unconventional shale systems a comparative study of the in source sweet spot developed in the lacustrine chang 7 shale and the marine barnett shale abstract the upper triassic chang 7 shale and the mississippian barnett shale two remarkable shale systems that are considered promising unconventional shale oil gas targets in china and the usa respectively have different kerogen types that formed under lacustrine and marine environments in this study seventy six and ninety seven drilled core samples were collected separately from the zhang 22 well ordos basin and the mesquite 1 well fort worth basin respectively for determining the hydrocarbon generation retention and migration behaviors as well as the intrasource fractionation in the two shale successions geochemical indications of potentially producible oil as indicated by the oil crossover effect and the tmax shift phenomenon as well as the geochemical and molecular compositions of retained hydrocarbon suggest two categories of intervals in the chang 7 and barnett shale systems namely the in source sweet spot and the generative unit oils retained in the in source sweet spot have migrated from the adjacent generative unit and have been subjected to stratigraphic fractionation over geological time these oils are proportionally rich in aliphatic fraction and moderate chain length moieties which significantly improve the fluid mobility and producibility the oil quality improved by fractionation the weak adsorptive affinity of oil to organic matter and the good shale frackability all provide promise for the exploration and production potential of shale oil from the chang 7 and the barnett shale systems

impact of high water pressure on oil generation and maturation in kimmeridge clay and monterey source rocks implications for petroleum retention and gas generation in shale gas systems this study presents results for pyrolysis experiments conducted on immature type ii and iis source rocks kimmeridge clay dorset uk and monterey shale california usa respectively to investigate the impact of high water pressure on source rock maturation and petroleum oil and gas generation using a 25 ml hastalloy vessel the source rocks were pyrolysed at low 180 and 245 bar and high 500 700 and 900 bar water pressure hydrous conditions at 350 c and 380 c for between 6 and 24 h for the kimmeridge clay kcf at 350 c rock eval hi of the pyrolysed rock residues were 30 44 mg g higher between 6 h and 12 h at 900 bar than at 180 bar also at 350 c for 24 h the gas expelled oil and vitrinite reflectance vr were all reduced by 46 61 and 0 25 ro respectively at 900 bar compared with 180 bar at 380 c the retardation effect of pressure on the kcf was less significant for gas generation however oil yield and vr were reduced by 47 and 0 3 ro respectively and rock eval hi was also higher by 28 mg g at 900 bar compared with 245 bar at 12 h the huge decrease in gas and oil yields and the vr observed with an increase in water pressure at 350 c for 24 h and 380 c for 12 h maximum oil generation were also observed for all other times and temperatures investigated for the kcf and the monterey shale this shows that high water pressure significantly retards petroleum generation and source rock maturation the retardation of oil generation and expulsion resulted in significant amounts of bitumen and oil being retained in the rocks pyrolysed at high pressures suggesting that pressure is a possible mechanism for retaining petroleum bitumen and oil in source rocks this retention of petroleum within the rock provides a mechanism for oil prone source rocks to become potential shale gas reservoirs the implications from this study are that in geological basins pressure temperature and time will all exert significant control on the extent of petroleum generation and source rock maturation for type ii source rocks and that the petroleum retained in the rocks at high pressures may explain in part why oil prone source rocks contain the most prolific shale gas resources

post oil solid bitumen network in the woodford shale usa a potential primary migration pathway abstract an important if not predominant component of porosity in many gas shales has been identified in organic matter an organic network in shales has been described in the literature as organic matter generalized term kerogen primary or bitumen secondary recognition of the type and origin of an organic network in shales has relevance in establishing the origin and timing of porosity and fracture development the pervasive nature of the organic network adopting the shape of pores in type ii kerogen rich woodford shale suggests it is the residue of primary oil migration we use the term post oil solid bitumen to distinguish this bitumen occurrence from pre oil solid bitumen defined as a precursor of oil three forms of this post oil solid bitumen network are recognized in reflected white light at 500 magnification and confirmed in backscattered scanning electron microscope images at 2500 magnification namely speckled 1 2 m wispy 2 5 m and connected 5 m the post oil solid bitumen network demonstrates the prior occurrence of oil generation and migration within this hydrocarbon source rock provides porosity for hydrocarbon storage sites and forms hydrocarbon migration pathways

deep basin gas new insights from kinetic modelling and isotopic fractionation in deep formed gas precursors abstract the formation and origin of high maturity gas from tertiary sediments in the mackenzie delta have been studied using programmed temperature closed system pyrolysis mssv different open system devices and numerical models for geological predictions a sample from the type iii taglu sequence was selected as being representative for one of the major hydrocarbon prone deltaic sediments in this area artificial maturation under closed system conditions was carried out at three different heating rates 0 2 0 7 and 5 0 k min the gas composition as well as carbon isotopes of formed methane were analysed using gc fid and gcirms structural characteristics of the residual macromolecules formed during these experiments were studied at different levels of thermal stress immature 360 412 and 470 c under closed system conditions the taglu sequence forms unusually high amounts of gas at extreme levels of thermal stress the recombination of previously formed hydrocarbons with residual kerogen coal through aromatisation polycondensation reactions is the best explanation for these high temperature features a feature previoulsy reported for the heather formation north sea when the neoformed material becomes active and forms gas at high levels of maturity carbon isotopes measured on methane fall to values that are 10 lighter than those from open system gas formation networks a kinetic model for hydrocarbon formation from this neoformed organic matter has been developed this predicts that the initial phase of the neoformation processes shift from post oil formation conditions at laboratory heating rates to peri oil formation conditions when it comes to geological heating rates this may indicate that recombination reactions through aromatisation polycondensation processes partly influence the major phase of petroleum formation in nature and also justifies an enhancement of gas prospectivity at great depths especially in deep basins where source rock maturities exceed 2 5 ro

using natural maturation series to evaluate the utility of parallel reaction kinetics models an investigation of toarcian shales and carboniferous coals germany abstract open system pyrolysis is routinely performed on immature samples in order to determine the kinetic parameters of petroleum generation at both bulk and molecular levels this study tested such predictions for type ii and type iii organic matter by making calibrations with both artificial and natural maturity sequences of toarcian shales posidonia shale 0 48 1 44 rr and carboniferous vitrains 0 74 2 81 rr both natural series showed little or no compositional variability attributable to kerogen type artificially matured samples were prepared by non isothermal heating 0 7 k min of the least mature samples up to end temperatures between 375 and 470 c under either closed or open system conditions measured generation rate versus temperature curves were analyzed assuming a distributed system of activation energies and a single frequency factor in each case the resulting kinetic parameters were then used to assess bulk petroleum formation rates for geological heating conditions in the case of all artificially matured samples measured and predicted bulk petroleum formation rate vs temperature curves for each maturation stage remain within the original envelope defined by the least mature sample despite an upward shift of tmax temperatures this confirms that the reactions taking place during both the pyrolysis measurements and simulated maturation processes are the same involving mainly homolytic cracking a similar pattern of measured and predicted rate curves is reproduced by the natural maturation sequence of the toarcian shales in the maturity range of 0 53 to 1 44 rr suggesting that petroleum generation within these natural systems also results from cracking reactions and therefore that petroleum generation over geological time can be reliably extrapolated from open system pyrolysis of the appropriate immature sample by contrast significant deviations are observed for the natural coal series with measured and predicted rate curves extending beyond the immature envelopes in accordance with the pronounced increase of frequency factors and of protonated aromatic carbon concentrations this behavior is attributed to solid state aromatization reactions which compete with product generation during natural coalification but which are not reproducible to the same extent by experimental heating it is concluded that petroleum generation from vitrinitic coals over geological time cannot be reliably extrapolated from open system pyrolysis of low rank samples

