stable carbon isotopes of coal derived gases sourced from the mesozoic coal measures in china coal derived large scale gas fields derived from the mesozoic coal measures in china are mainly distributed in the middle lower jurassic coal measures in the tarim junggar and turpan hami basins in northwest china and the upper triassic xujiahe formation coal measure in sichuan basin central china in 2011 the annual production was 21 6 109 m3 and the proved geological reserves were 2485 109 m3 accounting for 21 and 30 of the total in china respectively based on analyses of gas composition and stable carbon isotopes ratios of 203 samples and stable carbon isotopes of 102 co2 samples the following conclusions were made a based on diagnostic plots using the stable carbon isotopic and molecular composition of gas samples alkane gas from the mesozoic coal measures in china is shown to be coal derived b according to the 13c2 vs c2h6 plot of a great number of oil derived and coal derived gases in china it is concluded that gases with 13c2 28 5 are coal derived and those with 13c2 28 5 are oil derived in most cases c among the natural gases from the mesozoic coal measures in china primary coal derived gases with normal carbon isotopic distribution pattern among the c1 c4 alkanes i e 13c1 13c2 13c3 13c4 are dominant d carbon isotopic pattern reversal mainly results from the mixing of coal derived gases having different maturities but the same source and secondly from microbial oxidation of propane e g mu 3 and mu 4 wells in the gumudi gas field junggar basin e co2 in the coal derived gases from the mesozoic coal measures in china has both biogenic and abiogenic origins the biogenic origin is dominant and the abiogenic co2 is mainly found in the kuqa depression in the tarim basin and western sichuan basin f isotopic differences between heavy hydrocarbon gases and methane become less with increasing maturity

some potential applications of pyrolysis to basin studies a variety of pyrolysis systems can be used to obtain source rock evaluation and other data systems with bulk flow capabilities are best used to screen samples for subsequent detailed analysis but data must be interpreted in the light of possible mineral pyrolysate interactions non indigenous hydrocarbons can be detected by the same techniques but pyrolysis fid gc or alternatively pyrolysis gc plus pyrolysis bulk flow are required to identify and differentiate migrated hydrocarbons and refined petroleum products screening can be carried out in the laboratory or at the well location in the latter case data can be used for on site decision making as well as providing the groundwork for subsequent geochemical studies pyrolysis fid gc provides the most comprehensive means for screening in both laboratory and well site situations for detailed geochemical analysis pyrolysis gc is the most versatile technique providing both quantitative and qualitative ways to identify kerogen type classify bitumens and recognize contamination

organic geochemistry of oil and gas in the kuqa depression tarim basin nw china abstract the kuqa depression in the tarim basin nw china contains significant natural gas and condensate resources with only small amounts of black oil this study demonstrates that the primary reason for the accumulation of large natural gas reserves in the kuqa depression is the high maturity level of the jurassic coal bearing sequence that is currently at the peak stage of dry gas generation from the combined stable carbon isotopes and molecular biomarker data it is possible to identify two separate source rocks for the discovered hydrocarbon fluids the gases were primarily from the middle lower jurassic coals and associated clastic rocks and the oils were from the upper triassic lacustrine mudstones peak oil generation from the triassic source rocks occurred during the early miocene 23 12 ma b p these oils migrated laterally over relatively long distances 20 50 km reaching the outer periphery of the depression peak gas generation took place more recently perhaps during the past 5 ma the gases migrated mainly along faults over relatively short lateral distances resulting in accumulations adjacent to the over matured source kitchens different timings for the trap formation along the north and south margins and a late injection of gas into early oil accumulations provided favorable conditions for the formation of evaporative condensates and the preservation of gas pools in the more down dip reservoirs and oil pools in the more up dip locations

