and crystallization-induced stresses is required to maintain fluid circulation.

  19. Characterization of borehole fractures by the body and interface waves

    NARCIS (Netherlands)

    Henry, F.

    2005-01-01

    The success of the fracturing process in the oil and gas industry depends on our ability to define the hydraulic fracture geometry. To have a method of measurement for characterizing completely the fracture dimensions from a single well in reliable way, will be a primordial importance, in term of ec

  20. Neutron Imaging of Rapid Water Imbibition in Fractured Sedimentary Rock Cores

    Science.gov (United States)

    Cheng, Chu-Lin; Perfect, Edmund; Donnelly, Brendan; Bilheux, Hassina; Tremsin, Anton; McKay, Larry; Distefano, Victoria; Cai, Jianchao; Santodonato, Lou

    2015-03-01

    Advances in nondestructive testing methods, such as neutron, nuclear magnetic resonance, and x-ray imaging, have significantly improved experimental capabilities to visualize fracture flow in various important fossil energy contexts, e.g. enhanced oil recovery and shale gas. We present a theoretical framework for predicting the rapid movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over rough fracture surfaces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Dynamic neutron imaging of water imbibition in unsaturated fractured Berea sandstone cores was employed to evaluate the proposed model. The experiments were conducted at the Neutron Imaging Prototype Facility at Oak Ridge National Laboratory. Water uptake into both the matrix and fracture zone exhibited square-root-of-time behavior. Both theory and neutron imaging data indicated that fractures significantly increase imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increased the dispersion of the wetting front.

  1. Fracture mechanics and subcritical crack growth approach to model time-dependent failure in brittle rock

    OpenAIRE

    Rinne, Mikael

    2008-01-01

    Subcritical crack growth (SCG) takes place when a crack is stressed below its short-term strength. This slow fracturing process may lead to an accelerating crack velocity and to a sudden unstable failure event. SCG is thought to play an important role in long-term rock stability at all scales, ranging from laboratory samples to earthquake-generating faults. SCG can be detected as rock loosening or as sudden rock movements around excavations. A time-dependent crack growth model is develop...

  2. Ancient microbial activity recorded in fracture fillings from granitic rocks (Äspö Hard Rock Laboratory, Sweden).

    Science.gov (United States)

    Heim, C; Lausmaa, J; Sjövall, P; Toporski, J; Dieing, T; Simon, K; Hansen, B T; Kronz, A; Arp, G; Reitner, J; Thiel, V

    2012-07-01

    Fracture minerals within the 1.8-Ga-old Äspö Diorite (Sweden) were investigated for fossil traces of subterranean microbial activity. To track the potential organic and inorganic biosignatures, an approach combining complementary analytical techniques of high lateral resolution was applied to drill core material obtained at -450 m depth in the Äspö Hard Rock Laboratory. This approach included polarization microscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), confocal Raman microscopy, electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The fracture mineral succession, consisting of fluorite and low-temperature calcite, showed a thin (20-100 μm), dark amorphous layer lining the boundary between the two phases. Microscopic investigations of the amorphous layer revealed corrosion marks and, in places, branched tubular structures within the fluorite. Geochemical analysis showed significant accumulations of Si, Al, Mg, Fe and the light rare earth elements (REE) in the amorphous layer. In the same area, ToF-SIMS imaging revealed abundant, partly functionalized organic moieties, for example, C(x)H(y)⁺, C(x)H(y)N⁺, C(x)H(y)O⁺. The presence of such functionalized organic compounds was corroborated by Raman imaging showing bands characteristic of C-C, C-N and C-O bonds. According to its organic nature and the abundance of relatively unstable N- and O- heterocompounds, the organic-rich amorphous layer is interpreted to represent the remains of a microbial biofilm that established much later than the initial cooling of the Precambrian host rock. Indeed, δ¹³C, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr isotope data of the fracture minerals and the host rock point to an association with a fracture reactivation event in the most recent geological past.

  3. A Study on the Fracture Control of Rock Bolts in High Ground Pressure Roadways of Deep Mines

    Directory of Open Access Journals (Sweden)

    Wen Jinglin

    2015-01-01

    Full Text Available According to the frequent fractures of rock bolts in high ground pressure roadways of deep mines, this paper analyzes the mechanism of fractures and concludes that high ground pressure and material de-fects are main reasons for the fracture of rock bolts. The basic idea of fracture control of rock bolts in high ground pressure roadways of deep mines is to increase the yield load and the limit load of rock bolt materials and reduce the actual load of rock bolts. There are four ways of controlling rock bolt fracture: increasing the rock bolt diameter, strengthening bolt materials, weakening support rigidity and the implementation of double supporting. With the roadway support of the 2302 working face of a coal mine as the project background, this paper carries out a study on the effect of two schemes, increasing the rock bolt diameter and the double supporting technique through methods of theoretical analysis, numerical simulation and so on. It determines the most reasonable diam-eter of rock bolts and the best delay distance of secondary support. Practices indicate that rock bolt fracture can be effectively controlled through the double supporting technique, which strengthens the roof and two sides through the first supporting technique and strengthens side angles through the secondary supporting technique.

  4. Measuring dynamic fracture toughness of cement rock using a short rod specimen

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    As Daqing Oilfield is developing oil layer with a big potential,the requirement for the quality of well cementation is higher than ever before.Cement rock is a brittle material containing a great number of microcracks and defects.In order to reduce the damage to cement ring and improve sealed cementing property at the interface,it is necessary to conduct research on the modification of the cement rock available.According to the principle of super mixed composite materials,various fillers are added to the ingredients of cement rock.Dynamic fracture toughness of cement rock will be changed under the influence of filler.In this paper,short rod specimens of cement rock are employed in the experiments to investigate the dynamic fracture toughness of cement rocks with different ingredients using split Hopkinson Pressure Bar,and partial experimental results are given.The results indicate that fiber reinforcement is an effective way to improve the impact resistance of cement rock.

  5. Significance of fracture rim zone heterogeneity for tracer transport in crystalline rock

    Science.gov (United States)

    Cvetkovic, V.

    2010-03-01

    Conducting fractures of crystalline rock are typically altered over long periods of time. The fracture rim zone, a result of these alterations, will as a rule have different physical and chemical properties from the unaltered ("fresh") rock, depending on various microscopic and macroscopic factors of the alterations. In this paper, we study the impact of rim zone heterogeneity, exemplified by a decreasing porosity trend as inferred from the Äspö Hard Rock Laboratory site (Sweden), on short- and long-term tracer transport. Our main finding is that this particular rim zone structure will have a dominant effect on transport of moderately to strongly sorbing tracers on experimental time scales and a notable effect on application time scales. The findings of this work lend further support to the interpretation of the relatively strong retention reported by Cvetkovic et al. The fracture rim zone porosity structure may provide an additional safety margin for sorbing radionuclides in crystalline rock at sites where fracture alteration is prevalent.

  6. QTRACER PROGRAM FOR TRACER-BREAKTHROUGH CURVE ANALYSIS FOR KARST AND FRACTURED-ROCK AQUIFERS

    Science.gov (United States)

    Tracer tests are generally regarded as being the most reliable and efficient means of gathering subsurface hydraulic information. This is true for all types of aquifers, but especially so for karst and fractured-rock aquifers. Qualitative tracing tests have been conventionally em...

  7. A numerical procedure for the analysis of the hydromechanical coupling in fractured rock masses

    Science.gov (United States)

    Duarte Azevedo, I. C.; Vaz, L. E.; Vargas, E. A.

    1998-11-01

    This work presents a finite element implementation to treat the Hydromechanical Coupling (HM) in fractured rock masses under the framework of the so-called equivalent continuum' approach. The multilaminar concept, introduced by Zienkiewicz and Pande, is used to simulate the mechanical behaviour of both the intact rock and the families of fractures. In that concept, the non-linearities in the constitutive relations are dealt by means of fictitious viscoplasticity. In the present implementation, the mechanical behaviour of the fractures is modelled by means of Barton-Bandis model. The shear stress/shear displacement/dilatancy relationship is modelled as viscoplastic and the normal stress/normal displacement as non-linear viscoelastic. Flow along fractures is considered to occur as a sequence of permanent states. The permeability tensor of the equivalent continuum is determined from the hydraulic apertures, in accordance of Barton et al. From the numerical point of view, the basic aim of the work is the implementation of an efficient scheme to solve the above described problem. This is done by designing a self-adaptive time step control, transparent to the user, which determines the highest possible time step while assuming the conditions of precision, stability and convergence. The paper presents the numerical details of such scheme together with validation/comparative examples and the results obtained on the analysis of the fractured rock foundation of a hypothetical dam.

  8. Final Report - Advanced Conceptual Models for Unsaturated and Two-Phase Flow in Fractured Rock

    Energy Technology Data Exchange (ETDEWEB)

    Nicholl, Michael J.

    2006-07-10

    The Department of Energy Environmental Management Program is faced with two major issues involving two-phase flow in fractured rock; specifically, transport of dissolved contaminants in the Vadose Zone, and the fate of Dense Nonaqueous Phase Liquids (DNAPLs) below the water table. Conceptual models currently used to address these problems do not correctly include the influence of the fractures, thus leading to erroneous predictions. Recent work has shown that it is crucial to understand the topology, or ''structure'' of the fluid phases (air/water or water/DNAPL) within the subsurface. It has also been shown that even under steady boundary conditions, the influence of fractures can lead to complex and dynamic phase structure that controls system behavior, with or without the presence of a porous rock matrix. Complicated phase structures within the fracture network can facilitate rapid transport, and lead to a sparsely populated and widespread distribution of concentrated contaminants; these qualities are highly difficult to describe with current conceptual models. The focus of our work is to improve predictive modeling through the development of advanced conceptual models for two-phase flow in fractured rock.

  9. Hydromechanical coupling in fractured rock masses: mechanisms and processes of selected case studies

    Science.gov (United States)

    Zangerl, Christian

    2015-04-01

    Hydromechanical (HM) coupling in fractured rock play an important role when events including dam failures, landslides, surface subsidences due to water withdrawal or drainage, injection-induced earthquakes and others are analysed. Generally, hydromechanical coupling occurs when a rock mass contain interconnected pores and fractures which are filled with water and pore/fracture pressures evolves. In the on hand changes in the fluid pressure can lead to stress changes, deformations and failures of the rock mass. In the other hand rock mass stress changes and deformations can alter the hydraulic properties and fluid pressures of the rock mass. Herein well documented case studies focussing on surface subsidence due to water withdrawal, reversible deformations of large-scale valley flanks and failure as well as deformation processes of deep-seated rock slides in fractured rock masses are presented. Due to pore pressure variations HM coupling can lead to predominantly reversible rock mass deformations. Such processes can be considered by the theory of poroelasticity. Surface subsidence reaching magnitudes of few centimetres and are caused by water drainage into deep tunnels are phenomenas which can be assigned to processes of poroelasticity. Recently, particular focus was given on large tunnelling projects to monitor and predict surface subsidence in fractured rock mass in oder to avoid damage of surface structures such as dams of large reservoirs. It was found that surface subsidence due to tunnel drainage can adversely effect infrastructure when pore pressure drawdown is sufficiently large and spatially extended and differential displacements which can be amplified due to topographical effects e.g. valley closure are occurring. Reversible surface deformations were also ascertained on large mountain slopes and summits with the help of precise deformation measurements i.e. permanent GPS or episodic levelling/tacheometric methods. These reversible deformations are often

  10. Seismic Fracture Characterization Methodologies for Enhanced Geothermal Systems

    Energy Technology Data Exchange (ETDEWEB)

    Queen, John H. [Hi-Geophysical, Inc., Ponca, OK (United States)

    2016-05-09

    Executive Summary The overall objective of this work was the development of surface and borehole seismic methodologies using both compressional and shear waves for characterizing faults and fractures in Enhanced Geothermal Systems. We used both surface seismic and vertical seismic profile (VSP) methods. We adapted these methods to the unique conditions encountered in Enhanced Geothermal Systems (EGS) creation. These conditions include geological environments with volcanic cover, highly altered rocks, severe structure, extreme near surface velocity contrasts and lack of distinct velocity contrasts at depth. One of the objectives was the development of methods for identifying more appropriate seismic acquisition parameters for overcoming problems associated with these geological factors. Because temperatures up to 300º C are often encountered in these systems, another objective was the testing of VSP borehole tools capable of operating at depths in excess of 1,000 m and at temperatures in excess of 200º C. A final objective was the development of new processing and interpretation techniques based on scattering and time-frequency analysis, as well as the application of modern seismic migration imaging algorithms to seismic data acquired over geothermal areas. The use of surface seismic reflection data at Brady's Hot Springs was found useful in building a geological model, but only when combined with other extensive geological and geophysical data. The use of fine source and geophone spacing was critical in producing useful images. The surface seismic reflection data gave no information about the internal structure (extent, thickness and filling) of faults and fractures, and modeling suggests that they are unlikely to do so. Time-frequency analysis was applied to these data, but was not found to be significantly useful in their interpretation. Modeling does indicate that VSP and other seismic methods with sensors located at depth in wells will be the most

  11. Developments in characterization of surface topography of rock joint

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The approaches to characterizing the surface topography of a rock joint can be simply grouped into statistical approaches and fractal geometrical approaches. This paper reviews the developments in characterization of the surface topography of a rock joint. Moreover, several problems of the current researches are also discussed.

  12. Numerical Study on Crack Propagation in Brittle Jointed Rock Mass Influenced by Fracture Water Pressure

    Directory of Open Access Journals (Sweden)

    Yong Li

    2015-06-01

    Full Text Available The initiation, propagation, coalescence and failure mode of brittle jointed rock mass influenced by fissure water pressure have always been studied as a hot issue in the society of rock mechanics and engineering. In order to analyze the damage evolution process of jointed rock mass under fracture water pressure, a novel numerical model on the basis of secondary development in fast Lagrangian analysis of continua (FLAC3D is proposed to simulate the fracture development of jointed rock mass under fracture water pressure. To validate the feasibility of this numerical model, the failure process of a numerical specimen under uniaxial compression containing pre-existing fissures is simulated and compared with the results obtained from the lab experiments, and they are found to be in good agreement. Meanwhile, the propagation of cracks, variations of stress and strain, peak strength and crack initiation principles are further analyzed. It is concluded that the fissure water has a significant reducing effect on the strength and stability of the jointed rock mass.

  13. A Methodology to Hydraulically Parameterize Deformation Zones and Fracture Networks in Fractured Crystalline Rock Using Fracture Borehole Data and Inflow Data from Single- Hole Tests

    Science.gov (United States)

    Follin, S.; Hartley, L.; Rhen, I.; Selroos, J.

    2008-12-01

    Three-dimensional, regional, numerical models of groundwater flow and solute transport in fractured crystalline rock are used for two sites in Sweden that are considered for geological disposal of spent nuclear fuel. The models are used to underpin the conceptual modeling that is based on multi-disciplinary data and include descriptions of the geometry of geological features (deformation zones and fracture networks), transient hydrological and chemical boundary conditions, strong spatial heterogeneity in the hydraulic properties, density driven flow, solute transport including rock matrix diffusion, and mixing of different water types in a palaeo-hydrogeological perspective (last 10,000 years). The general approach applied in the numerical modeling was to first parameterize the deformation zones and fracture networks hydraulically using fracture and inflow data from single-hole tests. Second, a confirmatory step was attempted using essentially the same groundwater flow and solute transport model in terms of grid discretization and parameter settings for matching three types of independent field data: 1) large-scale cross-hole (interference) tests, 2) long- term monitoring of groundwater levels, and 3) hydrochemical composition of fracture water and matrix pore water in deep boreholes. We demonstrate here the adopted modelling approach for the first step, i.e. hydraulic parameterization of deformation zones and fracture networks, using single-hole test data from the site investigations undertaken at one of the sites in Sweden (Forsmark). The adopted modelling approach combines a deterministic representation of the major deformation zones with a stochastic representation of the less fractured bedrock outside these zones using the discrete fracture network (DFN) concept. An exponential model for the depth dependency of the in-plane deformation zone transmissivity was suggested based on the data. Lateral heterogeneity was simulated by adding a log-normal random deviate

  14. Mechanical interactions between proppants and rock and their effect on hydraulic fracture performance

    Energy Technology Data Exchange (ETDEWEB)

    Legarth, B.A.; Raab, S.; Huenges, E. [GeoForschungsZentrum Potsdam (Germany)

    2005-07-01

    Proppants interact mechanically with the rock matrix. This causes damage to the fracture face and influences propped fracture performance. Therefore, proppant embedment and proppant crushing phenomena were analysed in laboratory under simulated in situ conditions. The embedment tests were performed in a conductivity cell using reassembled core halves. Embedment features in the rock matrix were optically analyzed. In a separate unit single grain strength tests were performed on a wide range of ceramic proppant types (AI203-based, coated/uncoated) and sizes (diameter 0,2-1,6 mm). The experiment showed that areas in the fracture with low proppant concentration revealed severe proppant crushing and embedment that occurred already at low effective stress. Punctual loading was identified as reason for premature proppant failure. Grain strength testing showed that compressive fracture force increases with grain diameter, is influenced by the presence of a coating and might be additionally controlled by grain surface structure. Compressive fracture strength is largely independent from size for same proppant types. A contact model introduced by Hertz was applied to retrieve the stress magnitudes at grain failure. Proppant crushing leads to generation of fines in the matrix and the proppant pack. These fines can be transported and plug pore-throats and flow channels. Dependent on completion type and expected fracture widths proppant grain size should be maximized for higher fracture conductivity. Proppant crushing and embedment processes are enforced by decreasing proppant concentration. Considering natural conditions in a fracture - rough surfaces, tortuous-twisted paths that hinder even proppant distribution - low proppant concentrations appear to be very real, maybe even the normal case in nature. Thus, high proppant concentration is the key issue to mitigate fracture impairment. (orig.)

  15. Method to calculate fatigue fracture life of control fissure in perilous rock

    Institute of Scientific and Technical Information of China (English)

    CHEN Hong-kai; TANG Hong-mei

    2007-01-01

    Rupture and safety of perilous rock are dominated by control fissure behind perilous rock block. Based on model-Ⅰ and model-Ⅱ stress strength factors of control fissure under acting of weight of perilous rock, water pressure in control fissure and earthquake forces, method to calculate critical linking length of control fissure is established. Take water pressure in control fissure as a variable periodic load, and abide by P-M criterion, when control fissure is filled with water, establish the method to calculate fatigue fracture life of control fissure in critical status by contributing value of stress strength factor stemming from water pressure of control fissure in Paris's fatigue equation. Further, parameters(C and m)of sandstone with quartz and feldspar in the area of the Three Gorges Reservoir of China are obtained by fatigue fracture testing.

  16. Numerical Modeling of Porous Flow in Fractured Rock and Its Applications in Geothermal Energy Extraction

    Institute of Scientific and Technical Information of China (English)

    Yucang Wang; Shimin Wang; Sheng Xue; Deepak Adhikary

    2015-01-01

    Understanding the characteristics of hydraulic fracture, porous flow and heat transfer in fractured rock is critical for geothermal power generation applications, and numerical simulation can provide a powerful approach for systematically and thoroughly investigating these problems. In this paper, we present a fully coupled solid-fluid code using discrete element method (DEM) and lattice Boltzmann method (LBM). The DEM with bonded particles is used to model the deformation and fracture in solid, while the LBM is used to model the fluid flow. The two methods are two-way coupled, i.e., the solid part provides a moving boundary condition and transfers momentum to fluid, while the fluid exerts a dragging force to the solid. Two widely used open source codes, the ESyS_Particle and the OpenLB, are integrated into one code and paralleled with Message Passing Interface (MPI) library. Some preliminary 2D simulations, including particles moving in a fluid and hydraulic fracturing in-duced by injection of fluid into a borehole, are carried out to validate the integrated code. The prelimi-nary results indicate that the new code is capable of reproducing the basic features of hydraulic frac-ture and thus offers a promising tool for multiscale simulation of porous flow and heat transfer in fractured rock.

  17. Characterization of EGS Fracture Network Lifecycles

    Energy Technology Data Exchange (ETDEWEB)

    Gillian R. Foulger

    2008-03-31

    Geothermal energy is relatively clean, and is an important non-hydrocarbon source of energy. It can potentially reduce our dependence on fossil fuels and contribute to reduction in carbon emissions. High-temperature geothermal areas can be used for electricity generation if they contain permeable reservoirs of hot water or steam that can be extracted. The biggest challenge to achieving the full potential of the nation’s resources of this kind is maintaining and creating the fracture networks required for the circulation, heating, and extraction of hot fluids. The fundamental objective of the present research was to understand how fracture networks are created in hydraulic borehole injection experiments, and how they subsequently evolve. When high-pressure fluids are injected into boreholes in geothermal areas, they flow into hot rock at depth inducing thermal cracking and activating critically stressed pre-existing faults. This causes earthquake activity which, if monitored, can provide information on the locations of the cracks formed, their time-development and the type of cracking underway, e.g., whether shear movement on faults occurred or whether cracks opened up. Ultimately it may be possible to monitor the critical earthquake parameters in near-real-time so the information can be used to guide the hydraulic injection while it is in progress, e.g., how to adjust factors such as injectate pressure, volume and temperature. In order to achieve this, it is necessary to mature analysis techniques and software that were, at the start of this project, in an embryonic developmental state. Task 1 of the present project was to develop state-of-the-art techniques and software for calculating highly accurate earthquake locations, earthquake source mechanisms (moment tensors) and temporal changes in reservoir structure. Task 2 was to apply the new techniques to hydrofracturing (Enhanced Geothermal Systems, or “EGS”) experiments performed at the Coso geothermal field

  18. The roles of tectonics in erosion: Fracturing and fragmentation are key, rock uplift is not

    Science.gov (United States)

    Molnar, P.; Anderson, R. S.; Anderson, S. P.

    2005-12-01

    As Gilbert and Dutton recognized in the 19th century, erosion consists of two processes: "the disintegration of the rocks, reducing them to fragments, pebbles, sand, and clay" [Dutton, 1882] and then their transport. Tectonics contributes to both but more importantly to the first. Although many in the geomorphic community subscribe to "the emerging view that erosion rates adjust to high rates of tectonically driven rock uplift" [Montgomery and Brandon, 2002], numerical models are not needed to see that rather than ``driving" erosion, most "rock uplift" results from erosion via isostatic compensation. Relegation of rock uplift to consequence, not cause, of erosion, however, does not deny tectonics a role in erosion. Tectonics plays its key role by fracturing rock. Fractures not only provide avenues for water flow and thus promote weathering of rock, but also generate erodible fragments that can be extracted and transported on hillslopes or by rivers and glaciers. Tectonics does the first part of erosion (as defined by 19th century geologists): disintegration of massive rocks. Faults are not perfect planes; both local roughness and larger scale bends require straining of the adjacent rock masses upon slip on the fault, as shown well by aftershocks of major earthquakes. Although aftershocks of great earthquakes commonly occur on the faults that rupture in mainshocks, within continents many, if not most, aftershocks occur within the larger volume of rock of adjacent blocks that slipped past one another in mainshocks. Thus, they contribute to the dismemberment of these rock volumes into smaller blocks. Scaling rules for earthquakes suggest that dimensions of ruptures for very small earthquakes, Magnitude < -2, can be meters or less. The Gutenberg-Richter recurrence relationship implies that such earthquakes are common, as recordings by high-magnification seismographs in low-noise environments show. The large differences among fault plane solutions of aftershocks and of

  19. Modeling the Progressive Failure of Jointed Rock Slope Using Fracture Mechanics and the Strength Reduction Method

    Science.gov (United States)

    Zhang, Ke; Cao, Ping; Meng, Jingjing; Li, Kaihui; Fan, Wenchen

    2015-03-01

    The fracturing process during the progressive failure of a jointed rock slope is numerically investigated by using fracture mechanics and the strength reduction method (SRM). A displacement discontinuity method containing frictional elements is developed for the calculation of the stress intensity factor (SIF). The failure initiation of the jointed rock slope is analyzed by evaluating the SIF. A new joint model is proposed by combining solid elements with interface elements in the commercial software FLAC3D. These represent the discontinuous planes in a rock mass on which sliding or separation can occur. The progressive failure process is simulated by reducing the shear strength of the rock mass, which includes the process of stress concentration, crack initiation, crack propagation, slip weakening, and coalescence of failure surfaces. The factor of safety (FS) and location of the critical failure surface are determined by the SRM. The influence of the joint inclination is investigated using the FS and the SIF. Laboratory experiments on specimens containing an inclined flaw under compression-shear stress are also conducted to investigate the effect of the angle between the shear direction and the flaw inclination, which provides an experimental explanation for the shear behavior of jointed rock. The results show that the joint inclination dominates the failure behavior of jointed rock slope, and two failure patterns have been classified.

  20. High-resolution delineation of chlorinated volatile organic compounds in a dipping, fractured mudstone: Depth- and strata-dependent spatial variability from rock-core sampling.

    Science.gov (United States)

    Goode, Daniel J; Imbrigiotta, Thomas E; Lacombe, Pierre J

    2014-12-15

    Synthesis of rock-core sampling and chlorinated volatile organic compound (CVOC) analysis at five coreholes, with hydraulic and water-quality monitoring and a detailed hydrogeologic framework, was used to characterize the fine-scale distribution of CVOCs in dipping, fractured mudstones of the Lockatong Formation of Triassic age, of the Newark Basin in West Trenton, New Jersey. From these results, a refined conceptual model for more than 55years of migration of CVOCs and depth- and strata-dependent rock-matrix contamination was developed. Industrial use of trichloroethene (TCE) at the former Naval Air Warfare Center (NAWC) from 1953 to 1995 resulted in dense non-aqueous phase liquid (DNAPL) TCE and dissolved TCE and related breakdown products, including other CVOCs, in underlying mudstones. Shallow highly weathered and fractured strata overlie unweathered, gently dipping, fractured strata that become progressively less fractured with depth. The unweathered lithology includes black highly fractured (fissile) carbon-rich strata, gray mildly fractured thinly layered (laminated) strata, and light-gray weakly fractured massive strata. CVOC concentrations in water samples pumped from the shallow weathered and highly fractured strata remain elevated near residual DNAPL TCE, but dilution by uncontaminated recharge, and other natural and engineered attenuation processes, have substantially reduced concentrations along flow paths removed from sources and residual DNAPL. CVOCs also were detected in most rock-core samples in source areas in shallow wells. In many locations, lower aqueous concentrations, compared to rock core concentrations, suggest that CVOCs are presently back-diffusing from the rock matrix. Below the weathered and highly fractured strata, and to depths of at least 50 meters (m), groundwater flow and contaminant transport is primarily in bedding-plane-oriented fractures in thin fissile high-carbon strata, and in fractured, laminated strata of the gently

  1. Experimental fracture toughness characterization using the modified TSD specimen

    DEFF Research Database (Denmark)

    Berggreen, Christian; Quispitupa, Amilcar; Alonso, Jose L.;

    2010-01-01

    The modified Tilted Sandwich Debond (TSD) specimen provides an improved methodology for characterization of the face/core fracture resistance. An experimental mixed mode characterization of the fracture toughness spanning a large range of phase angles has been achieved by specific steel bar...

  2. Hydraulic and mechanical properties of natural fractures in low-permeability rock

    International Nuclear Information System (INIS)

    The results of a comprehensive laboratory study of the mechanical displacement, permeability, and void geometry of single rock fractures in a quartz monzonite are summarized and analyzed. A metal-injection technique was developed that provided quantitative data on the precise geometry of the void spaces between the fracture surfaces and the areas of contact at different stresses. At effective stresses of less than 20 MPa fluid flow was proportional to the mean fracture aperture raised to a power greater than 3. As stress was increased, contact area was increased and void spaces become interconnected by small tortuous channels that constitute the principal impediment to fluid flow. At effective stresses higher than 20 MPa, the mean fracture aperture continued to diminish with increasing stress, but this had little effect on flow because the small tortuous flow channels deformed little with increasing stress

  3. Approach for computing 1D fracture density: application to fracture corridor characterization

    Science.gov (United States)

    Viseur, Sophie; Chatelée, Sebastien; Akriche, Clement; Lamarche, Juliette

    2016-04-01

    Fracture density is an important parameter for characterizing fractured reservoirs. Many stochastic simulation algorithms that generate fracture networks indeed rely on the determination of a fracture density on volumes (P30) to populate the reservoir zones with individual fracture surfaces. However, only 1D fracture density (P10) are available from subsurface data and it is then important to be able to accurately estimate this entity. In this paper, a novel approach is proposed to estimate fracture density from scan-line or well data. This method relies on regression, hypothesis testing and clustering techniques. The objective of the proposed approach is to highlight zones where fracture density are statistically very different or similar. This technique has been applied on both synthetic and real case studies. These studies concern fracture corridors, which are particular tectonic features that are generally difficult to characterize from subsurface data. These tectonic features are still not well known and studies must be conducted to better understand their internal spatial organization and variability. The presented synthetic cases aim at showing the ability of the approach to extract known features. The real case study illustrates how this approach allows the internal spatial organization of fracture corridors to be characterized.

