Sample records for catagenesis

  1. Living microbial ecosystems within the active zone of catagenesis: Implications for feeding the deep biosphere

    Horsfield, B.; Schenk, H. J.; Zink, K.; Ondrak, R.; Dieckmann, V.; Kallmeyer, J.; Mangelsdorf, K.; di Primio, R.; Wilkes, H.; Parkes, R. J.; Fry, J.; Cragg, B.


    Earth's largest reactive carbon pool, marine sedimentary organic matter, becomes increasingly recalcitrant during burial, making it almost inaccessible as a substrate for microorganisms, and thereby limiting metabolic activity in the deep biosphere. Because elevated temperature acting over geological time leads to the massive thermal breakdown of the organic matter into volatiles, including petroleum, the question arises whether microorganisms can directly utilize these maturation products as a substrate. While migrated thermogenic fluids are known to sustain microbial consortia in shallow sediments, an in situ coupling of abiotic generation and microbial utilization has not been demonstrated. Here we show, using a combination of basin modelling, kinetic modelling, geomicrobiology and biogeochemistry, that microorganisms inhabit the active generation zone in the Nankai Trough, offshore Japan. Three sites from ODP Leg 190 have been evaluated, namely 1173, 1174 and 1177, drilled in nearly undeformed Quaternary and Tertiary sedimentary sequences seaward of the Nankai Trough itself. Paleotemperatures were reconstructed based on subsidence profiles, compaction modelling, present-day heat flow, downhole temperature measurements and organic maturity parameters. Today's heat flow distribution can be considered mainly conductive, and is extremely high in places, reaching 180 mW/m 2. The kinetic parameters describing total hydrocarbon generation, determined by laboratory pyrolysis experiments, were utilized by the model in order to predict the timing of generation in time and space. The model predicts that the onset of present day generation lies between 300 and 500 m below sea floor (5100-5300 m below mean sea level), depending on well location. In the case of Site 1174, 5-10% conversion has taken place by a present day temperature of ca. 85 °C. Predictions were largely validated by on-site hydrocarbon gas measurements. Viable organisms in the same depth range have been proven using 14C-radiolabelled substrates for methanogenesis, bacterial cell counts and intact phospholipids. Altogether, these results point to an overlap of abiotic thermal degradation reactions going on in the same part of the sedimentary column as where a deep biosphere exists. The organic matter preserved in Nankai Trough sediments is of the type that generates putative feedstocks for microbial activity, namely oxygenated compounds and hydrocarbons. Furthermore, the rates of thermal degradation calculated from the kinetic model closely resemble rates of respiration and electron donor consumption independently measured in other deep biosphere environments. We deduce that abiotically driven degradation reactions have provided substrates for microbial activity in deep sediments at this convergent continental margin.

  2. Differences in bitumen and kerogen-bound fatty acid fractions during diagenesis and early catagenesis in a maturity series of New Zealand coals

    Glombitza, Clemens; Mangelsdorf, Kai; Horsfield, Brian


    Oxygen-bearing functional groups, in particular the carboxylic groups of acids and esters, are mainly responsible for the chemical reactivity of sedimentary organic matter. We have studied kerogen and bitumen fractions from a coalification series from the New Zealand Coal Band covering the rank...... range from 0.28% to 0.80% vitrinite reflectance. We investigated the composition of fatty acids separated from the bitumen, and compared this to the distribution of kerogen-bound fatty acids (esters) obtained after selective chemical degradation of the macromolecular organic matter. We found remarkable...... differences in the fatty acid composition between bitumen and kerogen-bound acids, both in the short (< C20) and long chain (≥ C20) fatty acid range. The compositions of these two acid fractions changed independently as a function of maturation. This points to the long and short chain fatty acids in bitumen...

  3. Electromagnetic emission in mineral and rock dehydration

    Salnikov, V.; Popov, V.; Terre, D.


    The article considers regularities of radiofrequency electromagnetic radiation from minerals and rocks, with samples being heated in a vacuum to 20° C- 1000° C. The examples of electromagnetic emission correlation with electric conductivity, thermoluminescence and thermographic analysis during physic-chemical processes resulting from diagenesis, catagenesis and metagenesis have been provided.