organic geochemistry and petrography of lower cretaceous wealden black shales of the lower saxony basin the transition from lacustrine oil shales to gas shales abstract ninety seven wealden black shale samples from three wells in the lower saxony basin have been studied by organic geochemical and organic petrographical methods to determine their maturity organic facies and depositional environment the maturities of the three wells range from early mature ex a late to postmature ex c to overmature ex b as determined by vitrinite reflectance measurements diamondoid ratios and other geochemical maturity parameters ex c and ex b show distinct petrographic features related to oil generation and migration in particular the occurrence of dispersed solid bitumen replacing initial type i kerogen suggests a formerly active petroleum system structural and textural differences between early mature alginites and solid bitumen in postmature to overmature samples show an alteration of the pore system with increasing maturity a freshwater depositional environment is indicated by widespread occurrence of botryococcus algae and other small alginite particles predominating in the immature well these alginites are absent in the more mature gas shales of wells ex c and ex b geochemical evidence of algae and phytoplankton in general is provided by numerous biomarker parameters while the occurrence of carotane in some samples indicates events of increased salinity although no hypersaline conditions are inferred due to very low gammacerane indices increased amounts of vitrinite and inertinite in samples of ex b suggest locally significant terrigenous input of organic matter for some periods during wealden shale deposition high sulfur organic carbon ratios provide evidence for sulfate rich waters and partly anoxic bottom water conditions while the lower mature lacustrine source rocks generate paraffinic waxy oils gas and condensates are produced at post mature stages furthermore maturity distribution maps from 3d numerical petroleum systems modeling reveal substantial differences in respect to petroleum generation

temporal isotopic variations of dissolved silicon in a pristine boreal river abstract it has previously been concluded that the stable si isotopes are fractionated during geochemical and biogeochemical elemental transfers such as weathering and precipitation of clays and biogenic si which has opened up the possibility of using si as a tracer in natural terrestrial ecosystems furthermore quantification of the biogenic impact on the biogeochemical si cycle has attracted significant scientific interest since biological control has been suggested previous observations of seasonal variations in the dissolved si isotopic pattern further imply that high frequency riverine sampling during main hydrological events might provide important information about natural processes governing the fluvial biogeochemical si cycle therefore temporal variations in the isotopic composition of riverine dissolved si were investigated for the kalix river northern sweden the largest pristine river system in europe based on high frequency sampling during a period of 25 weeks from early april to early october 2006 temporal variations spanning 0 4 for 29si and 0 8 for 30si of dissolved si in the kalix river were observed during the period suggesting that the riverine dissolved si input to the oceans cannot be considered to have a constant si isotopic composition on a short time scale the results implicate biogeochemical si cycling via formation and dissolution of biogenic silica as processes significantly affecting the dissolved si transport in boreal systems during april to early october the si budget in the river system appeared to be controlled by relative si enrichment during high discharge events and relative si depletions in the subarctic mountainous and lake dominated areas the si enrichments and depletions were accompanied by decreasing and increasing riverine 29si and 30si respectively these isotope variations can be explained by release of plant derived silica depleted in heavier si isotopes during the spring snowmelt further increased volumetric contribution from the headwater and losses of dissolved si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes as further verified by land cover analysis

an investigation of the in reservoir conversion of oil to gas compositional and kinetic findings from closed system programmed temperature pyrolysis abstract the thermal alteration of reservoired petroleum upon burial was simulated by closed system non isothermal pyrolysis samples of a medium gravity oil from the norwegian north sea central graben were pyrolysed in microscale sealed glass or quartz vessels at heating rates of 0 1 0 7 and 5 0 k min 1 up to temperatures varying from 300 to 650 c the composition of the oil and gas in each vessel was determined by a single step on line gas chromatographic analysis with increasing rate of heating the onset of all oil degradation reactions was shifted to higher temperatures the same successive compositional changes occurred in each case increase in the total yield of gc detectable compounds significant gas c1 c4 generation accompanied by a decrease in yield of heavy components aromatisation and attainment of maximum gas yield and finally a cracking of the c2 gas components the stable final mixture consisted of methane aromatic hydrocarbons pyrobitumen and possibly hydrogen kinetic modelling of the oil to gas conversion resulted in a narrow gas potential vs activation energy distribution between 66 and 70 kcal mol assigning 35 of the total gas potential 460 mg per g of oil to an energy of 66 kcal mol and 29 to 67 kcal mol pre exponential factor 1 1 1016 s 1 by extrapolation to natural maturation conditions the onset of gas generation is predicted to occur between 160 and 190 c for geological heating rates between 0 53 and 5 3 k ma 1 predictions from the model are in accordance with the observed preservation of liquid hydrocarbons in a deep hot 165 c petroleum reservoir from the saga 2 4 14 well norwegian continental shelf

late gas generation potential for different types of shale source rocks implications from pyrolysis experiments abstract gas generation from shale source rocks typically occurs via cracking of both kerogen and retained oils such that it is difficult to predict and compare gas generation potentials of different shales because they are related not only to the kerogen type but also to the oil expulsion efficiency in this study five different shale kerogen samples were pyrolyzed in sealed gold tubes to investigate how kerogen type and oil expulsion efficiency affect their gas generation after oil window maturity the results illustrate that the maximum extractable organic matter eom and gas generation potentials of different original shale kerogens o kerogen in a closed system vary widely in the range of 229 790 mg g tocok and 308 594 ml g tocok respectively however the gas yields of different residual shale kerogens r kerogen with a starting equivalent vitrinite reflectance eqvro value of approximately 1 22 are quite similar and vary between 131 and 145 ml g tocrk pyrolysis experiments also reveal that the late gas generation potential eqvro 1 22 of shale is mainly controlled by the amount of retained eoms rather than kerogen type when the shale source rocks containing types i and ii kerogens have the same amount of retained eoms their gas generation potentials are quite similar under most geological conditions the late gas generation potentials of shale source rocks normalized to the toc of matured shale at 1 22 eqvro tocshale vary approximately in the range of 180 300 ml g tocshale to reach a gas content of 3 m3 ton shale for the present day overmature shale gas exploration in the lower palaeozoic shales of south china a conservative present day toc tocpd value of 2 0 is proposed as a screening parameter that can eliminate the risk of insufficient gas generation potential as much as possible

gas potential of proterozoic and phanerozoic shales from the nw himalaya india inferences from pyrolysis abstract organic richness and kerogen properties of sixty seven shales obtained from the outcrops and underground mines of jammu kashmir and ladakh regions of northwest himalaya india have been studied to evaluate their gas generation potential using rock eval pyrolysis ranging in age from the proterozoic to tertiary organic matter content and characteristics of the carbonaceous and coaly shales vary widely indicating that sedimentary and burial history significantly affected the preservation and maturation of organic components in rocks the total organic carbon toc content ranges from 0 01 to 1 2 in the permian jurassic and paleozoic tertiary shales of ladakh to as high as 32 5 in the eocene shales coaly shales from jammu the thermo labile hydrocarbons s1 and those from cracking of kerogen s2 released from the pyrolysis of eocene subathu shales are observed to be high from 0 1 to 2 6 and from 0 5 to 15 5 mg hc g rock respectively rock eval thermal maturity parameters indicated by tmax temperature at highest yield of s2 490 c and calculated vitrinite reflectance 1 5 to 3 7 ro suggest a post mature dry gas stage for the hydrocarbon generation based on hydrogen index hi and tmax correlations organic matter in the subathu shales is characterized by a late metagenetic gas prone type iii kerogen and a fair to excellent gas potential is exhibited by these shales the interbedded shale units in the proterozoic sirban limestone formation occurring as an isolated inlier in jammu show toc values from 0 1 to 1 4 with quite low s1 s2 and hi values thermal maturity of shales within the stromatolitic sirban succession indicates a post mature and or already spent hydrocarbon stage the plio pleistocene carbonaceous clays lignites and mudstones from the lower karewa group of kashmir basin are organically rich with toc content ranging from 5 86 to 29 4 a thermally immature type ii type iii kerogen is indicated by the hi 109 to 278 mg hc g toc and tmax 399 to 427 c plots of the karewa samples the exposed lower triassic black shales from the permian triassic boundary sections in kashmir are comparatively lean in organic matter with toc values ranging from 0 18 to 0 93 whereas the permian jurassic and paleozoic tertiary shales from ladakh have a toc content ranging from 0 01 to 1 22 the pyrolyzable organic carbon is