  4. A field and modeling study of fractured rock permeability reduction using microbially induced calcite precipitation.

    Science.gov (United States)

    Cuthbert, Mark O; McMillan, Lindsay A; Handley-Sidhu, Stephanie; Riley, Michael S; Tobler, Dominique J; Phoenix, Vernon R

    2013-01-01

    Microbially induced calcite precipitation (MICP) offers an attractive alternative to traditional grouting technologies for creating barriers to groundwater flow and containing subsurface contamination, but has only thus far been successfully demonstrated at the laboratory scale and predominantly in porous media. We present results of the first field experiments applying MICP to reduce fractured rock permeability in the subsurface. Initially, the ureolytic bacterium, Sporosarcina pasteurii, was fixed in the fractured rock. Subsequent injection of cementing fluid comprising calcium chloride and urea resulted in precipitation of large quantities (approximately 750 g) of calcite; significant reduction in the transmissivity of a single fracture over an area of several m(2) was achieved in around 17 h of treatment. A novel numerical model is also presented which simulates the field data well by coupling flow and bacterial and solute reactive transport processes including feedback due to aperture reduction via calcite precipitation. The results show that MICP can be successfully manipulated under field conditions to reduce the permeability of fractured rock and suggest that an MICP-based technique, informed by numerical models, may form the basis of viable solutions to aid pollution mitigation. PMID:24147737

  5. Theory and application of rock burst prevention using deep hole high pressure hydraulic fracturing

    Institute of Scientific and Technical Information of China (English)

    Shan-Kun ZHAO; Jun LIU; Xiang-Zhi WEI; Chuan-Hong DING; Yu-Lei LV; Gang-Feng LI

    2013-01-01

    In order to analyze the mechanism of deep hole high pressure hydraulic fracturing,nonlinear dynamic theory,damage mechanics,elastic-plastic mechanics are used,and the law of crack propagation and stress transfer under two deep hole hydraulic fracturing in tectonic stress areas is studied using seepage-stress coupling models with RFPA simulation software.In addition,the effects of rock burst control are tested using multiple methods,either in the stress field or in the energy field.The research findings show that with two deep holes hydraulic fracturing in tectonic stress areas,the direction of the main crack propagation under shear-tensile stress is parallel to the greatest principal stress direction.High-pressure hydraulic fracturing water seepage can result in the destruction of the coal structure,while also weakening the physical and mechanical properties of coal and rock.Therefore the impact of high stress concentration in hazardous areas will level off,which has an effect on rock burst prevention and control in the region.

  6. Wave Propagation in the Vicinities of Rock Fractures Under Obliquely Incident Wave

    Science.gov (United States)

    Zou, Yang; Li, Jianchun; He, Lei; laloui, Lyesse; Zhao, Jian

    2016-05-01

    Though obliquely incident plane wave across rock fractures has been extensively investigated by theoretical analysis, the quantitative identification of each wave emerged from fractures has not been achieved either in numerical simulation or laboratory experiment. On the other hand, there are no theoretical results describing the stress/velocity state of the rocks beside a fracture. The superposition of the multiple waves propagating in the media results in the variation of the stress/velocity state. To understand the superposition of the wave components in the adjacent rocks of a facture, based on the geometrical analysis of the wave paths, the lag times among passing waves at an arbitrary point are determined. The normalised critical distances from the fracture to the measuring locations where the corresponding harmonic waves depart from other waves for a certain duration are then derived. Discussion on the correction for an arbitrary incident wave is then carried out considering the changes of the duration of the reflected and transmitted waves. Under the guidance of the analysis, wave superposition is performed for theoretical results and separated waves are obtained from numerical model. They are demonstrated to be consistent with each other. The measurement and the data processing provide an approach for wave separation in a relatively unbounded media. In addition, based on the mechanical analysis on the wave front, an indirect wave separation method is proposed which provides a possibility for laboratory experiments of wave propagation with an arbitrary incident angle.

  7. Upscaling Fracture Network Models to Continua: An Example Using Weathered Granitic Rock

    Science.gov (United States)

    Clark, A.; Doe, T.; Jones, J. W.

    2006-12-01

    In the early 1990's, a proposed landfill site on the Campo Indian Reservation in San Diego County, California, was the object of a characterization program involving over ninety exploration and monitoring wells, geophysical investigations, flow meter logging, tracer testing, and fracture characterization. This intensively studied site rests on deeply weathered tonalite. The weathered zone extends several tens to about 100 feet below the surface; however, the deeply weathered material follows hydraulically active fractures to even greater depths. The flow meter logging was especially valuable both for locating conductive fractures but also, in un- pumped mode, for defining regions of upward and downward vertical flow. The deep weathering on the conductive fractures gives each pathway a large effective porosity that translates to lower flow velocities compared with unweathered fractures with similar transmissivities. The simulation of the groundwater flow at this site used a local-scale fracture network model which was upscaled to a continuum code at regional scales. At the largest scale we generated a small number of major fractures to match the topographic lineaments. At an intermediate scale we had geophysical lineaments that were deterministic under the site footprint, and stochastic elsewhere using generation parameters based on the lengths, orientations and intensities of the deterministic features. The fractures of the most detailed scale were background fractures that were stochastically generated from borehole data. The site-scale fracture network model was incorporated into a regional-scale MODFLOW model, by overlaying the MODFLOW grid on the fracture network model and calculating equivalent porous medium properties for each MODFLOW grid cell using the Oda tensor method. This fast algorithm calculates a permeability tensor for each MODFLOW grid cell by summing the oriented area-weighted permeabilities of each fracture. The resulting MODFLOW model was then

  8. Characterization of Fractured Reservoirs Using a Combination of Downhole Pressure and Self-Potential Transient Data

    Directory of Open Access Journals (Sweden)

    Yuji Nishi

    2012-01-01

    Full Text Available In order to appraise the utility of self-potential (SP measurements to characterize fractured reservoirs, we carried out continuous SP monitoring using multi Ag-AgCl electrodes installed within two open holes at the Kamaishi Mine, Japan. The observed ratio of SP change to pressure change associated with fluid flow showed different behaviors between intact host rock and fractured rock regions. Characteristic behavior peculiar to fractured reservoirs, which is predicted from numerical simulations of electrokinetic phenomena in MINC (multiple interacting continua double-porosity media, was observed near the fractures. Semilog plots of the ratio of SP change to pressure change observed in one of the two wells show obvious transition from intermediate time increasing to late time stable trends, which indicate that the time required for pressure equilibration between the fracture and matrix regions is about 800 seconds. Fracture spacing was estimated to be a few meters assuming several micro-darcies (10-18 m2 of the matrix region permeability, which is consistent with geological and hydrological observations.

  9. VSP [Vertical Seismic Profiling] and cross hole tomographic imaging for fracture characterization

    International Nuclear Information System (INIS)

    For the past several years LBL has been carrying out experiments at various fractured rock sites to determine the fundamental nature of the propagation of seismic waves in fractured media. These experiments have been utilizing high frequency (1000 to 10000 Hz.) signals in a cross-hole configuration at scales of several tens of meters. Three component sources and receivers are used to map fracture density, and orientation. The goal of the experiments has been to relate the seismological parameters to the hydrological parameters, if possible, in order to provide a more accurate description of a starting model for hydrological characterization. The work is ultimately aimed at the characterization and monitoring of the Yucca Mountain site for the storage of nuclear waste. In addition to these controlled experiments multicomponent VSP work has been carried out at several sites to determine fracture characteristics. The results to date indicate that both P-wave and S-wave can be used to map the location of fractures. In addition, fractures that are open and conductive are much more visible to seismic waves that non-conductive fractures. The results of these tests indicate direct use in an unsaturated environment. 12 refs., 10 figs

  10. An analytical solution for transient flow of Bingham viscoplastic materials in rock fractures

    Science.gov (United States)

    Amadei, B.; Savage, W.Z.

    2001-01-01

    We present below an analytical solution to model the one-dimensional transient flow of a Bingham viscoplastic material in a fracture with parallel walls (smooth or rough) that is subjected to an applied pressure gradient. The solution models the acceleration and the deceleration of the material as the pressure gradient changes with time. Two cases are considered: A pressure gradient applied over a finite time interval and an applied pressure gradient that is constant over time. The solution is expressed in dimensionless form and can therefore be used for a wide range of Bingham viscoplastic materials. The solution is also capable of capturing the transition that takes place in a fracture between viscoplastic flow and rigid plug flow. Also, it shows the development of a rigid central layer in fractures, the extent of which depends on the fluid properties (viscosity and yield stress), the magnitude of the pressure gradient, and the fracture aperture and surface roughness. Finally, it is shown that when a pressure gradient is applied and kept constant, the solution for the fracture flow rate converges over time to a steady-state solution that can be defined as a modified cubic law. In this case, the fracture transmissivity is found to be a non-linear function of the head gradient. This solution provides a tool for a better understanding of the flow of Bingham materials in rock fractures, interfaces, and cracks. ?? 2001 Elsevier Science Ltd. All rights reserved.

  11. A new method for real-time monitoring of grout spread through fractured rocks

    International Nuclear Information System (INIS)

    Reducing water ingress into the Shaft at Dounreay is essential for the success of future intermediate level waste (ILW) recovery using the dry retrieval method. The reduction is being realised by forming an engineered barrier of ultrafine cementitious grout injected into the fractured rock surrounding the Shaft. Grout penetration of 6 m in <50μm fractures is being reliably achieved, with a pattern of repeated injections ultimately reducing rock mass permeability by up to three orders of magnitude. An extensive field trials period, involving over 200 grout mix designs and the construction of a full scale demonstration barrier, has yielded several new field techniques that improve the quality and reliability of cementitious grout injection for engineered barriers. In particular, a new method has been developed for tracking in real-time the spread of ultrafine cementitious grout through fractured rock and relating the injection characteristics to barrier design. Fieldwork by the multi-disciplinary international team included developing the injection and real-time monitoring techniques, pre- and post injection hydro-geological testing to quantify the magnitude and extent of changes in rock mass permeability, and correlation of grout spread with injection parameters to inform the main works grouting programme. (authors)

  12. Multiphase fluid flow and subsequent geochemical transport invariably saturated fractured rocks: 1. Approaches

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Tianfu; Pruess, Karsten

    2000-08-08

    Reactive fluid flow and geochemical transport in unsaturated fractured rocks has received increasing attention for studies of contaminant transport, groundwater quality, waste disposal, acid mine drainage remediation, mineral deposits, sedimentary diagenesis, and fluid-rock interactions in hydrothermal systems. This paper presents methods for modeling geochemical systems that emphasize: (1) involvement of the gas phase in addition to liquid and solid phases in fluid flow, mass transport and chemical reactions, (2) treatment of physically and chemically heterogeneous and fractured rocks, (3) the effect of heat on fluid flow and reaction properties and processes, and (4) the kinetics of fluid-rock interaction. The physical and chemical process model is embodied in a system of partial differential equations for flow and transport, coupled to algebraic equations and ordinary differential equations for chemical interactions. For numerical solution, the continuum equations are discretized in space and time. Space discretization is based on a flexible integral finite difference approach that can use irregular gridding to model geologic structure; time is discretized fully implicitly as a first-order finite difference. Heterogeneous and fractured media are treated with a general multiple interacting continua method that includes double-porosity, dual-permeability, and multi-region models as special cases. A sequential iteration approach is used to treat the coupling between fluid flow and mass transport on the one hand, chemical reactions on the other. Applications of the methods developed here to variably saturated geochemical systems are presented in a companion paper (part 2, this issue).

  13. Fracture control of ground water flow and water chemistry in a rock aquitard.

    Science.gov (United States)

    Eaton, Timothy T; Anderson, Mary P; Bradbury, Kenneth R

    2007-01-01

    There are few studies on the hydrogeology of sedimentary rock aquitards although they are important controls in regional ground water flow systems. We formulate and test a three-dimensional (3D) conceptual model of ground water flow and hydrochemistry in a fractured sedimentary rock aquitard to show that flow dynamics within the aquitard are more complex than previously believed. Similar conceptual models, based on regional observations and recently emerging principles of mechanical stratigraphy in heterogeneous sedimentary rocks, have previously been applied only to aquifers, but we show that they are potentially applicable to aquitards. The major elements of this conceptual model, which is based on detailed information from two sites in the Maquoketa Formation in southeastern Wisconsin, include orders of magnitude contrast between hydraulic diffusivity (K/S(s)) of fractured zones and relatively intact aquitard rock matrix, laterally extensive bedding-plane fracture zones extending over distances of over 10 km, very low vertical hydraulic conductivity of thick shale-rich intervals of the aquitard, and a vertical hydraulic head profile controlled by a lateral boundary at the aquitard subcrop, where numerous surface water bodies dominate the shallow aquifer system. Results from a 3D numerical flow model based on this conceptual model are consistent with field observations, which did not fit the typical conceptual model of strictly vertical flow through an aquitard. The 3D flow through an aquitard has implications for predicting ground water flow and for planning and protecting water supplies.

  14. Field-Scale Effective Matrix Diffusion Coefficient for FracturedRock: Results From Literature Survey

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Quanlin; Liu, Hui Hai; Molz, Fred J.; Zhang, Yingqi; Bodvarsson, Gudmundur S.

    2005-03-28

    Matrix diffusion is an important mechanism for solutetransport in fractured rock. We recently conducted a literature survey onthe effective matrix diffusion coefficient, Dem, a key parameter fordescribing matrix diffusion processes at the field scale. Forty fieldtracer tests at 15 fractured geologic sites were surveyed and selectedfor study, based on data availability and quality. Field-scale Dem valueswere calculated, either directly using data reported in the literature orby reanalyzing the corresponding field tracer tests. Surveyed dataindicate that the effective-matrix-diffusion-coefficient factor FD(defined as the ratio of Dem to the lab-scale matrix diffusioncoefficient [Dem]of the same tracer) is generally larger than one,indicating that the effective matrix diffusion coefficient in the fieldis comparatively larger than the matrix diffusion coefficient at therock-core scale. This larger value could be attributed to the manymass-transfer processes at different scales in naturally heterogeneous,fractured rock systems. Furthermore, we observed a moderate trend towardsystematic increase in the emDFmDDF value with observation scale,indicating that the effective matrix diffusion coefficient is likely tobe statistically scale dependent. The FD value ranges from 1 to 10,000for observation scales from 5 to 2,000 m. At a given scale, the FD valuevaries by two orders of magnitude, reflecting the influence of differingdegrees of fractured rock heterogeneity at different sites. In addition,the surveyed data indicate that field-scale longitudinal dispersivitygenerally increases with observation scale, which is consistent withprevious studies. The scale-dependent field-scale matrix diffusioncoefficient (and dispersivity) may have significant implications forassessing long-term, large-scale radionuclide and contaminant transportevents in fractured rock, both for nuclear waste disposal and contaminantremediation.

  15. A study on the ground water flow and hydrogeochemical interaction in fractured rock masses

    International Nuclear Information System (INIS)

    A study site, the Precambrian gneiss complex in the vincinity of Chungyang has been investigated by geologic surface mapping, tunnel mapping and core drilling with chemical analysis and microscopic observation of rock samples and fracture filling materials. Four boreholes at depths between 50 and 200m were drilled. They are located in a potential fracture zone, which was selected based on the topographic characterisitcs and the fracture survey data. The hydraulic characteristics are described based on the results of constant pressure injection test and cross hole test. In the single hole test, the test sections varied between 1 and 5 m. The hydraulic conductivity of local fracture zones ranges from 1xlO-5 to lxlO-7 m/sec whereas that of the intact rock within the depth of 50 m is in the range of 7xlO-8 to 8xlO-9 m/sec. The field dispersivity values obtained from an injection phase range from 0.15 to 4.5 m at varying depths. The whole thickness dispersivity on the 18 m section obtained from a withdrawal phase is 0.4 m. The dispersion test in two well non-circulation mode was carried out along a single fracture set at depth between 11.5-14.5m. The longitudinal dispersivity obtained from the two well test is 8.14 m. The identified minerals of host rocks are quartz, K-feldspar,plagioclase, biotite, muscovite, sericite, chlorite, calcite, pyrite, zircon and opaque minerals. The primary minerals such as feldspar and biotite are highly altered into sericite and chlorite respectively. The fracture-filling materials from core samples identified by as calcite, kaolinite, smectite, chlorite, illitite, quartz, pyrite with fe- and Mn-oxides. (Author)

  16. Preliminary capillary hysteresis simulations for fractured rocks -- model development and results of simulations

    Energy Technology Data Exchange (ETDEWEB)

    Niemi, A.; Bodvarsson, G.S.

    1991-11-01

    As part of the code development and modeling work being carried out to characterize the flow in the unsaturated zone at Yucca Mountain, Nevada, capillary hysteresis models simulating the history-dependence of the characteristic curves have been developed. The objective of the work has been both to develop the hysteresis models, as well as to obtain some preliminary estimates of the possible hysteresis effects in the fractured rocks at Yucca Mountain given the limitations of presently available data. Altogether three different models were developed based on work of other investigators reported in the literature. In these three models different principles are used for determining the scanning paths: in model (1) the scanning paths are interpolated from tabulated first-order scanning curves, in model (2) simple interpolation functions are used for scaling the scanning paths from the expressions of the main wetting and main drying curves and in model (3) the scanning paths are determined from expressions derived based on the dependent domain theory of hysteresis.

  17. The study on bentonite slurry grout with ethanol for fractured rock masses

    International Nuclear Information System (INIS)

    The purpose of this paper is to propose the grouting material and method for fractured rock masses. So experimental study is executed in order to grasp that the properties of grouting material is stable and impermeable. In this study, experiments of hydraulic test and grouting injection test are performed on bentonite slurry mixes in the laboratory. From the results of the tests, a mixer of ethanol and bentonite is found to be very suitable for a grouting material. Also, dynamic grouting method is able to inject the concentrated bentonite slurry in the fractured aperture. (author)

  18. Advanced Conceptual Models for Unsaturated and Two-Phase Flow in Fractured Rock

    Energy Technology Data Exchange (ETDEWEB)

    Harihar Rajaram; Robert J. Glass; Michael J. Nicholl; Thomas R. Wood

    2007-06-24

    The Department of Energy Environmental Management Program is faced with two major issues involving two-phase flow in fractured rock; specifically, transport of dissolved contaminants in the Vadose Zone, and the fate of Dense Nonaqueous Phase Liquids (DNAPLs) below the water table. Conceptual models currently used to address these problems do not correctly include the influence of the fractures, thus leading to erroneous predictions. Recent work has shown that it is crucial to understand the topology, or 'structure' of the fluid phases (air/water or water/DNAPL) within the subsurface.

  19. Single well injection withdrawal tests (SWIW) in fractured rock. Some aspects on interpretation

    Energy Technology Data Exchange (ETDEWEB)

    Neretnieks, Ivars [Dept. of Chemical Engineering and Technology, Royal Inst. of Technology, Stockholm (Sweden)

    2007-08-15

    Single-Well-Injection-Withdrawal, SWIW, tests are used to try to extract information on fracture apertures, sorption and diffusion properties and dispersion information in individual fractures. It is done by injecting a given amount of traced water into an isolated fracture. After a waiting period water is withdrawn from the fracture and the tracer concentration is measured. The concentration time curve is fitted to a model and the parameter values quantifying the different interaction mechanisms are determined. A number of different mechanisms influence the recovery of the tracer. One or more of the following mechanisms are considered. They include: dispersion due to velocity differences, sorption on fracture surface and on infill, diffusion in rock fragments in the fracture, diffusion between 'streamlines', diffusion into rock matrix and other stagnant water volumes, sorption kinetics and slow drift of the plume caused by the natural gradient. Many of the interaction mechanisms can influence the recovery curve in a similar way. For example, diffusion into rock matrix water and into stagnant water in the fracture adjacent to the flowing channels cannot be distinguished if only one tracer is used. Tracers with different properties can in principle be used but they will encounter different parts of the fracture, the sorbing tracer will move out less from the injection point than a nonsorbing tracer will. Diffusion and sorption in small particles in the flowpath can influence the recovery curve in a similar way as rock matrix diffusion does. Dispersion caused by diffusion between 'streamlines', Taylor dispersion, can give very different results in channels of different shapes. Such dispersion effects can be difficult to distinguish from matrix diffusion effects. Dispersion coefficients obtained in a SWIW test may have little relation to dispersion of a tracer moving from A to B. This is partly due to the different mechanisms and partly due to

  20. Fractures inside crystalline rocks. Effects of deformations on fluid circulations; Fractures dans les roches cristallines. Effets des deformations sur les circulations de fluides

    Energy Technology Data Exchange (ETDEWEB)

    Gentier, S

    2005-07-01

    The modeling of fluid flows inside granite massifs is an important task for the evaluation of the feasibility of radioactive waste storage inside such formations. This document makes a synthesis of the works carried out since about 15 years, in particular by the French bureau of geological and mining research (BRGM), about the hydro-mechanical behaviour of a fracture and about the hydrodynamical characterization of fracture networks inside crystalline rocks: 1 - introduction; 2 - hydro-mechanical behaviour under normal stress: experimental results (hydro-mechanical behaviour, flow regimes, mechanical behaviour, test protocol, complementary tests, influence of samples size), geometrical interpretation of experimental results (relation with walls geometry, relation with voids geometry, relation with contacts geometry), hydro-mechanical modeling (hydraulic modeling, mechanical modeling); 3 - from the hydro-mechanical behaviour under normal stress to the coupling with heat transfers and chemistry: experiment for the study of the chemo-thermo-hydro-mechanical coupling (experimental results, relation with walls morphology), thermo-hydro-mechanical experiments, thermo-hydro-chemical experiments with fractures, conclusions; 4 - hydro-mechanical behaviour during shear: experimental results, geometrical interpretation (relation with the geometry of damaged zones, relation with voids geometry, relation with walls geometry), hydro-mechanical modeling (mechanical modeling, hydro-mechanical modeling of the behaviour during shear). (J.S.)

  1. Scale effect experiment in a fractured rock mass phase 2. Volume 2

    International Nuclear Information System (INIS)

    An experimental and theoretical study dealing with 'scale effect' on hydraulic and transport parameters in a fractured rock mass was carried out in the granitic site at Fanay-Augeres. The study is divided into two phases. Phase 2A: experimental study and modelling of groundwater flows (respectively volume 1 and volume 2). Phase 2 B: experimental study and modelling of tracer tests (respectively volume 3 and volume 4); determination of the in-situ state of stress in the rock mass (volume 5). This study is part of the coordinated project MIRAGE (radionuclide migration in the geosphere), research subject matter number 4 hydrogeology

  2. Estimation of migration characteristics of a nonsorbing tracer through an artificial rock fracture

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, B. H.; Park, J. K.; Han, P. S. [KAERI, Taejon (Korea, Republic of)

    1998-10-01

    Experiment on the transport of a nonsorbing tracer in an artificial rock fracture was carried out. The scale of an artificial rock was 50x20x5cm. The migration field was assumed as a two dimensional system. Eosine, a kind of an organic dye, was used as a nonsorbing tracer. This tracer was injected as a pulse function in a point source and point withdraw system. Volumetric flow rate was 0.5ml/min. The migration plume of the tracer was captured by a digital camera and compared with a result from transport modeling.

  3. Scale effects experiment in a fractured rock mass phase 2. Volume 4

    International Nuclear Information System (INIS)

    An experimental and theoretical study dealing with 'scale effect' on hydraulic and transport parameters in a fractured rock mass was carried out in the granitic site at Fanay-Augeres. The study is divided into two phases. Phase 2A: experimental study and modelling of groundwater flows (respectively volume 1 and volume 2). Phase 2 B: experimental study and modelling of tracer tests (respectively volume 3 and volume 4); determination of the in-situ state of stress in the rock mass (volume 5). This study is part of the coordinated project MIRAGE (radionuclide migration in the geosphere), research subject matter number 4 hydrogeology

  4. Characterizing Fracture Spatial Patterns by Using Semivariograms

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Semivariogram is applied to fracture data obtained from detailed scanline surveys of nine field sites in western New York, USA in order to investigate the spatial patterns of natural fractures. The length of the scanline is up to 36 m. How both fracture spacing and fracture length vary with distance is determined through semivariogram calculations. In this study, the authors developed a FORTRAN program to resample the fracture data from the scanline survey. By calculating experimental semivariogram, the authors found five different types of spatial patterns that can be described by linear, spherical, reversed spherical, polynomial I (for a0) models, of which the last three are newly proposed in this study. The well-structured semivariograms of fracture spacing and length indicate that both the location of the fractures and the length distribution within their structure domains are not random. The results of this study also suggest that semivariograms can provide useful information in terms of spatial correlation distance for fracture location and fracture length. These semivariograms can also be utilized to design more efficient sampling schemes for further surveys, as well as to define the limits of highly probable extrapolation of a structure domain.

  5. Dyke propagation and tensile fracturing at high temperature and pressure, insights from experimental rock mechanics.

    Science.gov (United States)

    Bakker, Richard; Benson, Philip; Vinciguerra, Sergio

    2014-05-01

    It is well known that magma ascends trough the crust by the process of dyking. To enable dyke emplacement, basement rocks typically fail in a mode 1 fracture, which acts as conduits for magma transport. An overpressure of the ascending magma will further open/widen the fracture and permit the fracture to propagate. In order to further understand the emplacement and arrest of dykes in the subsurface, analogue and numerical studies have been conducted. However, a number of assumptions regarding rock mechanical behaviour frequently has to be made as such data are very hard to directly measure at the pressure/temperature conditions of interest: high temperatures at relatively shallow depths. Such data are key to simulating the magma intrusion dynamics through the lithologies that underlie the volcanic edifice. Here we present a new laboratory setup, which allows us to investigate the tensile fracturing properties under both temperature and confining pressure, and the emplacement of molten material within the newly formed fracture. We have modified a traditional tri-axial test assembly setup to be able to use a Paterson type High Pressure, High Temperature deformation apparatus. Sample setup consists of cylindrical rock samples with a 22 mm diameter and a 8 mm bore at their centre, filled with a material chosen as such that it's in a liquid state at the experimental temperature and solid at room temperature to enable post-experiment analysis. The top and lower parts of the rock sample are fitted with plugs, sealing in the melt. The assembly is then placed between ceramic pistons to ensure there are no thermal gradients across the sample. The assembly is jacketed to ensure the confining medium (Ar) cannot enter the assembly. A piston is driven into the sample such that the inner conduit materials pressure is slowly increased. At some point a sufficient pressure difference between the inner and outer surfaces causes the sample to deform and fail in the tensile regime

  6. Fractured rock aquifer test in the Western Siberian Basin, Ozyorsk, Russia

    International Nuclear Information System (INIS)

    A series of multi-zone pumping tests was conducted in a contaminated fractured rock aquifer in the Western Siberian Basin, Ozyorsk, Russia. The tests were conducted adjacent to the Mishelyak River floodplain in fractured Paleozoic porphyrites, tufts, tuff breccia, and lava typical of the Ural mountain complex. Geophysical logs, borehole photography, core samples, and results from previous borehole contamination studies were used to identify the zones to be tested. A network of three uncased wells was tested using a system of inflatable packers, pressure transducers and data loggers. Seven zones were isolated and monitored in two of the uncased wells. A straddle packer assembly was used to isolate individual zones within the pumping well. Eight constant rate pumping tests were conducted. Results of the testing indicate that shallow groundwater migrates primarily in two intervals that are separated by an interval with low lateral conductivity. The water bearing intervals have moderate to high specific capacities (1.3 and 30 L/min/m). Several processes are responsible for fracturing present in the lower interval. The network of compound fractures produced a complex array of fracture intersections yielding a fractured media with hydraulic behavior similar to porous media. Models used for the analysis of pumping tests in porous media provide a good estimation of the hydraulic response of the lower interval to pumping. Future work will include more complex analysis of the data to determine hydraulic conductivity ellipses

  7. Fractured rock aquifer tests in the Western Siberian Basin, Ozyorsk, Russia

    Energy Technology Data Exchange (ETDEWEB)

    Nichols, R.L.; Looney, B.B.; Eddy-Dilek, C.A. [and others

    1997-10-01

    A series of multi-zone pumping tests was conducted in a contaminated fractured rock aquifer in the Western Siberian Basin, Ozyorsk, Russia. The tests were conducted adjacent to the Mishelyak River floodplain in fractured Paleozoic porphyrites, tufts, tuff breccia, and lava typical of the Ural mountain complex. Geophysical logs, borehole photography, core samples, and results from previous borehole contamination studies were used to identify the zones to be tested. A network of three uncased wells was tested using a system of inflatable packers, pressure transducers and data loggers. Seven zones were isolated and monitored in two of the uncased wells. A straddle packer assembly was used to isolate individual zones within the pumping well. Eight constant rate pumping tests were conducted. Results of the testing indicate that shallow groundwater migrates primarily in two intervals that are separated by an interval with low lateral conductivity. The water bearing intervals have moderate to high specific capacities (1.3 and 30 L/min/m). Several processes are responsible for fracturing present in the lower interval. The network of compound fractures produced a complex array of fracture intersections yielding a fractured media with hydraulic behavior similar to porous media. Models used for the analysis of pumping tests in porous media provide a good estimation of the hydraulic response of the lower interval to pumping. Future work will include more complex analysis of the data to determine hydraulic conductivity ellipses.