geochemistry characteristics and genetic types of natural gas in central part of the tarim basin nw china abstract according to the chemical carbon isotopic and hydrogen isotopic compositions and 3 he 4 he ratios of 127 natural gas samples the natural gas in the tarim basin is mainly composed of gaseous alkanes dominated by methane the contents of the gaseous alkanes decrease with the increase of their carbon numbers the 13 c values of ch 4 c 2 h 6 and c 3 h 8 in the platform area of the tarim basin vary in the range of 54 4 24 4 an average value of 39 2 43 1 26 7 an average value of 36 1 and 37 9 21 6 an average value of 31 8 respectively the overall carbon isotopic composition of the alkanes follows the trend of 13 c 1 13 c 2 13 c 3 13 c 4 and in some cases varies with 13 c 1 13 c 2 or 13 c 3 13 c 4 the lower carbon isotope values of methane 13 c 1 13 c 2 may be attributed to thermal sulfate reduction tsr and the higher propane value 13 c 3 13 c 4 was caused by the mixing of the natural gases of the same genetic type formed at different stages the methane hydrogen isotopes 2 h c 1 of the natural gases in the tarim basin are in the range of 195 122 with an average value of 156 the 3 he 4 he ratios of the natural gases are in the range of 2 3 10 8 66 8 10 8 suggesting that there is no deep mantle derived gas in the platform area of the tarim basin the carbon isotope fractionation of alkane gases 13 c 2 13 c 3 1 c 2 vs lnc 2 c 3 and c 2 c 3 vs 13 c 2 13 c 3 of the natural gases indicate that the oil type gas in the tarim basin has different predominant formation processes including kerogen cracking oil cracking oil and gas cracking secondary gas cracking and mixing of the kerogen cracking and oil cracking gases the gas evolved from gas cracking gas to oil and gas cracking gas and oil cracking gas along the direction from the west side of the manjar sag to the central tarim basin the natural gases in some areas of tazhong are the mixtures of the kerogen cracking and oil cracking gases

a reappraisal of kerogen formation abstract comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass kerogen and fossil fuels

revised models for hydrocarbon generation migration and accumulation in jurassic coal measures of the turpan basin nw china abstract whether or not the lower middle jurassic coal measures in the turpan basin of nw china have generated commercial quantities of liquid petroleums is a problem of considerable importance that remains contentious as it has not yet been resolved unequivocally this study provides evidence against the jurassic humic coals as the only major source for the oils discovered in the taibei depression of this basin and suggests additional significant contributions from the upper permian and middle lower jurassic lacustrine source rocks the carboniferous permian marine source rocks may have been important also in limited locations along the major basement faults molecular and petrographic data indicate that the majority of the middle jurassic strata are currently immature or marginally mature with respect to hydrocarbon generation within the major depocenters the middle lower jurassic coal bearing strata of the baodaowan and xishanyao formations has reached the conventional oil window i e with vitrinite reflectance 0 7 ro pre jurassic upper permian in particular derived hydrocarbons appear to be widespread in extracts of fractured jurassic coal and fine grained rocks large differences have been observed in the absolute concentrations of biomarker compounds in rock extracts of various source intervals thus coaly biomarker signatures of the oils most likely resulted from mixing and migration contamination when hydrocarbons derived from mature source rocks migrated up through highly fractured coal seams along deep seated faults in addition to conventional exploration targets revised petroleum generation and accumulation models predict that the focus in the turpan basin should also include deep structures within the carboniferous permian strata and subtle low magnitude anticlines and stratigraphic traps within the triassic jurassic sections crown copyright