guidelines for assessing the petroleum potential of coaly source rocks using rock eval pyrolysis abstract coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using rock eval pyrolysis the rank threshold for oil generation is indicated by the increase in bi s1 toc at rank sr 9 10 tmax 420 430 c ro 0 55 0 6 and the threshold for oil expulsion is indicated by the peak in qi s1 s2 toc at rank sr 11 12 5 tmax 430 440 c ro 0 65 0 85 the pronounced rank related increase in hi s2 toc prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation a more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion alternatively effective hi values i e his near the onset of expulsion can be estimated by translating the measured his of immature samples along the maturation pathway defined by the new zealand or other defined coal band coaly source rocks comprise a continuum of coaly lithologies including coals shaly coals and coaly mudstones determination of the total genetic potential of coaly source rock sequences is best made using lithology based samples near the onset of expulsion

geochemical anomalies in the lower silurian shale gas from the sichuan basin china insights from a rayleigh type fractionation model abstract to verify recent single well data from the sichuan basin we analyzed the molecular and isotopic composition of late mature longmaxi shale gases from the southwestern portion of the fuling block the gases are highly enriched in methane 96 1 and have low c2 hydrocarbon contents

thermal maturity source rock potential and kinetics of hydrocarbon generation in permian shales from the damodar valley basin eastern india abstract this study investigates the source rock characteristics of permian shales from the jharia sub basin of damodar valley in eastern india borehole shales from the raniganj barren measure and barakar formations were subjected to bulk and quantitative pyrolysis carbon isotope measurements mineral identification and organic petrography the results obtained were used to predict the abundance source and maturity of kerogen along with kinetic parameters for its thermal breakdown into simpler hydrocarbons the shales are characterized by a high toc 3 4 mature to post mature heterogeneous type ii iii kerogen raniganj and barren measure shales are in mature late oil generation stage rr raniganj 0 99 1 22 rr barren measure 1 1 1 41 vitrinite is the dominant maceral in these shales barakar shows a post mature kerogen in gas generation stage rr barakar 1 11 2 0 and consist mainly of inertinite and vitrinite the 13corg value of kerogen concentrate from barren measure shale indicates a lacustrine marine origin 24 6 30 84 vs vpdb and that of raniganj and barakar 22 72 25 03 vs vpdb show the organic provenance to be continental the 13c ratio of thermo labile hydrocarbons c1 c3 in barren measure suggests a thermogenic source discrete bulk kinetic parameters indicate that raniganj has lower activation energies e 42 62 kcal mol compared to barren measure and barakar e 44 68 kcal mol temperature for onset 10 middle 50 and end 90 of kerogen transformation is least for raniganj followed by barren measure and barakar mineral content is dominated by quartz 42 63 siderite 9 15 and clay 14 29 permian shales in particular the barren measure as inferred from the results of our study demonstrate excellent properties of a potential shale gas system

mechanisms controlling the silicon isotopic compositions of river waters it has been proposed that silicon si isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions in this study the first seasonal variations of stable isotope compositions of dissolved riverine si are reported and compared with concomitant changes in water chemistry four different rivers in switzerland were sampled between march 2004 and july 2005 the unique high resolution multi collector icp ms nu1700 has been used to provide simultaneous interference free measurements of 28si 29si and 30si abundances with an average limiting precision of 0 04 on 30si this precision facilitates the clarification of small temporal variations in isotope composition the average of all the data for the 40 samples is 30si 0 84 0 19 1 sd despite significant differences in catchment lithologies biomass climate total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved si in each river is strikingly similar with means of 0 70 0 12 for the birs 0 95 0 22 for the saane 0 93 0 12 for the ticino and 0 79 0 19 for the verzasca however the 30si undergoes seasonal variations of up to 0 6 comparisons between 30si and physico chemical parameters such as the concentration of dissolved si and other cations the discharge of the rivers and the resulting weathering fluxes permits an understanding of the processes that control the si budget and the fate of dissolved si within these rivers the main mechanism controlling the si isotope composition of the mountainous verzasca river appears to be a two component mixing between the seepage of soil ground waters with heavier si produced by clay formation and superficial runoff associated with lighter si during high discharge events a biologically mediated fractionation can be excluded in this particular river system the other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment in these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of si contributed by biological processes as opposed to abiotic weathering the presence of seasonal variations in si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved si delivered to the oceans the oceanic si isotope composition is very sensitive to even small changes in the riverine si isotope composition and this parameter appears to be more critical than plausible changes in the si flux therefore concurrent changes in weathering style may need to be considered when using the si isotopic compositions of diatoms sponges and radiolaria as paleoproductivity proxies

coal as a source rock for oil a review the geological debate about whether and to what extent humic coals have sourced oil is likely to continue for some time despite some important advances in our knowledge of the processes involved it is clear that not only liptinites but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification some liptinites especially alginite cutinite and suberinite contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are therefore more oil prone it is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed review of the distribution of oil prone coals in time and space reveals that most are jurassic tertiary with key examples from australia new zealand and indonesia methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals results are not entirely consistent among the different approaches and there is much overlap in the ranges of degradation but it seems probable that in the natural environment vitrinites begin to generate early followed by labile liptinites such as suberinite then cutinite sporinite and finally alginite petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro techniques especially fluorescence and infrared ir spectroscopy or bulk techniques such as elemental analysis and 13c nmr spectroscopy the latter three techniques enable a measure of the polymethylene component of the coal which now appears to be one of the best available approaches for determining petroleum potential no method of experimental simulation of petroleum generation from coals is without criticism and comparative results are highly variable however hydrous pyrolysis confined pyrolysis and forms of open system hydrous pyrolysis approach acceptable simulations whether and to what degree generated liquid hydrocarbons are expelled has long been the central problem in oil from coal studies the structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained recent studies show the pores are not interconnected combined with a dynamic model of pore generation it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries the main reason for poor expulsion is the adsorption of oil on the organic macromolecule which may be overcome 1 if coals are thin and interbedded with clastic sediments or 2 if the coals are very hydrogen rich and generate large quantities of oil the existence of oil in vitrinite is attested to by solvent extractions fluorescence properties and by microscopic observations of oil and bitumen experimental simulation of expulsion of oil from coals has only recently been attempted the relative timing of release of generated co2 and ch4 could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear as it is universally agreed that dispersed organic matter dom in some shales readily generates and expels petroleum it is curious that few consistent geochemical differences have been found between coal macerals and dom in interbedded shales unambiguous evidence of expulsion from coals is limited and in particular only a few commercial oil discoveries can be confidently correlated to coals these include upper cretaceous fruitland formation coals in the usa from which oil is produced new zealand tertiary coals and middle jurassic coals from the danish north sea it is likely that coals have at least contributed to significant oil discoveries in the gippsland basin australia in the turpan basin china and in the kutei and ardjuna basins in indonesia but this remains unproven early reports that early jurassic coals in mid norway were a major source of the reservoired oils have been shown to be inaccurate none of the proposed rules of thumb for generation or expulsion of petroleum from coals seem particularly robust decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information the assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain

scales of spatial variability for surface ocean pco2 in the gulf of alaska and bering sea toward a sampling strategy twenty four near exact repeat tracks over a 48 month period of ocean surface pco2 data from the north pacific offer an uprecedented opportunity to examine the space scales of pco2 in this region because previous basin scale studies of air sea carbon flux have shown that the field of pco2 air sea disequilibrium largely controls the field of flux and atmospheric pco2 is relatively constant knowing how to sample pco2 in seawater is a crucial element of the design of a basin scale carbon flux observing system unbiased within 3 atm along track means for pco2 can be obtained from measurements made every 40 km hourly for a ship traveling 20 knots we find distinctly different characteristics of spatial variability in two open ocean regions the bering sea and the gulf of alaska the first zero crossing of the mean spatial autocorrelation function is 1 5 longitude in the bering sea and 3 5 in the gulf of alaska when the cruise data are linearly detrended to remove the larger scale field there is a strong seasonal variation in the zero crossing with shorter scales in the summer in near shore waters there is extreme variability often with very small space scales and very large cruise to cruise differences neither the mean nor variability statistics from a single ship cruise data set appear likely to produce reliable information for designing an observing system