  8. Effect of specimen thickness on Mode Ⅱ fracture toughness of rock

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Anti-symmetric four-point bending specimens with different thickness, without and with guiding grooves, were used to conduct Mode Ⅱ fracture test and study the effect of specimen thickness on Mode Ⅱ fracture toughness of rock. Numerical calculations show that the occurrence of Mode Ⅱ fracture in the specimens without guiding grooves (when the inner and outer loading points are moved close to the notch plane) and with guiding grooves is attributed to a favorable stress condition created for Mode Ⅱ fracture, i.e. tensile stress at the notch tip is depressed to be lower than the tensile strength or to be compressive stress, and the ratio of shear stress to tensile stress at notch tip is very high. The measured value of Mode Ⅱ fracture toughness KⅡC decreases with the increase of the specimen thickness or the net thickness of specimen. This is because a thick specimen promotes a plane strain state and thus results in a relatively small fracture toughness.

  9. THE STRESS IMPACT ON MECHANICAL PROPERTIES OF ROCKS IN HYDRO FRACTURING TECHNIQUE

    Directory of Open Access Journals (Sweden)

    B. GURUPRASAD

    2012-02-01

    Full Text Available Ground water is considered to be the best safe protected drinking water source and bore wells are drilled in hard crystalline rock terrains for drinking water, irrigation and industrial purposes. Even after scientific location, some bore wells yield inadequate quantity of water or fail to yield. The success of bore wells depend largely onnumber, length, dilation and interconnectivity of fractures encountered on drilling. Considering the cost factor involved in drilling a new bore well, rejuvenation of failed bore well through some technique is thought off. The innovative technology of ‘hydro fracturing’ is a new interdisciplinary approach of Hydro mechanical tostimulate the bore well to improve the yield by applying water pressure into bore well by using a heavy duty mechanical compressor. The hydro fracturing technique was first used in oil well to increase oil and gas production. In this research paper, the hydraulic pressure applied increases with depth reflecting the rigidness,toughness of rock. The fracture development, propagation of fracture and stress behavior depends on the physical and mechanical properties of rocks. The hydro fracturing process has been conducted in three depth zones ranging from 8 m to 45 m below ground level in Annavasal union of Pudukottai district, Tamil Nadu, India. The Pressure application varies depending on the geological formations. This study pertains to a part of research work. The minimum and maximum pressures applied are 1 and 10 N/mm2 respectively. The maximumpressure of 10 N/mm2 has been recorded in the third zone, where the country rock is charnockite which is generally massive, compact and dense rock. Generally for the igneous rock in the third zone in the depth range of 40 to 50 m, more than 7 N/mm2 of pressure has been applied indicating extremely strong nature with uniaxial compressive strength 100 – 300 N/mm2, tensile strength 7- 25 N/mm2. Out of 37 bore wells 32.4% of bore wells have shown

  10. Study of Pumping Pressure and Stop Criteria in Grouting of Rock Fractures

    OpenAIRE

    Yaghoobi Rafi, Jalaleddin

    2014-01-01

    Today practice of grouting is based on empirical approaches in that, pumping pressure and stop criteria are determined by benchmarking similar projects. Considering a maximum limit for grouting pressure would allow applying a relatively high pressure that may lead to jacking of the fracture or even uplift of the rock mass. On the other hand, keeping the pressure lower than the overburden, in order to avoid any deformation, will prolong grouting process. Determination of pumping pressure is mo...

  11. Summary of three dimensional pump testing of a fractured rock aquifer in the western Siberian Basin

    International Nuclear Information System (INIS)

    A group of scientists from the Savannah River Technology Center and Russia successfully completed a 17 day field investigation of a fractured rock aquifer at the MAYAK PA nuclear production facility in Russia. The test site is located in the western Siberian Basin near the floodplain of the Mishelyak river. The fractured rock aquifer is composed of orphyrites, tuff, tuffbreccia and lava and is overlain by 0.5--12 meters of elluvial and alluvial sediments. A network of 3 uncased wells (176, 1/96, and 2/96) was used to conduct the tests. Wells 176 and 2/96 were used as observation wells and the centrally located well 1/96 was used as the pumping well. Six packers were installed and inflated in each of the observation wells at a depth of up to 85 meters. The use of 6 packers in each well resulted in isolating 7 zones for monitoring. The packers were inflated to different pressures to accommodate the increasing hydrostatic pressure. A straddle packer assembly was installed in the pumping well to allow testing of each of the individual zones isolated in the observation wells. A constant rate pumping test was run on each of the 7 zones. The results of the pumping tests are included in Appendix A. The test provided new information about the nature of the fractured rock aquifers in the vicinity of the Mishelyak river and will be key information in understanding the behavior of contaminants originating from process wastes discharged to Lake Karachi. Results from the tests will be analyzed to determine the hydraulic properties of different zones within the fractured rock aquifer and to determine the most cost effective clean-up approach for the site

  12. Summary of three dimensional pump testing of a fractured rock aquifer in the western Siberian Basin

    Energy Technology Data Exchange (ETDEWEB)

    Nichols, R.L.; Looney, B.B.; Eddy-Dilek, C.A. [Westinghouse Savannah River Co., Aiken, SC (United States); Drozhko, E.G.; Glalolenko, Y.V.; Mokrov, Y.G.; Ivanov, I.A. [P.A. Mayak, Chelyabinsk (Russian Federation); Glagolev, A.V.; Vasil`kova, N.A. [P.S.A. Hydrospetzgeologiya, Moscow (Russian Federation)

    1996-10-30

    A group of scientists from the Savannah River Technology Center and Russia successfully completed a 17 day field investigation of a fractured rock aquifer at the MAYAK PA nuclear production facility in Russia. The test site is located in the western Siberian Basin near the floodplain of the Mishelyak river. The fractured rock aquifer is composed of orphyrites, tuff, tuffbreccia and lava and is overlain by 0.5--12 meters of elluvial and alluvial sediments. A network of 3 uncased wells (176, 1/96, and 2/96) was used to conduct the tests. Wells 176 and 2/96 were used as observation wells and the centrally located well 1/96 was used as the pumping well. Six packers were installed and inflated in each of the observation wells at a depth of up to 85 meters. The use of 6 packers in each well resulted in isolating 7 zones for monitoring. The packers were inflated to different pressures to accommodate the increasing hydrostatic pressure. A straddle packer assembly was installed in the pumping well to allow testing of each of the individual zones isolated in the observation wells. A constant rate pumping test was run on each of the 7 zones. The results of the pumping tests are included in Appendix A. The test provided new information about the nature of the fractured rock aquifers in the vicinity of the Mishelyak river and will be key information in understanding the behavior of contaminants originating from process wastes discharged to Lake Karachi. Results from the tests will be analyzed to determine the hydraulic properties of different zones within the fractured rock aquifer and to determine the most cost effective clean-up approach for the site.

  13. Sensitivity analysis of GSI based mechanical characterization of rock mass

    CERN Document Server

    Ván, P

    2012-01-01

    Recently, the rock mechanical and rock engineering designs and calculations are frequently based on Geological Strength Index (GSI) method, because it is the only system that provides a complete set of mechanical properties for design purpose. Both the failure criteria and the deformation moduli of the rock mass can be calculated with GSI based equations, which consists of the disturbance factor, as well. The aim of this paper is the sensitivity analysis of GSI and disturbance factor dependent equations that characterize the mechanical properties of rock masses. The survey of the GSI system is not our purpose. The results show that the rock mass strength calculated by the Hoek-Brown failure criteria and both the Hoek-Diederichs and modified Hoek-Diederichs deformation moduli are highly sensitive to changes of both the GSI and the D factor, hence their exact determination is important for the rock engineering design.

  14. A science plan for a comprehensive assessment of water supply in the region underlain by fractured rock in Maryland

    Science.gov (United States)

    Fleming, Brandon J.; Hammond, Patrick A.; Stranko, Scott A.; Duigon, Mark T.; Kasraei, Saeid

    2012-01-01

    The fractured rock region of Maryland, which includes land areas north and west of the Interstate 95 corridor, is the source of water supply for approximately 4.4 million Marylanders, or approximately 76 percent of the State's population. Whereas hundreds of thousands of residents rely on wells (both domestic and community), millions rely on surface-water sources. In this region, land use, geology, topography, water withdrawals, impoundments, and other factors affect water-flow characteristics. The unconfined groundwater systems are closely interconnected with rivers and streams, and are affected by seasonal and climatic variations. During droughts, groundwater levels drop, thereby decreasing well yields, and in some cases, wells have gone dry. Low ground-water levels contribute to reduced streamflows, which in turn, can lead to reduced habitat for aquatic life. Increased demand, over-allocation, population growth, and climate change can affect the future sustainability of water supplies in the region of Maryland underlain by fractured rock. In response to recommendations of the 2008 Advisory Committee on the Management and Protection of the State's Water Resources report, the Maryland Department of the Environment's Water Supply Program, the Maryland Geological Survey, the Maryland Department of Natural Resources, Monitoring and Non-Tidal Assessment (MANTA) Division, and the U.S. Geological Survey have developed a science plan for a comprehensive assessment that will provide new scientific information, new data analysis, and new tools for the State to better manage water resources in the fractured rock region of Maryland. The science plan lays out five goals for the comprehensive assessment: (1) develop tools for the improved management and investigation of groundwater and surface-water resources; (2) characterize factors affecting reliable yields of individual groundwater and surface-water supplies; (3) investigate impacts on nearby water withdrawal users caused

  15. Field and numerical determinations of pneumatic flow parameters of unsaturated fractured porous rocks on various scales

    International Nuclear Information System (INIS)

    Air permeability is measured in the fractured crystalline rocks of the Roselend Natural Laboratory (France). Single-hole pneumatic injection tests as well as differential barometric pressure monitoring are conducted on scales ranging from 1 to 50 m, in both shallow and deep boreholes, as well as in an isolated 60 m3 chamber at 55 m depth. The field experiments are interpreted using numerical simulations in equivalent homogeneous porous media with their real 3-D geometry in order to estimate pneumatic parameters. For pneumatic injection tests, steady-state data first allow to estimate air permeability. Then, pressure recovery after a pneumatic injection test allows to estimate the air-filled porosity. Comparison between the various studied cases clarifies the influence of the boundary conditions on the accuracy of the often used 1-D estimate of air permeability. It also shows that permeabilities correlate slightly with fracture density. In the chamber, a 1 order-of-magnitude difference is found between the air permeabilities obtained from pneumatic injection tests and from differential barometric pressure monitoring. This discrepancy is interpreted as a scale effect resulting from the approximation of the heterogeneous fractured rock by a homogeneous numerical model. The difference between the rock volumes investigated by pneumatic injection tests and by differential barometric pressure monitoring may also play a role. No clear dependence of air permeability on saturation has been found so far. (authors)

  16. Chemically- and mechanically-mediated influences on the transport and mechanical characteristics of rock fractures

    Energy Technology Data Exchange (ETDEWEB)

    Min, K.-B.; Rutqvist, J.; Elsworth, D.

    2009-02-01

    A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities, which results in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolution-like behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated in a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be lower than they were in the case where chemical effects were not considered, with a net reduction apparent even after cooling to ambient temperature. These heretofore-neglected effects may have a correspondingly significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes.

  17. Analysis of propagation mechanisms of stimulation-induced fractures in rocks

    Science.gov (United States)

    Krause, Michael; Renner, Joerg

    2016-04-01

    Effectivity of geothermal energy production depends crucially on the heat exchange between the penetrated hot rock and the circulating water. Hydraulic stimulation of rocks at depth intends to create a network of fractures that constitutes a large area for exchange. Two endmembers of stimulation products are typically considered, tensile hydro-fractures that propagate in direction of the largest principal stress and pre-existing faults that are sheared when fluid pressure reduces the effective normal stress acting on them. The understanding of the propagation mechanisms of fractures under in-situ conditions is still incomplete despite intensive research over the last decades. Wing-cracking has been suggested as a mechanism of fracture extension from pre-existent faults with finite length that are induced to shear. The initiation and extension of the wings is believed to be in tensile mode. Open questions concern the variability of the nominal material property controlling tensile fracture initiation and extension, the mode I facture toughness KIC, with in-situ conditions, e.g., its mean-stress dependence. We investigated the fracture-propagation mechanism in different rocks (sandstones and granites) under varying conditions mimicking those representative for geothermal systems. To determine KIC-values we performed 3-point bending experiments. We varied the confining pressure, the piston velocity, and the position of the chevron notch relative to the loading configuration. Additional triaxial experiments at a range of confining pressures were performed to study wing crack propagation from artificial flaws whose geometrical characteristics, i.e., length, width, and orientation relative to the axial load are varied. We monitored acoustic emissions to constrain the spacio-temporal evolution of the fracturing. We found a significant effect of the length of the artificial flaw and the confining pressure on wing-crack initiation but did not observe a systematic dependence

  18. Radionuclide migration in fractured rock: hydrological investigations at an experimental site in the Carnmennellis granite, Cornwall

    International Nuclear Information System (INIS)

    The objectives, methods and results of hydrological investigation of the granite at an experimental site in Cornwall are described and discussed. Constant head injection tests and radioactive tracer experiments have revealed a fracture permeability in which water movement is confined to discrete fractures separated by rock of very low permeability. Data on flow path frequency, orientation and effective hydraulic aperture, required for network modelling, are presented for a 700 m borehole, with additional hydraulic data from three other boreholes. In addition to fractures of average hydraulic conductivity a small number of major hydraulic features (''main drains'') with major implications for radionuclide migration have been identified. A mean hydraulic conductivity for the granite investigated of 1.57x10-7ms-1 has been obtained, 2.11x10-8ms-1 if the major hydraulic features are excluded

  19. Fracture characterization from formation microlmager data

    NARCIS (Netherlands)

    Ponziani, M.; Slob, E.C.; Luthi, S.M.; Bloemenkamp, R.F.; Le Nir, I.

    2013-01-01

    The Formation MicroImager (mark of Schlumberger) is an electric imaging tool that produces electrical scans of the borehole walls. These measurements provide useful information on the fracture aperture of naturally fractured reservoirs. In this paper, we present a laboratory set-up that was realized

  20. Characterization of fracture loci in metal forming

    DEFF Research Database (Denmark)

    Martins, P.A.F.; Bay, Niels; Tekkaya, A.E.;

    2014-01-01

    Fracture in metal forming can occur in three different modes: (i) tensile; (ii) in-plane shear; and (iii) out-of-plane shear (respectively the same as modes I, II and III of fracture mechanics). The circumstances under which each mode will occur are identified in terms of plastic flow and microst...

  1. Effective-stress-law behavior of Austin chalk rocks for deformation and fracture conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Warpinski, N.R.; Teufel, L.W.

    1994-08-01

    Austin chalk core has been tested to determine the effective law for deformation of the matrix material and the stress-sensitive conductivity of the natural fractures. For deformation behavior, two samples provided data on the variations of the poroelastic parameter, {alpha}, for Austin chalk, giving values around 0.4. The effective-stress-law behavior of a Saratoga limestone sample was also measured for the purpose of obtaining a comparison with a somewhat more porous carbonate rock. {alpha} for this rock was found to be near 0.9. The low {alpha} for the Austin chalk suggests that stresses in the reservoir, or around the wellbore, will not change much with changes in pore pressure, as the contribution of the fluid pressure is small. Three natural fractures from the Austin chalk were tested, but two of the fractures were very tight and probably do not contribute much to production. The third sample was highly conductive and showed some stress sensitivity with a factor of three reduction in conductivity over a net stress increase of 3000 psi. Natural fractures also showed a propensity for permanent damage when net stressed exceeded about 3000 psi. This damage was irreversible and significantly affected conductivity. {alpha} was difficult to determine and most tests were inconclusive, although the results from one sample suggested that {alpha} was near unity.

  2. Study on Smooth-Blasting Results in Jointed and Fractured Rock

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Factors that affect blasting results may be grouped into those factors that can be controlled and those that cannot be controlled. The controllable factors include explosive properties, initiation timing, and blast geometry. The uncontrollable factors comprise the rock’s natural structures, such as joints and fractures, and the properties, such as elastic constants, density and strength. Among these, the influence of rock structural planes often contributes a high degree of variability to blasting results. This paper presents a theoretical analysis of rock structural plane influences on smooth-blasting results based on elasticity and stress wave propagation theory with an emphasis on smooth blasting techniques. Two types of simulated experiments in lab (using strain and acoustic emission measurements) are used to verify the theoretical analysis. The results show that it is difficult to achieve smooth-blasting results when the angle between the natural rock structural planes and the blast-induced fracture planes ranges from 10° to 60°. Among these angles, 30° is the least desirable angle to produce a smooth wall. For angles less than 10° and greater than 60°, the influence of rock structural planes on blasting results can be ignored.

  3. The Fracture Influence on the Energy Loss of Compressed Air Energy Storage in Hard Rock

    Directory of Open Access Journals (Sweden)

    Hehua Zhu

    2015-01-01

    Full Text Available A coupled nonisothermal gas flow and geomechanical numerical modeling is conducted to study the influence of fractures (joints on the complex thermohydromechanical (THM performance of underground compressed air energy storage (CAES in hard rock caverns. The air-filled chamber is modeled as porous media with high porosity, high permeability, and high thermal conductivity. The present analysis focuses on the CAES in hard rock caverns at relatively shallow depth, that is, ≤100 m, and the pressure in carven is significantly higher than ambient pore pressure. The influence of one discrete crack and multiple crackson energy loss analysis of cavern in hard rock media are carried out. Two conditions are considered during each storage and release cycle, namely, gas injection and production mass being equal and additional gas injection supplemented after each cycle. The influence of the crack location, the crack length, and the crack open width on the energy loss is studied.

  4. Investigation of fracture permeability around an underground opening in metamorphic rocks

    International Nuclear Information System (INIS)

    This report is the fifth in a series describing experiments conducted by the Colorado School of Mines for the Office of Crystalline Repository Development (OCRD) to determine the extent of blast damage in rock surrounding an underground opening. The report describes the instrumentation and method for testing permeability in crystalline rock masses. We applied the instruments in the CSM/OCRD test room in the Colorado School of Mines Experimental Mine (Edgar Mine) in Idaho Springs, Colorado. Even though this mine will not be a repository site, the equipment and methodology developed in this research program is applicable to other sites. The results presented in this report consider the variation of permeability measured with injection techniques. Preliminary results of core logging and deterministic fracture mapping program are briefly discussed. An attempt has also been made to relate the permeability variations to the stress field modification due to removal of the supporting rock mass

  5. FIELD-SCALE EFFECTIVE MATRIX DIFFUSION COEFFICIENT FOR FRACTURED ROCK:RESULTS FROM LITERATURE SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Q. Zhou; Hui-Hai Liu; F.J. Molz; Y. Zhang; G.S. Bodvarsson

    2005-04-08

    Matrix diffusion is an important mechanism for solute transport in fractured rock. We recently conducted a literature survey on the effective matrix diffusion coefficient, D{sub m}{sup e}, a key parameter for describing matrix diffusion processes at the field scale. Forty field tracer tests at 15 fractured geologic sites were surveyed and selected for the study, based on data availability and quality. Field-scale D{sub m}{sup e} values were calculated, either directly using data reported in the literature or by reanalyzing the corresponding field tracer tests. Surveyed data indicate that the effective-matrix-diffusion-coefficient factor F{sub D} (defined as the ratio of D{sub m}{sup e} to the lab-scale matrix diffusion coefficient [D{sub m}] of the same tracer) is generally larger than one, indicating that the effective matrix diffusion coefficient in the field is comparatively larger than the matrix diffusion coefficient at the rock-core scale. This larger value can be attributed to the many mass-transfer processes at different scales in naturally heterogeneous, fractured rock systems. Furthermore, we observed a moderate trend toward systematic increase in the F{sub D} value with observation scale, indicating that the effective matrix diffusion coefficient is likely to be statistically scale dependent. The F{sub D} value ranges from 1 to 10,000 for observation scales from 5 to 2,000 m. At a given scale, the F{sub D} value varies by two orders of magnitude, reflecting the influence of differing degrees of fractured rock heterogeneity at different sites. In addition, the surveyed data indicate that field-scale longitudinal dispersivity generally increases with observation scale, which is consistent with previous studies. The scale-dependent field-scale matrix diffusion coefficient (and dispersivity) may have significant implications for assessing long-term, large-scale radionuclide and contaminant transport events in fractured rock, both for nuclear waste disposal

  6. Fracture Dissolution of Carbonate Rock: An Innovative Process for Gas Storage

    Energy Technology Data Exchange (ETDEWEB)

    James W. Castle; Ronald W. Falta; David Bruce; Larry Murdoch; Scott E. Brame; Donald Brooks

    2006-10-31

    The goal of the project is to develop and assess the feasibility and economic viability of an innovative concept that may lead to commercialization of new gas-storage capacity near major markets. The investigation involves a new approach to developing underground gas storage in carbonate rock, which is present near major markets in many areas of the United States. Because of the lack of conventional gas storage and the projected growth in demand for storage capacity, many of these areas are likely to experience shortfalls in gas deliverability. Since depleted gas reservoirs and salt formations are nearly non-existent in many areas, alternatives to conventional methods of gas storage are required. The need for improved methods of gas storage, particularly for ways to meet peak demand, is increasing. Gas-market conditions are driving the need for higher deliverability and more flexibility in injection/withdrawal cycling. In order to meet these needs, the project involves an innovative approach to developing underground storage capacity by creating caverns in carbonate rock formations by acid dissolution. The basic concept of the acid-dissolution method is to drill to depth, fracture the carbonate rock layer as needed, and then create a cavern using an aqueous acid to dissolve the carbonate rock. Assessing feasibility of the acid-dissolution method included a regional geologic investigation. Data were compiled and analyzed from carbonate formations in six states: Indiana, Ohio, Kentucky, West Virginia, Pennsylvania, and New York. To analyze the requirements for creating storage volume, the following aspects of the dissolution process were examined: weight and volume of rock to be dissolved; gas storage pressure, temperature, and volume at depth; rock solubility; and acid costs. Hydrochloric acid was determined to be the best acid to use because of low cost, high acid solubility, fast reaction rates with carbonate rock, and highly soluble products (calcium chloride

  7. Mechanical and hydraulic performance of sludge-mixed cement grout in rock fractures

    Directory of Open Access Journals (Sweden)

    Khomkrit Wetchasat

    2014-08-01

    Full Text Available The objective is to assess the performance of sludge mixed with commercial grade Portland cement type I for use in minimizing the permeability of fractured rock mass. The fractures were artificially made by applying a line load to sandstone block specimens. The sludge comprises over 80% of quartz with grain sizes less than 75 μm. The results indicate that the mixing ratios of sludge:cement (S:C of 1:10, 3:10, 5:10 with water:cement ratio of 1:1 by weight are suitable for fracture grouting. For S:C = 3:10, the compressive strength and elastic modulus are 1.22 MPa and 224 MPa which are comparable to those of bentonite mixed with cement. The shear strengths between the grouts and fractures surfaces are from 0.22 to 0.90 MPa. The S:C ratio of 5:10 gives the lowest permeability. The permeability of grouted fractures with apertures of 2, 10, and 20 mm range from 10-16 to 10-14 m2 and decrease with curing time.

  8. VSP in crystalline rocks - from downhole velocity profiling to 3-D fracture mapping

    International Nuclear Information System (INIS)

    VSP surveys have been carried out at several potential nuclear waste disposal sites in Finland since the mid 80s. To date, more than 200 three-component profiles have been measured. The main purpose of the surveys was to detect fracture zones in the crystalline bedrock and to determine their position. Most seismic events could be linked to zones of increased fracturing observed in the borehole logs. The more pronounced seismic reflectors could be correlated with hydrogeologically significant zones, which have been the main targets in the investigations. Processing and interpretation methods have been developed specifically for VSP surveys in crystalline rocks: Weak reflections from thin fracture zones are enhanced by multi-channel filtering techniques based on the Radon transform. The position and orientation of the fracture zones are determined by polarisation analysis and by combining data from several shot points. The compilation of the results from several boreholes gives a comprehensive image of the fracture zones at the scale of the whole site. The discussion of the methodology is based on examples from the Olkiluoto site, in SW Finland

  9. Inclusion-based effective medium models for the field-scale permeability of 3D fractured rock masses

    Science.gov (United States)

    Ebigbo, Anozie; Lang, Philipp S.; Paluszny, Adriana; Zimmerman, Robert W.

    2016-04-01

    Fractures that are more permeable than their host rock can act as preferential, or at least additional, pathways for fluid to flow through the rock. The additional transmissivity contributed by these fractures will be of great relevance in several areas of earth science and engineering, such as radioactive waste disposal in crystalline rock, exploitation of fractured hydrocarbon and geothermal reservoirs, or hydraulic fracturing. In describing or predicting flow through fractured rock, the effective permeability of the rock mass, comprising both the rock matrix and a network of fractures, is a crucial parameter, and will depend on several geometric properties of the fractures/networks, such as lateral extent, aperture, orientation, and fracture density. This study investigates the ability of classical inclusion-based effective medium models (following the work of Sævik et al., Transp. Porous Media, 2013) to predict this permeability. In these models, the fractures are represented as thin, spheroidal inclusions, the interiors of which are treated as porous media having a high (but finite) permeability. The predictions of various effective medium models, such as the symmetric and asymmetric self-consistent schemes, the differential scheme, and Maxwell's method, are tested against the results of explicit numerical simulations of mono- and polydisperse isotropic fracture networks embedded in a permeable rock matrix. Comparisons are also made with the Hashin-Shrikman bounds, Snow's model, and Mourzenko's heuristic model (Mourzenko et al., Phys. Rev. E, 2011). This problem is characterised mathematically by two small parameters, the aspect ratio of the spheroidal fractures, α, and the ratio between matrix and fracture permeability, κ. Two different regimes can be identified, corresponding to α/κ 1. The lower the value of α/κ, the more significant is flow through the matrix. Due to differing flow patterns, the dependence of effective permeability on fracture

  10. Engineering biomineralised groundwater flow barriers for inhibiting radionuclide transport in fractured rocks

    Science.gov (United States)

    Blundell, N.; Cuthbert, M. O.; Riley, M. S.; Handley-Sidhu, S.; Renshaw, J. C.

    2012-04-01

    Microbially induced carbonate precipitation (MICP) is a promising engineering solution for inhibiting pollution transport in fractured rocks through permeability reduction of fine aperture fractures surrounding nuclear decommissioning sites or repositories. However, although many batch and column studies of MICP within porous media have been carried out, the method has yet to be successfully applied within fractured materials and upscaled to block and field scales to demonstrate its potential utility. This paper presents results of laboratory MICP experiments within artificial granite-perspex fractures (30 cm x 10 cm x 150 µm) under flowing conditions using ureolytic bacteria and a 'cementing solution' comprising dissolved urea and calcium chloride. A variety of injection combinations and bacterial/solute concentrations were trialled and changes in hydraulic conductivity of the fractures were measured over time. Injected bacteria were successfully 'fixed' by adding sufficient calcium chloride to encourage flocculation and hence mechanical filtration to trap the bacteria. Observed reductions in hydraulic conductivity of up to 3 orders of magnitude were achieved after 4 x 4 hour phases of injection with a decreasing mass of precipitate with distance from the inlet manifold. Although the results are very promising, a remaining challenge for successful upscaling of the technique to the field scale is in controlling the spatial distribution of bacterial fixing and precipitation to enable sealing of fractures at larger distances from the point of injection. In comparison to existing grouting techniques, MICP has the advantage of being low viscosity and is therefore potentially useful for very fine scale fractures while also potentially providing greater mechanical strength.

  11. Breaking down of linear models of rock fracturing and fault wear

    Science.gov (United States)

    Reches, Z.; Sagy, A.; Boneh, Y.