  4. Changes in bulk properties and molecular compositions within New Zealand Coal Band solvent extracts from early diagenetic to catagenetic maturity levels

    Vu, T.T.A.; Zink, K.G.; Mangelsdorf, K.; Sykes, R.; Wilkes, H.; Horsfield, B. [GFZ German Research Center of Geoscience, Potsdam (Germany)


    The bulk properties and bitumen molecular compositions of a rank-series of 38 humic coals from the New Zealand Coal Band (Cretaceous-Cenozoic) have been analysed to investigate early maturation processes affecting coaly organic matter through diagenesis to moderate catagenesis (Rank(S-r) 0.0-11.8, R-o 0.23-0.81%). The samples comprise a relatively restricted range of vitrinite rich coal types formed largely from higher land plant material under relatively oxic conditions, but with a significant contribution from microbial biomass. With increasing rank, total organic carbon contents show a general increase, whereas moisture and asphaltene contents decrease. Bitumen yields also decrease through the stages of diagenesis and early catagenesis (Rank(S{sub r}) < 9, R{sub o} < 0.55%), indicating partial loss of initial bitumen during early maturation. Thermal generation of hydrocarbons begins slowly at Rank(S{sub r}) about 5-6 (R{sub o} about 0.40%) as indicated by the constant occurrence and gradual increase of isoprenoids (e.g., pristane and phytane) and hopanoids in their more mature alpha beta configuration. This early phase of catagenesis, not previously recognised in New Zealand coals, is followed at Rank(S{sub r}) about 9 (R{sub o}) about 0.55%) by the main catagenesis phase characterised by a more rapid increase in the generation of hydrocarbons, including total n-alkanes, isoprenoids and alpha beta-hopanes. Changes in the maturity of New Zealand coals can be traced by the Carbon Preference Index and several hopane maturity parameters, including 22S/(22S + 22R), {alpha} {beta}/({alpha}{beta} + {beta}{alpha}) and {beta} {beta}/({alpha}{beta} + {beta}{alpha} + {beta}{beta}).

  5. Formation of magnetic minerals at hydrocarbon-generation conditions

    Abubakar, R.; Muxworthy, A. R.; Sephton, M.A.; Southern, P.; Watson, J. S.; Fraser, A.J.; Almeida, T.P.


    In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low-temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (...

  6. Maturation related changes in the distribution of ester bound fatty acids and alcohols in a coal series from the New Zealand Coal Band covering diagenetic to catagenetic coalification levels

    Glombitza, C.; Mangelsdorf, K.; Horsfield, B. [German Research Cemter of Geoscience GFZ, Potsdam (Germany)


    Several lignites and coals of low to moderate maturation levels from the New Zealand Coal Band were investigated using alkaline ester cleavage experiments to reveal compositional changes of ester bound components during increasing maturation. Ester bound alcohols are found to be present in highest amounts in the very immature lignite samples but show a rapid decrease during early diagenesis. Ester bound fatty acids also show an initial exponential decrease during diagenesis but reveal an intermittent increase during early catagenesis before decreasing again during main catagenesis. This was related to the short chain fatty acids. To obtain a maturity related signal and to eliminate facies related scattering in the amounts of fatty acids in the coal samples, the carbon preference index of fatty acids (CPIFA) parameter is introduced. For the long chain fatty acids the CPIFA decreases with increasing maturity. During diagenesis, the same trend can be observed for the short chain fatty acids but the intermittent increase in the amounts of short chain fatty acids is also accompanied by high CPIFA values. This indicates less altered organic biomass at this maturation level and is in contrast to the mature CPIFA signal of the long chain fatty acids of the same samples. Thus could be due to extremely different amounts of short and long chain fatty acids in the original source organic matter or it could due to the incorporation of immature bacterial biomass from deep microbial communities containing C{sub 16} and C{sub 18} fatty acids as main cell membrane components. Deep microbial life might be stimulated at this interval by the increasing release of thermally generated potential substrates from the organic matrix during early catagenesis. The high amounts of alcohols in the immature lignite samples are also visible in the alkene distribution from the open system pyrolysis experiments of the organic matrix before and after saponification.