anatomy of an intruded coal ii effect of contact metamorphism on organic δ13c and implications for the release of thermogenic methane springfield no 5 coal illinois basin abstract concerns about the present day accelerated rate of carbon input to the atmosphere have prompted the search for comparable events throughout earth s history recent research has attempted to determine the cause of such events represented as negative 13 c excursions within the sedimentary record and their subsequent effect on the earth it has been suggested that such excursions could be the result of the large scale release of 13 c depleted thermogenic methane produced by the intrusion of large igneous provinces lips into organic rich rocks and or coal e g mcelwain et al 2005 svensen et al 2004 2007 our study asserts that if intrusions result in significant release of 13 c depleted thermogenic methane from intruded coals 13 c enriched coal should be observed adjacent to the intrusions in this study values of bulk organic 13 c 13 c org are reported for fifteen samples along a coal transect in the illinois basin where a pennsylvanian age coal the springfield or no 5 coal is intruded by a permian ultramafic dike the samples reveal significant bulk geochemical and petrographic changes within the alteration halo for example volatile matter vm decreases towards the intrusion whereas fixed carbon fc and vitrinite reflectance r r both increase accompanied by the development of natural coke both isotropic and anisotropic mosaic structure devolatilization vacuoles and carbonate mineralization reflectance levels and coke development are consistent with exposure to temperatures 450 500 c despite the high level of alteration of the organic matter no significant change is observed in 13 c org values across the transect vary by less than 0 5 along this transect 13 c org does not correlate with r r and does not appear to be influenced by maceral composition the intruded coals show no evidence of pyrolytic carbon that could influence 13 c org the relatively high vm contents of the intruded coals compared to coals that have undergone normal burial maturation and the lack of any trend in 13 c org approaching the intrusion raises questions about previously published models of the effects of large scale igneous intrusions on atmospheric composition and 13 c org excursions associated with oceanic anoxic events this study underscores the importance of the use of organic petrography in combination with isotope geochemistry to determine if contact metamorphosed coals and organic rich shales could have released a significant amount of 13 c org depleted volatiles leading to negative 13 c org excursions in the sedimentary record

carbon and hydrogen stable isotope variations in kerogen during laboratory simulated thermal maturation carbon and hydrogen stable isotope measurements on sapropelic and humic kerogen isolated from laboratory heated sediments reveal several isotopic trends an initial depletion of 13c and d 2h or deuterium in kerogen isolated from the heated sapropelic sediment appears to be the result of isotopic heterogeneity interaction with soluble organic matter and or volatilization of a heat labile fraction of the protokerogen during the main isotopic trend the sapropelic kerogen becomes enriched in 13c and d by about 5 and 50 ppt parts per thousand respectively theoretical calculations based on a rayleigh fractionation process suggest that this trend is largely controlled by the generation of isotopically light methane directly from the ker gen this argument also applies to the main hydrogen isotopic trend for the humic kerogen which becomes enriched in d by about 90 ppt the main 13c trend for the humic kerogen however results in a maximum enrichment in 13c of only about 1 6 ppt and appears to be largely controlled by factors other than methane a final depletion trend in 13c and d occurs for the sapropelic kerogen at very high temperatures this may be due to a reduced isotopic fractionation at higher temperatures or to the indirect generation of methane from kerogen through a liquid intermediate which is subsequently coked to pyrobitumen

origin of natural gas from the ordovician paleo weathering crust and gas filling model in jingbian gas field ordos basin china abstract the ordos basin the second largest natural gas producing basin in china is one of the most tectonically stable sedimentary basins favorable to natural gas generation and preservation the origin and potential source of the jingbian gas field one of the five giant gas fields in the basin containing the ordovician paleo weathering crust as reservoir strata remains unclear the question is whether gas is generated from carboniferous permian coal measures or ordovician carbonates this study provides abundant gas geochemical evidence which clarifies its origin and source among 82 natural gas samples collected from the ordovician paleo weathering crust in the jingbian gas field c1 c4 gaseous hydrocarbons are dominant with low amounts of non hydrocarbons co2 h2s and n2 the content of c1 c4 ranges from 79 26 to 99 93 with a gas dryness c1 c1 4 of 0 981 0 999 suggesting that natural gases are dry and possibly originate from a high to over mature source the carbon isotopic compositions of methane and its homologues in natural gases from the ordovician paleo weathering crust vary widely with 13c1 13c2 and 13c3 values of 38 9 to 29 1 37 5 to 22 2 and 30 0 to 20 9 respectively the 13c2 and 13c3 values in the jingbian gas field are much more negative than those of typical coal type gas in sulige wushenqi yulin daniudi and kela2 gas fields the carbon isotopic signature suggests that the natural gas in the ordovician paleo weathering crust in the jingbian gas field most likely originates from ordovician carbonates containing sapropelic organic matter the measured d values of methane range from 177 to 155 and support our hypothesis of the natural gases originating from marine sapropelic organic matter the thermal maturity of the natural gases in the ordovician paleo weathering crust is at a high to over mature stage suggesting that the gases originated from secondary cracking of oil and gas at high temperature and pressure thermochemical sulfate reduction tsr might partially play a role in the alteration of gas dryness and 13c1 in those areas where gypsum is present as an effective cap rock mixing of high to over mature secondary cracking gas from the ordovician source and coal type gas from carboniferous permian coal in the jingbian gas field is minor