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

the origin of hydrocarbon source rocks in the austrian molasse basin eocene oligocene transition organic rich rocks schoneck formation from five wells representing a section across the northern paleo slope of the austrian molasse basin were studied using a multi method approach including petrography x ray diffraction organic and inorganic geochemistry and c and n isotopes of the organic material organic matter accumulation commenced during the latest eocene and was dependent on variations of currents salinity organic productivity and nutrient supply initial marl deposition and phosphorite formation under dysoxic conditions was followed by organic rich mud deposition associated with benthic and photic zone anoxia this paleoceanographic situation resembles the first isolation of the western central paratethys deposition of organic rich rocks terminated during lower oligocene time when changing current patterns and decreasing salinity caused a breakdown of water column stratification even though the schoneck formation is an excellent source rock major differences exist in the petroleum potential of the schoneck formation deposited in upper and lower basin slope settings the schoneck formation from the upper slope is characterised by toc contents up to 12 and hi values between 500 and 600 mghc gtoc in the lower slope settings toc values are generally below 2

interaction of coal and oil in confined pyrolysis experiments insight from the yields and carbon isotopes of gas and liquid hydrocarbons abstract isothermal confined gold capsule pyrolysis experiments were performed for coal alone oil alone and coal plus oil with oil coal ratios ranging from 0 006 to 0 171 at 315 c 345 c and 375 c respectively and 50 mpa for 72 h in the experiment for coal plus oil the amounts and compositions of hydrocarbon gases are substantially different from those predicted from the results in the experiments for oil alone and coal alone the results of these experiments demonstrate that kerogen and oil do not crack separately in the experiments of coal plus oil the interaction between kerogen and oil components leads to the generation of hydrocarbon gases with oil coal ratio increasing the amounts of individual and total hydrocarbon gases decrease at first and then increase rapidly up to several times those calculated from the yields of these components in the experiments for oil alone and coal alone the c1 c1 5 ratios of hydrocarbon gases decrease and are increasingly lower than those calculated from the yields of hydrocarbon gases in the experiments for oil alone and coal alone the amount and carbon isotopes of individual n alkane demonstrate that the free liquid n alkanes were incorporated into kerogen and replaced the bound liquid n alkanes covalently bonded alkyl groups in kerogen carbon isotopes of hydrocarbon gases further suggest that the bound liquid n alkanes in kerogen preferentially crack into hydrocarbon gases

silicon isotope study on rice plants from the zhejiang province china silicon isotope compositions of 16 rice plants from the zhejiang province were studied and potential applications of silicon isotope study to agriculture and biogeochemistry were discussed it is found that the sio2 contents in ignited rice plant samples increased generally from roots through sl stem and leaves to husks large and systematic silicon isotope fractionation was observed among different organs of individual rice plants their 30si values show a generally increasing trend from roots and sl through husks to grains which can be explained by kinetic isotope fractionation in a rayleigh process a 30si value of 6 1 was obtained from two samples of rice grains which is much greater than the highest value 3 4 observed in terrestrial samples before it is inferred that monosilicic acid is the major silicon bearing component taken up by rice roots passive uptake of silicon is important for rice and evapotranspiration may be the major mechanism for the transportation and precipitation of silicon in rice plants it is suggested that silicon isotope study has a potential application to agriculture and biogeochemistry

a model for lignin alteration part i a kinetic reaction network model a new quantitative model is presented which simulates the maturation of lignin derived sedimentary organic matter under geologic conditions in this model compositionally specific reactants evolve to specific intermediate and mobile products through balanced nth order processes by way of a network of sequential and parallel reactions the chemical kinetic approach is based primarily on published observed structural transformations of naturally matured lignin derived sedimentary organic matter assuming that upper cretaceous williams fork coal in the piceance basin is primarily lignin derived the model is calibrated for the multi well experiment mwx site in this basin this kind of approach may be applied to other selectively preserved chemical components of sedimentary organic matter

microbial production and modification of gases in sedimentary basins a geochemical case study from a devonian shale gas play michigan basin an expanded data set for gases produced from the antrim shale a devonian black shale in the michigan basin united states has allowed for a detailed examination of the related chemical and isotopic compositional changes in the solid gas liquid systems that discriminate between microbial and thermogenic gas origin in the antrim shale economic microbial gas deposits are located near the basin margins where the shale has a relatively low thermal maturity and fresh water infiltrates the permeable fracture network the most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water along the basin margins there is also a systematic enrichment in 13c of ethane and propane with decreasing concentrations that suggests microbial oxidation of these thermogenic gas components microbial oxidation accounts not only for the shift in 13c values for ethane but also in part for the geographic trend in gas composition as ethane and higher chain hydrocarbons are preferentially removed this oxidation is likely an anaerobic process involving a syntrophic relationship between methanogens and sulfate reducing bacteria the results of this study are integrated into a predictive model for microbial gas exploration based on key geochemical indicators that are present in both gas and coproduced water one unequivocal signature of microbial methanogenesis is the extremely positive carbon isotope values for both the dissolved inorganic carbon in the water and the coproduced co2 gas in contrast the 13c value of methane is of limited use in these reservoirs as the values typically fall between the commonly accepted fields for thermogenic and microbial gas in addition the confounding isotopic and compositional overprint of microbial oxidation increasing the values to typically thermogenic values may obscure the distinction between methanogenic and thermogenic gas

influence of in situ bitumen on the generation of gas and oil in new zealand coals new zealand coals of peat to high volatile bituminous rank have been studied in order to assess the effect of in situ bitumen soluble in a methanol acetone chloroform azeotrope on petroleum potential during progressive maturation both non extracted and extracted coals as well as the extracted bitumen itself were analyzed using rock eval and pyrolysis gas chromatography the difference in yields between non extracted and extracted coals attributable to the influence of bitumen were compared with direct measurements made on the bitumen itself major compositional changes in pyrolysis products were seen when the bitumen was finely dispersed throughout the kerogen matrix notably second order reactions between kerogen and bitumen during pyrolysis reduce primary gas yield and enhance both oil yield and potential secondary gas yield the stabilization of free radicals and prevention of recombination repolymerization processes have been attributed to the presence of the dispersed in situ bitumen these results demonstrate that petroleum formation in coals likely proceeds via intermolecular interactions and not simply first order cracking the common procedure of employing solvent extraction prior to pyrolysis is clearly not appropriate when assessing the petroleum potential of coal

modelling petroleum formation from heterogeneous source rocks the influence of frequency factors on activation energy distribution and geological prediction abstract the application of basin modelling programs permits the prediction of organic matter transformation to oil and gas under variable geological conditions simplified kinetic models are commonly applied with a distribution of activation energies and a single average frequency factor here it will be shown that such simplified kinetic models are not sufficient to correctly predict organic matter transformation in heterogeneous kerogens under geological conditions in the present paper individual pairs of frequency factors and activation energies were calculated from the temperature shift of nine different levels of organic matter transformation ranging from 0 1 to 0 9 tr at different heating rates 0 1 0 7 and 5 0 k min this type of extended kinetic evaluation has been applied on samples from the green river shale the toarcian shale the duvernay formation the draupne formation a type ii s source rock petroleum asphaltenes and a tertiary coal from the mackenzie delta respectively for terrestrial and heterogeneous marine source rocks the frequency factors systematically increase with increasing level of transformation while such an increase was insignificant or absent when homogeneous source rocks were studied by applying geological heating rates it was possible to illustrate the significance of the extended calculation of individual frequency factors the predicted onset temperature of petroleum formation was displaced to 60 70 c in case of lignites coals and type ii s source rocks which was up to 30 40 c lower than predicted by the use of a conventional single frequency factor model to a lesser extend such a shift was also documented for some marine shales e g draupne formation and the duvernay formation the reason for this phenomenon is that an average single frequency factor suppresses the initial formation of petroleum at geological heating rates because high activation energies are needed to maintain the kinetic equation at low generation temperatures in contrast correct activation energies derive from individual frequency factors which keep the activation energies low at low levels of organic matter transformation and result in a more reliable description of the low energy bonds in the heterogeneous organic matter types

the role of phytolith formation and dissolution in controlling concentrations of silica in soil solutions and streams abstract by integrating the results of recent studies on the concentration and flux of si in european forest soils podzols and acid brown soils with published evidence on the amounts of si cycled through forest vegetation we conclude that phytoliths must be the principal immediate source and sink of silica in soil solution although mineral weathering is the ultimate source during the growing season forest vegetation takes up most of the si made available by weathering of soil minerals and by phytolith dissolution and converts it into phytoliths phytoliths will be the principal source of si leached from the soil during winter rains and spring snowmelt this work accounts for the plateau concentrations of si observed in laboratory equilibrations of bs horizon soils for the maximum si concentration reported for b horizons in the field for a deep sink for si in bs horizons and for the fact that the concentrations of si in soil drainage water and in streams all fall in or below the range expected for phytolith solubility concentrations of si in surface horizons can exceed these levels during droughts the common assumption that the concentration of si in soil solution is a result of a dynamic balance between si released by mineral weathering and that lost by leaching is untenable for bs horizons