  7. Soret band porphyrin structure index via 3rd derivative UV/VIS spectroscopy

    This paper reports on Soret band wavelength which provides a porphyrin structure index which is useful to classify natural metalloporphyrin extracts. The approach involves rapid measurement by photodiode array spectrophotometry. The average value for a porphyrin mixture. λSoret ± 0.1 nm, is obtained by third derivative computation. A blue shift in λSoret implies an increasing etio to exocycle ratio. High ratios have been associated with catagenesis (Dydik, 1975, Baker, et al., 1978, 1983), and with predispositional generation (Baker and Louda (1984). As a reference, we measured the Soret band response to simulated maturation of a Woodford Shale (350 Ma) sample after hydrous pyrolysis (Lewan, 1981), as described in greater detail elsewhere at this meeting

  8. Low temperature hydrothermal maturation of organic matter in sediments from the Atlantis II Deep, Red Sea

    Simoneit, Bernd R. T.; Grimalt, Joan O.; Hayes, J. M.; Hartman, Hyman


    Hydrocarbons and bulk organic matter of two sediment cores within the Atlantis II Deep are analyzed, and microbial inputs and minor terrestrial sources are found to represent the major sedimentary organic material. Results show that extensive acid-catalyzed reactions are occurring in the sediments, and the Atlantis II Deep is found to exhibit a lower degree of thermal maturation than other hydrothermal or intrusive systems. The lack of carbon number preference noted among the n-alkanes suggests that the organic matter of these sediments has undergone some degree of catagenesis, though yields of hydrocarbons are much lower than those found in other hydrothermal areas, probably due to the effect of lower temperature and poor source-rock characteristics.

  9. A Study of Porphyrins in Petroleum Source Rocks

    Huseby, Berit


    This thesis discusses several aspects of porphyrin geochemistry. Degradation experiments have been performed on the Messel oil shale (Eocene, Germany) to obtain information on porphyrins bound or incorporated into macromolecular structures. Thermal heating of the preextracted kerogen by hydrous pyrolysis was used to study the release of porphyrins and their temperature dependent changes during simulated diagenesis and catagenesis. Selective chemical degradation experiments were performed on the preextracted sediment to get more detailed information about porphyrins that are specifically bound to the macromolecular structures via ester bonds. From the heating experiments, in a separate study, the porphyrin nitrogen content in the generated bitumens was compared to the bulk of organic nitrogen compounds in the fraction. The bulk nitrogen contents in the generated bitumens, the water phase and the residual organic matter was recorded to establish the distribution of nitrogen between the kerogen and product phases. Porphyrins as biomarkers were examined in naturally matured Kimmeridge clay source rocks (Upper Jurassic, Norway), and the use of porphyrins as general indicators of maturity was evaluated. Underlying maturity trends in the biomarker data was investigated by Partial Least Squares analysis. Porphyrin as indicators of depositional conditions was also addressed, where the correlations between the (amounts) abundance of nickel and vanadyl porphyrins were mapped together with other descriptors that are assumed to be indicative of redox depositional conditions. 252 refs., 28 figs., 4 tabs.

  10. Thermal stability of ladderane lipids as determined by hydrous pyrolysis

    Jaeschke, A.; Lewan, M.D.; Hopmans, E.C.; Schouten, S.; Sinninghe, Damste J.S.


    Anaerobic ammonium oxidation (anammox) has been recognized as a major process resulting in loss of fixed inorganic nitrogen in the marine environment. Ladderane lipids, membrane lipids unique to anammox bacteria, have been used as markers for the detection of anammox in marine settings. However, the fate of ladderane lipids after sediment burial and maturation is unknown. In this study, anammox bacterial cell material was artificially matured by hydrous pyrolysis at constant temperatures ranging from 120 to 365 ??C for 72 h to study the stability of ladderane lipids during progressive dia- and catagenesis. HPLC-MS/MS analysis revealed that structural alterations of ladderane lipids already occurred at 120 ??C. At temperatures >140 ??C, ladderane lipids were absent and only more thermally stable products could be detected, i.e., ladderane derivatives in which some of the cyclobutane rings were opened. These diagenetic products of ladderane lipids were still detectable up to temperatures of 260 ??C using GC-MS. Thus, ladderane lipids are unlikely to occur in ancient sediments and sedimentary rocks, but specific diagenetic products of ladderane lipids will likely be present in sediments and sedimentary rocks of relatively low maturity (i.e., C31 hopane 22S/(22S + 22R) ratio 0.5). ?? 2008 Elsevier Ltd.