fluid evolution at the variscan front in the vicinity of the aachen thrust quartz carbonate chlorite veins were studied in borehole samples of the rwth 1 well in aachen veins formed in devonian rocks in the footwall of the aachen thrust during variscan deformation and associated fluid flow primary fluid inclusions indicate subsolvus unmixing of a homogenous h2o co2 ch4 n2 na k cl fluid into a h2o na k cl solution and a vapour rich co2 h2o ch4 n2 fluid the aqueous end member composition resembles that of metamorphic fluids of the variscan front zone with salinities ranging from 4 to 7 nacl equiv and maximum homogenisation temperatures of close to 400 c pressure estimates indicate a burial depth between 4 500 and 8 000 m at geothermal gradients between 50 and 75 c 26 mpa but pressure decrease to sublithostatic conditions is also indicated probably as a consequence of fracture opening during episodic seismic activity a second fluid system mainly preserved in pseudo secondary and secondary fluid inclusions is characterised by fluid temperatures between 200 and 250 c and salinities of 5 nacl equiv bulk stable isotope analyses of fluids released from vein quartz calcite and dolomite by decrepitation yielded dh2o values from 89 to 113 13cch4 from 26 9 to 28 9 vpdb and 13cco2 from 12 8 to 23 3 vpdb the low d and 13c range of the fluids is considered to be due to interaction with cracked hydrocarbons the second fluid influx caused partial isotope exchange and disequilibrium it is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the stavelot venn massif the metamorphic fluid was focused along major thrust faults of the variscan front zone such as the aachen thrust a second fluid influx was introduced from formation waters in the footwall of the aachen thrust as a consequence of progressive deformation mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics

sources and mechanisms of formation of gaseous hydrocarbons in sedimentary rocks abstract accepted concepts of principal stages of hydrocarbon formation fail to satisfactorily explain the accumulation of supergiant gasfields in west siberia u s s r such as for example urengoy which comprise 30 of the proven gas reserves of the world a new mathematical model has been developed which applies the concept of activation energy distribution to the formation of gases characteristic differences in the molecular structure of humic and sapropelic source organic matter are expressed in different activation energy distributions the model allows the calculation of isotope values for different types of organic matter and their dependence on maturity application of the model to west siberia suggests that the supergiant gas accumulations in urengoy are more likely formed from terrestrial organic matter through thermochemical reactions at moderate depths and are not the result of either deep overmature or bacteriogenic processes the new mathematical model suggests that humic organic matter in general has a high methane generating capacity at comparably low maturities of organic matter equivalent to 0 5 0 7 on the vitrinite reflectance scale

reconstructing a mid cretaceous landscape from paleosols in western canada abstract the albian stage of the mid cretaceous was a time of equable climate conditions with high sea levels and broad shallow epeiric seas that may have had a moderating affect on continental climates a late albian landscape surface that developed during a regression and subsequent sea level rise in the western canada foreland basin is reconstructed on the basis of correlation of paleosols penetrated by cores through the paddy member of the peace river formation reconstruction of this landscape refines chronostratigraphic relationships and will benefit future paleoclimatological studies utilizing continental sphaerosiderite proxy records the paleosols developed in estuarine sandstones and mudstones and they exhibit evidence of a polygenetic history upon initial exposure and pedogenesis the paddy member developed deeply weathered well drained cumulative soil profiles later stages of pedogenesis were characterized by hydromorphic soil conditions the stages of soil development interpreted for the paddy member correlate with inferred stages of pedogenic development in time equivalent formations located both basinward and downslope upper viking formation and landward and upslope boulder creek formation on the basis of the genetic similarity among paleosols in these three correlative formations the paleosols are interpreted as having formed along a single continuous landscape surface results of this study indicate that the catena concept of pedogenesis along sloping landscapes is applicable to ancient successions sphaerosiderites in the paddy member paleosols are used to provide proxy values for meteoric 18o values at 52 n paleolatitude in the cretaceous western interior basin the meteoric 18o values are used to refine existing interpretations about the mid cretaceous paleolatitudinal gradient in meteoric 18o values and the mid cretaceous hydrologic cycle