    2012-12-01

    Linear models of deformation commonly have a limited range of applicability, and their utilization outside the validity range could lead to major errors. We present here two cases of model breakdown, fracture density in layered rocks and wear-rate of faults. Models of tensile fracturing in layered media usually consider sequences of alternating brittle and ductile layers subjected to layer-parallel extension. The contacts between the layers are assumed to by elastic or viscoelastic bonding or frictional resistance to slip. Every fracture relaxes the tensile stresses at its proximity, and thus reduces the likelihood for a new fracture to grow at its proximity. The layer-parallel extension recovers at some distance from the fracture by build-up of shear stresses along the layer contacts. This linear model leads to a maximum fracture spacing that approximately scales with the layer thickness, in agreement with many field observations (Sagy & Reches, 2005).This lower bound on fracture spacing is however contradicted by field and experimental observations of tightly spaced fractures, with spacing that are merely 1/10 to 1/30 of layer thickness. The reason for this discrepancy is that the linear models assume, explicitly or implicitly, that the fractures grow by slow, quasi-static propagation. The tight spacing can be explained by the large surface area of fast, dynamic fractures (Sagy et al., 2001). The classical model of Archard (1953) postulates that wear intensity under steady-state is proportional to the normal stress and slip distance. The adaptation of this model to natural faults (Scholz, 1987) implies that gouge thickness is proportional to the cumulative displacement (assuming that fault depth did not change significantly during its activity period). In our recent experimental analysis of wear-rate along carbonate faults, we analyzed the friction and wear of carbonate faults in the slip velocity range of 0.002-0.96 m/s, and normal stress range of 0.25-6.9 MPa

  12. The role of acoustic emission in the study of rock fracture

    Science.gov (United States)

    Lockner, D.

    1993-01-01

    The development of faults and shear fracture systems over a broad range of temperature and pressure and for a variety of rock types involves the growth and interaction of microcracks. Acoustic emission (AE), which is produced by rapid microcrack growth, is a ubiquitous phenomenon associated with brittle fracture and has provided a wealth of information regarding the failure process in rock. This paper reviews the successes and limitations of AE studies as applied to the fracture process in rock with emphasis on our ability to predict rock failure. Application of laboratory AE studies to larger scale problems related to the understanding of earthquake processes is also discussed. In this context, laboratory studies can be divided into the following categories. 1) Simple counting of the number of AE events prior to sample failure shows a correlation between AE rate and inelastic strain rate. Additional sorting of events by amplitude has shown that AE events obey the power law frequency-magnitude relation observed for earthquakes. These cumulative event count techniques are being used in conjunction with damage mechanics models to determine how damage accumulates during loading and to predict failure. 2) A second area of research involves the location of hypocenters of AE source events. This technique requires precise arrival time data of AE signals recorded over an array of sensors that are essentially a miniature seismic net. Analysis of the spatial and temporal variation of event hypocenters has improved our understanding of the progression of microcrack growth and clustering leading to rock failure. Recently, fracture nucleation and growth have been studied under conditions of quasi-static fault propagation by controlling stress to maintain constant AE rate. 3) A third area of study involves the analysis of full waveform data as recorded at receiver sites. One aspect of this research has been to determine fault plane solutions of AE source events from first motion

  13. Development of Reservoir Characterization Techniques and Production Models for Exploiting Naturally Fractured Reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Wiggins, Michael L.; Brown, Raymon L.; Civan, Frauk; Hughes, Richard G.

    2001-08-15

    Research continues on characterizing and modeling the behavior of naturally fractured reservoir systems. Work has progressed on developing techniques for estimating fracture properties from seismic and well log data, developing naturally fractured wellbore models, and developing a model to characterize the transfer of fluid from the matrix to the fracture system for use in the naturally fractured reservoir simulator.

  14. Testing study of subcritical crack growth rate and fracture toughness in different rocks

    Institute of Scientific and Technical Information of China (English)

    CAO Ping; LI Jiang-teng; YUAN Hai-ping

    2006-01-01

    Subcritical crack growth of double torsion specimens made of ore, lherzolite, marble and granite was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-Ⅰ stress intensity factor KI versus the subcritical crack growth velocity v and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed for different rocks. The results show that lgKI-lgv relations of four kinds of rocks measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity and stress intensity factor have a power law, which is in good agreement with CHARLES theory. lgKI-lgv curves move to top left corner with the decrease of the elastic modulus, which implies that the subcritical crack growth velocity speeds up. The maximum subcritical crack growth velocity exhibits negative exponential increase, and mode-Ⅰ fracture toughness KIC decreases with the decrease of elastic modulus. The testing results provide a basis for time-dependence of rock engineering stability.

  15. Geophysical methods for fracture characterization in and around potential sites for nuclear waste disposal

    International Nuclear Information System (INIS)

    Historically, geophysical methods have been used extensively to successfully explore the subsurface for petroleum, gas, mineral, and geothermal resources. Their application, however, for site characterization, and monitoring the performance of near surface waste sites or repositories has been somewhat limited. Presented here is an overview of the geophysical methods that could contribute to defining the subsurface heterogeneity and extrapolating point measurements at the surface and in boreholes to volumetric descriptions in a fractured rock. In addition to site characterization a significant application of geophysical methods may be in performance assessment and in monitoring the repository to determine if the performance is as expected

  16. Estimation of Fracture Toughness of Anisotropic Rocks by Semi-Circular Bend (SCB) Tests Under Water Vapor Pressure

    Science.gov (United States)

    Kataoka, M.; Obara, Y.; Kuruppu, M.

    2015-07-01

    In order to investigate the influence of water vapor pressure in the surrounding environment on mode I fracture toughness ( K Ic) of rocks, semi-circular bend (SCB) tests under various water vapor pressures were conducted. Water vapor is one of the most effective agents which promote stress corrosion of rocks. The range of water vapor pressure used was 10-2 to 103 Pa, and two anisotropic rock types, African granodiorite and Korean granite, were used in this work. The measurement of elastic wave velocity and observation of thin sections of these rocks were performed to investigate the microstructures of the rocks. It was found that the distribution of inherent microcracks and grains have a preferred orientation. Two types of specimens in different orientations, namely Type-1 and Type-3, were prepared based on the anisotropy identified by the differences in the elastic wave velocity. K Ic of both rock types was dependent on the water vapor pressure in the surrounding environment and decreased with increasing water vapor pressure. It was found that the degree of the dependence is influenced by the orientation and density of inherent microcracks. The experimental results also showed that K Ic depended on the material anisotropy. A fracture process was discussed on the basis of the geometry of fractures within fractured specimens visualized by the X-ray computed tomography (CT) method. It was concluded that the dominant factor causing the anisotropy of K Ic is the distribution of grains rather than inherent microcracks in these rocks.

  17. Reactive transport modeling of the interaction between water and a cementitious grout in a fractured rock. Application to ONKALO (Finland)

    International Nuclear Information System (INIS)

    Highlights: → It is planned to seal conductive fractures near a repository with cementitious grout. → Modeling includes simultaneous hydration and leaching of the grout. → Modeling results show a very limited formation of the high-pH plume. → Results are in qualitative agreement with borehole monitoring data. - Abstract: Grouting of water-conducting fractures with low-alkali cement is foreseen for the potential future repository for spent nuclear fuel in Finland (ONKALO). A possible consequence of the interaction between groundwater and grout is the formation of high-pH solutions which will be able to react with the host rock (gneisses) and alter its mineralogy and porosity. A reactive transport modeling study of this possible alteration has been conducted. First, the hydration of the low-alkali cementitious grout has been modeled, using results from the literature as a guide. The hydrated cement is characterized by the absence of portlandite and the presence of a C-S-H gel with a Ca/Si ratio about 0.8 after tens of years (Ca/Si is about 1.7 in Ordinary Portland Cement). Second, calculations have simulated the interaction between flowing water and grout and the formation of an alkalinity plume, which flows beyond the grouted section of the fracture. The calculations include the hydration and simultaneous leaching of the grout through diffusive exchange between the porewater in the grout and the flowing water in the fracture. The formation of an alkaline plume is extremely limited when the low-pH grout is used. Even when using a grout with a lower silica fume content, the extent and magnitude of the alkaline plume is quite minor. These results are in qualitative agreement with monitoring at ONKALO.

  18. Fractured rock modeling in the National Waste Terminal Storage Program: a review of requirements and status

    Energy Technology Data Exchange (ETDEWEB)

    St. John, C.; Krug, A.; Key, S.; Monsees, J.

    1983-05-01

    Generalized computer codes capable of forming the basis for numerical models of fractured rock masses are being used within the NWTS program. Little additional development of these codes is considered justifiable, except in the area of representation of discrete fractures. On the other hand, model preparation requires definition of medium-specific constitutive descriptions and site characteristics and is therefore legitimately conducted by each of the media-oriented projects within the National Waste Terminal Storage program. However, it is essential that a uniform approach to the role of numerical modeling be adopted, including agreement upon the contribution of modeling to the design and licensing process and the need for, and means of, model qualification for particular purposes. This report discusses the role of numerical modeling, reviews the capabilities of several computer codes that are being used to support design or performance assessment, and proposes a framework for future numerical modeling activities within the NWTS program.

  19. Fractured rock modeling in the National Waste Terminal Storage Program: a review of requirements and status

    International Nuclear Information System (INIS)

    Generalized computer codes capable of forming the basis for numerical models of fractured rock masses are being used within the NWTS program. Little additional development of these codes is considered justifiable, except in the area of representation of discrete fractures. On the other hand, model preparation requires definition of medium-specific constitutive descriptions and site characteristics and is therefore legitimately conducted by each of the media-oriented projects within the National Waste Terminal Storage program. However, it is essential that a uniform approach to the role of numerical modeling be adopted, including agreement upon the contribution of modeling to the design and licensing process and the need for, and means of, model qualification for particular purposes. This report discusses the role of numerical modeling, reviews the capabilities of several computer codes that are being used to support design or performance assessment, and proposes a framework for future numerical modeling activities within the NWTS program

  20. Rock mass characterization for tunnels in the Copenhagen limestone

    DEFF Research Database (Denmark)

    Foged, Niels Nielsen; Jakobsen, Lisa; Jackson, Peter;

    2007-01-01

    Tunnels in Copenhagen are drilled through highly anisotropic limestone comprising alternating strongly lithified and less lithified parts. The mass quality of the limestone is usually defined from fracture spacing registered in core samples. The deposit is, however, affected destructively by dril...... by drilling activity yielding a low Rock Quality Designation RQD. In-situ observations of the limestone in excavations or televiewer logs reveal only few natural discontinuities compared to core logging, indicating a very good suitability for tunneling.......Tunnels in Copenhagen are drilled through highly anisotropic limestone comprising alternating strongly lithified and less lithified parts. The mass quality of the limestone is usually defined from fracture spacing registered in core samples. The deposit is, however, affected destructively...

  1. Inference of Fractured Rock Transport Properties by Joint Inversion of Push-Pull and Single-Hole Ground Penetrating Radar Data

    Science.gov (United States)

    Shakas, A.; Linde, N.; Bour, O.; Le Borgne, T.

    2015-12-01

    Flow and transport characterization of fractured rock formations is very challenging and important for a multitude of applications that include groundwater extraction, nuclear waste storage and geothermal energy production. One popular hydrogeological method to study fractured rock is a push-pull test, in which injection and retrieval of a tracer is made at the same depth interval in a borehole. In theory, push-pull tests are not sensitive to changes in the heterogeneity of the tracer flow path since the retrieval at the injection location minimizes advective effects and makes the test more sensitive to time-dependent transport processes. This assumption is limiting in the presence of a natural hydraulic gradient or if non-neutrally buoyant tracers are used, but these limitations can be reduced by monitoring push-pull tests with ground penetrating radar (GPR). We present a methodology for combined modeling and inversion of a series of push-pull tests that we monitored with the single hole ground penetrating radar (GPR) method. For the GPR modeling we use a newly developed approach to simulate the GPR response in fractured rock. We coupled the GPR model to a flow-and-transport simulator that we use to define the electrical properties of the fracture filling. The combined model can cope with heterogeneous fractures of any orientation, aperture and size and allows for the effect of density driven flow (that is strong during the saline tracer tests). We use the combined simulator to create synthetic datasets for both the time-series of the GPR traces at different locations and the tracer breakthrough curves. Since the combined problem is highly non-linear and the inverse solution is ill-posed, we use stochastic inversion techniques to obtain probabilistic estimates of the parameters of interest (fracture length, orientation and aperture distribution) and assess the use of different measures to compare the simulated and experimental data.

  2. Displacement and stress fields around rock fractures opened by irregular overpressure variations

    Directory of Open Access Journals (Sweden)

    Shigekazu eKusumoto

    2014-05-01

    Full Text Available Many rock fractures are entirely driven open by fluids such as ground water, geothermal water, gas, oil, and magma. These are a subset of extension fractures (mode I cracks; e.g., dikes, mineral veins and joints referred to as hydrofractures. Field measurements show that many hydrofractures have great variations in aperture. However, most analytical solutions for fracture displacement and stress fields assume the loading to be either constant or with a linear variation. While these solutions have been widely used, it is clear that a fracture hosted by heterogeneous and anisotropic rock is normally subject to loading that is neither constant nor with a linear variation. Here we present new general solutions for the displacement and stress fields around hydrofractures, modelled as two-dimensional elastic cracks, opened by irregular overpressure variations given by the Fourier cosine series. Each solution has two terms. The first term gives the displacement and stress fields due to the average overpressure acting inside the crack; it is given by the initial term of the Fourier coefficients expressing the overpressure variation. The second term gives the displacement and stress fields caused by the overpressure variation; it is given by general terms of the Fourier coefficients and solved through numerical integration. Our numerical examples show that the crack aperture variation closely reflects the overpressure variation. Also, that the general displacement and stress fields close to the crack follow the overpressure variation but tend to be more uniform far from the crack. The present solutions can be used to estimate the displacement and stress fields around any fluid-driven crack, that is, any hydrofracture, as well as its aperture, provided the variation in overpressure can be described by Fourier series. The solutions add to our understanding of local stresses, displacements, and fluid transport associated with hydrofractures in the crust.

  3. Seismoacoustic emission and electromagnetic radiation of fractured rocks in deep wells

    Science.gov (United States)

    Troyanov, A. K.; D'Yakonov, B. P.; Martyshko, P. S.; Astrakhantsev, Yu. G.; Nachapkin, N. I.; Gavrilov, V. A.; Beloglazova, N. A.

    2011-01-01

    The results of simultaneous measurements in seismoacoustic emission (SAE) and electromagnetic radiation (EMR), carried out with the help of a program-apparatus complex developed at the Institute of Geophysics, Ural Division, Russian Academy of Sciences, are considered. Measurements have been carried out in the wells with varied structures located in Karelia, Yamal-Nenets Autonomous Area, and Kamchatka. It has been shown that intervals of fractured rocks are simultaneously recorded in anomalies of SAE and EMR signals. This fact allows us to detect these zones of high tensosensitivity in a geomedium volume for the purposes of monitoring in geodynamic phenomena in the Earth's crust.

  4. Characterization of fracture toughness of epoxy resin after hygrothermal aging

    KAUST Repository

    Quispe, Gustavo Q.

    2013-07-01

    Characterization of fracture toughness of epoxy resin after hygrothermal ageing Gustavo Quino Quispe The aim of this work is to characterize the e ects of hygrothermal aging in the plain strain fracture toughness of the epoxy system composed by cycloaliphatic epoxy resin and diglycidyl ether of bisphenol-A (DGEBA). For this, after having been under hygrothermal aging in a climatic chamber, epoxy samples were studied using ASTM D5045 fracture toughness test, and micrography and roughness measurements of the fracture surface. It is reported a rapid decrease of GIc and KIc during the rst 2 days. Moreover, a numerical model [13] was used to simulate and see with more detail the water absorption in the aged samples. From that, it was observed the heterogeneous distribution of water. Accordingly, it was proposed that the results should be correlated with the water content at the vicinity of the crack tip. Consequently, it was possible to obtain, by quasi-static simulations, the ideal load-displacement curves of crack propagation in the heterogeneous samples. Finally, another contribution of this work is the study of the fracture surface, that gives a clue of the relationship among the fracture energy, the appearance of microcracks in the fracture surface, and the roughness (Ra).

  5. Radon in a fractured bedrock aquifer: Relationships with rock type and distribution of parent radionuclides

    Energy Technology Data Exchange (ETDEWEB)

    Folger, P.F.; Wanty, R.B.; Day, W.; Frishman, D.; Taylor, T. (Geological Survey, Denver, CO (United States). Denver Federal Center); Poeter, E. (Colorado School of Mines, Golden, CO (United States))

    1992-01-01

    Ground-water samples collected from 35 domestic water wells in the Elk Creek drainage 30 miles southwest of Denver, Colorado, show a strong relationship between dissolved Rn-222 concentration and host-rock lithology. Wells completed in Precambrian Pikes Peak Granite (Ypp) average 11,000 pCi/L, whereas wells completed in Precambrian migmatitic rocks (Xm) average 4,000 pCi/L. Geophysical logs of three boreholes completed in the same rock type (Ypp) show significant differences in natural gamma traces and correspondingly different radon concentrations. One well shows a monotonous gamma response with depth, averaging 500 counts per second (cps); water from this well contains 5,300 pCi/L Rn-222. Water from the second well contains 11,000 pCi/L and the third well contain over 20,000 pCi/L. If Rn-222 parent radionuclides are homogeneously distributed along fracture walls, then Rn-222 concentration should decrease with an increasing water-volume-to-rock surface-area ratio. An inverse relationship between transmissivity and Rn-222 concentration is not observed for these 3 wells. The 2 wells with 5,300 pCi/L and 20,000 pCi/L Rn-222 in water have transmissivities of 26 and 75 gallons per day per foot (gpd/ft), respectively, whereas transmissivity for the well with 11,000 pCi/L is 195 gpd/ft. Single-well pumping tests on 29 other wells belie a systematic correlation between transmissivity and Rn-222 concentration, suggesting that local heterogeneous accumulations of Rn-222 parent radionuclides on fracture walls may strongly affect Rn-222 concentration in these wells.

  6. Radon in a fractured bedrock aquifer: Relationships with rock type and distribution of parent radionuclides

    International Nuclear Information System (INIS)

    Ground-water samples collected from 35 domestic water wells in the Elk Creek drainage 30 miles southwest of Denver, Colorado, show a strong relationship between dissolved Rn-222 concentration and host-rock lithology. Wells completed in Precambrian Pikes Peak Granite (Ypp) average 11,000 pCi/L, whereas wells completed in Precambrian migmatitic rocks (Xm) average 4,000 pCi/L. Geophysical logs of three boreholes completed in the same rock type (Ypp) show significant differences in natural gamma traces and correspondingly different radon concentrations. One well shows a monotonous gamma response with depth, averaging 500 counts per second (cps); water from this well contains 5,300 pCi/L Rn-222. Water from the second well contains 11,000 pCi/L and the third well contain over 20,000 pCi/L. If Rn-222 parent radionuclides are homogeneously distributed along fracture walls, then Rn-222 concentration should decrease with an increasing water-volume-to-rock surface-area ratio. An inverse relationship between transmissivity and Rn-222 concentration is not observed for these 3 wells. The 2 wells with 5,300 pCi/L and 20,000 pCi/L Rn-222 in water have transmissivities of 26 and 75 gallons per day per foot (gpd/ft), respectively, whereas transmissivity for the well with 11,000 pCi/L is 195 gpd/ft. Single-well pumping tests on 29 other wells belie a systematic correlation between transmissivity and Rn-222 concentration, suggesting that local heterogeneous accumulations of Rn-222 parent radionuclides on fracture walls may strongly affect Rn-222 concentration in these wells

  7. Impact of Micro-to Meso-scale Fractures on Sealing Behavior of Argillaceous Cap Rocks For CO2 Sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Evans, James [Utah State Univ., Logan, UT (United States)

    2016-08-01

    This multi-disciplinary project evaluated seal lithologies for the safety and security of long-term geosequestration of CO2. We used integrated studies to provide qualitative risk for potential seal failure; we integrated data sets from outcrop, core, geochemical analysis, rock failure properties from mechanical testing, geophysical wireline log analysis, and geomechanical modeling to understand the effects of lithologic heterogeneity and changing mechanical properties have on the mechanical properties of the seal. The objectives of this study were to characterize cap rock seals using natural field analogs, available drillhole logging data and whole-rock core, geochemical and isotopic analyses. Rock deformation experiments were carried out on collected samples to develop better models of risk estimation for potential cap rock seal failure. We also sampled variably faulted and fractured cap rocks to examine the impacts of mineralization and/or alteration on the mechanical properties. We compared CO2 reacted systems to non-CO2 reacted seal rock types to determine response of each to increased pore fluid pressures and potential for the creation of unintentional hydrofractures at depth.

  8. Mechanism of evolution on winter-time natural convection cooling effect of fractured-rock embankment in permafrost regions

    Institute of Scientific and Technical Information of China (English)

    SUN Binxiang; XU Xuezu; LAI Yuanming; WANG Shuangjie; ZHANG Jinzhao

    2005-01-01

    Mechanism and evolution of the pore-air natural convection cooling effect in fractured-rock embankments in permafrost regions are studied using a numerical representation of the non-dimensional governing equations in variable permeability porous media. The analyses show that winter-time natural convection in fractured-rock embankments begins to occur in the side slope portions and gradually develops from the left and right side slope portions to the middle portion of embankment. The more significant distortion of isotherms from their initial orientations due to heat conduction alone is that the cooling effect of winter-time natural convection on the fractured-rock embankment is stronger. The minimum critical Rayleigh numbers triggering natural convection of the pore-air in the side slope portions and the middle portion of embankment were obtained. The factors of influence on triggering winter-time convection cooling effect in fractured-rock embankments were analyzed.Finally, the assertion that the techniques of the fractured-rock revetment and berm are the effective measures to maintain the heat stability of the roadbed in permafrost regions is theoretically demonstrated.

  9. Experimental study on time-dependent stress and strain of in-plane shear(ModeⅡ) fracture process of rock

    Institute of Scientific and Technical Information of China (English)

    王志; 饶秋华; 谢海峰

    2008-01-01

    Shear-box test with strain measurement was used to study time-dependent stress and strain of in-plane shear(Mode Ⅱ) fracture process of rock and to reveal the mechanism of Mode Ⅱ fracture.Numerical results show that the maximum shear stress τmax at the crack tip is much larger than the maximum tensile stress σ1 and the ratio of τmax/σ1 is about 5,which favors Mode Ⅱ fracture of rock.Test results indicate that the strain-time curve comprises three stages:the linear deformation stage,the micro-cracking stage and the macroscopic crack propagation.The strain in the direction of the original notch plane is negative,due to restraining effect of compressive loading applied to the original notch plane.Both σ1 and τmax are increased as the load increases,but the slope of τmax is larger than that of σ1 and the value of τmax is always larger than that of σ1.Therefore,τmax reaches its limited value at peak load before σ1 and results in Mode Ⅱ fracture of rock.Shear-box(i.e.compression-shear) test becomes a potential standard method for achieving the true Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock.

  10. The Influence of Shale Rock Fracturing Equipment Operation on Atmospheric Air Quality

    Science.gov (United States)

    Bogacki, Marek; Macuda, Jan

    2014-12-01

    The hydraulic fracturing jobs performed on shale rocks are connected with atmospheric emissions of dusts and exhaust gases from high-power motors supplying pump aggregates used for fracturing operations and from other technological devices. The total power of motors driving technological systems depends on the specific character of deposit and well and may range between a dozen to tens of thousands kW. An exemplary set of technological systems used for frac jobs is presented in figure 1. The following substances are emitted to the atmosphere during engine operation, e.g. nitrogen oxides (NOx), sulfur dioxide (SO2), carbon oxide (CO), dust PM10, ammonia, benzo(a)pyrene (B(a)P), benzene, toluene, xylene, formaldehyde, acetaldehyde, acrolein. As a consequence admissible concentrations of these substances in air can be exceeded. The influence of dust and gaseous emissions accompanying shale rock fracturing jobs is addressed in this paper. Model analyses were performed. An exemplary model of a process used for simulating propagation of atmospheric emissions in a specified calculation area (1,150 m × 1,150 m) were based on the analysis of hydraulic fracturing jobs performed in wells in Poland and abroad. For making calculations more actual, the model was located in the Gdańsk area and was ascribed its typical meteorological and orographic parameters. In the center of this area a rig site 150 m x 150 m was distinguished. The emission field was generated by 12 high-power engines supplying pump aggregates, 1680 kW each. The time of work of particular engines was established for 52 hrs (13 frac jobs, each lasting 4 hrs). It was assumed that all engines will operate simultaneously and using 100% of their power. Attention was paid to the correct modelling of the real emission field. Technical parameters of motors and the applied fuels were characterized. Emission indices were worked out by, e.g. U.S. Environmental Protection Agency or European Environment Agency. The

  11. A simplified fracture network model for studying the efficiency of a single well semi open loop heat exchanger in fractured crystalline rock

    Science.gov (United States)

    de La Bernardie, Jérôme; de Dreuzy, Jean-Raynald; Bour, Olivier; Thierion, Charlotte; Ausseur, Jean-Yves; Lesuer, Hervé; Le Borgne, Tanguy

    2016-04-01

    Geothermal energy is a renewable energy source particularly attractive due to associated low greenhouse gas emission rates. Crystalline rocks are in general considered of poor interest for geothermal applications at shallow depths (energy storage at these shallow depths is still remaining very challenging because of the complexity of fractured media. The purpose of this study is to test the possibility of efficient thermal energy storage in shallow fractured rocks with a single well semi open loop heat exchanger (standing column well). For doing so, a simplified numerical model of fractured media is considered with few fractures. Here we present the different steps for building the model and for achieving the sensitivity analysis. First, an analytical and dimensional study on the equations has been achieved to highlight the main parameters that control the optimization of the system. In a second step, multiphysics software COMSOL was used to achieve numerical simulations in a very simplified model of fractured media. The objective was to test the efficiency of such a system to store and recover thermal energy depending on i) the few parameters controlling fracture network geometry (size and number of fractures) and ii) the frequency of cycles used to store and recover thermal energy. The results have then been compared to reference shallow geothermal systems already set up for porous media. Through this study, relationships between structure, heat exchanges and storage may be highlighted.

  12. Measurement system for systematic hydrological characterization of unsaturated fractured welded tuff in a mined underground tunnel.

    Science.gov (United States)

    Cook, P J; Salve, R; Freifeld, B M; Tsang, Y T

    2003-01-01

    A field investigation of unsaturated flow through a lithophysal unit of fractured welded tuff containing lithophysal cavities has been initiated. To characterize flow in this spatially heterogeneous medium, a systematic approach has been developed to perform tests in boreholes drilled at regular intervals in an underground tunnel (drift). The purpose of the testing is to quantify the amounts of water seeping into the drift versus the amount of water moving around the drift when released into boreholes at many equidistant locations along the drift. In this paper, we describe the test equipment system that has been built for this purpose. Because the field-scale measurements--of liquid flow in the unsaturated, fractured rocks--require continuous testing for periods of days to weeks, the control of test equipment has been fully automated, allowing operation with no human presence at the field site. Preliminary results from the first set of tests indicate that, while the effects of evaporation on characterization of hydrological properties of the rock can be significant, these effects can be controlled and quantified. These tests give insight into the role of the cavities as potential storage during the initial transient flow prior to the breakthrough of water at the drift crown, as well as the role of connected fractures that provide the subsequent quasi-steady flow. In addition to the stated purpose of realizing the flow partitioning, the results yield values for the effective porosity in the pathways for liquid flow in the regions tested thus far. PMID:12873008

  13. Electromagnetic Emissions During Rock-fracturing Experiments Inside Magnetic Field Free Space

    Science.gov (United States)

    Wang, H.; Zhou, J.; Zhu, T.; Jin, H.

    2012-12-01

    Abnormal electromagnetic emission (EME) signal is one type of the most important precursors before earthquake, which has been widely observed and recorded before large earthquake, but the physical mechanism underlying the phenomenon is unclear and under controversy. Monitoring the EME signals during rock-fracturing experiments in laboratory is an effective way to study the phenomena and their underlying mechanism. Electromagnetic noise is everywhere because industrial and civilian electrical equipments have been widely used, which make difficulties to the in-lab experiments and field monitoring. To avoid the interference from electromagnetic noise, electromagnetic experiments must be carried out inside shielded space. Magnetic Field Free Space (MFFS) was constructed by Institute of Geophysics, China Earthquake Administration in 1980s. MFFS is a near-spherical polyhedron 'space' with 26 faces and inside diameter about 2.3 m. It is enclosed by 8-layer permalloy 1J85 for shielding magnetic field and 2-layer purified aluminium for shielding electric field. MFFS mainly shields static magnetic field by a factor of 160-4000 for the magnetic signals with the frequencies ranging from 0.01 Hz to 10 Hz. The intensity of magnetic field inside the space is less than 20 nT and its fluctuation is less than 0.3 nT in 90 hours. MFFS can dramatically shield EME signals in the frequency range of EME antennas utilized in our experiments, (several to ~320) kHz, by at least 90%, based on observation. Rock specimens (granite, marble) were fractured by two ways inside MFFS. 1) Cuboid bulk specimens were drilled, filled with static cracking agent, and then dilated from inside until fracture. 2) Cylindrical rock specimens were stressed until fracture by using a non-magnetic rock testing machine with the maximum testing force 300kN. EME, acoustic emission (AE) and strain signals were collected synchronously by the same data acquisitor, Acoustic Emission Workstation made by Physical Acoustics

  14. Study of fractures in Precambrian crystalline rocks using field technique in and around Balarampur, Purulia district, West Bengal, India

    Indian Academy of Sciences (India)

    Monalisa Mitra; Tapas Acharya

    2015-12-01

    Location of recharge zone in Precambrian crystalline rock is still unclear. The present study attempts to perform a detailed analysis of the joints/fractures developed in a Precambrian metamorphic terrain in and around Balarampur in Purulia district of West Bengal, India using bedrock data. The analysis shows that the orientations of major fracture trends are variable along with varying lithological units and structural affinities. The application of lithology-based analysis technique identifies highly predominant fracture frequency and fracture aperture in mica schist and phyllite in the area. This property is not evident in the granite gneiss and epidiorite. The moderate to high fracture permeability value is also associated with the fractures occurring in the shear zone. Mica schist and phyllite associated with the shear zone may represent a permeable recharge zone in the region.