  11. Characteristics of Mire Soils and Its Sustainable Utilization in Xianghai Mire Wetland.%向海沼泽湿地土壤特征及可持续利用

    白军红; 余国营; 张玉霞


    On the basis of the study about the conditions and process of formation of mire soils in Xianghai mire wetland, this paper classifies the soil into four soil subtypes, and describes their main characters such as distribution laws, profile features etc. respectively. In addition, it also puts forward such ways of sustainable exploitation and utilization to solve such problems as salinization, desertification and catagenesis etc..%基于对向海沼津湿地土壤形成条件和主要成土过程的研究,将其沼泽土壤划分为4个亚类型,并分别描述了各自的分布规律和剖面特征。在向海沼泽湿地土壤盐渍化、沙化、退化问题日益严重的大前提下提出了可持续开发利用对策。

  12. The relationship between dolomitization and organic matter occurrence in Lower Paleozoic carbonate in the Ordos Basin


    Based on observations on the core and surface sections of Lower Paleozoic carbonate in the Ordos Basin, petrography research and measurements of TOC, TOS , Ro, XRD, and comparative study with dolomite in modern Coorong Lake, it has been revealed that: (i)dolomitization may occur in micrite limestone, gypsum-halite and argillaceous sandstone, and it can be divided into three types: sedimentary penecontemporaneous-early diagenesis, late diagenesis of deep burial and catagenesis of uplift period. However, the crystal cell of the second type less than 35 μ m in size is most closely associated with gas pool; (ii) the highest content of organic matter (OM) is produced in samples from the argillic dolomite which may be formed by argillaceous fluid through gypsum-halite; (iii) in the evolution process from penecontemporaneous dolomite into stoichiometric dolomite, the crystal order of dolomite and the porosity of its host rock tend to increase, which is favorable to the formation of an available migration network. When the power of the fluid is high enough, the network is mainly favorable to the migration and transport of heat, but when the power of the fluid goes down, the network system is favorable, due to its large space, to OM deposition in it.

  13. Forecast of phase state and composition of hydrocarbon systems of subsalt formations of the north Caspian region

    Full text : Major concentrations of hydrocarbon resources of the Caspian basin are associated with deep horizons. In experimental investigations the forecast of hydrocarbon phase state at the great depths of the oil, gas condensate and gas fields of Precaspian basin has been made and the postion petroleum within the phase-genetic range of the vertical zonation of hydrocarbons from the Precaspain are has been determined from a series of geological and geochemical indices (composition petroleum, individual composition of light and heavy fractions of hydrocarbons. The extended catagenesis zonation and consequently, a low temperature gradient of west and south areas have predetermined generation of gas-condensate and gas pools. Ona can assign those systems to supercritical under saturated systems associated with the high temperature and pressure. The violation of a normal relation in a distribution of liquid and gaseous phases exhibited in those systems is owed to the occurrence of acid components in the composition of formation gas. The content of condensate and gas factor are controlled by the concentration of acid components of formation system. The The higher content of acid components (Hs, S, CO2) in formation gas the lower is the condensate content and gas factor of the oil.

  14. Diamondoid hydrocarbons as a molecular proxy for thermal maturity and oil cracking: Geochemical models from hydrous pyrolysis

    Wei, Z.; Moldowan, J.M.; Zhang, S.; Hill, R.; Jarvie, D.M.; Wang, Hongfang; Song, F.; Fago, F.


    A series of isothermal hydrous pyrolysis experiments was performed on immature sedimentary rocks and peats of different lithology and organic source input to explore the generation of diamondoids during the thermal maturation of sediments. Oil generation curves indicate that peak oil yields occur between 340 and 360 ??C, followed by intense oil cracking in different samples. The biomarker maturity parameters appear to be insensitive to thermal maturation as most of the isomerization ratios of molecular biomarkers in the pyrolysates have reached their equilibrium values. Diamondoids are absent from immature peat extracts, but exist in immature sedimentary rocks in various amounts. This implies that they are not products of biosynthesis and that they may be generated during diagenesis, not just catagenesis and cracking. Most importantly, the concentrations of diamondoids are observed to increase with thermal stress, suggesting that they can be used as a molecular proxy for thermal maturity of source rocks and crude oils. Their abundance is most sensitive to thermal exposure above temperatures of 360-370 ??C (R0 = 1.3-1.5%) for the studied samples, which corresponds to the onset of intense cracking of other less stable components. Below these temperatures, diamondoids increase gradually due to competing processes of generation and dilution. Calibrations were developed between their concentrations and measured vitrinite reflectance through hydrous pyrolysis maturation of different types of rocks and peats. The geochemical models obtained from these methods may provide an alterative approach for determining thermal maturity of source rocks and crude oils, particularly in mature to highly mature Paleozoic carbonates. In addition, the extent of oil cracking was quantified using the concentrations of diamondoids in hydrous pyrolysates of rocks and peats, verifying that these hydrocarbons are valuable indicators of oil cracking in nature. ?? 2006 Elsevier Ltd. All rights