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

sensitivity of silicon isotopes to whole ocean changes in the silica cycle a 2 box model has been used to assess the impact of both long and short term budgetary imbalance in the silica cycle on the average silicon isotopic composition 30si of the ocean and marine sediments over a 100 ky time span such as a quaternary glacial cycle a sustained change in the riverine flux of silicon to the oceans could alter the average 30si of seawater and the average 30si of opal outputs by a few hundredths to a few tenths of permil this would be largely tied to a change in the 30si of silicon entering the ocean due to a shift in the proportion of riverine and non riverine sources of silicon a doubling of the riverine flux of silicon would have little impact on average marine 30si but a sustained halving of river inputs could interfere with use of 30si as a tracer of nutrient utilization studies on the longer term focussed on the transition from a high silicic acid to low silicic acid ocean associated with the rise of the diatoms this transition is marked by drop in the average 30si of seawater from greater than 1 9 down to about 0 8 the isotopic composition of diatom opal however has an isotopic composition that sticks close to the 0 8 of the inputs and is thus unlikely to provide information about the transition to the low silicic acid ocean of the modern day however the 30si of opal produced in the deep sea for example by sponges should document this transition

a model of hydrocarbon generation from type i kerogen application to uinta basin utah we have developed a computer model that can predict when and how much oil and gas are generated from a source rock during its burial and later uplift kinetic parameters for the oil and gas generation reactions are obtained from high pressure pyrolysis experiments carried out over a wide range of heating rates and temperatures in our kinetic model which applies only to green river shale we use a single activation energy of 52 4 kcal mole and different pre exponential factors for different products of primary pyrolysis which allows us to extrapolate laboratory derived kinetics to geologic heating rates this model is in contrast to the wide distributions of activation energies or artificially low apparent activation energies used in some models of petroleum formation hen extrapolated to geologic heating rates on the order of 10 c m y our kinetics show that the temperature of the maximum rate of oil generation tp changes by about 15 c when the heating rate is changed by an order of magnitude changes in pressure have relatively minor effects on the kinetics of oil generation but are important for gas generation reactions we used geophysical data from oil fields in the uinta basin of utah to develop a thermal history model of green river formation source rocks this time temperature history was used to predict the maturation level of the kerogen at a given depth and to predict changes in the compositional characteristics of the oil the shape of calculated oil generation rate curves as a function of depth in the basin mimics the shape of the overpressure curves this similarity suggests that oil gas generation may be an important cause of overpressuring maturation levels and compositional characteristics of the oil predicted by our model agree very well with characteristics of the oil recovered from the basin

oil retention and intrasource migration in the organic rich lacustrine chang 7 shale of the upper triassic yanchang formation ordos basin central china the zhang 22 well was drilled in the ordos basin penetrating the chang 7 member of the triassic yanchang formation which cumulatively has more than 80 m 260 ft of black organic rich shale of oil window maturity using 76 samples collected every 1 m 3 ft from the well the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the chang 7 shale were qualitatively and quantitatively documented the organic rich intervals 1 2 and 5 having an average total organic carbon toc of 6 79 wt and pyrolyzable hydrocarbon potential of 9 40 mg g rock i e the amount of hydrocarbons generated by pyrolysis between 300 c and 650 c s2 are defined as generative units in the chang 7 shale system compared to the in source reservoirs or sweet spots i e the third and fourth intervals which contain a lower average toc of 4 19 wt and an average s2 value of 7 17 mg g rock but the highest amount of free oil average total oil of 7 35 mg g rock geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings for example bitumens from the generative units proportionally possess lower saturated hydrocarbons 56 66 than those from the in source reservoirs up to 81 the proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart the individual molecular weight distribution of sample extracts displays more light end moieties being enriched in the generative units by applying the compositional mass balance calculation the overall and compound specific expulsion efficiencies in the in source reservoirs are abnormally negative compared to the positive values in the generative intervals this finding in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in source reservoirs indicates a short distance intrasource migration of generated petroleum into the sweet spot intervals intervals 3 and 4 from the overlying units intervals 1 and 2 and the underlying interval 5 furthermore when quantifying the total amount of retained petroleum in the shale system an amended assessment has been introduced to overcome the systematic misestimations if only unextracted values for the amount of thermally extractable hydrocarbons volatilized at 300 c mg hc g rock were considered thus the oil crossover effect temperature at which the rate of s2 generation is at maximum shift phenomenon and the hydrogen index being shifted to higher values after extraction all account for identifying intervals 3 and 4 as the in source reservoirs in this study we have not only identified a set of promising in source targets for shale oil exploration and production but we also presented the chemical and molecular composition for these shale oils we have additionally speculated for the intrasource migration model and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation as well as the stratigraphic fractionation on differentiating the chemical compositions during migration the improved oil quality by fractionation the extra storage potential derived from microfossil quartz the weak adsorptive affinity of oil to organic matter and the good shale susceptibility to hydraulic fracturing all give a promising prospective for exploring and producing shale oil from the chang 7 shale system in the ordos basin

comparison of kinetic analysis of source rocks and kerogen concentrates abstract shales and kerogen concentrates from the green river rundel ohio draupne and phosphoria formations were examined by pyromat ii micropyrolysis and kinetic parameters were determined by the shift in t max discrete distribution modified friedman and modified coats redfern methods overall the shales and corresponding kerogens exhibited very similar kinetic parameters green river rundel and ohio shales and kerogens exhibited principal discrete activation energies of 54 57 kcal mol narrow distributions and t max at 25 c min heating rate around 480 c draupne and phosphoria shales and kerogens exhibited kinetic parameters typical of type ii source rocks principal discrete activation energies of 54 57 kcal mol broad distributions and t max at 25 c min around 459 c the discrete distribution kinetic parameters were used to calculate oil generation at laboratory and geological heating rates each shale and corresponding kerogen exhibited generation curves and 50 generation temperatures that were very similar the principal difference was that the kerogens exhibited slightly more oil generation at low temperatures compared to the corresponding shales some kerogens exhibited curves which were also shifted to slightly lower temperatures than those of the corresponding shales for these specific shales and kerogens the results indicate that kerogen isolation does little to affect the pyrolysis kinetic parameters although from a limited number of samples these results suggest kerogen isolation may not be necessary to derive valid kinetic parameters

hydrological alterations with river damming in northern sweden implications for weathering and river biogeochemistry hydrological alterations with river damming in northern sweden implications for weathering and river biogeochemistry