the relationship between aromaticity vitrinite reflectance and maceral composition of coals implications for the use of vitrinite reflectance as a maturation parameter abstract previous studies on the aromaticity f a of coals have either limited themselves to the effects of rank or to differences between the macerals and generally conclude that f a and rank increase simultaneously although not necessarily linearly this study contains 13 c cp mas nmr analysis data of more than 70 coals obtained from different coal basins these are combined with published data to produce a data base with more than 130 analyses the aim is to determine the influence of rank and maceral composition on the measured f a of coals a plot of f a vs r o vitrinite reflectance shows a non linear relationship that can be described by a polynomial equation the shape of the curve produced by this equation is determined by the processes that occur during maturation only approx 50 of the coals in the data base have f a values that are accurately predicted by the vitrinite reflectance this is an indication of the large spread of values observed in the plot of f a vs r o as a result of the processes that occur during maturation the influence of the maceral composition on the f a was restricted to coals with r omax values 0 70 r o the equation generated shows that more than 80 of the coals tested with this level of rank have f a values that can be accurately predicted by an equation containing the r omax value the total vitrinite content and the contents of fusinite semifusinite and macrinite in the coals comparison of the f a values obtained from vitrinitic type iii kerogen with the f a values obtained from liptinitic sporinites and type ii kerogens reveals a pattern which illustrates the structural changes that occur during maturation both vintrinites and liptinites show a change in the slope in an f a vs r o plot although the reflectance level at which the change in slope occurs differs between the two kerogen types the changes in molecular structure that occur within the two kerogen types during maturation are discussed the implications of the f a r o relationship of vitrinites on the use of vitrinite reflectance as a maturation parameter are also discussed

evaluating the gas content of coals and isolated maceral concentrates from the paleocene guasare coalfield venezuela abstract this work presents the results from evaluating the gases sorbed by coal samples extracted from the paleocene guasare coalfield marcelina formation northwestern venezuela as well as by their distinct maceral concentrates the aim of this work has been to obtain an initial experimental main value of the gas content per unit weight of high volatile bituminous a coal samples from the open pit paso diablo mine an additional goal was to study differences in the ch 4 storage ability of the distinct maceral groups forming part of the coal matrix both the coal samples and the maceral concentrates were studied by thermogravimetric analysis tga in order to determine the temperature to be used in subsequent experiments on line analyses of hydrocarbons c 1 c 2 c 3 and co 2 yielded gas concentrations plus 13 c values thermogenic gas is prevalent in the guasare coals with vitrinite reflectance r o values from 0 65 to 0 88 the amount of gas retained in the coals and maceral concentrates was measured with a special device that allows determination of the volume of gas sorbed by a solid sample subjected to controlled thermal treatment the average coalbed gas concentration obtained was 0 51 cm 3 g the following list of maceral concentrates shows the relative capacity for the volume of sorbed gas per unit weight inertinite low density vitrinite liptinite high density vitrinite it is concluded that the gas volumes retained in the distinct maceral concentrates are not controlled by porosity but rather by their microscopic morphology