  15. Hot dry rock reservoir characterization and modeling. Progress report, October 1, 1978-September 30, 1979. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Achenbach, J.D.; Bazant, Z.P.; Dundurs, J.; Keer, L.M.; Nemat-Nasser, S.; Mura, T.; Weertman, J.

    1980-02-01

    Resuls of analytical and experimental studies on hydraulic fracturing and on the characterization and modeling of hot dry rock geothermal energy reservoirs are presented. The first four Chapters are concerned with problems of thermal cracking and heat transfer, with fluid flow through large cracks, and with the stable and unstable growth of water-filled cracks under internal pressure and thermal loading. Experiments are reported, which present visually observable hydraulic fractures in transparent materials to demonstrate the interaction between hydraulic fractures and the development of thermal cracks. Seismic detection of hydraulic fractures is discussed, and a method to invert crack-scattering data is presented. Separate abstracts were prepared for each of the six chapters.

  16. Random Neighborhood Graphs as Models of Fracture Networks on Rocks: Structural and Dynamical Analysis

    CERN Document Server

    Estrada, Ernesto

    2016-01-01

    We propose a new model to account for the main structural characteristics of rock fracture networks (RFNs). The model is based on a generalization of the random neighborhood graphs to consider fractures embedded into rectangular spaces. We study a series of 29 real-world RFNs and find the best fit with the random rectangular neighborhood graphs (RRNGs) proposed here. We show that this model captures most of the structural characteristics of the RFNs and allows a distinction between small and more spherical rocks and large and more elongated ones. We use a diffusion equation on the graphs in order to model diffusive processes taking place through the channels of the RFNs. We find a small set of structural parameters that highly correlates with the average diffusion time in the RFNs. In particular, the second smallest eigenvalue of the Laplacian matrix is a good predictor of the average diffusion time on RFNs, showing a Pearson correlation coefficient larger than $0.99$ with the average diffusion time on RFNs. ...

  17. Numerical simulation of gas flow through unsaturated fractured rock at Yucca Mountain, Nevada

    International Nuclear Information System (INIS)

    Numerical analysis is used to identify the physical phenomena associated with barometrically driven gas (air and water vapor) flow through unsaturated fractured rock at Yucca Mountain, Nevada. Results from simple finite difference simulations indicate that for a fractured rock scenario, the maximum velocity of air out of an uncased 10 cm borehole is 0.002 m s-1. An equivalent porous medium (EPM) model was incorporated into a multiphase, multicomponent simulator to test more complex conceptual models. Results indicate that for a typical June day, a diurnal pressure wave propagates about 160 m into the surrounding Tiva Canyon hydrogeologic unit. Dry air that enters the formation evaporates water around the borehole which reduces capillary pressure. Multiphase countercurrent flow develops in the vicinity of the hole; the gas phase flows into the formation while the liquid phase flows toward the borehole. The effect occurs within 0.5 m of the borehole. The amount of water vapor leaving the formation during 1 day is 900 cm3. This is less than 0.1% of the total recharge into the formation, suggesting that the barometric effect may be insignificant in drying the unsaturated zone. However, gas phase velocities out of the borehole (3 m s-1), indicating that observed flow rates from wells along the east flank of Yucca Mountain were able to be simulated with a barometric model

  18. Hydraulic Anisotropy Characterization Using Azimuthal Self Potential Gradient [ASPG]: Results from Pneumatic Fracturing of Tight Clay Soils

    Science.gov (United States)

    Slater, L.; Wishart, D.; Schnell, D.; Hermann, G.

    2008-12-01

    Recent studies have shown that bulk hydraulic anisotropy associated with fractures in fractured rock aquifers can be inferred from Azimuthal Self Potential Gradient (ASPG) measurements. This extremely simple technique involves measuring the self potential gradient as a function of azimuth with a pair of non polarizing electrodes connected to a voltmeter. The electrokinetic effect associated with the flow of fluids within fractures is the source of the ASPG signal. Fracture strike mapping at multiple sites has repeatedly demonstrated the effectiveness of the method at the field scale and indicated that the direction of flow can be determined from the polarity of relatively large ASPG signals. A laboratory study was conducted to determine whether ASPG could also be used to characterize the hydraulic anisotropy associated with the enhancement of permeability and porosity of tight unconsolidated soils (e.g. clays) as a result of pneumatic fracturing, a technique to improve the effectiveness of remediation efforts. Compressed kaolinite sediments were pneumatically fractured following industry procedures. The resulting fracture geometry was quantified from strike analysis of visible fractures combined with strike data from optical borehole televiewer (BHTV) imaging. ASPG measurements were then made during injection of a simulated remedial treatment (electrolyte/dye) under an applied gas pressure. Consistent with previous findings in fractured rock aquifers, ASPG lobes are well correlated with azimuths of high fracture strike density suggesting that the ASPG anisotropy is a proxy measure of hydraulic anisotropy created by the pneumatic fracturing. The magnitude of the ASPG signal scales linearly (linear correlation coefficients > 0.74) with the applied gas pressure gradient for any particular hydraulically-active fracture set and the positive lobe of the ASP anomaly denotes the flow direction within that fracture set. These findings demonstrate that applications of the

  19. Aespoe Hard Rock Laboratory. Analysis of fracture networks based on the integration of structural and hydrogeological observations on different scales

    International Nuclear Information System (INIS)

    Fracture networks at Aespoe have been studied for several rock types exhibiting different degrees of ductile and brittle deformation, as well as on different scales. Mesoscopic fault systems have been characterised and classified in an earlier report, this report focuses mainly on fracture networks derived on smaller scales, but also includes mesoscopic and larger scales. The TRUE-1 block has been selected for detailed structural analysis on a small scale due to the high density of relevant information. In addition to the data obtained from core materials, structural maps, BIP data and the results of hydro tests were synthesised to derive a conceptual structural model. The approach used to derive this conceptual model is based on the integration of deterministic structural evidence, probabilistic information and both upscaling and downscaling of observations and concepts derived on different scales. Twelve fracture networks mapped at different sites and scales and exhibiting various styles of tectonic deformation were analysed for fractal properties and structural and hydraulic interconnectedness. It was shown that these analysed fracture networks are not self-similar. An important result is the structural and hydraulic interconnectedness of fracture networks on all scales in the Aespoe rocks, which is further corroborated by geochemical evidence. Due to the structural and hydraulic interconnectedness of fracture systems on all scales at Aespoe, contaminants from waste canisters placed in tectonically low deformation environments would be transported - after having passed through the engineered barriers -from low-permeability fractures towards higher permeability fractures and may thus eventually reach high-permeability features

  20. Aespoe Hard Rock Laboratory. Analysis of fracture networks based on the integration of structural and hydrogeological observations on different scales

    Energy Technology Data Exchange (ETDEWEB)

    Bossart, P. [Geotechnical Inst. Ltd., Bern (Switzerland); Hermanson, Jan [Golder Associates, Stockholm (Sweden); Mazurek, M. [Univ. of Bern (Switzerland)

    2001-05-01

    Fracture networks at Aespoe have been studied for several rock types exhibiting different degrees of ductile and brittle deformation, as well as on different scales. Mesoscopic fault systems have been characterised and classified in an earlier report, this report focuses mainly on fracture networks derived on smaller scales, but also includes mesoscopic and larger scales. The TRUE-1 block has been selected for detailed structural analysis on a small scale due to the high density of relevant information. In addition to the data obtained from core materials, structural maps, BIP data and the results of hydro tests were synthesised to derive a conceptual structural model. The approach used to derive this conceptual model is based on the integration of deterministic structural evidence, probabilistic information and both upscaling and downscaling of observations and concepts derived on different scales. Twelve fracture networks mapped at different sites and scales and exhibiting various styles of tectonic deformation were analysed for fractal properties and structural and hydraulic interconnectedness. It was shown that these analysed fracture networks are not self-similar. An important result is the structural and hydraulic interconnectedness of fracture networks on all scales in the Aespoe rocks, which is further corroborated by geochemical evidence. Due to the structural and hydraulic interconnectedness of fracture systems on all scales at Aespoe, contaminants from waste canisters placed in tectonically low deformation environments would be transported - after having passed through the engineered barriers -from low-permeability fractures towards higher permeability fractures and may thus eventually reach high-permeability features.

  1. New perspectives on the transition between discrete fracture, fragmentation, and pulverization during brittle failure of rocks

    Science.gov (United States)

    Griffith, W. A.; Ghaffari, H.; Barber, T. J.; Borjas, C.

    2015-12-01

    The motions of Earth's tectonic plates are typically measured in millimeters to tens of centimeters per year, seemingly confirming the generally-held view that tectonic processes are slow, and have been throughout Earth's history. In line with this perspective, the vast majority of laboratory rock mechanics research focused on failure in the brittle regime has been limited to experiments utilizing slow loading rates. On the other hand, many natural processes that pose significant risk for humans (e.g., earthquakes and extraterrestrial impacts), as well as risks associated with human activities (blow-outs, explosions, mining and mine failures, projectile penetration), occur at rates that are hundreds to thousands of times faster than those typically simulated in the laboratory. Little experimental data exists to confirm or calibrate theoretical models explaining the connection between these dramatic events and the pulverized rocks found in fault zones, impacts, or explosions; however the experimental data that does exist is thought-provoking: At the earth's surface, the process of brittle fracture passes through a critical transition in rocks at high strain rates (101-103s-1) between regimes of discrete fracture and distributed fragmentation, accompanied by a dramatic increase in strength. Previous experimental works on this topic have focused on key thresholds (e.g., peak stress, peak strain, average strain rate) that define this transition, but more recent work suggests that this transition is more fundamentally dependent on characteristics (e.g., shape) of the loading pulse and related microcrack dynamics, perhaps explaining why for different lithologies different thresholds more effectively define the pulverization transition. In this presentation we summarize some of our work focused on this transition, including the evolution of individual defects at the microscopic, microsecond scale and the energy budget associated with the brittle fragmentation process as a

  2. Localization and characterization of hydrothermal alteration zones in a geothermal reservoir and their significance for rock mechanics

    OpenAIRE

    Meller, Carola

    2014-01-01

    The present thesis introduces a method to localize hydrothermally altered zones in a crystalline geothermal reservoir. On the basis of synthetic clay content logs, the geomechanical significance of clay zones is demonstrated. It is shown that clay zones reduce the rock strength, thus creating aseismic slips on fractures and affecting the evolution of induced seismicity. The results of the thesis highlight the importance of hydrothermal alteration for hydro-mechanical reservoir characterization.

  3. Mathematical algorithm development and parametric studies with the GEOFRAC three-dimensional stochastic model of natural rock fracture systems

    Science.gov (United States)

    Ivanova, Violeta M.; Sousa, Rita; Murrihy, Brian; Einstein, Herbert H.

    2014-06-01

    This paper presents results from research conducted at MIT during 2010-2012 on modeling of natural rock fracture systems with the GEOFRAC three-dimensional stochastic model. Following a background summary of discrete fracture network models and a brief introduction of GEOFRAC, the paper provides a thorough description of the newly developed mathematical and computer algorithms for fracture intensity, aperture, and intersection representation, which have been implemented in MATLAB. The new methods optimize, in particular, the representation of fracture intensity in terms of cumulative fracture area per unit volume, P32, via the Poisson-Voronoi Tessellation of planes into polygonal fracture shapes. In addition, fracture apertures now can be represented probabilistically or deterministically whereas the newly implemented intersection algorithms allow for computing discrete pathways of interconnected fractures. In conclusion, results from a statistical parametric study, which was conducted with the enhanced GEOFRAC model and the new MATLAB-based Monte Carlo simulation program FRACSIM, demonstrate how fracture intensity, size, and orientations influence fracture connectivity.

  4. Numerical Simulation of the Process of Fracture of Echelon Rock Joints

    Science.gov (United States)

    Sarfarazi, V.; Ghazvinian, A.; Schubert, W.; Blumel, M.; Nejati, H. R.

    2014-07-01

    The effect of joint overlap on the full failure behavior of a rock bridge in the shear-box test was numerically investigated by means of the particle flow code in two dimensions (PFC2D). Initially, the PFC2D was calibrated by use of data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical model's response. Furthermore, validation of the simulated models was cross-checked with the results from direct shear tests performed on non-persistent jointed physical models. By use of numerical direct shear tests, the failure process was visually observed and the failure patterns were seen to be in reasonable accordance with experimental results. Discrete element simulations demonstrated that macro shear fractures in rock bridges are because of microscopic tensile breakage of a large number of bonded discs. The failure pattern is mostly affected by joint overlap whereas the shear strength is closely related to the failure pattern. The results show that non-overlapping joints lost their loading capacity when nearly 50 % of total cracks developed within the rock bridge whereas the overlapping joints lost their loading capacity as soon as cracks initiated from the joint walls. Furthermore, progressive failure or stable crack growth was seen to develop for non-overlapped joints whereas brittle failure or unstable crack growth was seen to develop in overlapped joints.

  5. Solute transport through fractured rock: Radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain

    Science.gov (United States)

    Mahmoudzadeh, Batoul; Liu, Longcheng; Moreno, Luis; Neretnieks, Ivars

    2016-05-01

    The paper presents a model development to derive a semi-analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry. The model accounts for advection through the channel, radial diffusion into the adjacent heterogeneous rock matrix comprising different geological layers, adsorption on both the channel surface, and the geological layers of the rock matrix and radioactive decay chain. Not only an arbitrary-length decay chain, but also as many number of the rock matrix layers with different properties as observed in the field can be handled. The solution, which is analytical in the Laplace domain, is transformed back to the time domain numerically e.g. by use of de Hoog algorithm. The solution is verified against experimental data and analytical solutions of limiting cases of solute transport through porous media. More importantly, the relative importance and contribution of different processes on solute transport retardation in fractured rocks are investigated by simulating several cases of varying complexity. The simulation results are compared with those obtained from rectangular model with linear matrix diffusion. It is found that the impact of channel geometry on breakthrough curves increases markedly as the transport distance along the flow channel and away into the rock matrix increase. The effect of geometry is more pronounced for transport of a decay chain when the rock matrix consists of a porous altered layer.

  6. Effects of crustal stresses on fluid transport in fractured rock: Case studies from northeastern and southwestern USA

    Science.gov (United States)

    Morin, R.H.; Savage, W.Z.

    2003-01-01

    The link between stress and hydrologic properties was examined at two sites that are distinguished by different rock types and different stress states. This investigation is based upon the analysis and interpretation of geophysical logs obtained in water wells at the two locations. At the northeast site (Newark Basin), the hydrologic characteristics of sedimentary rocks are dependent upon the relationship to the current regional stress field of two primary types of orthogonal features that serve as preferential pathways for fluid flow. Subhorizontal bedding-plane partings are highly transmissive near the surface and delineate transversely isotropic fluid flow at shallow depths. With increasing depth, the subhorizontal planes become less dominant and steeply dipping fractures become more influential hydrologically. These high-angle features define anisotropic flow pathways that are preferentially oriented along strike. At the southwest site (west Texas), extrusive rocks are subjected to topographically modified tectonic and gravitational stresses that vary spatially within a valley setting. The attendant changes in stress invariants cause fracture connectivity within the rock mass to systematically increase with depth along the valley flanks, but to remain relatively low in the central valley. The degree of fracture connectivity predicted within this valley configuration is consistent with variations in transmissivity determined at several well locations. In each of these cases, the idealized understanding of the hydrologic system is enhanced by considering the effects of regional and local stresses that act upon the fractured-rock aquifer.

  7. Numerical Simulation of P-Wave Propagation in Rock Mass with Granular Material-Filled Fractures Using Hybrid Continuum-Discrete Element Method

    Science.gov (United States)

    Gui, Y. L.; Zhao, Z. Y.; Zhou, H. Y.; Wu, W.

    2016-10-01

    In this paper, a cohesive fracture model is applied to model P-wave propagation through fractured rock mass using hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC). First, a cohesive fracture model together with the background of UDEC is presented. The cohesive fracture model considers progressive failure of rock fracture rather than an abrupt damage through simultaneously taking into account the elastic, plastic and damage mechanisms as well as a modified failure function. Then, a series of laboratory tests from the literature on P-wave propagation through rock mass containing single fracture and two parallel fractures are introduced and the numerical models used to simulate these laboratory tests are described. After that, all the laboratory tests are simulated and presented. The results show that the proposed model, particularly the cohesive fracture model, can capture very well the wave propagation characteristics in rock mass with non-welded and welded fractures with and without filling materials. In the meantime, in order to identify the significance of fracture on wave propagation, filling materials with different particle sizes and the fracture thickness are discussed. Both factors are found to be crucial for wave attenuation. The simulations also show that the frequency of transmission wave is lowered after propagating through fractures. In addition, the developed numerical scheme is applied to two-dimensional wave propagation in the rock mass.

  8. Blended head analyses to reduce uncertainty in packer testing in fractured-rock boreholes

    Science.gov (United States)

    Quinn, Patryk; Parker, Beth L.; Cherry, John A.

    2016-02-01

    Open boreholes in fractured rock often cross-connect fractures with differing hydraulic head and the head differences between these fractures cause vertical flow in the water column. This cross-connection has potential to bias transmissivity ( T) values obtained from straddle packer tests. This study demonstrates how measurements of the blended head in the open-hole segments above and below the straddle-packer test interval can be used to correct packer tests for cross-connection effects. A pressure response observed in the open-hole segment above and/or below the packers isolating a test interval during a hydraulic test indicates short-circuiting of water from the injection interval through the vertically connected fracture network to the open-hole segments, resulting in the overestimation of T. A method is presented using blended head concepts to minimize this error using a trial-and-error procedure to determine the short-circuiting flow rate to account for the head conditions in the open-hole segments during each hydraulic test. Observed differences between the measured head and the calculated blended head in the open-hole segments above and below the test interval are attributed to cross-connection effects around the 1-m-long packers. The head and corrected T values determined from packer tests are used to estimate the flow in and out of the open hole at each of the intervals tested for assessing the cross-connection effects under open borehole conditions. Understanding open-hole flow dynamics gives insight about the potential for vertical cross connection of chemical constituents caused by the open hole.

  9. A coupled thermo-poro-mechanical finite element analysis of fractured porous rocks using a cohesive interface element

    Science.gov (United States)

    Wang, W.; Regueiro, R. A.

    2014-12-01

    The coupling between multiphase flow, heat transfer, and poromechanics in fractured geomaterials has aroused great interest in the areas of geomechanics, geoenvironmental engineering, and petroleum engineering. Relevant applications include nuclear waste repositories, geological sequestration of CO2, geothermal systems, and exploitation of shale gas reservoirs. The paper presents a fully coupled thermo-poro-mechanical (TPM) cohesive interface element (CIE) model, which can represent fluid and heat flow along and across the fracture, and shear/normal deformation of the fracture surfaces. The proposed model is then applied to analyze two popular geological engineering problems using the finite element method (FEM) with a small strain formulation. The first application is the fracturing process in organic-rich shale due to heating. In the finite element analysis, multiple horizontal microcracks parallel to the bedding plane are assumed to preexist in the porous source rock, and are represented by coupled TPM cohesive interface elements. The porous bulk rock is assumed to be homogeneous, isotropic (for the time being, with transverse isotropy a natural extension), and linearly elastic. The excess pore fluid pressure, which mainly causes the development of the fractures, is actually induced by the rapid decomposition of organic matter during heating according to the literature. However, the involved complex chemical reaction process is beyond the scope of the paper, and is therefore substituted by a fluid injection process within the cracks under room temperature (25C) and high temperature (400C) in the paper. We investigate the fracture propagation due to pore fluid pressure increase and the development of fracture-induced permeability. The second application is a nuclear waste repository in a partially saturated fractured rock. Multiphase transport of moisture and heat, thermally-induced stress, as well as the change of fracture apertures are investigated due to short

  10. Permeability of intact and fractured rocks in Krafla geothermal reservoir, Iceland

    Science.gov (United States)

    Eggertsson, Gudjon; Lavallée, Yan; Markusson, Sigurdur

    2016-04-01

    .5 - 1.5 MPa (at an average pore pressure of 1.25 MPa). We present the results of permeability-porosity relationships for each rock as a function of confining pressure and discuss the permeability of the fluid reservoir as a function of effective pressure (i.e., = confining pressure - pore pressure) to constrain fluid flow during different pressurisation events. Complementary Brazilian tests were also performed to induce a fracture in the samples and the permeability of these fractured rocks will be measured to describe the role of macrofractures in controlling fluid flow. Permeability measurements at high temperature (up to ~500 C) will be performed on selected rocks. The aim of these experiments will be to discover the relative role of the various lithologies on the permeability of the reservoir, which will inform us how to improve the geothermal productivity of the proposed deep well through thermo-mechanical stimulations.

  11. A composite material model for investigation of micro-fracture mechanism of brittle rock subjected to uniaxial compression

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A two-phase model of rock was proposed in order to investigate the mechanism of brittle fracture due to uniaxial compression, in which rock was considered to be a composite material consisting of hard grains and colloids. The stress state in colloid region near grains was calculated using Finite Element Metnod ( FEM). The influence of the tensile stresses on the crack initiation and failure process of brittle rock subjected to uniaxial compression was investigated by numerical experiments. The FE results show that tensile stresses are induced easily in the neighboring area of hard grains with the maximum value near grain boundaries. The distribution of tensile stresses depends on the relative position of hard grains. The cracks initiated just near the boundary area of hare grains, which was governed by tensile stress. These results dearly reveal the micro-fracture mechanism of brittle rock loaded by uniaxial compression. It can be concluded that the failure mode of brittle rock under uniaxial compression is still tensile fracture from the point view of microstructure. However,since the wide colloid region is still under compressive stress state, further propagation of boundary, cracks through this region obviously needs more external load, thus causing the uniaxial compressive strength of rock much higher than its tensile strength obtained via Brazilian (splitting) experiment.

  12. Permeability and tracer test with using laboratory hydrology testing system on mass transport in fractured rock. Results until 2001 years

    Energy Technology Data Exchange (ETDEWEB)

    Yoshino, Naoto [Japan Nuclear Cycle Development Inst., Tokai, Ibaraki (Japan). Tokai Works; Sato, Hisashi [Inspection Development Co. Ltd., Tokai, Ibaraki (Japan)

    2002-03-01

    We have carried out the permeability tests and tracer tests using LABROCK (LABoratory test on mass transport in fractured ROCK) which was developed in order to get basic information relevant to the HLW geological disposal program. We have been focusing on the parallel single fracture and natural single fracture. Much knowledge about permeability and tracer transport was acquired as a result of examinations. This report summarize these knowledge. In future, we will measure the aperture of natural single fracture. If we will be able to develop the model of natural fracture based on measured aperture distribution and to explain permeability and tracer transport character described in this report, this research will play an important role in the HLW geological disposal program. (author)

  13. MODELING OF HYDRAULIC FRACTURING PRESSURE IN RESERVOIR ROCK FOR AN OIL SAND RESERVOIR IN SOUTH WEST OF IRAN

    Directory of Open Access Journals (Sweden)

    Masoomi R.

    2016-04-01

    Full Text Available Fracture geometry depends on stresses and rock properties in hydraulic fracturing operation. Poisson’s ratio imports directly in the calculations related to formation stresses. The most important reason for limiting fracture height is the natural stresses contrast resulting from the differences with Poisson ratios. Without this difference, fracture would have largely uncontrolled height. The goal of this study is mathematical investigation of the effect of Poisson’s ratio on the formation stresses that is necessary to select value of breakdown pressure in hydraulic fracturing operation. In this article, a mathematical model has been coded using “MATLAB” software for prediction of stresses in the various layers. This designed program is able to present both digital and graphical output results for different values of Poisson’s ratio. At the end, stresses exerted on the different layers of the several real oil reservoirs have simulated and breakdown pressures have determined

  14. Checking a Conceptual Model for Groundwater Flow in the Fractured Rock at Äspö, Sweden

    Science.gov (United States)

    Kröhn, K. P.

    2015-12-01

    The underground Hard Rock Laboratory (HRL) at Äspö, Sweden, is located in granitic rock and dedicated to investigations concerning deep geological disposal of radioactive waste. Several in-situ experiments have been performed in the HRL, among them the recent Buffer-Rock Interaction Experiment (BRIE) and, on a much larger scale, the long-term Prototype Repository (PR) experiment.Interpretation of such experiments requires a profound understanding of the groundwater flow system. Often assumed is a conceptual model where the so-called "intact rock" is interspersed with stochastically distributed fractures. It is also a common assumption, though, that fractures in granite exist on all length-scales implying that the hydraulically relevant rock porosity is basically made up of micro fractures. The conceptual approach of GRS' groundwater flow code d3f thus appeared to be fitting where large fractures are represented discretely by lower-dimensional features while the remaining set of smaller fractures - also called "background fractures" - is assumed to act like an additional homogeneous continuum besides what is believed to be the undisturbed matrix. This approach was applied to a hydraulic model of the BRIE in a cube-like domain of 40 m side length including drifts, boreholes and three intersecting large fractures. According to observations at the underground rock laboratories Stripa and the HRL a narrow zone of reduced permeability - called "skin" - was additionally arranged around all geotechnical openings. Calibration of the model resulted in a considerable increase of matrix permeability due to adding the effect of the background fractures. To check the validity of this approach the calibrated data for the BRIE were applied to a model for the PR which is also located in the HRL but at quite some distance. The related brick-shaped model domain has a size of 200 m x 150 m x 50 m. Fitting the calculated outflow from the rock to the measured outflow distribution

  15. Field assessment of the use of borehole pressure transients to measure the permeability of fractured rock masses

    International Nuclear Information System (INIS)

    A field experiment to evaluate the transient pressure pulse technique as a method of determining the in-situ hydraulic conductivity of low permeability fractured rock was made. The experiment attempted to define: the radius of influence of a pressure pulse-test in fractured rock and the correlation between pressure-pulse tests and steady-state flow tests performed in five boreholes drilled in fractured granite. Twenty-five test intervals, 2 to 3 m in length, were isolated in the boreholes, using air-inflated packers. During pressure pulse and steady-state tests, pressures were monitored in both the test and observation cavities. Rock-mass conductivities were calculated from steady-state test results and were found to range from less than 10-11 to 10-7 cm/sec. However, there was no consistent correlation between the steady-state conductivity and the pressure pulse decay characteristics of individual intervals. These conflicting test results can be attributed to the following factors: differences in volumes of rock affected by the test techniques; effects of equipment configuration and compliance; and complexity of the fracture network. Although the steady-state flow tests indicate that hydraulic connections exist between most of the test cavities, no pressure responses were noted in the observation cavities (located at least 0.3 m from the test cavities) during the pulse tests. This does not mean, however, that the pressure-pulse radius of influence is <0.3 m, because the observation cavities were too large (about 7 liters). The lack of correlation between steady-state conductivities and the corresponding pressure pulse decay times does not permit use of existing single-fracture type curves to analyze pulse tests performed in multiple-fracture intervals. Subsequent work should focus on the detailed interpretation of field results with particular reference to the effects of the fracture system at the test site

  16. Image-based modeling of the flow transition from a Berea rock matrix to a propped fracture

    Science.gov (United States)

    Sanematsu, P.; Willson, C. S.; Thompson, K. E.

    2013-12-01

    In the past decade, new technologies and advances in horizontal hydraulic fracturing to extract oil and gas from tight rocks have raised questions regarding the physics of the flow and transport processes that occur during production. Many of the multi-dimensional details of flow from the rock matrix into the fracture and within the proppant-filled fracture are still unknown, which leads to unreliable well production estimations. In this work, we use x-ray computed micro tomography (XCT) to image 30/60 CarboEconoprop light weight ceramic proppant packed between berea sandstone cores (6 mm in diameter and ~2 mm in height) under 4000 psi (~28 MPa) loading stress. Image processing and segmentation of the 6 micron voxel resolution tomography dataset into solid and void space involved filtering with anisotropic diffusion (AD), segmentation using an indicator kriging (IK) algorithm, and removal of noise using a remove islands and holes program. Physically-representative pore network structures were generated from the XCT images, and a representative elementary volume (REV) was analyzed using both permeability and effective porosity convergence. Boundary conditions were introduced to mimic the flow patterns that occur when fluid moves from the matrix into the proppant-filled fracture and then downstream within the proppant-filled fracture. A smaller domain, containing Berea and proppants close to the interface, was meshed using an in-house unstructured meshing algorithm that allows different levels of refinement. Although most of this domain contains proppants, the Berea section accounted for the majority of the elements due to mesh refinement in this region of smaller pores. A finite element method (FEM) Stokes flow model was used to provide more detailed insights on the flow transition from rock matrix to fracture. Results using different pressure gradients are used to describe the flow transition from the Berea rock matrix to proppant-filled fracture.