geochemical characterisation of organic matter in keg river formation elk point group middle devonian la crete basin western canada carbonates from the keg river formation la crete basin alberta western canada were examined in order to define a oil source rock potential b bulk maceral composition c extract yield and finally d facies variations using py gc ms thirty samples from 6 different wells were examined from the lower keg river member and 4 from the upper keg river member using conventional geochemical methods as maturity differences are absent within the sample set variations in toc tmax hydrogen index organic petrography and extract yields are caused by variability in organic matter input which is revealed by molecular characterisation using py gc ms lower keg river member bituminous wackestones are excellent potential source rocks containing types i ii and type ii organic matter types i ii organic matter contains large well preserved up to 200 m in diameter thick walled tasmanites 10 15 of sample and akinete algal cells indicative of algal blooms within an amorphous bituminite type ii organic matter contains a higher proportion of degraded alginites bituminite relative to well preserved alginites extract yields mg g toc were seen to increase from types i ii to type ii organic matter py gc ms revealed that 1 2 3 4 tetramethylbenzene was a major peak in most samples this is a pyrolysis product arising from cleavage of c40 diaromatic carotenoids incorporated within the kerogen during diagenesis the source of this compound is thought to be from an unknown diaromatic compound with a 2 3 6 3 4 5 trimethyl substitution pattern and isorenieratene which is specific to photosynthetic green sulphur bacteria chlorobiaceae suggesting that the photic zone was at least partially anoxic during deposition of these samples the relative abundance of this compound n c11 alkene and organic sulphur calculated from the thiophene ratio both increase from types i ii to type ii organic matter this trend was grossly similar to the trend seen in the variability of extract yield with hydrogen index a similar trend for hi and tmax indicates samples containing a higher proportion of degraded alginites bituminite relative to well preserved alginite are more labile than type i ii organic matter upper keg river member marls contain type ii organic matter which is characterised by heavily degraded algal material within a bituminous groundmass pyrolysates of two of the marl samples contain only low amounts of 1 2 3 4 tetramethylbenzene in contrast to the bituminous wackestones indicating that the depositional environment source input was different during deposition of the marl samples although both marls contain similar organic matter their pyrolysates were significantly different one marl 1141 9 m was highly paraffinic containing dominantly short chain alkene alkane doublets while the other marl 1137 6 m contained a bimodal n alkane alkene distribution and high amounts of alkylphenols which may be derived from preservation of resistant algal polyphenolic molecules or suggest a terrestrial input

irradiation of organic matter by uranium decay in the alum shale sweden the alum shale of sweden contains black shales with anomalously high uranium concentrations in excess of 100 ppm syngenetic or early diagenetic origin of this uranium indicates that organic matter within these shales has been irradiated by decaying uranium for approximately 500 ma radiation induced polymerization of alkanes through a free radical cross linking mechanism appears to be responsible for major alterations within the irradiated organic matter specific radiation induced alterations include generation of condensate like oils at reduced yields from hydrous pyrolysis experiments decrease in atomic h c ratios of kerogens decrease in bitumen organic carbon ratios and a relative increase in low molecular weight triaromatic steroid hydrocarbons conversely stable carbon isotopes of kerogens reflectance of vitrinite like macerais oil generation kinetics and isomerization of 20r to 20s c29 steranes were not affected by radiation the radiation dosage needed to cause the alterations observed in the alum shale has been estimated to be in excess of 105 mrads with respect to organic carbon this value is used to estimate the potential for radiation damage to thermally immature organic matter in black shales through the geological rock record high potential for radiation damage is not likely in cenozoic and mesozoic black shales but becomes more likely in lower paleozoic and precambrian black shales

plant impact on the biogeochemical cycle of silicon and related weathering processes abstract the contribution of plants to the biogeochemical cycle of si and related weathering processes was studied in an equatorial rainforest ecosystem congo where the biologic turnover of si is high 58 to 76 kg ha y litterfall leaves a soil profile and groundwaters were analysed phytoliths and organic matter have a similar distribution with depth in the soil profile the model of a bicompartmental distribution of organic matter is applied to phytolith distribution and shows that about 92 of the biogenic silica input is rapidly recycled while about 8 of the biogenic silica input supplies a stable pool of phytoliths with a lower turnover reprecipitation of silica was observed at the base of the soil profile indicating a local geochemical environment that is oversaturated with respect to amorphous silica a balance in biogeochemical cycle of si requires that the vegetation absorb dissolved silicon released from weathering of minerals which otherwise would be available for mineral neoformation or export from the profile towards regional drainages plant uptake of si increases the chemical weathering rate without increasing the denudation rate this study shows that the uptake storage and release of si by the vegetation have to be taken into account when using dissolved si for tracing chemical weathering dynamics

evolution of porosity and pore types in organic rich calcareous lower toarcian posidonia shale low and high resolution petrographic studies have been combined with mineralogical toc rockeval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature oil window and gas window samples from the lower toarcian posidonia shale formation a series of 26 samples from three boreholes wickensen harderode and haddessen in the hils syncline was investigated the main primary components of the shales are microfossiferous calcite 30 50 clay minerals 20 30 and type ii organic matter toc 7 15 hi 630 720 mg gc in immature samples characteristic sub centimetric light and dark lamination reflects rapid changes in the relative supply of these components total porosities decrease from 10 to 14 at ro 0 5 to 3 5 at ro 0 9 and then increase to 9 12 at ro 1 45 these maturity related porosity changes can be explained by a the primary composition of the shales b carbonate diagenesis c compaction and d the maturation micro migration local trapping and gasification of heterogeneous organic phases calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence pores quantifiable in sem ca 50 nm account for 14 25 of total porosity at ro 0 5 sem visible macropores1 are associated mainly with biogenic calcite at this maturity clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity porosity loss into the oil window reflects a compaction b carbonate cementation and c perhaps the swelling of kerogen by retained oil in addition porosity is occluded by a range of bituminous phases especially in microfossil macropores and microfractures in the gas window mineral hosted porosity is still the primary form of macroporosity most commonly observed at the organic inorganic interface increasing porosity into the gas window also coincides with the formation of isolated spongy and complex meso and macropores within organic particles related to thermal cracking and gas generation this intraorganic porosity is highly heterogeneous point counted macroporosity of individual organic particles ranges from 0 to 40 with 65 of organic particles containing no macropores we suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained the development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window major contributions also come from the increased volume of organic micro and meso porosity and perhaps by kerogen shrinkage

characterization of methane adsorption on overmature lower silurian upper ordovician shales in sichuan basin southwest china experimental results and geological implications abstract a series of methane adsorption isotherms were measured at 35 4 c 50 6 c and 65 4 c at pressures up to 15 0 mpa for eight dried overmature lower silurian upper ordovician shale samples collected from the sichuan basin with toc values in the range of 1 87 5 74 the measured maxima of excess adsorption capacity of methane range from 1 25 to 2 50 cm 3 g rock at 65 4 c the maxima are slightly enhanced at 35 4 c but all are positively correlated with total organic carbon toc both the supercritical dubinin radushkevich sdr and langmuir based excess adsorption models were found to represent the experimental excess adsorption isotherms equally well within the experimental range the temperature dependent densities of adsorbed methane resulting from the parameter fit of the sdr based excess adsorption model are in the range of 297 415 mg cm 3 for the langmuir based excess adsorption model the adjusted densities range from 386 mg cm 3 to 1027 mg cm 3 and most of them are much larger than the liquid density of methane at its boiling point 424 mg cm 3 nevertheless the maxima of absolute methane adsorption capacity fitted by both models are not significantly different and are linearly correlated one of the contributors to the uncertainty of the gas in place estimation in geological conditions is the inconsistent utilization of experimental excess sorption data as absolute sorption values particularly at high pressures however the choice of adsorption model itself langmuir or sdr based and the fitting procedure assuming either constant or temperature dependent adsorbed phase density and maximum sorption capacity do not significantly affect the estimated gips for the geological system studied here with depths of less than 4000 m

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

metagenetic methane generation in gas shales i screening protocols using immature samples abstract the gas generative potential of organic matter is one key parameter for the calculation of total gas in place gip when evaluating thermogenic shale gas plays having first demonstrated that late gas forming structures are present in coals of anthracite rank 2 r0 we go on to examine other rocks at the immature stage of maturity and report on how to recognise which might generate significant amounts of late dry gas at geologic temperatures well in excess of 200 c in the zone of metagenesis r0 2 0 i e subsequent to primary and secondary gas generation by thermal cracking of kerogen or retained oil such a distinction could clearly be of major value when assessing risks and pinning down sweet spots a large selection 51 samples of source rocks i e shales and coals stemming from different depositional environments and containing various types of organic matter which contribute to the formation of petroleum in putative gas shales were investigated using open and closed system pyrolysis methods for the characterisation of kerogen type molecular structure and late gas generative behaviour a novel rapid closed system pyrolysis method which consists of heating crushed whole rock samples in mssv tubes from 200 c to 2 different end temperatures 560 c 700 c at 2 c min provides the basis for a newly proposed approach to discriminate between source rocks with low high or intermediate late gas potential it is noteworthy that late gas potential goes largely unnoticed when only open system pyrolysis screening methods are used high late gas potentials seem to be mainly associated with heterogeneous admixtures or structures in terrestrially influenced in some cases marine type iii and type ii iii coals and shales aromatic and or phenolic signatures are therefore indicative of the possible presence of elevated late gas potential at high maturities high temperature methane was calculated to potentially contribute an additional 10 40 mg g toc which would equal up to 30 of the total initial primary petroleum potential in many cases low late gas potentials are associated with homogeneous paraffinic organic matter of aquatic lacustrine and marine origin source rocks exhibiting intermediate late gas potentials might generate up to 20 mg g toc late dry gas and seem to be associated with heterogeneous marine source rocks containing algal or bacterial derived precursor structures of high aromaticity or with aquatic organic matter containing only minor amounts of aromatic phenolic higher land plant material