  15. Characteristics of organic matter in uranium-rich coaly shales from miocene sequence at Kanamaru

    We obtained a continuous 45 m-long core from the Miocene sedimentary sequence and basement Cretaceous granite at Kanamaru, northeast Japan. The Miocene sequence intercalates with a uranium-rich seam (U=25-100 ppm; Th=23-42 ppm). We analyzed the kerogen and biomarkers in the core to characterize the organic matter. Visual kerogen analysis indicated that coaly and woody kerogen is abundant in relatively organic-rich samples, while amorphous kerogen is abundant in organic-lean samples. Pyrolysis gas chromatography-mass spectrometry demonstrated that the organic matter in pyrolysates comprises mainly alkyl-aromatic hydrocarbons (alkyl-benzenes, alkyl-indenes, alkyl-naphthalenes, etc.) and n-alkanes. Acyclic isoprenoid alkanes (mainly pristane), n-alkenes, and n-fatty acids were detected as minor components. Most of these compounds are characteristic of the type-III kerogen that derived from terrestrial higher plants. These results suggest that amorphous kerogen originated from terrestrial higher plants, and we speculate that they were heavily degraded by oxidation and lost their woody texture. Thermal alteration index (TAI) of Pinus pollen was about 2.6, and Tmax values of Rock-Eval pyrolysis range from 441degC to 444degC, which indicate that the thermal maturation of the coaly shale reached the stage of early catagenesis. This maturity was also suggested by high abundance of diagenetically generated isomers of hopanes in pyrolysates. In the sediment sequence, a peak of uranium and uranium/thorium ratio is ca. 2 m shallower than the peak of organic carbon content, but it corresponds to a lithological boundary. This inconsistency suggests that organic matter was not involved in concentrating uranium. Uranium was possibly concentrated from groundwater at the lithological boundaries between different redox levels during the period of high groundwater level. (author)

  16. Temperature effects on kerogen and on molecular and isotopic composition of organic matter in Pierre Shale near an igneous dike

    Clayton, J.L.; Bostick, N.H.


    A suite of siltstone samples from the Upper Cretaceous Pierre Shale from the contact zone of a 130-cm thick igneous dike near Wolcott, Colorado, U.S.A., was taken from the contact to 170 cm from the dike to study the effects of temperature on the organic matter. The sampled bedding interval was about 10 cm thick, so variation in lithology and type of organic matter is minimal. Vitrinite reflectance values (R0) increase from 0.4 far from the dike, to 3.3% near the dike contact. Geochemical measurements show systematic thermal effects analogous to those often observed for catagenesis and metagenesis in the depth range of 1-4 km within a sedimentary basin. The H/C ratio of kerogen and the hydrogen index (Rock-Eval) decrease most rapidly in the 0.6-1.7% R0 range, in which the transformation ratio (Rock-Eval) increases from 0.1 to 0.3. Based on extraction of C15+ compounds, the main increase of hydrocarbons and total extractable organic matter occurs between 0.6 and 1.0% reflectance. The saturated/aromatic hydrocarbon ratio increases almost twofold in this range of maturity. However, the pristane/phytane ratio is essentially constant through the hydrocarbon generation zone but decreases slightly at high levels of thermal alteration (R0 > 1.2%). The ??13C values for aromatic and saturated hydrocarbons are about -27 and -29???, respectively, and are constant to about 1.0% R0, then both become heavier by about 2??? at higher R0 values. ?? 1986.

  17. Evolution of the West Siberian Basin

    Rudkevich, M.Y. [Tyumenskij Industrial`nyj Inst., Tyumen (Russian Federation)