  17. Development of evaluation methodology for effects of cementitious grouting materials on groundwater and rock in fractured media

    International Nuclear Information System (INIS)

    Leachates from cementitious grouting materials used for reducing water inflow are hyperalkaline and chemically reactive with the engineered barriers and host rock for geological disposal of high-level radioactive waste. Evaluation methods for long-term alteration of the fractured rock have been developed since the extent of chemical modification may influence the transport and retardation properties of radionuclides in the far field. The present study shows the current status of the development of the methodology (i.e., procedure, models, and simulation codes) for evaluating the effects of cementitious grouting materials on groundwater and rock. (author)

  18. Analytical solutions for groundwater flow with arbitrary dimensionality and a finite well radius in fractured rock

    Science.gov (United States)

    Rehbinder, G.

    2010-03-01

    The generalized radial flow model describes mathematically nonsteady flow of arbitrary dimensionality from a source in a porous medium. Closed solutions of the corresponding equation have hitherto been considered as impractical except for one simple special case. Two closed solutions of the generalized radial flow equation, corresponding to given head in or given discharge from the source have been derived. The noninteger dimensionality is the only parameter in the problem. The solutions become not valid if the time tends to infinity, such as for 1-D and 2-D flows. The influence of a possible noninteger dimensionality has attracted interest in connection with the flow of groundwater in fractured rock, particularly around a repository for nuclear waste or in connection with grouting. In contrast to numerical solutions, the closed solutions offer simple means for evaluation of field tests.

  19. Water pressure resistance of liquid-type grout in rock fracture

    International Nuclear Information System (INIS)

    We have conducted several tests of durable liquid-type grout (colloidal silica) to investigate basic characteristics of liquid-type grout for geological disposal of high-level waste (HLW). Liquid-type grout is inferior to cement grout in the resistance strength against high water pressure. Laboratory tests were performed to measure resistance strength of liquid-type grout in rock fracture, which was modelized by a parallel plane made of iron and acryl plate. As tests results, the shear resistance of the liquid-type grout could be expected about 3% of shear strength derived from triaxial compression tests. Based on test results, we conducted simple calculation for required grout injection area. (author)

  20. An integrated methodology for sub-surface fracture characterization using microseismic data: A case study at the NW Geysers

    Science.gov (United States)

    Aminzadeh, Fred; Tafti, Tayeb A.; Maity, Debotyam

    2013-04-01

    Geothermal and unconventional hydrocarbon reservoirs are often characterized by low permeability and porosity. So, they are difficult to produce and require stimulation techniques, such as thermal shear deactivation and hydraulic fracturing. Fractures provide porosity for fluid storage and permeability for fluid movement and play an important role in production from this kind of reservoirs. Hence, characterization of fractures has become a vitally important consideration in every aspect of exploration, development and production so as to provide additional energy resources for the world. During the injection or production of fluid, induced seismicity (micro-seismic events) can be caused by reactivated shears created fractures or the natural fractures in shear zones and faults. Monitoring these events can help visualize fracture growth during injection stimulation. Although the locations of microseismic events can be a useful characterization tool and have been used by many authors, we go beyond these locations to characterize fractures more reliably. Tomographic inversion, fuzzy clustering, and shear wave splitting are three methods that can be applied to microseismic data to obtain reliable characteristics about fractured areas. In this article, we show how each method can help us in the characterization process. In addition, we demonstrate how they can be integrated with each other or with other data for a more holistic approach. The knowledge gained might be used to optimize drilling targets or stimulation jobs to reduce costs and maximize production. Some of the concepts discussed in this paper are general in nature, and may be more applicable to unconventional hydrocarbon reservoirs than the metamorphic and igneous reservoir rocks at The Geysers geothermal field.

  1. Fluid-Rock Characterization and Interactions in NMR Well Logging

    Energy Technology Data Exchange (ETDEWEB)

    Hirasaki, George J.; Mohanty, Kishore K.

    2003-02-10

    The objective of this project was to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity.

  2. Fluid-Rock Characterization and Interactions in NMR Well Logging

    Energy Technology Data Exchange (ETDEWEB)

    Hirasaki, George J.; Mohanty, Kishore K.

    2003-02-10

    The objective of this project was to characterize the fluid properties and fluid-rock interactions which are needed for formation evaluation by NMR well logging. NMR well logging is finding wide use in formation evaluation. The formation parameters commonly estimated were porosity, permeability, and capillary bound water. Special cases include estimation of oil viscosity, residual oil saturation, location of oil/water contact, and interpretation on whether the hydrocarbon is oil or gas.

  3. Flow and transport in unsaturated fractured rock: Effects of multiscale heterogeneity of hydrogeologic properties

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Quanlin; Liu, Hui-Hai; Bodvarsson, Gudmundur S.; Oldenburg, Curtis M.

    2002-07-09

    The heterogeneity of hydrogeologic properties at different scales may have different effects on flow and transport processes in a subsurface system. A model for the unsaturated zone of Yucca Mountain, Nevada, is developed to represent complex heterogeneity at two different scales: (1) layer scale corresponding to geologic layering and (2) local scale. The layer-scale hydrogeologic properties are obtained using inverse modeling, based on the available measurements collected from the Yucca Mountain site. Calibration results show a significant lateral and vertical variability in matrix and fracture properties. Hydrogeologic property distributions in a two-dimensional, vertical cross section of the site are generated by combining the average layer-scale matrix and fracture properties with local-scale perturbations generated using a stochastic simulation method. The unsaturated water flow and conservative (nonsorbing) tracer transport through the cross section are simulated for different sets of matrix and fracture property fields. Comparison of simulation results indicates that the local-scale heterogeneity of matrix and fracture properties has a considerable effect on unsaturated flow processes, leading to fast flow paths in fractures and the matrix. These paths shorten the travel time of a conservative tracer from the source (repository) horizon in the unsaturated zone to the water table for small fractions of total released tracer mass. As a result, the local-scale heterogeneity also has a noticeable effect on global tracer transport processes, characterized by an average breakthrough curve at the water table, especially at the early arrival time of tracer mass. However, the effect is not significant at the later time after 20 percent tracer mass reaches the water table. The simulation results also verify that matrix diffusion plays an important role in overall solute transport processes in the unsaturated zone at Yucca Mountain.

  4. Advanced Reservoir Characterization and Evaluation of C02 Gravity Drainage in the Naturally Fractured Sprayberry Trend Area

    Energy Technology Data Exchange (ETDEWEB)

    David S. Schechter

    1998-04-30

    The objective is to assess the economic feasibility of CO2 flooding of the naturally fractured Straberry Trend Area in west Texas. Research is being conducted in the extensive characterization of the reservoirs, the experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, the analytical and numerical simulation of Spraberry reservoirs, and the experimental investigations on CO2 gravity drainage in Spraberry whole cores.

  5. Statistical analysis of surface lineaments and fractures for characterizing naturally fractured reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Genliang; George, S.A.; Lindsey, R.P.

    1997-08-01

    Thirty-six sets of surface lineaments and fractures mapped from satellite images and/or aerial photos from parts of the Mid-continent and Colorado Plateau regions were collected, digitized, and statistically analyzed in order to obtain the probability distribution functions of natural fractures for characterizing naturally fractured reservoirs. The orientations and lengths of the surface linear features were calculated using the digitized coordinates of the two end points of each individual linear feature. The spacing data of the surface linear features within an individual set were, obtained using a new analytical sampling technique. Statistical analyses were then performed to find the best-fit probability distribution functions for the orientation, length, and spacing of each data set. Twenty-five hypothesized probability distribution functions were used to fit each data set. A chi-square goodness-of-fit test was used to rank the significance of each fit. A distribution which provides the lowest chi-square goodness-of-fit value was considered the best-fit distribution. The orientations of surface linear features were best-fitted by triangular, normal, or logistic distributions; the lengths were best-fitted by PearsonVI, PearsonV, lognormal2, or extreme-value distributions; and the spacing data were best-fitted by lognormal2, PearsonVI, or lognormal distributions. These probability functions can be used to stochastically characterize naturally fractured reservoirs.

  6. A laboratory acoustic emission experiment and numerical simulation of rock fracture driven by a high-pressure fluid source

    Directory of Open Access Journals (Sweden)

    Xinglin Lei

    2016-02-01

    Full Text Available In order to improve our understanding of rock fracture and fault instability driven by high-pressure fluid sources, the authors carried out rock fracture tests using granite under a confining pressure of 80 MPa with fluid injection in the laboratory. Furthermore, we tested a number of numerical models using the FLAC3D modeling software to find the best model to represent the experimental results. The high-speed multichannel acoustic emission (AE waveform recording system used in this study made it possible to examine the total fracture process through detailed monitoring of AE hypocenters and seismic velocity. The experimental results show that injecting high-pressure oil into the rock sample can induce AE activity at very low stress levels and can dramatically reduce the strength of the rock. The results of the numerical simulations show that major experimental results, including the strength, the temporal and spatial patterns of the AE events, and the role of the fluid can be represented fairly well by a model involving (1 randomly distributed defect elements to model pre-existing cracks, (2 random modification of rock properties to represent inhomogeneity introduced by different mineral grains, and (3 macroscopic inhomogeneity. Our study, which incorporates laboratory experiments and numerical simulations, indicates that such an approach is helpful in finding a better model not only for simulating experimental results but also for upscaling purposes.

  7. Distinct element modelling of fracture plan control in continuum and jointed rock mass in presplitting method of surface mining

    Institute of Scientific and Technical Information of China (English)

    Sharafisafa Mansour; Aliabadian Zeinab; Alizadeh Rezvan; Mortazavi Ali

    2014-01-01

    Controlled blasting techniques are used to control overbreak and to aid in the stability of the remaining rock formation. Presplitting is one of the most common methods which is used in many open pit mining and surface blast design. The purpose of presplitting is to form a fracture plane across which the radial cracks from the production blast cannot travel. The purpose of this study is to investigate of effect of pre-splitting on the generation of a smooth wall in continuum and jointed rock mass. The 2D distinct element code was used to simulate the presplitting in a rock slope. The blast load history as a function of time was applied to the inner wall of each blasthole. Important parameters that were considered in the analysis were stress tensor and fracturing pattern. The blast loading magnitude and blasthole spacing and jointing pattern were found to be very significant in the final results.

  8. Interpretation of tracer tests performed in fractured rock of the Lange Bramke basin, Germany

    Science.gov (United States)

    Maloszewski, Piotr; Herrmann, Andreas; Zuber, Andrzej

    Two multitracer tests performed in one of the major cross-fault zones of the Lange Bramke basin (Harz Mountains, Germany) confirm the dominant role of the fault zone in groundwater flow and solute transport. Tracers having different coefficients of molecular diffusion (deuterium, bromide, uranine, and eosine) yielded breakthrough curves that can only be explained by a model that couples the advective-dispersive transport in the fractures with the molecular diffusion exchange in the matrix. For the scale of the tests (maximum distance of 225m), an approximation was used in which the influence of adjacent fractures is neglected. That model yielded nearly the same rock and transport parameters for each tracer, which means that the single-fracture approximation is acceptable and that matrix diffusion plays an important role. The hydraulic conductivity of the fault zone obtained from the tracer tests is about 1.5×10-2m/s, whereas the regional hydraulic conductivity of the fractured rock mass is about 3×10-7m/s, as estimated from the tritium age and the matrix porosity of about 2%. These values show that the hydraulic conductivity along the fault is several orders of magnitude larger than that of the remaining fractured part of the aquifer, which confirms the dominant role of the fault zones as collectors of water and conductors of fast flow. Résumé Deux multitraçages ont été réalisés dans l'une des zones principales de failles du bassin de Lange Bramke (massif du Harz, Allemagne); les résultats confirment le rôle prédominant de la zone de failles pour l'écoulement souterrain et le transport de soluté. Les traceurs, possédant des coefficients de diffusion différents (deutérium, bromure, uranine et éosine), ont fourni des courbes de restitution qui ne peuvent être expliquées que par un modèle qui associe un transport advectif-dispersif dans les fractures à un échange par diffusion moléculaire dans la matrice. A l'échelle des expériences (distance

  9. Interpretation of tracer tests performed in fractured rock of the Lange Bramke basin, Germany

    Science.gov (United States)

    Maloszewski, Piotr; Herrmann, Andreas; Zuber, Andrzej

    Two multitracer tests performed in one of the major cross-fault zones of the Lange Bramke basin (Harz Mountains, Germany) confirm the dominant role of the fault zone in groundwater flow and solute transport. Tracers having different coefficients of molecular diffusion (deuterium, bromide, uranine, and eosine) yielded breakthrough curves that can only be explained by a model that couples the advective-dispersive transport in the fractures with the molecular diffusion exchange in the matrix. For the scale of the tests (maximum distance of 225m), an approximation was used in which the influence of adjacent fractures is neglected. That model yielded nearly the same rock and transport parameters for each tracer, which means that the single-fracture approximation is acceptable and that matrix diffusion plays an important role. The hydraulic conductivity of the fault zone obtained from the tracer tests is about 1.5×10-2m/s, whereas the regional hydraulic conductivity of the fractured rock mass is about 3×10-7m/s, as estimated from the tritium age and the matrix porosity of about 2%. These values show that the hydraulic conductivity along the fault is several orders of magnitude larger than that of the remaining fractured part of the aquifer, which confirms the dominant role of the fault zones as collectors of water and conductors of fast flow. Résumé Deux multitraçages ont été réalisés dans l'une des zones principales de failles du bassin de Lange Bramke (massif du Harz, Allemagne); les résultats confirment le rôle prédominant de la zone de failles pour l'écoulement souterrain et le transport de soluté. Les traceurs, possédant des coefficients de diffusion différents (deutérium, bromure, uranine et éosine), ont fourni des courbes de restitution qui ne peuvent être expliquées que par un modèle qui associe un transport advectif-dispersif dans les fractures à un échange par diffusion moléculaire dans la matrice. A l'échelle des expériences (distance

  10. An Experimental Investigation into Failure and Localization Phenomena in the Extension to Shear Fracture Transition in Rock

    Science.gov (United States)

    Choens, R. C., II; Chester, F. M.; Bauer, S. J.; Flint, G. M.

    2014-12-01

    Fluid-pressure assisted fracturing can produce mesh and other large, interconnected and complex networks consisting of both extension and shear fractures in various metamorphic, magmatic and tectonic systems. Presently, rock failure criteria for tensile and low-mean compressive stress conditions is poorly defined, although there is accumulating evidence that the transition from extension to shear fracture with increasing mean stress is continuous. We report on the results of experiments designed to document failure criteria, fracture mode, and localization phenomena for several rock types (sandstone, limestone, chalk and marble). Experiments were conducted in triaxial extension using a necked (dogbone) geometry to achieve mixed tension and compression stress states with local component-strain measurements in the failure region. The failure envelope for all rock types is similar, but are poorly described using Griffith or modified Griffith (Coulomb or other) failure criteria. Notably, the mode of fracture changes systematically from pure extension to shear with increase in compressive mean stress and display a continuous change in fracture orientation with respect to principal stress axes. Differential stress and inelastic strain show a systematic increase with increasing mean stress, whereas the axial stress decreases before increasing with increasing mean stress. The stress and strain data are used to analyze elastic and plastic strains leading to failure and compare the experimental results to predictions for localization using constitutive models incorporating on bifurcation theory. Although models are able to describe the stability behavior and onset of localization qualitatively, the models are unable to predict fracture type or orientation. Constitutive models using single or multiple yield surfaces are unable to predict the experimental results, reflecting the difficulty in capturing the changing micromechanisms from extension to shear failure. Sandia

  11. Summary of Radionuclide Reactive Transport Experiments in Fractured Tuff and Carbonate Rocks from Yucca Flat, Nevada Test Site

    Energy Technology Data Exchange (ETDEWEB)

    Zavarin, M; Roberts, S; Reimus, P; Johnson, M

    2006-10-11

    , Mercury, Nevada. Readers are referred to the original reports ''Radionuclide Transport in Tuff and Carbonate Fractures from Yucca Flat, Nevada Test Site'' (Zavarin et al., 2005) and ''Radionuclide Sorption and Transport in Fractured Rocks of Yucca Flat, Nevada Test Site'' (Ware et al., 2005) for specific details not covered in this summary report.

  12. Numerical Investigation of Dynamic Rock Fracture Toughness Determination Using a Semi-Circular Bend Specimen in Split Hopkinson Pressure Bar Testing

    Science.gov (United States)

    Xu, Y.; Dai, F.; Xu, N. W.; Zhao, T.

    2016-03-01

    The International Society for Rock Mechanics (ISRM) has suggested a notched semi-circular bend technique in split Hopkinson pressure bar (SHPB) testing to determine the dynamic mode I fracture toughness of rock. Due to the transient nature of dynamic loading and limited experimental techniques, the dynamic fracture process associated with energy partitions remains far from being fully understood. In this study, the dynamic fracturing of the notched semi-circular bend rock specimen in SHPB testing is numerically simulated for the first time by the discrete element method (DEM) and evaluated in both microlevel and energy points of view. The results confirm the validity of this DEM model to reproduce the dynamic fracturing and the feasibility to simultaneously measure key dynamic rock fracture parameters, including initiation fracture toughness, fracture energy, and propagation fracture toughness. In particular, the force equilibrium of the specimen can be effectively achieved by virtue of a ramped incident pulse, and the fracture onset in the vicinity of the crack tip is found to synchronize with the peak force, both of which guarantee the quasistatic data reduction method employed to determine the dynamic fracture toughness. Moreover, the energy partition analysis indicates that simplifications, including friction energy neglect, can cause an overestimation of the propagation fracture toughness, especially under a higher loading rate.

  13. Numerical simulations of water flow and contaminants transport near mining wastes disposed in a fractured rock mass

    Institute of Scientific and Technical Information of China (English)

    Ben Abdelghani Farouk; Aubertin Michel; Simon Richard; Therrien René

    2015-01-01

    A numerical tool, called Hydro-Geosphere, was used to simulate unsaturated water flow and contami-nants migration around an open pit filled with mining wastes. Numerical simulations had been carried out to assess the influence of various factors on water flow and solute transport in and around the surface openings including recharge, properties of the waste material and presence of fractures in the surround-ing rock mass. The effect of the regional hydraulic gradient was also investigated. The analyses were con-ducted by simulating various 2D cases using experimentally obtained material properties and controlled boundary conditions. The effects of the hydrogeological properties of the filling material (i.e., water reten-tion curve and hydraulic conductivity function), fracture network characteristics and conductivity of the joints were assessed. The results illustrate that fractures control water flow and contaminants transport around the waste disposal area. A fracture network can desaturate the system and improve the regional gradient effect.

  14. Structural characterization of Turtle Mountain anticline (Alberta, Canada) and impact on rock slope failure

    Science.gov (United States)

    Humair, Florian; Pedrazzini, Andrea; Epard, Jean-Luc; Froese, Corey R.; Jaboyedoff, Michel

    2013-10-01

    This paper proposes a structural investigation of the Turtle Mountain anticline (Alberta, Canada) to better understand the role of the different tectonic features on the development of both local and large scale rock slope instabilities occurring in Turtle Mountain. The study area is investigated by combining remote methods with detailed field surveys. In particular, the benefit of Terrestrial Laser Scanning for ductile and brittle tectonic structure interpretations is illustrated. The proposed tectonic interpretation allows the characterization of the fracturing pattern, the fold geometry and the role of these tectonic features in rock slope instability development. Ten discontinuity sets are identified in the study area, their local variations permitting the differentiation of the study zone into 20 homogenous structural domains. The anticline is described as an eastern verging fold that displays considerable geometry differences along its axis and developed by both flexural slip and tangential longitudinal strain folding mechanisms. Moreover, the origins of the discontinuity sets are determined according to the tectonic phases affecting the region (pre-folding, folding, post-folding). The localization and interpretation of kinematics of the different instabilities revealed the importance of considering the discrete brittle planes of weakness, which largely control the kinematic release of the local instabilities, and also the rock mass damage induced by large tectonic structures (fold hinge, thrust).

  15. Multi-scale characterization of rock mass discontinuities and rock slope geometry using terrestrial remote sensing techniques

    Science.gov (United States)

    Sturzenegger, Matthieu

    Terrestrial remote sensing techniques including both digital photogrammetry and laser scanning, represent useful complements to conventional field mapping and rock mass discontinuity characterization. Several studies have highlighted practical advantages at close-range (design projects has grown substantially over recent years. As these techniques are increasingly applied by geologists and geological engineers, it is important that their use be properly evaluated. Furthermore, guidelines to optimize their application are required in a similar manner to standardization of conventional discontinuity mapping techniques. An important thesis objective is to develop recommendations for optimal applications of terrestrial remote sensing techniques for discontinuity characterization, based on a quantitative evaluation of various registration approaches, sampling bias and extended manual mapping of 3D digital models. It is shown that simple registration networks can provide adequate measurement of discontinuity geometry for engineering purposes. The bias associated with remote sensing mapping is described. The advantages of these techniques over conventional mapping are demonstrated, including reliable discontinuity orientation measurements. Persistence can be precisely quantified instead of approximately estimated, resulting in a new class for extremely persistent discontinuities being suggested. Secondary roughness and curvature can also be considered at larger scales. The techniques are suitable for the definition of discontinuity sets, and the estimation of both trace intensity and block size/shape, if sampling bias is correctly accounted for. A new type of sampling window, suitable for the incorporation of remote sensing data into discrete fracture network models is presented. Another significant thesis objective is the extension of terrestrial digital photogrammetric methods to greater distances (> 1 km), using f = 200-400 mm lenses. This has required a careful

  16. Coupling analysis of unsteady seepage and stress fields in discrete fractures network of rock mass in dam foundation

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The drag force of water flow through single fracture and the coupling characteristics of seepage and stress in single fracture surface are analyzed,and a three dimensional model of coupled unsteady seepage and stress fields is proposed.This model is used to the analysis of foundation rock mass of a high dam.If the coupling effects are considered,the changes of boundary heads have less influence on the inner head of rock mass,and the strong permeability of main fractures appears.If the coupling effects are not considered,the fractures distribution affects the inner head more greatly.When the upstream water head declines,the inner head of dam foundation slightly declines and the hydraulic gradient distribution becomes smoother.A bigger upstream water level declining velocity has a stronger lag effect,meanwhile the values of stress components change more greatly.Therefore the upstream water level declining velocity directly affects the stability of rock mass in dam foundation and we should take into account the above factors to make sure the safety of the dam during reservoir level fluctuation period.

  17. Influence of confining stress on fracture characteristics and cutting efficiency of TBM cutters conducted on soft and hard rock

    Institute of Scientific and Technical Information of China (English)

    LIU Jing-shuo; CAO Ping; LIU Jie; JIANG Zhe

    2015-01-01

    Combined with numerical simulation, the influence of confining stress on cutting process, fracture conditions and cutting efficiencies of soft and hard rock has been conducted on the triaxial testing machine (TRW-3000) designed and manufactured in Central South University (China). Results are obtained by performing analysis on the fracture scopes of cement and granite plates, the characteristics of cutting force in cutting processes and the cutting efficiency. Firstly, the increase of latitude fracture scope and the decrease of longitude fracture scope are both more notable in the tests conducted on cement plates subjected to the increasing confining stresses; secondly, the increase tendency of peak penetration forces obtained from tests conducted on granite plates is more obvious, however, the increase tendencies of average penetration forces achieved from cement and granite plates are close to each other; thirdly, the cutting efficiency could be improved by increasing the spacing between cutters when the confining stress which acts on soft and hard rock increases in a certain degree, and the cutting efficiency of soft rock is more sensitive to the varying confining stresses.

  18. Interpretation of seismic data from hydraulic fracturing experiments at the Fenton Hill, New Mexico, hot dry rock geothermal site

    Energy Technology Data Exchange (ETDEWEB)

    Aki, K.; Fehler, M.; Aamodt, R.L.; Albright, J.N.; Potter, R.M.; Pearson, C.M.; Tester, J.W.

    1982-02-10

    An attempt was made to synthesize the results of active seismic experiments carried out by the Los Alamos National Laboratory's Hot Dry Rock Project staff for determining the geometrical and physical properties of the fracture system produced by hydraulic fracturing in a hot, low-permeability rock. Interpretation of data from several reflection, transmission, and attenuation experiments using seismic probes in the frequency range from a few hundred to more than 10/sup 4/ Hz led us to postulate the existence of a highly complex fracture system consisting of major discrete vertical cracks intersected by several inclined joints which are surrounded by a large volume of rock containing small-scale cracks. We found an interesting coincidence between the mean square fluctuation of P arrival time and Q/sup -1/ of coda waves. Both are increased by nearly the same amount (35approx.40%) when fluid pressure in the reservoir is increased. Another coincidence is the scale length of the inhomogeneity of roughly 3 m obtained from the frequency dependence of attenuation and also from the spatial variation of P arrival time. These results suggest that the seismic attenuation in the fractured region is caused primarily by scattering.

  19. Geochemical Interaction of Middle Bakken Reservoir Rock and CO2 during CO2-Based Fracturing

    Science.gov (United States)

    Nicot, J. P.; Lu, J.; Mickler, P. J.; Ribeiro, L. H.; Darvari, R.

    2015-12-01

    This study was conducted to investigate the effects of geochemical interactions when CO2 is used to create the fractures necessary to produce hydrocarbons from low-permeability Middle Bakken sandstone. The primary objectives are to: (1) identify and understand the geochemical reactions related to CO2-based fracturing, and (2) assess potential changes of reservoir property. Three autoclave experiments were conducted at reservoir conditions exposing middle Bakken core fragments to supercritical CO2 (sc-CO2) only and to CO2-saturated synthetic brine. Ion-milled core samples were examined before and after the reaction experiments using scanning electron microscope, which enabled us to image the reaction surface in extreme details and unambiguously identify mineral dissolution and precipitation. The most significant changes in the reacted rock samples exposed to the CO2-saturated brine is dissolution of the carbonate minerals, particularly calcite which displays severely corrosion. Dolomite grains were corroded to a lesser degree. Quartz and feldspars remained intact and some pyrite framboids underwent slight dissolution. Additionally, small amount of calcite precipitation took place as indicated by numerous small calcite crystals formed at the reaction surface and in the pores. The aqueous solution composition changes confirm these petrographic observations with increase in Ca and Mg and associated minor elements and very slight increase in Fe and sulfate. When exposed to sc-CO2 only, changes observed include etching of calcite grain surface and precipitation of salt crystals (halite and anhydrite) due to evaporation of residual pore water into the sc-CO2 phase. Dolomite and feldspars remained intact and pyrite grains were slightly altered. Mercury intrusion capillary pressure tests on reacted and unreacted samples shows an increase in porosity when an aqueous phase is present but no overall porosity change caused by sc-CO2. It also suggests an increase in permeability

  20. Fluid-Rock Characterization and Interactions in NMR Well Logging

    Energy Technology Data Exchange (ETDEWEB)

    Hirasaki, George J.; Mohanty, Kishore, K.

    2001-07-13

    The objective of this project is to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. This is the first annual progress report submitted to the DOE. It reports on the work completed during the reporting period even if it may have started before this period. This project is a partnership between Professor George J. Hirasaki at Rice University and Professor Kishore Mohanty at University of Houston. In addition to the DOE, this project is supported by a consortium of oil companies and service companies. The fluid properties characterization has emphasized the departure of live oils from correlations based on dead oils. Also, asphaltic components can result in a difference between the T1 and T2 relaxation time distributions as well as reduce the hydrogen index. The fluid rock characterizations that are reported here are the effects of wettability and internal magnetic field gradients. A pore reconstruction method ha s been developed to recreate three-dimensional porous media from two-dimensional images that reproduce some of their key statistical properties. A Monte Carlo simulation technique has been developed to calculate the magnetization decay in fluid saturated porous media given their pore structure.