sequence stratigraphy of a condensed low accommodation succession lower upper cretaceous dakota sandstone henry mountains southeastern utah cretaceous low accommodation deposits have been extensively studied in the subsurface of the western interior of north america because of their prolific hydrocarbon production and remaining potential understanding the stratigraphic complexities of these deposits in the subsurface relies strongly on detailed outcrop analogs in this study the dakota sandstone was examined along 100 km 62 mi of semicontinuous outcrop between the towns of hanksville and ticaboo in the henry mountains of southeastern utah this region represented a low accommodation setting located over the forebulge of the cretaceous western interior basin during accumulation of the unit the dakota sandstone is 0 to 38 m 125 ft thick of cenomanian age and records multiple cycles of sediment accumulation the dakota sandstone is subdivided into two condensed top truncated stratigraphic sequences the upper of which contains two parasequences the basal parts of both sequences are composed of braided fluvial conglomerates and sandstone overlain by tidally influenced fluvial sandstone inclined heterolithically stratified estuarine mudstone carbonaceous shale and coal the overlying parasequences consist of coarsening upward lower to upper shoreface mudstone sandstone tidal inlet deposits and oyster shell concentrations these facies define tripartite subdivisions of depositional environments typical of wave dominated estuaries the fluvial deposits may represent lowstand deposits but overall sediments accumulated during transgressive systems tracts tst the parasequences recorded in the henry mountains are similar to the dakota sandstone of northwestern new mexico and to high frequency sequences identified in the kaiparowits plateau approximately 80 km 50 mi to the southwest which suggests eustatic driving mechanisms the best potential for hydrocarbon reservoirs occurs in fluvial sandstones and conglomerates

geochemical characteristics and source of natural gases from southwest depression of the tarim basin nw china abstract the molecular compositions and stable carbon and hydrogen isotopes of natural gases from the kekeya kedong and akemomu gas fields in the southwestern depression of the tarim basin were investigated to distinguish between coal derived and oil associated gases the carbon and hydrogen isotope ratios indicate that the gaseous alkanes from these three fields were mainly coal derived and sourced from the middle lower jurassic humic source rocks the gaseous alkanes in natural gas from the kekeya and kedong fields were generated from low maturity humic source rocks however the light hydrocarbons display the characteristics of marine sapropelic gas and the high d 1 values and partial carbon isotopic reversal of alkanes indicated that the gases had been mixed with oil associated gas derived from the carboniferous permian sapropelic source rocks the alkanes in natural gas from the akemomu field display high carbon isotopic ratios and were probably derived from the middle lower jurassic humic source rocks in high to overmature stage the high contents of co 2 with high 13 c co2 values were mainly derived from the thermal decomposition of carboniferous limestones the high content of n 2 was likely derived from highly overmature coal measure source rocks

incision and filling of a lowstand valley late albian viking formation at crystal alberta canada abstract crystal field in the albian viking formation represents the fill of a lowstand incised valley at least 55 km long 7 12 km wide and up to 32 m deep the valley trends south north with a smaller arm trending east west the open sea lay to the north and east the valley cuts into five regionally extensive sandier upward successions of open marine bioturbated mudstones and sandstones there were two separate episodes of valley filling the first consists of 1 dominantly parallel laminated sandstones in the south that grade northward into 2 bioturbated mudstones in the central part of the valley these grade in turn into 3 bioturbated sandstones at the northern seaward end of the valley the valley morphology restricted trace fauna and tripartite facies distribution suggest an estuarine environment the sandstones in the south are interpreted as deposits of a bay head delta and the central basin mudstones represent the turbidity maximum the bioturbated sandstones in the north were emplaced into the estuary from the marine end there is little evidence of tidal deposits and the estuary appears to have been wave dominated the second valley at crystal is narrower and cuts into the first till the second fill consists of 1 interbedded fluvial sandstones and conglomerates in the south that grade northward through 2 sandstones into 3 bioturbated sandstones there are no central basin mudstones and the filling appears to have been fluvially dominated the base of valley 1 represents an original fluvially formed sequence boundary completely modified by marine transgression whereas the base of valley 2 is a fluvially cut sequence boundary in the south and a marine modified sequence boundary in the north the valley fill deposits are truncated by a transgressive surface of erosion the valley morphology suggests a drop of relative sea level of at least 30 m to incise valley 1 and an equivalent rise to fill the valley there was then a second 30 m relative fall and a second 30 m rise to fill valley 2 the sandbodies within the valley are poorly connected as reservoirs their distribution is related to the two separate phases of valley cutting and filling and to the different points of coarse sediment input the bayhead delta and the marine ends of the main valley and the east arm