    The west Siberian basin results form a Paleozoic rifting in its north-northeastern segment (the Yamal-Taz depression) and from a Triassic rifting in its central-western segment (in the Ob Arch). Its Mesozoic-Cenozoic sedimentary cover has a maximum thickness of 8 km in the Yamal-Taz depression and 4 km in the Ob-Arch. Deep basins (with a water depth of 600 m) were not compensated by clay and siliceous sedimentation during the post-rift evolution of the area. Local extension still occurred during the Callovian, Tithonian, early Albian, Turonian and Eocene. The main axes of the Mesozoic and Paleogene deep-water basins were located in the west along the Urals and Paikhoy Ranges. Shortening affected the deep-water zones, whereas sedimentation increased in shelf regions, with the accumulation of marine pro-gradational lobes. Later on, shallow marine sedimentation and continental formations filled up the basin, reflecting the late stage compressional history of the west Siberian platform. The Neocomian stages of extension and compression were the most important for oil generation. The Malm and Neocomian horizons constitute five regional oil-and gas-bearing complexes. In each complex, the argilites are the source rocks, whereas pro-gradational lobes are the conducts for an eastward-directed hydrocarbon migration but also comprise good reservoirs. The shallow-water undaform zones are the main zones of hydrocarbon accumulation in the structural traps. Various lithologies occur, whereas the successive geochemical catagenesis zones affect progressively deeper horizons. Biogenic gas and immature oil occur at a depth of 0.6-1.7 km, whereas oil, gas and condensate occur at a depth of 1.7-4.0 km. (author). 1 ref., 3 figs., 1 tab.

  18. Paleoenvironmental and source rock assessment of black shales of Pennsylvanian Age, Powder River and northern Denver basins

    Clayton, J.L.; King, J.D.; Lubeck, C.M.; Leventhal, J.S.; Daws, T.A.


    Thin Middle Pennsylvanian (Desmoinesian) organic-rich black shales (cumulative thickness < 50 ft) underlie much of the northern Denver basin and southeastern Powder River basin. In the Powder River basin, these shales are part of the middle member of the Minnelusa Formation. During Desmoinesian time, the present area of the southeastern Powder River basin and Nebraska was a shallow, at times highly saline, restricted sea. In contrast, in the present area of northeastern Colorado, black shales were deposited in a marine environment with normal salinity that was probably continuous with the Mid-Continent Pennsylvanian sea. Assessment of the paleoenvironment has been carried out using organic geochemical parameters. Shales deposited in the restricted basin setting contain abundant porphyrins (25,000-30,000 ppm relative to total extractable organic matter) and significant quantities of aryl isoprenoids. The aryl isoprenoid compounds (1) are evidence for the presence of the sulfur bacteria families Chlorobiaceae and possibly Chromatiaceae and (2) indicate that euxinic conditions existed in the water column. High ratios of sulfur to carbon in the shales support this interpretation. In contrast, extracts from black shale in the normal sea to the south contain lower porphyrin concentrations (generally less than 1000 ppm) and aryl isoprenoids are minor constituents or are absent. Sulfur/carbon ratios in these latter shales are similar to those observed for normal marine shales (that is, not euxinic conditions). Other paleoenvironmental indicators (sterane composition, alkane distribution) are consistent with these observations. Bulk organic matter in the black shales from both environments is type II and has good source potential for generation of liquid hydrocarbons during catagenesis. Pyrolysis yields of 50 kg/MT (50,000 ppm) are common, and in some shales, yield is 100 kg/MT (100,000 ppm).

  19. Carbon and hydrogen isotopic reversals in deep basin gas: Evidence for limits to the stability of hydrocarbons

    Burruss, R.C.; Laughrey, C.D.


    During studies of unconventional natural gas reservoirs of Silurian and Ordovician age in the northern Appalachian basin we observed complete reversal of the normal trend of carbon isotopic composition, such that ??13C methane (C1) >??13C ethane (C2) >??13C propane (C3). In addition, we have observed isotopic reversals in the ??2H in the deepest samples. Isotopic reversals cannot be explained by current models of hydrocarbon gas generation. Previous observations of partial isotopic reversals have been explained by mixing between gases from different sources and thermal maturities. We have constructed a model which, in addition to mixing, requires Rayleigh fractionation of C2 and C3 to cause enrichment in 13C and create reversals. In the deepest samples, the normal trend of increasing enrichment of 13C and 2H in methane with increasing depth reverses and 2H becomes depleted as 13C becomes enriched. We propose that the reactions that drive Rayleigh fractionation of C2 and C3 involve redox reactions with transition metals and water at late stages of catagenesis at temperatures on the order of 250-300??C. Published ab initio calculated fractionation factors for C-C bond breaking in ethane at these temperatures are consistent with our observations. The reversed trend in ??2H in methane appears to be caused by isotopic exchange with formation water at the same temperatures. Our interpretation that Rayleigh fractionation during redox reactions is causing isotopic reversals has important implications for natural gas resources in deeply buried sedimentary basins. ?? 2010.