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

ba sr ca sr and 87sr 86sr ratios in soil water and groundwater implications for relative contributions to stream water discharge abstract barium sr and ca sr ratios have been used to model the relative importance of different sources of stream water major and trace element concentrations together with 87sr 86sr ratios were measured in precipitation soil water groundwater and stream water in a small 9 4 km2 catchment in northern sweden the study catchment is drained by a first order stream and mainly covered with podzolized quaternary till of granitic composition it is underlain by a 1 8 ga granite a model with mixing equations used in an iterative mode was developed in order to separate the stream water into 3 subsurface components soil water shallow groundwater and deep groundwater contributions from precipitation are thus not included in the model this source may be significant for the stream water generation but it does not interfere with the calculations of the relative contributions from the subsurface components the results show that the deep groundwater constitutes between 5 and 20 of the subsurface water discharge into the stream water the highest values of the deep groundwater fraction occur during base flow soil water dominates during snowmelt seasons whereas during base flow it is the least important fraction soil water accounts for 10 100 of the subsurface water discharge into the stream water shallow groundwater accounts for up to 80 of the subsurface water discharge with the lowest values at peak discharge during snowmelt seasons and the highest values during base flow the validity of the model was tested by comparing the measured 87sr 86sr ratios in the stream water with the 87sr 86sr ratios predicted by the model there was a systematic difference between the measured and modelled 87sr 86sr ratios which suggests that the fraction of soil water is overestimated by the model especially during spring flood as a consequence of this overestimation of soil water the amount of shallow groundwater is probably underestimated during this period however it is concluded that the differences between measured and predicted values are relatively small and that element ratios are potentially effective tracers for different subsurface water flowpaths in catchments

pmod a flexible model of oil and gas generation cracking and expulsion a new computer program pmod is used to develop and test a wide variety of global models of varied complexity for the generation and destruction of hydrocarbons from petroleum source rocks chemical reaction models are constructed interactively by supplying the empirical formula of the reactants and products desired reactions and reaction constraints pmod calculates stoichiometric coefficients that conserve elemental balance the chemical reactions are integrated into two compaction and bulk flow expulsion models in order to predict the amounts and compositions of products expelled from the source rock under geological conditions a variety of published and unpublished experiments are used to show when various model types are required and to derive the parameters for the various models this exercise provides a good means to compare the strengths and weaknesses of the various models and provides guidance on the types of information needed to calibrate them chemical properties calculated by pmod for all models include apparent rock eval parameters and other common geochemical measurements

identification of microbial and thermogenic gas components from upper devonian black shale cores illinois and michigan basins differentiation of microbial versus thermogenic methane in coalbed and black shale accumulations can affect strategies for exploration and may influence the total gas content in a given area early identification of these processes from crushed core materials even before formation fluids and produced gas samples are available could permit a more efficient and cost effective exploration total gas contents and compositional and isotopic data from new albany shale core materials are presented which delineate regional occurrence of microbial thermogenic and mixed gas generation in the illinois basin these trends are consistent with those identified from detailed prior studies of produced gas and water chemistry from the same locations the most useful markers for microbial gas in crushed core gases are elevated co2 contents characterized by high values 5 core gas analyses from wells in which microbial gas is identified commonly have significantly more total gas absorbed than do core samples from wells producing gases solely of thermogenic origin these observations are independent of variations in sample depth and organic carbon content in a given core thus this integrated case study of core and produced gases in the illinois basin illustrates that the areas containing microbial gas in addition to early thermogenic gas may be more productive than pure thermogenic zones for these early to immature unconventional gas deposits

the micro scale simulation of maturation outline of a new technique and its potential applications a micro analytical technique has been developed for artifically maturing sedimentary organic matter and then quantifying the major components generated during this process in a single analytical step such a capability is well suited for examining the compositional relationships between kerogens and petroleums determining reaction kinetics and making precursor product mass balances according to this technique simulations are made using sealed glass capillary tubes heated here for three days at 300 c 330 c and 350 c pyrolysis products are then released directly into a combined thermovaporisation pyrolysis gc instrument and the major components of the entire c1 yto c35 range can be quantified in a single step using gas chromatography alkene yields are very low and pyrolysates are oil like this is exemplified by the fact that then c9 c19 alkane distribution range of simulated whole petroleum chromatograms from originally immaturegloeocapsamorpha typz alginite a resembles that seen in crude oils generated from this same kerogen type in nature sealed tube experiments usingbotryococcus type alginite a generated a high wax pyrolysate the relative abundance ofn alkanes in the c2 c32 range of many kerogen pyrolysates does not appear to change significantly despite an approximately fifteen fold difference inn alkane yield between the 300 c and 350 c experiments kerogens which are paraffinic oil prone and whose pyrolysates are very rich inn alkanes might therefore generate petroleums in nature with a fixed wet gas c2 c4 to oil c5 ratio alginite b in a greenland shale is much more thermally labile than eitherbotryococcus type alginite a orgloeocapsamorpha type alginite a the mass balance capabilities of the technique have been tested using alum shale kerogen two gas chromatograms were obtained one for the free compounds generated during simulation and one for the high temperature pyrolysate of the kerogen residue for each heating experiment precursor product relationships were qualitatively assessed and dead carbon formation was quantified in this exercise

stable isotope geochemistry of coal bed and shale gas and related production waters a review coal bed and shale gas can be of thermogenic microbial or of mixed origin with the distinction made primarily on the basis of the molecular and stable isotope compositions of the gases and production waters methane ethane carbon dioxide and nitrogen are the main constituents of coal bed and shale gases with a general lack of c2 hydrocarbon species in gases produced from shallow levels and more mature coals and shales evidence for the presence of microbial gas include 13c ch4 values less than 50 covariation of the isotope compositions of gases and production water carbon and hydrogen isotope fractionations consistent with microbial processes and positive 13c values of dissolved inorganic carbon in production waters the co2 reduction pathway is distinguished from acetate methyl type fermentation by somewhat lower 13c ch4 and higher d ch4 but can also have overlapping values depending on the openness of the microbial system and the extent of substrate depletion crossplots of 13c ch4 versus 13c co2 and d ch4 versus 13c h2o may provide a better indication of the origin of the gases and the dominant metabolic pathway than the absolute carbon and hydrogen isotope compositions of methane in the majority of cases microbial coal bed and shale gases have carbon and hydrogen isotope fractionations close to those expected for co2 reduction primary thermogenic gases have 13c ch4 values greater than 50 and 13c values that systematically increase from c1 to c4 and define a relatively straight line when plotted against reciprocal carbon number although coals and disseminated organic matter in shales represent a continuum as hydrocarbon source rocks current data suggest a divergence between these two rock types at the high maturity end in deep basin shale gas reversals or rollovers in molecular and isotopic compositions are increasingly reported in what is effectively a closed shale system as opposed to the relative openness in coal measure environments detailed geochemical studies of coal bed and shale gas and related production waters are essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gases