variation in pyrolysate composition of sediments from the jurassic walloon coal measures eastern australia as a function of thermal maturation examination of a natural maturity sequence from the jurassic walloon coal measures by quantitative flash pyrolysis gas chromatography py gc and low temperature sealed tube pyrolysis reveals systematic changes in pyrolysate composition in particular gas to oil ratios composition of gas and liquid normal hydrocarbons aromatic and heteroatom content are examined for this immature oil prone rock as it is taken artificially and naturally through the oil window liquid hydrocarbon generation giving a product with a high wax content is shown to occur over a relatively narrow range of maturation significant quantities of gas are generated and the gas to oil ratio remains relatively constant during the main phase of oil generation this reflects a uniform distribution of oil and gas precursors in the original labile kerogen at higher rank where increasing generation from the residual refractory kerogen occurs there is a progressive decrease in the yield of liquid hydrocarbons concomitant with an increase in the gas to oil ratio

new insights into the chemical composition of chitinozoans the chemical structure of isolated chitinozoan specimens extracted from early silurian marine rocks has been investigated by micro ftir laser micro raman spectroscopy and laser micropyrolysis gas chromatography mass spectrometry lmpy gc ms the samples were subjected to relatively low thermal stress as attested by several indices lmpy gc ms and micro ftir indicate that chitinozoans consist mostly of a kerogen network dominated by aromatic groups with a low contribution of aliphatics and oxygen or nitrogen bearing compounds no chitin related product was found in the pyrolysate of the chitinozoans confirming previous findings on the occurrence of this biopolymer in the fossil record

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

assessment of hydrocarbon source rock potential of polish bituminous coals and carbonaceous shales abstract we analyzed 40 coal samples and 45 carbonaceous shale samples of varying thermal maturity vitrinite reflectance 0 59 to 4 28 from the upper carboniferous coal bearing strata of the upper silesian lower silesian and lublin basins poland to evaluate their potential for generation and expulsion of gaseous and liquid hydrocarbons we evaluated source rock potential based on rock eval pyrolysis yield elemental composition atomic h c and o c and solvent extraction yields of bitumen an attempt was made to relate maceral composition to these source rock parameters and to composition of the organic matter and likely biological precursors a few carbonaceous shale samples contain sufficient generation potential pyrolysis assay and elemental composition to be considered potential source rocks although the extractable hydrocarbon and bitumen yields are lower than those reported in previous studies for effective type iii source rocks most samples analysed contain insufficient capacity for generation of hydrocarbons to reach thresholds required for expulsion primary migration to occur in view of these findings it is improbable that any of the coals or carbonaceous shales at the sites sampled in our study would be capable of expelling commercial amounts of oil inasmuch as a few samples contained sufficient generation capacity to be considered potential source rocks it is possible that some locations or stratigraphic zones within the coals and shales could have favourable potential but could not be clearly delimited with the number of samples analysed in our study because of their high heteroatomic content and high amount of asphaltenes the bitumens contained in the coals are less capable of generating hydrocarbons even under optimal thermal conditions than their counterpart bitumens in the shales which have a lower heteroatomic content

revelation of organic matter sources and sedimentary environment characteristics for shale gas formation by petrographic analysis of middle jurassic dameigou formation northern qaidam basin china abstract the 7th member of middle jurassic dameigou formation j2d7 in northern qaidam basin china was proposed to have good hydrocarbon generating potential in previous studies here we apply an integrated petrographic and geochemical analysis to investigate the depositional environment real thermal maturity and shale gas potential of organic matter om rich assemblage the relatively high content of c29 regular sterane 56 8 62 8 and vitrinite predominance in maceral composition suggesting plenty of higher plant input combined with the high pristane phytane ratio pr ph 2 8 8 2 and low gammacerane index 0 2 0 4 reveals oxic water column with in situ depositional condition of carbonaceous mudstone when the lower j2d7 was deposited the maceral composition of oil shale at the upper part of j2d7 is mainly amorphous om with small proportion of reworked vitrinite and inertinite consistent with a mainly algea and small amount of exogenous om input when associated with low pr ph 0 8 and high gammacerane index 4 3 the oil shale was deposited in an anoxic saline water column with mainly zooplankton om source the geochemical and petrographic result implies a transitional environment ranging from suboxic semi saline to oxic fresh water environment with varying proportion of higher plant and algae input by in situ deposition and distant transportation for the mudstone at the middle part of j2d7 by use of random reflectance ro distribution two sedimentary environment microcycles which are confirmed by maceral composition from the depth of 1983 m to 1962 m and 1954 m to 1931 9 m are differentiated within the homogenous mudstone section the variation of om input condition and alternation of depositional environment led to accumulation and deposition of various kinds of abundant om when j2d7 was deposited although the om has actually low maturity at oil window with vitrinite reflectance around 0 6 according to the petrographic results the liptinite inherited from higher plants especially suberinite is the main maceral to generate gaseous hydrocarbons at the low maturity which implies that the dameigou formation j2d7 of qaidam basin is of gas potential