  20. Studying of shale organic matter structure and pore space transformations during hydrocarbon generation

    Giliazetdinova, Dina; Korost, Dmitry; Gerke, Kirill


    Due to the increased interest in the study of the structure, composition, and oil and gas potential of unconventional hydrocarbon resources, investigations of the transformation of the pore space of rocks and organic matter alterations during the generation of hydrocarbon fluids are getting attention again. Due to the conventional hydrocarbon resources decreasing, there will be a necessity to develop new unconventional hydrocarbon resources. Study of the conditions and processes of hydrocarbon generation, formation and transformation of the pore space in these rocks is pivotal to understand the mechanisms of oil formation and determine the optimal and cost effective ways for their industrial exploration. In this study, we focus on organic matter structure and its interaction with the pore space of shales during hydrocarbon generation and report some new results. Collected rock samples from Domanic horizon of South-Tatar arch were heated in the pyrolyzer to temperatures closely corresponding to different catagenesis stages. X-ray microtomography method and SEM were used to monitor changes in the morphology of the pore space and organic matter structure within studied shale rocks. By routine measurements we made sure that all samples (10 in total) had similar composition of organic and mineral phases. All samples in the collection were grouped according to initial structure and amount of organics and processed separately to: 1) study the influence of organic matter content on the changing morphology of the rock under thermal effects; 2) study the effect of initial structure on the primary migration processes for samples with similar organic matter content. An additional experiment was conducted to study the dynamics of changes in the structure of the pore space and prove the validity of our approach. At each stage of heating the morphology of altered rocks was characterized by formation of new pores and channels connecting primary voids. However, it was noted that

  1. Comparison of GC-MS, GC-MRM-MS, and GC × GC to characterise higher plant biomarkers in Tertiary oils and rock extracts

    Eiserbeck, Christiane; Nelson, Robert K.; Grice, Kliti; Curiale, Joseph; Reddy, Christopher M.


    Higher plant biomarkers occur in various compound classes with an array of isomers that are challenging to separate and identify. Traditional one-dimensional (1D) gas chromatographic (GC) techniques achieved impressive results in the past, but have reached limitations in many cases. Comprehensive two-dimensional gas chromatography (GC × GC) either coupled to a flame ionization detector (GC × GC-FID) or time-of-flight mass spectrometer (GC × GC-TOFMS) is a powerful tool to overcome the challenges of 1D GC, such as the resolution of unresolved complex mixture (UCM). We studied a number of Tertiary, terrigenous oils, and source rocks from the Arctic and Southeast Asia, with special focus on angiosperm biomarkers, such as oleanoids and lupanoids. Different chromatographic separation and detection techniques such as traditional 1D GC-MS, metastable reaction monitoring (GC-MRM-MS), GC × GC-FID, and GC × GC-TOFMS are compared and applied to evaluate the differences and advantages in their performance for biomarker identification. The measured 22S/(22S + 22R) homohopane ratios for all applied techniques were determined and compare exceptionally well (generally between 2% and 10%). Furthermore, we resolved a variety of angiosperm-derived compounds that co-eluted using 1D GC techniques, demonstrating the superior separation power of GC × GC for these biomarkers, which indicate terrigenous source input and Cretaceous or younger ages. Samples of varying thermal maturity and biodegradation contain higher plant biomarkers from various stages of diagenesis and catagenesis, which can be directly assessed in a GC × GC chromatogram. The analysis of whole crude oils and rock extracts without loss in resolution enables the separation of unstable compounds that are prone to rearrangement (e.g. unsaturated triterpenoids such as taraxer-14-ene) when exposed to fractionation techniques like molecular sieving. GC × GC-TOFMS is particularly valuable for the successful separation of

  2. Propriétés optiques de résidus de la pyrolyse kérogènes Optical Properties of Kerogen Pyrolysis Residues

    Alpern B.


