natural gas hydrates on the southeast u s margin constraints from full waveform and travel time inversions of wide angle seismic data strong bottom simulating reflectors bsr have been mapped over a region of approximately 50 000 km2 on the southeastern u s margin and have been associated with possible abundance of natural gas hydrates in june 1992 coincident single channel seismic and wide angle ocean bottom seismic data were acquired in the region focusing on the blake ridge and the carolina rise wide angle reflections from the bsrs were clearly observed at offsets up to 6 km joint travel time inversion was conducted with wide angle and vertical incidence data in order to explore possible regional variation and the resultant two dimensional average velocity models imply higher background velocities on the carolina rise full waveform inversion was then performed to determine the seismic origin of the bsrs the best fit model shows a similar low velocity 1 4 km s beneath the bsr at both sites indicating trapped free gas with low saturation 10 the inversion results also indicate that a thin high velocity wedge with a maximum velocity of 2 3 km s is present just above the blake ridge bsr sediment reflectivities were also calculated and higher reflectivities are observed on the carolina rise an increase in reflectivity below the bsr seems to correspond to the gas bearing zone at both sites concentration of hydrates were estimated based on these velocity models whereas average hydrate concentration of 3 of the total sediment volume is suggested for the lower half of the hydrate stability zone at the blake ridge only a very low average concentration of hydrate can be expected at the carolina rise the hydrates seem to be concentrated near the base of the hydrate stability zone and the maximum hydrate concentration is estimated as 20 at the blake ridge and 7 at the carolina rise both of which are too high to be explained by in situ biogenic activity only and require some secondary accumulation mechanism it is suggested that hydrate recycling caused by the stability field migration may have effectively condensed hydrates at both sites additional enhancement by upward fluid expulsion may also be viable for the blake ridge

sediment dewatering in the makran accretionary prism abstract sediments within the makran accretionary prism are considerably more compacted than the material entering the subduction zone due to the additional tectonic stresses resulting from plate convergence and accretionary processes tectonic compaction of the offscraped sediments has been documented by deriving in situ porosities in the upper 4 km from their seismic velocities wide angle seismic reflection refraction profiles were analysed from a transect crossing both the makran accretionary prism and the undeformed abyssal plain sediments to the south the 6 7 km thick abyssal plain sediments exhibit normal compaction with depth the sediments incorporated into the accretionary prism have higher seismic velocities at all depths corresponding to reductions in porosity of 30 40 mapping the porosity depth gradient across the prism shows that there is a marked change in porosity at the seaward toe of the prism the frontal fold there is then little further change until further folding begins to occur 70 km landward of the toe the dewatering and consolidation of the sediments is an important control on deformation occurring within the sedimentary prism

a geochemical study of oil migration at source rock reservoir contacts stable isotopes abstract whereas organic geochemical analyses of oils and potential source rocks have enabled correlations to be drawn and have been utilized to suggest modes of migration only limited data has been published relating a known source rock in contact with an oil filled reservoir this paper presents initial results from the examination of an approximately 100 m continuous core through the kimmeridge shale of the north sea the variability in extractable source rock hydrocarbon contents kerogen toc asphaltene and their carbon isotopic contents are documented nitrogen isotopic content of kerogens and asphaltenes as well as kerogen and asphaltene ton are relatively constant carbon isotopic compositions of kerogen extractable hydrocarbons and asphaltenes covaried significantly as did nitrogen isotopic compositions of kerogen and asphaltenes average isotopic compositions of the asphaltene free extracts and asphaltenes were nearly identical to the oil in the primary reservoir small chemical differences are noted among extracts

xrf based chemostratigraphy between and across two disconformities in the ordovician trenton group and utica shale of central new york u s a abstract thick mudstone successions contain a wealth of elemental proxy information than can be readily accessed by hand held x ray fluorescence xrf spectroscopy mudstones of the upper ordovician trenton group and utica shale record drowning of a carbonate shelf in a peripheral foreland basin during the taconic orogeny two discrete episodes of shelf erosion the thruway and honey hill disconformities followed by deepening occurred during this period xrf based bulk rock elemental data coupled with detailed lithologic descriptions and xrd analysis highlight previously unidentified changes in the composition of siliciclastic detritus across these disconformities this likely relates to variation in the relative contribution of sediment derived from the cratonic interior eroded carbonate shelf and rising orogenic wedge as well as possible exhumation of the adirondack massif the data also indicate that mudstones of the lower indian castle shale the interval of the utica shale deposited between the thruway and honey hill disconformities are more carbonate rich than the underlying mudstones of the trenton group this is surprising given the large volume of limestone in the trenton group and attests to the considerable amount of intrabasinal carbonate winnowed from the shelf during formation of the thruway disconformity drowning following erosion along the honey hill disconformity diminished this sediment source and led to a significant reduction in the amount of carbonate mudstone present in the upper indian castle shale the concentrations of redox sensitive trace elements normalized to al increase sharply across the thruway disconformity suggesting increased bottom water anoxia and organic matter preservation in a deepening basin increases in the s and fe concentrations above the honey hill disconformity suggest a shift to even more strongly reducing conditions results of this study are consistent with previous interpretations indicating that higher resolution xrf based elemental concentration data may reveal more cryptic changes in sediment provenance and bottom water redox conditions in the taconic foreland basin and in other thick mudstone successions