aryl isoprenoids and diaromatic carotenoids in paleozoic source rocks and oils from the western canada and williston basins abstract aryl isoprenoids in the range c13 c31 have been identified in source rock bitumens and oils from several paleozoic age petroleum systems in the western canada and williston basins the principal compounds possess the 2 alkyl 1 3 4 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria two c40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the duvernay late devonian petroleum system pyrolysis gas chromatograms of kerogens isolated from several paleozoic source rocks show an unusual abundance of 1 2 3 4 tetramethylbenzene it is proposed that this compound arises from cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure with increasing maturation concentrations of the aryl isoprenoids in duvernay source rock bitumens increase to a point whereas the c40 perhydrodiaromatic carotenoids decrease steadily previous studies have suggested that aryl isoprenoids may be indicators of enhanced salinity environments this is not supported by the present work which shows high concentrations in source rocks associated with presumed normal marine salinities there is however a general association with intervals of condensed clastic or mixed clastic carbonate sedimentation within carbonate depositional systems from the association found and from parallels to modern habitats of photosynthetic bacteria it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic anoxic boundary layer in sub tropical to tropical marine environments

compositional modeling of petroleum generation and expulsion trial application to a local mass balance in the smorbukk sor field haltenbanken area norway 1 we present an application of a compositional kinetic model of petroleum generation degradation into gas and residue and simultaneous expulsion petroleum composition is described by four carbon fractions c 1 c 2 c 5 c 6 c 14 c 15 and expulsion is related to a petroleum saturation threshold expulsion is important because rapid expulsion of petroleum from source rocks favors oil whereas late expulsion increases the cracking reactions and favors gas accumulation such a model is tested against field data for the first time by applying it to the smorbukk sor field previously named smorbukk greek beta located in the norwegian sea geometrical and one dimensional thermal reconstructions are performed followed by a computation of a mass balance of expelled and unexpelled products for each source rock throughout the drainage area comparison of the model results is made with rock eval data vitrinite reflectance and actual composition of accumulations lower jurassic coals were the main source expelling gas and oil mainly since 5 ma as the present accumulation accounts for less than 10 of total expelled petroleum major petroleum losses probably occurred through the structural spillpoint this migration scheme is supported by the simila composition of the reservoired petroleum and the petroleum expelled since 0 5 ma although various uncertainties are possible this study shows that our model has the capability to quantify expulsion consistently with the observed amounts of unexpelled petroleum in mature source rocks and with the reported composition of the accumulation

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

modeling of gas generation from the barnett shale fort worth basin texas the generative gas potential of the mississippian barnett shale in the fort worth basin texas was quantitatively evaluated by sealed gold tube pyrolysis kinetic parameters for gas generation and vitrinite reflectance ro changes were calculated from pyrolysis data and the results used to estimate the amount of gas generated from the barnett shale at geologic heating rates using derived kinetics for ro evolution and gas generation quantities of hydrocarbon gas generated at ro 1 1 are about 230 l t 7 4 scf t and increase to more that 5800 l t 186 scf t at ro 2 0 for a sample with an initial total organic carbon content of 5 5 and ro 0 44 the volume of shale gas generated will depend on the organic richness thickness and thermal maturity of the shale and also the amount of petroleum that is retained in the shale during migration gas that is reservoired in shales appears to be generated from the cracking of kerogen and petroleum that is retained in shales and that cracking of the retained petroleum starts by ro 1 1 this result suggests that the cracking of petroleum retained in source rocks occurs at rates that are faster than what is predicted for conventional siliciclastic and carbonate reservoirs and that contact of retained petroleum with kerogen and shale mineralogy may be a critical factor in shale gas generation shale gas systems together with overburden can be considered complete petroleum systems although the processes of petroleum migration accumulation and trap formation are different from what is defined for conventional petroleum systems

pore characterization of organic rich lower cambrian shales in qiannan depression of guizhou province southwestern china abstract nine organic rich shale samples of lower cambrian black shales were collected from a recently drilled well in the qiannan depression guizhou province where they are widely distributed with shallower burial depth than in sichuan basin and their geochemistry and pore characterization were investigated the results show that the lower cambrian shales in qiannan depression are organic rich with toc content ranging from 2 81 to 12 9 thermally overmature with equivalent vitrinite reflectance values in the range of 2 92 3 25 and clay contents are high and range from 32 4 to 53 2 the samples have a total helium porosity ranging from 2 46 to 4 13 and total surface area in the range of 9 08 37 19 m2 g the estimated porosity in organic matters defined as the ratio of organic pores to the volume of total organic matters based on the plot of toc vs helium porosity is about 10 for the lower cambrian shales in qiannan depression and is far lower than that of the lower silurian shales 36 in and around sichan basin this indicates that either the organic pores in the lower cambrian shale samples have been more severely compacted than or they did not develop organic pores as abundantly as the lower silurian shales our studies also reveal that the micropore volumes determined by dubinin radushkevich dr equation is usually overestimated and this overestimation is closely related to the non micropore surface area of shales i e the surface area of meso and macro pores however the modified bet equation can remove this overestimation and be conveniently used to evaluate the micropore volumes surface area and the non micropore surface areas of micropore rich shales

thermal maturation of gas shale systems shale gas systems serve as sources reservoirs and seals for unconventional natural gas accumulations these reservoirs bring numerous challenges to geologists and petroleum engineers in reservoir characterization most notably because of their heterogeneous character due to depositional and diagenetic processes but also because of their constituent rocks fine grained nature and small pore size much smaller than in conventional sandstone and carbonate reservoirs significant advances have recently been achieved in unraveling the gaseous hydrocarbon generation and retention processes that occur within these complex systems in addition cutting edge characterization technologies have allowed precise documentation of the spatial variability in chemistry and structure of thermally mature organic rich shales at the submicrometer scale revealing the presence of geochemical heterogeneities within overmature gas shale samples and notably the presence of nanoporous pyrobitumen such research advances will un

upper permian junggar and upper triassic ordos lacustrine source rocks in northwest and central china organic geochemistry petroleum potential and predicted organofacies abstract two sets of lacustrine source rocks in the junggar basin and ordos basin have been analysed by organic geochemical approach and organic petrographic technique one of these source rocks the junggar shales lucaogou formation and hongyanchi formation was deposited in a hydrologically closed brackish lake under a sub humid climate in higher latitude 39 43 n and consisted of organic rich profundal lake shales lucaogou formation and lean fluvial lacustrine lake margin mudstones the other one the chang 7 shale was deposited in a hydrologically open freshwater lake under a humid climate in a 31 n palaeolatitude and was characterized by high concentration of alginite rich organic matter the profundal lucaogou shale and chang 7 3 shale possess abundant total organic carbon high generative potential s2 and high hydrogen indices which rank as the best prolific source rocks in both basins followed by chang 7 1 shale hongyanchi formation and chang 7 2 are much leaner than their counterparts and contain relatively small portion of alginite but more terrigenous macerals this nature of organic matter makes them less prolific and becoming gas prone potential these differences in petroleum potential mirror depositional environment changes in source rocks formation potential source rocks in both basins have the potential for generating high wax oil but the brackish system clearly contains more pna oil the kerogen structures revealed by pyrolysis gas chromatography allowexplaining this trend the lucaogou chang 7 3 and chang 7 1 shales enriching in long and moderate alkyl chains share a nature of high wax oil generation trend in contrast the hongyanchi and chang 7 2 shales appears to be dominated by short to moderated chain length distribution and higher overall aromaticity to generate more pna oil even gas and condensate thermal liability was shown to be linked to kerogen structure in particular the presence of alicyclic and oxygen containing moieties and these in turn are correlate with total organic carbon content

calculation of petroleum masses generated and expelled from source rocks abstract an algebraic scheme for calculating the masses of petroleum formed in mature source rocks has been constructed the scheme exploits routine geochemical measurements and a basic understanding of the behaviour of sedimentary organic matter at elevated temperatures under both laboratory and subsurface conditions application of these techniques to data from a wide range of source rock types has led to the following general conclusions 1 1 major oil and gas generation from kerogen occurs between 120 and 150 c in the subsurface gas generation continues to temperatures 160 c 2 2 oil prone source rocks with average initial potential 5 kgt 1 of rock and average organic carbon contents 1 5 expel 60 90 of the total oil generated 3 3 oil expulsion from leaner source rocks is less efficient most of the oil generated remains in the source rock it is subsequently converted to lighter components at higher temperatures and expelled in the vapour state 4 4 the major loss of organic carbon from rich oil prone source rocks during generation and expulsion means that the petroleum potential and organic carbon content of mature source rocks are much less than their initial immature values hence the algebraic scheme must be used to calculate the initial values before expelled petroleum masses can be determined