    Full Text Available On étudie l'évolution des propriétés optiques de trois kérogènes peu évolués au cours de leur pyrolyse sous azote en programmation de température. Le premier appartient à une série lacustre (Green River Shales, le second à une série marine (Toarcien du bassin de Paris, le troisième à une série deltaïque (Crétacé du Cameroun. On constate la ressemblance de l'évolution artificielle avec la catagenèse (évolution accompagnant l'enfouissement des sédiments. On observe dans les deux premiers kérogènes l'existence de particules ressemblant à de la vitrinite, mais dont les propriétés optiques évoluent différemment. On incite en conséquence à une grande prudence dans l'utilisati n du pouvoir réflecteur de telles particules pour localiser dans les séries lacustres et marines la zone de formation du pétrole. On note l'intérêt de mesurer le pour réflecteur de la grande masse du kérogène et de mettre son évolution en relation avec celle des autres propriétés physiques. This article examines the evolution of the optical properties of three immature kerogens during their pyrolysis in nitrogen ut programmed temperature. The first kerogen comes from a lacustrine series (Green River Shales, the second from a marine series (Tourcian from the Paris Basin, and the third from a deltaic series (Cretaceous from Cameroon. There is a resemblance in their artificial evolution with catagenesis (evolution accompanying the burial of the sédiments. The first two kerogens cari be seen to contain particles resembling vitrinite, although with optical properties which evolve differently. Therefore, great cure must be taken in using the reflecting power of such particules ta situate the petroleum forming zone in lacustrine and marines séries. It is important ta measure the reflecting power of the general mass of the kerogen and to compare its evolution with that of the other physical properties.

  3. Organic geochemical study of domanik deposits, Tatarstan Republic.

    Nosova, F. F.; Pronin, N. V.


    in reducing environments. Mass chromatograms show the distribution of regular steranes, iso-steranes, lower molecular weight C21 and C22 steranes (pregnanes) (m/z 217) and triterpanes (m/z 191). The biomarkers distribution of the domanic samples generally suggests a major marine phytoplankton contribution relative to terrigenous land plant source input. The marine affinity is evident from the relatively abundant C27 steranes, which are biomarkers for marine algal contribution to organic matter and low C29 sterane contens. In this present study, samples are dominated by 5α, 14α, 17α (H)-20R and 5β, 14α, 17α (H)-20R steranes (biological configuration). The ratios of 20S/(20S+20R) for αααC29 steranes and ββ/(αα + ββ) for 5α-C29 steranes in the samples, are 0.21 to 0.55 and to 0.12 to 0.50, respectively. The thermal maturity level, assessed by values of several biomarker parameters has been estimated to be within end of diagenesis/eginning of catagenesis and correspond to theoretical vitrinite values (R0) in the range 0.57-0.65%.

  4. Organic geochemical study of domanik deposits, Tatarstan Republic.

    Nosova, F. F.; Pronin, N. V.


    the relatively abundant C27 steranes, which are biomarkers for marine algal contribution to organic matter and low C29 sterane contens. In this present study, samples are dominated by 5α, 14α, 17α (H)-20R and 5β, 14α, 17α (H)-20R steranes (biological configuration). The ratios of 20S/(20S+20R) for αααC29 steranes and ββ/(αα + ββ) for 5α-C29 steranes in the samples, are 0.21 to 0.55 and to 0.12 to 0.50, respectively. The thermal maturity level, assessed by values of several biomarker parameters has been estimated to be within end of diagenesis/eginning of catagenesis and correspond to theoretical vitrinite values (R0) in the range 0.57-0.65%.

  5. Résines et asphaltènes : évolution en fonction des types de matière organique et de leur enfouissement Resins and Asphaltenes: Evolution As a Function of Organic-Matter Type and Burial

    Castex H.


    several basins. It was shown that: (a Resins have higher mean carbon and hydrogen values as well as a lower C/H ratio than asphaltenes. Resins thus have a more aliphatic and or more alicyclic structure. On the other hand, asphaltenes contain more sulfur, oxygen end nitrogen. (b Sulfur and oxygen are not parameters enabling basins to be differentiated. (c Different types of organic matter are revealed by an H/C, O/C diagram. Their chemical evolution with burial is characterized by a decrease in hydrogen, oxygen and sulfur contents. Proton nuclear magnetic resonance (NMR and infrared spectroscopy (IRS were used to follow the structural evolution of resins and asphaltenes coming from different types of organic matter (algal, marine and terrestrial buried at increasing depths. NMR can be used to compute several structural parameters such as FA aromaticity and the degree of sigma substitution of the aromatic system. The FA factor seems to increase with burial and according to the type of organic matter, while sigma seems to decrease. These data were completed by infrared spectroscopy. The surface areas of the bands corresponding to the following functions were computed: (a OH in the 3700-2700 cm-1 range; (b carbonyl C-O around 1700 cm-1; (c aliphatic C-H at 2900, 2455 and 1380 cm-1; (d aromatic C-H at 1610 cm-1. Variations in the intensity of bands: (a decrease of aliphatic C-H and of C-O functions; (b increase of aromatic C-H and C-C are related to both the type of organic matter and its catagenesis.