characterization of pyrolysates from maceral components of tarim coals in closed system experiments and implications to natural gas generation abstract the macerals vitrinite exinite fusinite and semi fusinite from low maturity coal vrr 0 40 of the manjiaer sag tarim basin were isolated and subjected to isothermal pyrolysis in a sealed stainless steel reactor at temperatures ranging from 250 to 550 c in 50 c intervals for a duration of 72 h gas yields chemical and isotopic compositions vary significantly for the different coal macerals total gas yields predominantly ch4 and co2 from exinite and vitrinite are much higher than those from fusinite and semi fusinite carbon dioxide generated from exinite is slightly enriched in 13c 13 c co 2 range 19 7 to 12 2 as compared to co2 produced from vitrinite 13 c co 2 range 22 4 to 19 1 methane produced from exinite 13 c ch 4 range 35 0 to 30 3 tends to be isotopically lighter than methane generated from inertinite fusinite and semi fusinite 13 c ch 4 range 33 7 to 25 2 interestingly the 13 c ch 4 values of all macerals show a similar evolution pattern with temperature the initial gas is isotopically heavy then becomes lighter at moderate temperatures and finally becomes heavier again this may be an indication of isotopic heterogeneity within the coal precursors hydrocarbon potential of coal closely depends on the maceral composition exinite shows the highest hydrocarbon generation potential followed by vitrinite while inertinite has only a poor hydrocarbon potential with increasing thermal stress n alkane parameters such as oep and cpi decrease while the c 21 c 22 ratio increases and the bimodal pattern of the n alkane distribution changes to a unimodal pattern the pr ph ratio varies irregularly through catagenesis

organic geochemical and stable carbon isotopic investigation of coals formed in low lying and raised mires within the eastern alps austria abstract up to 16 m thick coal seams formed in miocene pull apart basins within the eastern alps in low lying and raised mires despite similar rank sub bituminous stage coal quality differs significantly coals from low lying mires e g fohnsdorf are characterized by significantly higher ash yields and sulfur contents than coals from raised mires e g leoben organic geochemical and carbon isotope investigations were performed to assess the differences in facies the fohnsdorf coals are characterized by higher yields of soluble organic matter som slightly higher proportions of hydrocarbons in the som generally lower pristane phytane ratios and the occurrence of high corg normalized n alkane concentrations only n alkane patterns in the leoben samples show a marked odd over even predominance these differences are indicative of a more intensive dys to anaerobic biochemical degradation of plant material within the fohnsdorf mire terpenoid biomarkers characteristic of conifers and angiosperms were detected in the leoben coals whereas the latter are missing in the fohnsdorf samples in the leoben coals higher saturated to aromatic diterpenoid ratios were detected than in the fohnsdorf coals because of similar rank enhanced aromatisation in the fohnsdorf basin is probably related to microbial activity despite this the fohnsdorf coals are characterized by lower hopane concentrations the results imply that the aromatisation of terpenoid biomarkers is governed by the activity of anaerobic rather than aerobic bacteria an overall negative correlation between 13c of organic matter and the degree of aromatisation of diterpenoid biomarkers is observed it is suggested that the carbon isotopic composition results from different extents of microbial degradation of the biomass the fohnsdorf coals are rich in sulfur high contents of coalbed methane were encountered during mining suggesting high activities of anaerobic bacteria in a nearly neutral sulfate bearing brackish environment of the low lying mire and methanogenesis during or after coalification sulfate reduction and methanogenesis are known to increase 13c values of residual organic matter