  1. Computational characterization of fracture healing under reduced gravity loading conditions.

    Science.gov (United States)

    Gadomski, Benjamin C; Lerner, Zachary F; Browning, Raymond C; Easley, Jeremiah T; Palmer, Ross H; Puttlitz, Christian M

    2016-07-01

    The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1206-1215, 2016. PMID:26704186

  2. Contaminant transport in fracture networks with heterogeneous rock matrices. The Picnic code

    Energy Technology Data Exchange (ETDEWEB)

    Barten, Werner [Paul Scherrer Inst., CH-5232 Villigen PSI (Switzerland); Robinson, Peter C. [QuantiSci Limited, Henley-on-Thames (United Kingdom)

    2001-02-01

    different timescales. To account for one-dimensional matrix diffusion into homogeneous planar or cylindrical rock layers, analytical relations in the Laplace domain are used. To deal with one-dimensional or two-dimensional matrix diffusion into heterogeneous rock matrices, a finite-element method is embedded. The capability of the code for handling two-dimensional matrix diffusion is - to our knowledge - unique in fracture network modelling. To ensure the reliability of the code, which merges methods from graph theory, Laplace transformation, finite-element methods, analytical and algebraic transformations and a convolution to calculate complex radionuclide transport processes over a large and diverse application range, implementation of the code and careful verification have been alternated for iterative improvement and especially the elimination of bugs. The internal mathematical structure of PICNIC forms the basis of the verification strategy. The code is verified in a series of seven steps with increasing complexity of the rock matrix. Calculations for single nuclides and nuclide decay chains are carefully tested and analysed for radionuclide transport in single legs, in pathways and in networks. Different sources and boundary conditions are considered. Quantitative estimates of the accuracy of the code are derived from comparisons with analytical solutions, cross-comparisons with other codes and different types of self -consistency tests, including extended testing of different refinements of the embedded finite- element method for different rock matrix geometries. The geosphere barrier efficiency is a good single indicator of the code accuracy. Application ranges with reduced accuracy of the code are also considered. For one-dimensional matrix diffusion into homogeneous and heterogeneous rock matrices, cross-comparisons with other codes are performed. For two-dimensional matrix diffusion, however, no code for cross-comparison is available. Consequently, the

  3. Contaminant transport in fracture networks with heterogeneous rock matrices. The Picnic code

    International Nuclear Information System (INIS)

    timescales. To account for one-dimensional matrix diffusion into homogeneous planar or cylindrical rock layers, analytical relations in the Laplace domain are used. To deal with one-dimensional or two-dimensional matrix diffusion into heterogeneous rock matrices, a finite-element method is embedded. The capability of the code for handling two-dimensional matrix diffusion is - to our knowledge - unique in fracture network modelling. To ensure the reliability of the code, which merges methods from graph theory, Laplace transformation, finite-element methods, analytical and algebraic transformations and a convolution to calculate complex radionuclide transport processes over a large and diverse application range, implementation of the code and careful verification have been alternated for iterative improvement and especially the elimination of bugs. The internal mathematical structure of PICNIC forms the basis of the verification strategy. The code is verified in a series of seven steps with increasing complexity of the rock matrix. Calculations for single nuclides and nuclide decay chains are carefully tested and analysed for radionuclide transport in single legs, in pathways and in networks. Different sources and boundary conditions are considered. Quantitative estimates of the accuracy of the code are derived from comparisons with analytical solutions, cross-comparisons with other codes and different types of self -consistency tests, including extended testing of different refinements of the embedded finite- element method for different rock matrix geometries. The geosphere barrier efficiency is a good single indicator of the code accuracy. Application ranges with reduced accuracy of the code are also considered. For one-dimensional matrix diffusion into homogeneous and heterogeneous rock matrices, cross-comparisons with other codes are performed. For two-dimensional matrix diffusion, however, no code for cross-comparison is available. Consequently, the verification for

  4. Some Open Issues on Rockfall Hazard Analysis in Fractured Rock Mass: Problems and Prospects

    Science.gov (United States)

    Ferrero, Anna Maria; Migliazza, Maria Rita; Pirulli, Marina; Umili, Gessica

    2016-09-01

    Risk is part of every sector of engineering design. It is a consequence of the uncertainties connected with the cognitive boundaries and with the natural variability of the relevant variables. In soil and rock engineering, in particular, uncertainties are linked to geometrical and mechanical aspects and the model used for the problem schematization. While the uncertainties due to the cognitive gaps could be filled by improving the quality of numerical codes and measuring instruments, nothing can be done to remove the randomness of natural variables, except defining their variability with stochastic approaches. Probabilistic analyses represent a useful tool to run parametric analyses and to identify the more significant aspects of a given phenomenon: They can be used for a rational quantification and mitigation of risk. The connection between the cognitive level and the probability of failure is at the base of the determination of hazard, which is often quantified through the assignment of safety factors. But these factors suffer from conceptual limits, which can be only overcome by adopting mathematical techniques with sound bases, not so used up to now (Einstein et al. in rock mechanics in civil and environmental engineering, CRC Press, London, 3-13, 2010; Brown in J Rock Mech Geotech Eng 4(3):193-204, 2012). The present paper describes the problems and the more reliable techniques used to quantify the uncertainties that characterize the large number of parameters that are involved in rock slope hazard assessment through a real case specifically related to rockfall. Limits of the existing approaches and future developments of the research are also provided.

  5. Hydrogeologic controls on episodic H2 release from precambrian fractured rocks--energy for deep subsurface life on earth and mars.

    Science.gov (United States)

    Sherwood Lollar, B; Voglesonger, K; Lin, L-H; Lacrampe-Couloume, G; Telling, J; Abrajano, T A; Onstott, T C; Pratt, L M

    2007-12-01

    Dissolved H(2) concentrations up to the mM range and H(2) levels up to 9-58% by volume in the free gas phase are reported for groundwaters at sites in the Precambrian shields of Canada and Finland. Along with previously reported dissolved H(2) concentrations up to 7.4 mM for groundwaters from the Witwatersrand Basin, South Africa, these findings indicate that deep Precambrian Shield fracture waters contain some of the highest levels of dissolved H(2) ever reported and represent a potentially important energy-rich environment for subsurface microbial life. The delta (2)H isotope signatures of H(2) gas from Canada, Finland, and South Africa are consistent with a range of H(2)-producing water-rock reactions, depending on the geologic setting, which include both serpentinization and radiolysis. In Canada and Finland, several of the sites are in Archean greenstone belts characterized by ultramafic rocks that have under-gone serpentinization and may be ancient analogues for serpentinite-hosted gases recently reported at the Lost City Hydrothermal Field and other hydrothermal seafloor deposits. The hydrogeologically isolated nature of these fracture-controlled groundwater systems provides a mechanism whereby the products of water-rock interaction accumulate over geologic timescales, which produces correlations between high H(2) levels, abiogenic hydrocarbon signatures, and the high salinities and highly altered delta (18)O and delta (2)H values of these groundwaters. A conceptual model is presented that demonstrates how periodic opening of fractures and resultant mixing control the distribution and supply of H(2) and support a microbial community of H(2)-utilizing sulfate reducers and methanogens.

  6. Geologic characterization of fractures as an aid to hydrologic modeling of the SCV block at the Stripa mine

    International Nuclear Information System (INIS)

    A series of hydrologic tests have been conducted at the Stripa research mine in Sweden to develop hydrologic characterization techniques for rock masses in which fractures form the primary flow paths. The structural studies reported here were conducted to aid in the hydrologic examination of a cubic block of granite with dimensions of 150 m on a side. This block (the SCV block) is located between the 310- and 460-m depth levels at the Stripa mine. This report describes and interprets the fracture system geology at Stripa as revealed in drift exposures, checks the interpretive model against borehole records and discusses the hydrologic implication of the model, and examines the likely effects of stress redistribution around a drift (the Validation drift) on inflow to the drift along a prominent fracture zone. (72 refs.) (au)

  7. Building confidence in radionuclide transport models for fractured rock: the Nagra/JNC radionuclide retardation programme

    International Nuclear Information System (INIS)

    The joint Nagra/JNC Radionuclide Retardation Programme has now been ongoing for 15 years with the main aim of direct testing of radionuclide transport models in as realistic a manner as possible. A large programme of field, laboratory and natural analogue studies has been carried out at the Grimsel Test Site in the central Swiss Alps and the Kamaishi In Situ Test Site in north-east Japan. The understanding and modelling of both the processes and the structures influencing radionuclide transport/retardation in fractured host rocks have matured as has the experimental technology, which has contributed to develop confidence in the applicability of the underlying research models in a repository performance assessment. In this paper, the successes and set-backs of this programme are discussed as is the general approach to the thorough testing of the process models and of model assumptions. In addition, a set of key findings is presented, involving discussions on the enhancement of confidence through the program. Copyright (2001) Material Research Society

  8. Inverse model of fully coupled fluid flow and stress in fractured rock masses

    Science.gov (United States)

    Wang, Y.; Rutqvist, J.

    2008-12-01

    In order to reflect the real behavior of the seepage field and deformation field during the environment change and construction process£¬the basic equations and FEM methods for fully coupled analysis of fluid flow and stress are developed£¬based on the assumptions of small deformation and incompressible water flow in complicated fractured rock masses. Both the equivalent continuum media model and the discrete media model are adopted. And the modified initial flow method is used to deal with the free surface of unconfined seepage. Due to the difficulty in determining the parameters of water flow field, stress field and their coupling relations, an inverse model is presented for the fully coupled problem in which both the data of water head and displacement are taken into consideration. Objective function is defined based on sensitivity analysis of parameters, and the relative values of water head, displacement on parameters are adopted in the establishment of objective function. A hybrid genetic algorithm is proposed as optimization method. The probability of crossover and mutation is determined according to chromosome fitness and a concept of self- adaptive probability is given. In addition, simplex method is also applied to increase the ability of local search, the operation of accelerated cycle is used in order to decrease optimization time.

  9. Anaerobic microbial processes in a petroleum plume in fractured rock, northern Canada

    International Nuclear Information System (INIS)

    Fuel plumes are among the most common groundwater pollution problems at polluted sites throughout Canada, including the Canadian Shield region. However, the microbial processes that occur under cold climate conditions in fuel-contaminated groundwater are poorly understood. This study focused on evidence for anaerobic microbial processes in fuel plumes in groundwater at a Canadian Shield site in the Northwest Territories, within a zone mapped as having extensive discontinuous permafrost. In particular, the study examined redox-sensitive species in the groundwater, specifically iron, manganese, sulfate and nitrate. The data reported in the paper were based on a sampling program conducted in September 2007. The data showed strong evidence that anaerobic microorganisms are active in fuel-contaminated groundwater in fractured rock at the study site. The microbial processes include the reduction of electron acceptors, notably sulfate, ferric iron, manganese and possibly nitrate. It is possible that such anaerobic processes play an important role in the biodegradation of dissolved petroleum hydrocarbons in the groundwater at this site. However, it was concluded that additional analysis is needed in order to infer rates of these processes in the groundwater and to understand the relationship of these processes to degradation of the fuel plume. 14 refs., 8 figs.

  10. Fracture Characterization of Sandwich Face/Core Interfaces

    DEFF Research Database (Denmark)

    Manca, Marcello

    Sandwich structures are nowadays widely used in lightweight structural applications because oftheir superior stiffness/weight and strength/weight ratios compared with traditional metallic as well as monolithic structures made from composite materials. A major limiting factor of wider application...... of load transfer between the faces and the core layer is lost, the debonds are considered as primary damage initiators. Under fatigue loading the debonds may evolve into cracks that cause a reduction in structural performance and consequent failure. At present most structural design is based on “life-time...... such result it is important to devise new experimental and analytical techniques to establish the multi-mode fracture characteristics of sandwich plate structures and accordingly develop methods to inhibit defect propagation. This thesis deals with characterization of fracture between face and core...

  11. Fluid-Rock Characterization and Interactions in NMR Well Logging

    Energy Technology Data Exchange (ETDEWEB)

    George J. Hirasaki; Kishore K. Mohanty

    2005-09-05

    The objective of this report is to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity. Oil based drilling fluids can have an adverse effect on NMR well logging if it alters the wettability of the formation. The effect of various surfactants on wettability and surface relaxivity are evaluated for silica sand. The relation between the relaxation time and diffusivity distinguishes the response of brine, oil, and gas in a NMR well log. A new NMR pulse sequence in the presence of a field gradient and a new inversion technique enables the T{sub 2} and diffusivity distributions to be displayed as a two-dimensional map. The objectives of pore morphology and rock characterization are to identify vug connectivity by using X-ray CT scan, and to improve NMR permeability correlation. Improved estimation of permeability from NMR response is possible by using estimated tortuosity as a parameter to interpolate between two existing permeability models.

  12. Rockfall source characterization at high rock walls in complex geological settings by photogrammetry, structural analysis and DFN techniques

    Science.gov (United States)

    Agliardi, Federico; Riva, Federico; Galletti, Laura; Zanchi, Andrea; Crosta, Giovanni B.

    2016-04-01

    Rockfall quantitative risk analysis in areas impended by high, subvertical cliffs remains a challenge, due to the difficult definition of potential rockfall sources, event magnitude scenarios and related probabilities. For this reasons, rockfall analyses traditionally focus on modelling the runout component of rockfall processes, whereas rock-fall source identification, mapping and characterization (block size distribution and susceptibility) are over-simplified in most practical applications, especially when structurally complex rock masses are involved. We integrated field and remote survey and rock mass modelling techniques to characterize rock masses and detect rockfall source in complex geo-structural settings. We focused on a test site located at Valmadrera, near Lecco (Southern Alps, Italy), where cliffs up to 600 m high impend on a narrow strip of Lake Como shore. The massive carbonates forming the cliff (Dolomia Principale Fm), normally characterized by brittle structural associations due to their high strength and stiffness, are here involved in an ENE-trending, S-verging kilometre-scale syncline. Brittle mechanisms associated to folding strongly controlled the nature of discontinuities (bedding slip, strike-slip faults, tensile fractures) and their attributes (spacing and size), as well as the spatial variability of bedding attitude and fracture intensity, with individual block sizes up to 15 m3. We carried out a high-resolution terrestrial photogrammetric survey from distances ranging from 1500 m (11 camera stations from the opposite lake shore, 265 pictures) to 150 m (28 camera stations along N-S directed boat routes, 200 pictures), using RTK GNSS measurements for camera station geo-referencing. Data processing by Structure-from-Motion techniques resulted in detailed long-range (1500 m) and medium-range (150 to 800 m) point clouds covering the entire slope with maximum surface point densities exceeding 50 pts/m2. Point clouds allowed a detailed

  13. Characterization of fracture processes by continuum and discrete modelling

    Science.gov (United States)

    Kaliske, M.; Dal, H.; Fleischhauer, R.; Jenkel, C.; Netzker, C.

    2012-09-01

    A large number of methods to describe fracture mechanical features of structures on basis of computational algorithms have been developed in the past due to the importance of the topic. In this paper, current and promising numerical approaches for the characterization of fracture processes are presented. A fracture phenomenon can either be depicted by a continuum formulation or a discrete notch. Thus, starting point of the description is a micromechanically motivated formulation for the development of a local failure situation. A current, generalized method without any restriction to material modelling and loading situation in order to describe an existing crack in a structure is available through the material force approach. One possible strategy to simulate arbitrary crack growth is based on an adaptive implementation of cohesive elements in combination with the standard discretization of the body. In this case, crack growth criteria and the determination of the crack propagation direction in combination with the modification of the finite element mesh are required. The nonlinear structural behaviour of a fibre reinforced composite material is based on the heterogeneous microstructure. A two-scale simulation is therefore an appropriate and effective way to take into account the scale differences of macroscopic structures with microscopic elements. In addition, fracture mechanical structural properties are far from being sharp and deterministic. Moreover, a wide range of uncertainties influence the ultimate load bearing behaviour. Therefore, it is evident that the deterministic modelling has to be expanded by a characterization of the uncertainty in order to achieve a reliable and realistic simulation result. The employed methods are illustrated by numerical examples.

  14. Structural analysis of the Jebel Fadeloun anticline, Tunisia: Impact of fractures and faults on the petrophysical properties of carbonate rocks

    OpenAIRE

    Kjelkenes, Fredrik Sebastian

    2015-01-01

    Recognizing the structure, evolution and fluid flow within the earth's crust is a critical issue for both academic and applied geoscience. This study presents structural analysis of an anticline, which aim is to elucidate the (1) structure and evolution of the fold, as well as the associated faults and fractures, (2) to better investigate how tectonics have impacted the microstructural character of the host rock, and (3) to discuss possible implications for petro...

  15. Experimental and Numerical Studies on Development of Fracture Process Zone (FPZ) in Rocks under Cyclic and Static Loadings

    Science.gov (United States)

    Ghamgosar, M.; Erarslan, N.

    2016-03-01

    The development of fracture process zones (FPZ) in the Cracked Chevron Notched Brazilian Disc (CCNBD) monsonite and Brisbane tuff specimens was investigated to evaluate the mechanical behaviour of brittle rocks under static and various cyclic loadings. An FPZ is a region that involves different types of damage around the pre-existing and/or stress-induced crack tips in engineering materials. This highly damaged area includes micro- and meso-cracks, which emerge prior to the main fracture growth or extension and ultimately coalescence to macrofractures, leading to the failure. The experiments and numerical simulations were designed for this study to investigate the following features of FPZ in rocks: (1) ligament connections and (2) microcracking and its coalescence in FPZ. A Computed Tomography (CT) scan technique was also used to investigate the FPZ behaviour in selected rock specimens. The CT scan results showed that the fracturing velocity is entirely dependent on the appropriate amount of fracture energy absorbed in rock specimens due to the change of frequency and amplitudes of the dynamic loading. Extended Finite Element Method (XFEM) was used to compute the displacements, tensile stress distribution and plastic energy dissipation around the propagating crack tip in FPZ. One of the most important observations, the shape of FPZ and its extension around the crack tip, was made using numerical and experimental results, which supported the CT scan results. When the static rupture and the cyclic rupture were compared, the main differences are twofold: (1) the number of fragments produced is much greater under cyclic loading than under static loading, and (2) intergranular cracks are formed due to particle breakage under cyclic loading compared with smooth and bright cracks along cleavage planes under static loading.

  16. A Modified TSD Specimen for Fracture Toughness CharacterizationFracture Mechanics Analysis and Design

    DEFF Research Database (Denmark)

    Berggreen, Christian; Carlsson, Leif A.

    2010-01-01

    The tilted sandwich debond (TSD) specimen has been recognized as a viable candidate for characterization of the face/core fracture resistance. Analysis, however, shows that the range of phase angles that can be realized by altering the tilt angle and other parameters of the test is quite limited....... A method to extend the range of mode-mixities of the TSD specimen is to introduce a larger amount of transverse shear by reinforcing the loaded upper face with a stiff metal plate. Analysis shows that this method extends the range of phase angles to a practically useful range. Guidelines on selection...

  17. Coal Rock Fracture and its Detection Technology%煤岩破裂及其探测技术

    Institute of Scientific and Technical Information of China (English)

    白庆升; 史先影; 王磊

    2009-01-01

    After seeing previous articles in a wide range of basic research results,this text expatiates the mechanisms of coal rock fracture and its dynamic disasters, and introduces the basic principles of sound wave, acoustic emission, electromagnetic radiation, geoelectric and infrared temperature in detecting coal rock fracture,then summarizes the detection techniques of coal rock fracture's application in laboratory and actual production, and analyses their strengths and weaknesses as well as the need to improve or perfect.%在广泛参阅前人研究成果的基础上,阐述了煤岩破裂及其动力灾害的机理,介绍了声波、声发射、电磁辐射、地电和红外温度等技术在煤岩破裂探测方面的基本原理.总结了煤岩破裂探测技术在实验室及实际生产中的应用,分析了它们的优缺点以及需要改进或完善的方面.

  18. Rock fracture as a precursor to lava dome eruptions at Mount St Helens from June 1980 to October 1986

    Science.gov (United States)

    Smith, R.; Kilburn, C. R. J.; Sammonds, P. R.

    2007-04-01

    Following its plinian eruption on 18 May 1980, Mount St Helens (Washington State, USA) entered a period of intermittent lava-dome extrusion until 1986. Renewed extrusion was frequently preceded by accelerating rates of seismicity, with more precursory seismicity observed prior to eruptions later in the sequence. Here the failure forecasting method (FFM) is used to investigate changes in the observed rate of volcano tectonic (VT) seismicity. The analysis indicates that: (1) all VT crises resulted in an eruption within 3 weeks (usually less than 10 days), (2) the majority of eruptions had VT precursors, and (3) patterns of precursory seismicity showed fluctuations about the ideal model trend. Thus, although these seismic events could be used to warn of an impending eruption, specific forecasts were subject to an uncertainty of weeks or more. It is proposed that: (1) increased seismicity prior to later eruptions is a result of a larger and more solidified dome acting as a greater impediment to magma ascent; (2) the consistency of seismic swarms resulting in an eruption indicates that stresses high enough to initiate fracturing in the country rock and lava dome carapace were only achieved once the approach to an eruption had already begun; and (3) discrepancies between models of accelerating rock fracture and the observed seismicity may arise due to a significant amount of the rocks deforming through ductile mechanisms rather than seismogenic fracture.

  19. Transport and attenuation of carboxylate-modified latex microspheres in fractured rock laboratory and field tracer tests

    Science.gov (United States)

    Becker, M.W.; Reimus, P.W.; Vilks, P.

    1999-01-01

    Understanding colloid transport in ground water is essential to assessing the migration of colloid-size contaminants, the facilitation of dissolved contaminant transport by colloids, in situ bioremediation, and the health risks of pathogen contamination in drinking water wells. Much has been learned through laboratory and field-scale colloid tracer tests, but progress has been hampered by a lack of consistent tracer testing methodology at different scales and fluid velocities. This paper presents laboratory and field tracer tests in fractured rock that use the same type of colloid tracer over an almost three orders-of-magnitude range in scale and fluid velocity. Fluorescently-dyed carboxylate-modified latex (CML) microspheres (0.19 to 0.98 ??m diameter) were used as tracers in (1) a naturally fractured tuff sample, (2) a large block of naturally fractured granite, (3) a fractured granite field site, and (4) another fractured granite/schist field site. In all cases, the mean transport time of the microspheres was shorter than the solutes, regardless of detection limit. In all but the smallest scale test, only a fraction of the injected microsphere mass was recovered, with the smaller microspheres being recovered to a greater extent than the larger microspheres. Using existing theory, we hypothesize that the observed microsphere early arrival was due to volume exclusion and attenuation was due to aggregation and/or settling during transport. In most tests, microspheres were detected using flow cytometry, which proved to be an excellent method of analysis. CML microspheres appear to be useful tracers for fractured rock in forced gradient and short-term natural gradient tests, but longer residence times may result in small microsphere recoveries.Understanding colloid transport in ground water is essential to assessing the migration of colloid-size contaminants, the facilitation of dissolved contaminant transport by colloids, in situ bioremediation, and the health risks

  20. Theoretical relation between water flow rate in a vertical fracture and rock temperature in the surrounding massif

    CERN Document Server

    Maréchal, Jean-Christophe

    2010-01-01

    A steady-state analytical solution is given describing the temperature distribution in a homogeneous massif perturbed by cold water flow through a discrete vertical fracture. A relation is derived to express the flow rate in the fracture as a function of the temperature measured in the surrounding rock. These mathematical results can be useful for tunnel drilling as it approaches a vertical cold water bearing structure that induces a thermal anomaly in the surrounding massif. During the tunnel drilling, by monitoring this anomaly along the tunnel axis one can quantify the flow rate in the discontinuity ahead before intersecting the fracture. The cases of the Simplon, Mont Blanc and Gotthard tunnels (Alps) are handled with this approach which shows very good agreement between observed temperatures and the theoretical trend. The flow rates before drilling of the tunnel predicted with the theoretical solution are similar in the Mont Blanc and Simplon cases, as well as the flow rates observed during the drilling....

  1. Active and passive seismic methods for characterization and monitoring of unstable rock masses: field surveys, laboratory tests and modeling.

    Science.gov (United States)

    Colombero, Chiara; Baillet, Laurent; Comina, Cesare; Jongmans, Denis; Vinciguerra, Sergio

    2016-04-01

    Appropriate characterization and monitoring of potentially unstable rock masses may provide a better knowledge of the active processes and help to forecast the evolution to failure. Among the available geophysical methods, active seismic surveys are often suitable to infer the internal structure and the fracturing conditions of the unstable body. For monitoring purposes, although remote-sensing techniques and in-situ geotechnical measurements are successfully tested on landslides, they may not be suitable to early forecast sudden rapid rockslides. Passive seismic monitoring can help for this purpose. Detection, classification and localization of microseismic events within the prone-to-fall rock mass can provide information about the incipient failure of internal rock bridges. Acceleration to failure can be detected from an increasing microseismic event rate. The latter can be compared with meteorological data to understand the external factors controlling stability. On the other hand, seismic noise recorded on prone-to-fall rock slopes shows that the temporal variations in spectral content and correlation of ambient vibrations can be related to both reversible and irreversible changes within the rock mass. We present the results of the active and passive seismic data acquired at the potentially unstable granitic cliff of Madonna del Sasso (NW Italy). Down-hole tests, surface refraction and cross-hole tomography were carried out for the characterization of the fracturing state of the site. Field surveys were implemented with laboratory determination of physico-mechanical properties on rock samples and measurements of the ultrasonic pulse velocity. This multi-scale approach led to a lithological interpretation of the seismic velocity field obtained at the site and to a systematic correlation of the measured velocities with physical properties (density and porosity) and macroscopic features of the granitic cliff (fracturing, weathering and anisotropy). Continuous

  2. Characterization of crystalline rocks in deep boreholes. The Kola, Krivoy Rog and Tyrnauz boreholes

    International Nuclear Information System (INIS)

    SKB studies, as one alternative, the feasibility of disposing of spent nuclear fuel in very deep boreholes. As a part of this work NEDRA has compiled geoscientific data from three superdeep boreholes within the former Soviet Union. The holes considered were: the Kola borehole, 12261 m deep and located on the Kola Peninsula, the Krivoy Rog borehole, 5000 m deep and located in Ukraine, and the Tyrnauz borehole, 4001 m deep and located between the Black Sea and the Caspian Sea. These boreholes all penetrate crystalline formations, but major differences are found when their tectonic environments are compared. Excluding the uppermost horizon affected by surface phenomena, data do not indicate any general correlation between depth and the state of rock fracturing, which is instead governed by site specific, lithological and tectonical factors. This applies also to fracture zones, which are found at similar frequencies at all depths. As opposed to the structural data, the hydrogeological and hydrochemical information reveals a vertical zonation, with clear similarities between the three boreholes. An upper zone with active circulation and fresh or slightly mineralized groundwaters reaches down 1000-2000 m. The interval from 1000-2000 m down to 4000-5000 m can be characterized as a transition zone with lower circulation rates and gradually increasing mineralisation. Below 4000-5000 m, strongly mineralized, stagnant, juvenile or metamorphogenic waters are found. Geothermal data verify the existence of this zonation. 28 figs, 30 tabs

  3. Key issues in the hydraulic and hydrochemical characterization of argillaceous rocks

    International Nuclear Information System (INIS)

    Clay-rich media have a very marked capacity to retard the movement of radionuclides by sorption, filtration and other mechanisms. In the absence of pervasive fracturing, the required low-flow environment for underground disposal of radioactive waste is more or less assured and, in the less indurated mud rocks, the propensity for plastic deformation and for self-healing of fractures by swelling are valuable attributes. The chemical conditions prevailing at depth within argillaceous formations are also favourable in so far as the generally alkaline pore water limits the solubility of many of the radioelements and the chemical speciation of these elements in the reducing environment serves to minimize their mobility. Clays are characterized, not only by their low hydraulic conductivity, but also by the very large specific surface of the mineral phase, the ultra-small dimensions of the pore channels, the deformability of the matrix and the complex interactions which occur between clay mineral surfaces, water molecules and dissolved chemical species. These features are of utmost importance when we examine advective and diffusive mass transport in clay-rich media. It would appear that physico-chemical interactions occurring in the thin film separating clay mineral surfaces can produce a general lowering of the chemical potential of the water in these films. Water molecules are drawn into these interparticle regions where they exert a disjoining pressure which may be regarded as a component of the total stress acting on the argillaceous medium. (J.S.). 43 refs., 8 figs., 2 tabs

  4. Advanced reservoir characterization and evaluation of CO2 gravity drainage in the naturally fractured Spraberry Trend Area. Annual report, September 1, 1996--August 31, 1997

    Energy Technology Data Exchange (ETDEWEB)

    McDonald, P.

    1998-06-01

    The objective of the Spraberry CO{sub 2} pilot project is to determine the technical and economic feasibility of continuous CO{sub 2} injection in the naturally fractured reservoirs of the Spraberry Trend. In order to describe, understand, and model CO{sub 2} flooding in the naturally fractured Spraberry reservoirs, characterization of the fracture system is a must. Additional reservoir characterization was based on horizontal coring in the second year of the project. In addition to characterization of natural fractures, horizontal coring has confirmed a previously developed rock model for describing the Spraberry Trend shaly sands. A better method for identifying Spraberry pay zones has been verified. The authors have completed the reservoir characterization, which includes matrix description and detection (from core-log integration) and fracture characterization. This information is found in Section 1. The authors have completed extensive imbibition experiments that strongly indicate that the weakly water-wet behavior of the reservoir rock may be responsible for poor waterflood response observed in many Spraberry fields. The authors have also made significant progress in analytical and numerical simulation of performance in Spraberry reservoirs as seen in Section 3. They have completed several suites of CO{sub 2} gravity drainage in Spraberry and Berea whole cores at reservoir conditions and reported in Section 4. The results of these experiments have been useful in developing a model for free-fall gravity drainage and have validated the premise that CO{sub 2} will recover oil from tight, unconfined Spraberry matrix.

  5. Experimental deformation of a mafic rock - interplay between fracturing, reaction and viscous deformation

    Science.gov (United States)

    Marti, Sina; Stünitz, Holger; Heilbronner, Renée; Plümper, Oliver; Drury, Martyn

    2016-04-01

    Deformation experiments were performed on natural Maryland Diabase (˜ 55% Plg, 42% Px, 3% accessories, 0.18 wt.-% H2O added) in a Griggs-type deformation apparatus in order to explore the brittle-viscous transition and the interplay between deformation and mineral reactions. Shear experiments at strain rates of ˜ 2e-5 /s are performed, at T=600, 700 and 800°C and confining pressures Pc=1.0 and 1.5 GPa. Deformation localizes in all experiments. Below 700°C, the microstructure is dominated by brittle deformation with a foliation formed by cataclastic flow and high strain accommodated along 3-5 major ultracataclasite shear bands. At 700°C, the bulk of the material still exhibits abundant microfractures, however, deformation localizes into an anastomosing network of shear bands (SB) formed from a fine-grained (structures such as fractures and SB. Experiments at 800°C show extensive mineral reactions, with the main reaction products Amph+Plg (+Zo). Deformation is localized in broad C' and C SB formed by a fine-grained (0.1 - 0.8 μm) mixture of Plg+Amph (+Zo). The onset of mineral reactions in the 700°C experiments shows that reaction kinetics and diffusional mass transport are fast enough to keep up with the short experimental timescales. While in the 700°C experiments brittle processes kinematically contribute to deformation, fracturing is largely absent at 800°C. Diffusive mass transfer dominates. The very small grain size within SB favours a grain size sensitive deformation mechanism. Due to the presence of water (and relatively high supported stresses), dissolution-precipitation creep is interpreted to be the dominant strain accommodating mechanism. From the change of Amph coronas around Px clasts with strain, we can determine that Amph is re-dissolved at high stress sites while growing in low stress sites, showing the ability of Amph to accommodate strain via dissolution precipitation creep. The transition from dominantly brittle, to dominantly viscous

  6. Multidisciplinary investigation of the fate, transport, and remediation of chlorinated solvents in fractured rocks at the former Naval Air Warfare Center (NAWC): Scientific and management challenges, and strategies for a successful research program

    Science.gov (United States)

    Tiedeman, C. R.; Goode, D. J.; Shapiro, A. M.; Lacombe, P. J.; Chapelle, F. H.; Bradley, P. M.; Imbrigiotta, T. E.; Williams, J. H.; Curtis, G. P.; Hsieh, P. A.

    2008-12-01

    At the former Naval Air Warfare Center (NAWC) in West Trenton NJ, the U.S. Geological Survey, in cooperation with the U.S. Navy and under support from the Strategic Environmental Research and Development Program (SERDP), is investigating the fate, transport, and remediation of trichloroethylene (TCE) and its daughter products in dipping, fractured mudstones underlying the site. TCE concentrations in ground water are as high as ~100 mg/L. Objectives of multidisciplinary research at the NAWC include (1) understanding the physical, chemical, and microbiological processes and properties affecting the fate, transport, and removal of chlorinated solvents in fractured rocks, (2) assessing the efficiency of different remediation methods (pump and treat, natural and enhanced biodegradation), and (3) transferring the results to help remediate other contaminated fractured rock aquifers. There are numerous scientific and technical challenges to meeting these goals, including the extreme spatial variability of flow and transport properties at the NAWC and the complex distribution of contaminants, geochemical constituents, and microorganisms in fractures and the rock matrix. In addition, there are management challenges that are equally important to address in order to achieve a successful research program. These include balancing the requirements of the many parties involved at the site, including researchers, the site owner, and regulatory agencies; and ensuring that limited research funds are directed towards work that addresses the most important scientific questions as well as stakeholder concerns. Strategies for the scientific challenges at NAWC include developing a carefully planned program to characterize spatial variability in rock properties and groundwater constituents so that the data obtained are applicable to solving research questions focused on remediation. Strategies for the management challenges include fostering open lines of communication among all parties and

  7. Characterization of weathering profile in granites and volcanosedimentary rocks in West Africa under humid tropical climate conditions. Case of the Dimbokro Catchment (Ivory Coast)

    Science.gov (United States)

    Koita, M.; Jourde, H.; Koffi, K. J. P.; da Silveira, K. S.; Biaou, A.

    2013-06-01

    In granitic rocks, various models of weathering profile have been proposed, but never for the hard rocks of West Africa. Besides, in the literature there is no description of the weathering profile in volcanosedimentrary rocks. Therefore, we propose three models describing the weathering profiles in granites, metasediments, and volcanic rocks for hard rock formations located in West Africa. For each of these models proposed for granitic and volcanosedimentary rocks of the Dimbokro catchment, vertical layered weathering profiles are described, according to the various weathering and erosion cycles (specific to West Africa) that the geological formations of the Dimbokro catchment experienced from the Eocene to the recent Quaternary period. The characterization of weathering profiles is based on: i) bedrocks and weathering profile observations at outcrop, and ii) interpretation and synthesis of geophysical data and lithologs from different boreholes. For each of the geological formations (granites, metasediments, and volcanic rocks), their related weathering profile model depicted from top to bottom comprises four separate layers: alloterite, isalterite, fissured layer, and fractured fresh basement. These weathering profiles are systematically covered by a soil layer. Though granites, metasediments and volcanic rocks of the Dimbokro catchment experience the same weathering and erosion cycles during the palaeoclimatic fluctuations from Eocene to recent Quaternary period, they exhibit differences in thickness. In granites, the weathering profile is relatively thin due to the absence of iron crust which protects weathering products against dismantling. In metasediments and volcanic rocks iron crusts develop better than in granites; in these rocks the alterite are more resistant to dismantling.

  8. Characterization of weathering profile in granites and volcanosedimentary rocks in West Africa under humid tropical climate conditions. Case of the Dimbokro Catchment (Ivory Coast)

    Indian Academy of Sciences (India)

    M Koita; H Jourde; K J P Koffi; K S Da Silveira; A Biaou

    2013-06-01

    In granitic rocks, various models of weathering profile have been proposed, but never for the hard rocks of West Africa. Besides, in the literature there is no description of the weathering profile in volcanosedimentrary rocks. Therefore, we propose three models describing the weathering profiles in granites, metasediments, and volcanic rocks for hard rock formations located in West Africa. For each of these models proposed for granitic and volcano sedimentary rocks of the Dimbokro catchment, vertical layered weathering profiles are described, according to the various weathering and erosion cycles (specific to West Africa) that the geological formations of the Dimbokro catchment experienced from the Eocene to the recent Quaternary period. The characterization of weathering profiles is based on: i) bedrocks and weathering profile observations at outcrop, and ii) interpretation and synthesis of geophysical data and lithologs from different boreholes. For each of the geological formations (granites, metasediments, and volcanic rocks), their related weathering profile model depicted from top to bottom comprises four separate layers: alloterite, isalterite, fissured layer, and fractured fresh basement. These weathering profiles are systematically covered by a soil layer. Though granites, metasediments and volcanic rocks of the Dimbokro catchment experience the same weathering and erosion cycles during the palaeoclimatic fluctuations from Eocene to recent Quaternary period, they exhibit differences in thickness. In granites, the weathering profile is relatively thin due to the absence of iron crust which protects weathering products against dismantling. In metasediments and volcanic rocks iron crusts develop better than in granites; in these rocks the alterite are more resistant to dismantling.

  9. Poorly characterized critical rock units within the southern Oklahoma Aulacogen

    Energy Technology Data Exchange (ETDEWEB)

    Gilbert, M.C.; Hogan, J.P. (Univ. of Oklahoma, Norman, OK (United States). School of Geology and Geophysics); Denison, R.E. (Kingstree, Dallas, TX (United States)); Lidiak, E.G. (Univ. of Pittsburgh, PA (United States). Dept. of Geology and Planet Science)

    1993-02-01

    The Southern Oklahoma Aulacogen (SOA) apparently developed during late Proterozoic-early Cambrian rifting of the southern continental margin. This margin appears to be related to the Grenville suture' formed when the Llano terrane was accreted to N.A. The SOA is representative, as well as the best exposed, of a series of penecontemporaneous rifts along the southern and eastern margin of the North American plate. Pronounced Pennsylvanian structural inversion has lifted the igneous basal sections of this rift (the SOA) to shallow crustal levels and exposed parts of it in the Wichita Mountains. Two previously identified but poorly characterized rock units within the SOA, the Tillman Metasedimentary Group and the Navajoe Mountain Basalt/Spilite Group, do not crop out at the surface, having only been recognized from well cuttings. No well-described or well-dated samples exist. The Tillman may be the basement rock which was extended during initial rifting and hosted the igneous infill of the SOA. The Navajoe may represent the earliest phase of magmatism in the SOA. Isotopic dating and geochemistry, and textural/structural relations, of 100--500 m core sections in these two units would go a long way toward clarifying paleotectonic relations and crustal structure in the late Proterozoic. Several drill sites for scientific holes up to 1 km in depth targeted to these enigmatic units can be identified and the rationale for their selection will be presented.

  10. Controls on {sup 222}Rn variations in a fractured crystalline rock aquifer evaluated using aquifer tests and geophysical logging

    Energy Technology Data Exchange (ETDEWEB)

    Folger, P.F. [Office of Senator Pete V. Domenici, Washington, DC (United States)]|[Colorado School of Mines, Golden, CO (United States). Dept. of Geology and Geologic Engineering; Poeter, E. [Colorado School of Mines, Golden, CO (United States). Dept. of Geology and Geologic Engineering; Wanty, R.B.; Frishman, D.; Day, W.

    1996-03-01

    Concentrations of {sup 222}Rn in ground water may vary considerably within megascopically homogeneous rocks over relatively short distances. Calculations indicate that different hydraulic apertures of water-bearing fractures may account for variations in dissolved {sup 222}Rn concentration measured in domestic water wells completed in fractured Pikes Peak Granite, assuming that all other factors influencing dissolved {sup 222}Rn concentrations are constant. Concentrations of dissolved {sup 222}Rn range from 124 to 840 kBq/m{sup 3} [3,360 to 22,700 picocuries/liter] within a 2.5 km{sup 2} well field. Aquifer tests show that transmissivities range from 0.072 to 160 m{sup 2}/day within the well field. Acoustic televiewer and heat-pulse flow meter logging of four wells reveals that, despite tens to hundreds of fractures that intersect each well, a single fracture supplies all the flow to three wells, and one fracture provides 65% of the flow to the fourth well. Type-curve interpretation of early-time data from aquifer tests reveals classic half-slope behavior on log-log plots of drawdown versus time for two wells, suggesting linear flow to a single fracture. Drawdown versus time for the other two wells indicates radial or pseudo-radial flow, which suggests a higher degree of fracture interconnectivity near those boreholes. Hydraulic apertures calculated using the cubic law are 0.024 and 0.038 cm for producing fractures in the first hydraulically connected well pair and 0.011 and 0.020 cm for flowing fractures in the second well pair. Assuming uniform distribution of {sup 226}Ra along fracture walls and long residence time of water relative to {sup 222}Rn decay, the ratio of fracture apertures should equal the inverse ratio of {sup 222}Rn concentration in each well. Differences in {sup 222}Rn concentration between wells in the hydraulically connected pairs can be attributed solely to differences in hydraulic aperture.

  11. MODE Ⅱ AND MIXED MODE Ⅰ-Ⅱ ROCK FRACTURE RESEARCH%岩石Ⅱ型和Ⅰ-Ⅱ混合型断裂研究

    Institute of Scientific and Technical Information of China (English)

    于海勇

    2004-01-01

    For the mode I rock fracture toughness measurement, three standard methods have beenrecommended by the ISRM, but there has not been a standard method for the determination of mode II and mixedmode I-II rock fracture toughness. However mode II and mixed mode I-II fracturing of rock structures is morecommonly observed than mode I in various geological and structural engineering settings. So it is of greatimportant to thoroughly research these rock fracture problems and establish a standard method for determining themode II or mixed mode I-II fracture toughness for rock materials. Based on the progress made for mode I rock fracture research, the cracked chevron notched Brazilian disk(CCNBD) specimen was also introduced for mode II and mixed mode I-II rock fracture toughness measurement.When the crack is orientated at an angle with respect to the diametrical loading, the crack of the CCNBD specimenis exposed to the mode II or mixed mode I-II stress distribution conditions. The solutions for stress intensityfactors in the vicinity of the crack tip have been evaluated by the stepwise superimposition technique. In order tomake sure that the theoretical analysis is correct, numerical calculation method has been employed to calibrate thetheoretical results. It has been proved that the theoretical results yielded by the dislocation method are correct andreliable. According to the characteristic that the propagation of the crack in the CCNBD specimen is in its own planeand application of the energy superposition principle, the stress intensity factor of the mixed mode I-II has beendefined in dimensionless terms as Y≠mix = [(Y1*)2 + (Y*11)2]1/2. It was found that the curve of Y*mix was concave. Thereexists a lowest point which corresponds to the maximum external load and indicates the crack has reached itscritical state. Since the values of Y*mix, Y*1 and Y*II are only dependent on the specimen geometry(α0, α1, αB and θ), the critical values of Y*mix, Y1* and Y*II can be

  12. Characterization of Rock Mechanical Properties Using Lab Tests and Numerical Interpretation Model of Well Logs

    Directory of Open Access Journals (Sweden)

    Hao Xu

    2016-01-01

    Full Text Available The tight gas reservoir in the fifth member of the Xujiahe formation contains heterogeneous interlayers of sandstone and shale that are low in both porosity and permeability. Elastic characteristics of sandstone and shale are analyzed in this study based on petrophysics tests. The tests indicate that sandstone and mudstone samples have different stress-strain relationships. The rock tends to exhibit elastic-plastic deformation. The compressive strength correlates with confinement pressure and elastic modulus. The results based on thin-bed log interpretation match dynamic Young’s modulus and Poisson’s ratio predicted by theory. The compressive strength is calculated from density, elastic impedance, and clay contents. The tensile strength is calibrated using compressive strength. Shear strength is calculated with an empirical formula. Finally, log interpretation of rock mechanical properties is performed on the fifth member of the Xujiahe formation. Natural fractures in downhole cores and rock microscopic failure in the samples in the cross section demonstrate that tensile fractures were primarily observed in sandstone, and shear fractures can be observed in both mudstone and sandstone. Based on different elasticity and plasticity of different rocks, as well as the characteristics of natural fractures, a fracture propagation model was built.

  13. Capturing poromechanical coupling effects of the reactive fracturing process in porous rock via a DEM-network model

    Science.gov (United States)

    Ulven, Ole Ivar; Sun, WaiChing

    2016-04-01

    Fluid transport in a porous medium has important implications for understanding natural geological processes. At a sufficiently large scale, a fluid-saturated porous medium can be regarded as a two-phase continuum, with the fluid constituent flowing in the Darcian regime. Nevertheless, a fluid mediated chemical reaction can in some cases change the permeability of the rock locally: Mineral dissolution can cause increased permeability, whereas mineral precipitation can reduce the permeability. This might trigger a complicated hydro-chemo-mechanical coupling effect that causes channeling of fluids or clogging of the system. If the fluid is injected or produced at a sufficiently high rate, the pressure might increase enough to cause the onset and propagation of fractures. Fractures in return create preferential flow paths that enhance permeability, localize fluid flow and chemical reaction, prevent build-up of pore pressure and cause anisotropy of the hydro-mechanical responses of the effective medium. This leads to a complex coupled process of solid deformation, chemical reaction and fluid transport enhanced by the fracture formation. In this work, we develop a new coupled numerical model to study the complexities of feedback among fluid pressure evolution, fracture formation and permeability changes due to a chemical process in a 2D system. We combine a discrete element model (DEM) previously used to study a volume expanding process[1, 2] with a new fluid transport model based on poroelasticity[3] and a fluid-mediated chemical reaction that changes the permeability of the medium. This provides new insights into the hydro-chemo-mechanical process of a transforming porous medium. References [1] Ulven, O. I., Storheim, H., Austrheim, H., and Malthe-Sørenssen, A. "Fracture Initiation During Volume Increasing Reactions in Rocks and Applications for CO2 Sequestration", Earth Planet. Sc. Lett. 389C, 2014a, pp. 132 - 142, doi:10.1016/j.epsl.2013.12.039. [2] Ulven, O. I

  14. Effect of chemical environment and rock composition on fracture mechanics properties of reservoir lithologies in context of CO2 sequestration

    Science.gov (United States)

    Major, J. R.; Eichhubl, P.; Callahan, O. A.

    2015-12-01

    The coupled chemical and mechanical response of reservoir and seal rocks to injection of CO2 have major implications on the short and long term security of sequestered carbon. Many current numerical models evaluating behavior of reservoirs and seals during and after CO2 injection in the subsurface consider chemistry and mechanics separately and use only simple mechanical stability criteria while ignoring time-dependent failure parameters. CO2 injection irreversibly alters the subsurface chemical environment which can then affect geomechanical properties on a range of time scales by altering rock mineralogy and cements through dissolution, remobilization, and precipitation. It has also been documented that geomechanical parameters such as fracture toughness (KIC) and subcritical index (SCI) are sensitive to chemical environment. Double torsion fracture mechanics testing of reservoir lithologies under controlled environmental conditions relevant to CO2 sequestration show that chemical environment can measurably affect KIC and SCI. This coupled chemical-mechanical behavior is also influenced by rock composition, grains, amount and types of cement, and fabric. Fracture mechanics testing of the Aztec Sandstone, a largely silica-cemented, subarkose sandstone demonstrate it is less sensitive to chemical environment than Entrada Sandstone, a silty, clay-rich sandstone. The presence of de-ionized water lowers KIC by approximately 20% and SCI 30% in the Aztec Sandstone relative to tests performed in air, whereas the Entrada Sandstone shows reductions on the order of 70% and 90%, respectively. These results indicate that rock composition influences the chemical-mechanical response to deformation, and that the relative chemical reactivity of target reservoirs should be recognized in context of CO2 sequestration. In general, inert grains and cements such as quartz will be less sensitive to the changing subsurface environment than carbonates and clays.

  15. The ISRM suggested methods for rock characterization, testing and monitoring 2007-2014

    CERN Document Server

    2015-01-01

    This book is a collection of ISRM suggested methods for testing or measuring properties of rocks and rock masses both in the laboratory and in situ, as well as for monitoring the performance of rock engineering structures. The first collection (Yellow Book) has been published in 1981. In order to provide access to all the Suggested Methods in one volume, the ISRM Blue Book was published in 2007 (by the ISRM via the Turkish National Group) and contains the complete set of Suggested Methods from 1974 to 2006 inclusive. The papers in this most recent volume have been published during the last seven years in international journals, mainly in Rock Mechanics and Rock Engineering. They offer guidance for rock characterization procedures and laboratory and field testing and monitoring in rock engineering. These methods provide a definitive procedure for the identification, measurement and evaluation of one or more qualities, characteristics, or properties of rocks or rock systems that produces a test result.

  16. Fractures network analysis and interpretation in carbonate rocks using a multi-criteria statistical approach. Case study of Jebal Chamsi and Jebal Belkhir, South-western part of Tunisia

    Science.gov (United States)

    Msaddek, Mohamed Haythem; Moumni, Yahya; Chenini, Ismail; Mercier, Eric; Dlala, Mahmoud

    2016-11-01

    The quantitative analysis of fractures in carbonate rocks across termination folds is important for the understanding of the fractures network distribution and arrangement. In this study, we performed a quantitative analysis and interpretation of fracture network to identify the fracture networks type. For this reason, we used a multi-criteria statistical analysis. The distribution of directional families in all measured stations and their elemental distribution are firstly examined. Then we performed the analysis of directional criteria for each of the two and three neighbouring stations. Finally, the elemental analyses of fracture families crossing others were carried out. This methodology was applied to the folds of Jebal Chamsi and Jebal Belkhir areas located in south western Tunisia characterized by simple folds of carbonate geological formations. The application of the global and the elemental statistical analysis criteria of directional families show a random arrangement of fractures. However, elemental analysis of two and three neighbouring stations for families crossing one another shows a pseudo-organization of fracture arrangements.

  17. Supercritical CO2/brine transport in a fractured rock under geologic sequestration conditions

    Science.gov (United States)

    Kim, Kue-Young; Oh, Junho; Han, Weon Shik

    2013-04-01

    Carbon capture and storage (CCS) is a promising technology for mitigating CO2 emissions into the atmosphere. In general, densely fractured natural reservoirs are rarely considered as suitable candidates due to issues related to safe and secure long-term storage. Nevertheless, assessment of CO2 storage processes in a storage medium with fractures is critical, as fractures occur in nearly all geological settings and play a major role in hydrocarbon migration as well as entrapment. We evaluated the impact of fractures on CO2/brine transport under geologic sequestration conditions by conducting both experimental and numerical studies. Laboratory experimental results showed a piston-like brine displacement with gravity over-run effects in the homogeneous core regardless of CO2 injection rates. In the fractured core, however, two distinctive types of brine displacements were observed; one showing brine displacement only in the fracture whereas the other shows brine displacement both in the fracture and matrix with different rates, depending on the magnitude of the pressure build-up in the matrix. In the experiments, the injectivity in the fractured core was twice greater than that in the homogeneous core at our experimental condition, while the estimated storage capacity was greater in the homogeneous core than in the fractured core by over 1.5 times. Capillary pressure curves were illustrated for both cores including entry pressures and irreducible brine saturation. The free-phase CO2 transfer in a fracture-matrix system was addressed by numerical simulation, and provided transient flux exchange processes during the brine displacement by CO2. The pressure gradient between the fracture and matrix induced CO2 transfer from fracture into matrix at the front of CO2 plume in fracture. In contrast, at the rear zone of CO2 plume, the reversal of pressure gradient resulted in a reverse CO2 flux. Additionally, the influence of fracture aperture on CO2 transfer between fracture

  18. A Methodology for Confirmatory Testing of Numerical Models of Groundwater Flow and Solute Transport in Fractured Crystalline Rock

    Science.gov (United States)

    Hartley, L.; Follin, S.; Rhen, I.; Selroos, J.

    2008-12-01

    Three-dimensional, regional, numerical models of groundwater flow and solute transport in fractured crystalline rock are used for two sites in Sweden that are considered for geological disposal of spent nuclear fuel. The models are used to underpin the conceptual modeling that is based on multi-disciplinary data and include descriptions of the geometry of geological features (deformation zones and fracture networks), transient hydrological and chemical boundary conditions, strong spatial heterogeneity in the hydraulic properties, density driven flow, solute transport including rock matrix diffusion, and mixing of different water types in a palaeo-hydrogeological perspective (last 10,000 years). From a credibility point of view, comparisons between measured and simulated data are important and provide a means to address our ability to understand complex hydrogeological systems, and hence what particular applications of a hydrogeological model of a physical system that are justified, e.g. in subsequent repository performance assessment studies. For instance, it has been suggested that an understanding of the hydrochemical evolution throughout geological time is a powerful tool to predict the future evolution of groundwater flow and its chemical composition. The general approach applied in the numerical modeling was to first parameterize the deformation zones and fracture networks hydraulically using fracture and inflow data from single-hole tests. Second, the confirmatory step relies on using essentially the same groundwater flow and solute transport model in terms of grid discretization and parameter settings for matching three types of independent field data: 1) large-scale cross-hole (interference) tests, 2) long-term monitoring of groundwater levels, and 3) hydrochemical composition of fracture water and matrix pore water in deep boreholes. We demonstrate here the modelling approach of the second step - confirmatory testing - using data from the site

  19. U.S. National Committee for Rock Mechanics; and Conceptual model of fluid infiltration in fractured media. Project summary, July 28, 1997--July 27, 1998

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-09-01

    The title describes the two tasks summarized in this report. The remainder of the report contains information on meetings held or to be held on the subjects. The US National Committee for Rock Mechanics (USNC/RM) provides for US participation in international activities in rock mechanics, principally through adherence to the International Society for Rock Mechanics (ISRM). It also keeps the US rock mechanics community informed about new programs directed toward major areas of national concern in which rock mechanics problems represent critical or limiting factors, such as energy resources, excavation, underground storage and waste disposal, and reactor siting. The committee also guides or produces advisory studies and reports on problem areas in rock mechanics. A new panel under the auspices of the US National Committee for Rock Mechanics has been appointed to conduct a study on Conceptual Models of Fluid Infiltration in Fractured Media. The study has health and environmental applications related to the underground flow of pollutants through fractured rock in and around mines and waste repositories. Support of the study has been received from the US Nuclear Regulatory Commission and the Department of Energy`s Yucca Mountain Project Office. The new study builds on the success of a recent USNC/RM report entitled Rock Fractures and Fluid Flow: Contemporary Understanding and Applications (National Academy Press, 1996, 551 pp.). A summary of the new study is provided.

  20. U.S. National Committee for Rock Mechanics and conceptual model of fluid infiltration in fractured media. Project summary, July 28, 1997 - July 27, 1998

    International Nuclear Information System (INIS)

    The title describes the two tasks summarized in this report. The remainder of the report contains information on meetings held or to be held on the subjects. The US National Committee for Rock Mechanics (USNC/RM) provides for US participation in international activities in rock mechanics, principally through adherence to the International Society for Rock Mechanics (ISRM). It also keeps the US rock mechanics community informed about new programs directed toward major areas of national concern in which rock mechanics problems represent critical or limiting factors, such as energy resources, excavation, underground storage and waste disposal, and reactor siting. The committee also guides or produces advisory studies and reports on problem areas in rock mechanics. A new panel under the auspices of the US National Committee for Rock Mechanics has been appointed to conduct a study on Conceptual Models of Fluid Infiltration in Fractured Media. The study has health and environmental applications related to the underground flow of pollutants through fractured rock in and around mines and waste repositories. Support of the study has been received from the US Nuclear Regulatory Commission and the Department of Energy's Yucca Mountain Project Office. The new study builds on the success of a recent USNC/RM report entitled Rock Fractures and Fluid Flow: Contemporary Understanding and Applications (National Academy Press, 1996, 551 pp.). A summary of the new study is provided

  1. A methodology to constrain the parameters of a hydrogeological discrete fracture network model for sparsely fractured crystalline rock, exemplified by data from the proposed high-level nuclear waste repository site at Forsmark, Sweden

    Science.gov (United States)

    Follin, Sven; Hartley, Lee; Rhén, Ingvar; Jackson, Peter; Joyce, Steven; Roberts, David; Swift, Ben

    2014-03-01

    The large-scale geological structure of the crystalline rock at the proposed high-level nuclear waste repository site at Forsmark, Sweden, has been classified in terms of deformation zones of elevated fracture frequency. The rock between deformation zones was divided into fracture domains according to fracture frequency. A methodology to constrain the geometric and hydraulic parameters that define a discrete fracture network (DFN) model for each fracture domain is presented. The methodology is based on flow logging and down-hole imaging in cored boreholes in combination with DFN realizations, fracture connectivity analysis and pumping test simulations. The simulations suggest that a good match could be obtained for a power law size distribution where the value of the location parameter equals the borehole radius but with different values for the shape parameter, depending on fracture domain and fracture set. Fractures around 10-100 m in size are the ones that typically form the connected network, giving inflows in the simulations. The report also addresses the issue of up-scaling of DFN properties to equivalent continuous porous medium (ECPM) bulk flow properties. Comparisons with double-packer injection tests provide confidence that the derived DFN formulation of detailed flows within individual fractures is also suited to simulating mean bulk flow properties and their spatial variability.

  2. Rock physics and seismic modeling of shale reservoirs with horizontal fractures

    Institute of Scientific and Technical Information of China (English)

    LIU Xiwu; DONG Ning; GUO Zhiqi

    2016-01-01

    The presence of horizontal fractures enhances seismic anisotropy of shales.Calculation based on the effective medium theory indicates that horizontal fractures have little effects on velocities along the direction pa-rallel to fractures,but can significantly reduce velocities along the direction normal to fractures.Seismic respon-ses of shales with horizontal fractures are calculated based on the reflector model and the anisotropic propagator matrix method,in which the reflections are a combination of the contrast in impedance due to the variations in fracture density,anisotropic propagation of waves within the shales,and the tuning and interferences associated with layer thickness.Calculated results indicate that seismic reflections are sensitive to reservoir layer thickness and fracture density.Anisotropic propagation alters amplitudes and phases of reflections.It corresponds to high-er reflection amplitudes for the case of surrounding