the expulsinator versus conventional pyrolysis the differences of oil gas generation and expulsion simulation under near natural conditions abstract the expulsinator provides a new technique to simulate generation and expulsion of hydrocarbons under near natural conditions this is realized by application of lithostatic pressure onto an intact source rock disc with undisturbed mineral matrix and kerogen network and by hydrous pyrolysis conducted in open flow through mode conventional pyrolysis methodologies serve well in generation kinetics assessment but are only of limited use for investigation of primary migration and expulsion due to destructive sample preparation inappropriate pressure regimes and pyrolysis in closed mode and or in the absence of water however comparison of results generated with conventional pyrolysis with expulsinator experiments is important to assess the performance of the generation and expulsion simulation carried out with the expulsinator thus the generation and expulsion behaviour of this new methodology has been compared with established pyrolysis methodologies like hypy and closed small vessel pyrolysis csvp and has been assessed by rock eval pyrolysis expulsinator experiments released higher amounts of bitumen than csvp this has been attributed to increased cross linking reactions of bitumen in case of the classic pyrolysis favouring formation of pyrobitumen differences in yields and composition of n alkanes were controlled not by generation kinetics exclusively but also by expulsion effects in particular delayed expulsion caused by geochromatography expulsinator conversion rates of toc exceeded 81 whereas those of hydrous csvp remained at 65 higher expulsinator toc conversion was accompanied by lower gas generation compared to csvp this is attributed to the open setup of the expulsion experiment which by rapid removal of products generated prevents their secondary alteration particularly polymerization to pyrobitumen and oil to gas cracking at higher temperatures hypy of expulsinator pyrolysis residues verified a low generation potential remaining after the expulsion experiment the expulsinator device delivers oil and gas generation data which can be applied in numerical modelling exercises

some pragmatic perspectives in source rock geochemistry abstract conceptual advances in petroleum source rock geochemistry made during the last decade are reviewed and some problem areas in analytical geochemistry are outlined areas of discussion include views of source rocks based on assessment of hydrocarbon expulsion kinetic models of kerogen maturation vitrinite reflectance evolution and a discussion of the data dilemma facing modern source rock geochemistry the increased application of petroleum geochemistry to the quantitative solution of geological problems is stressed

revealing hydrocarbon migration pathways in this paper a general concept for revealing hydrocarbon migration pathways in rock sequences is introduced the concept uses a multidisciplinary approach based on a geochemical and a petrophysical or mineralogical index these two indices provide together the migration plot which shows the direction of hydrocarbon movement

the barnett shale compositional fractionation associated with intraformational petroleum migration retention and expulsion abstract the marathon 1 mesquite well was drilled in hamilton county texas targeting the barnett shale with late oil window maturity combining a large suite of petrologic and high resolution organic geochemical analyses on 120 core samples we have been able to document qualitatively and quantitatively the effects of petroleum retention within and expulsion from five intervals within the barnett shale lithological heterogeneities control the composition and amount of retained fluids the sorption of oil by solid organic matter is important in all intervals applying empirical formulas we have been able to demonstrate not only that retention is primarily controlled by total organic carbon toc but also that the live or labile component rather than dead or inert carbon constitutes the most active sorptive sites additional retention in the micropores provided by biogenic microcrystalline quartz sponge spicules accounts for the sweet spot defined by an oil crossover in the 9 14 m 30 ft thick second interval the fluorescing oil occurring in the axial chamber of the sponge spicules and that sorbed on organic particles are together enriched in saturated hydrocarbons whereas the dispersed oil from the adjacent interval 3 is depleted in this compound class mass balance calculations reveal that short distance migration of petroleum into this reservoir interval second fractionates the generated oil into a higher quality oil by preferential retention in the order polar compounds aromatic hydrocarbons saturated hydrocarbons within the underlying organic matter and clay rich third interval source unit furthermore molecular fractionation i e a preferential expulsion of lower molecular weight hydrocarbons n alkanes could be calculated an additional practical result for source rock assessment is that corrected s2 petroleum generated by pyrolysis and toc values should be calculated by combining rock eval pyrolysis data on whole rocks and rocks following soxhlet extraction using parameters based on unextracted rock only the expulsion of petroleum is systematically overestimated and the degree of kerogen conversion is therefore concomitantly underestimated

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

millimeter scale concentration gradients of hydrocarbons in archean shales live oil escape or fingerprint of contamination abstract archean shales from the pilbara in western australia contain biomarkers that have been interpreted as evidence for the existence of cyanobacteria and eukaryotes 2 7 billion years ga ago with far reaching implications for the evolution of earth s early biosphere to re evaluate the provenance of the biomarkers this study determined the spatial distribution of hydrocarbons in the original drill core material rock samples were cut into millimeter thick slices and the molecular content of each slice was analyzed in core from the hamersley group 2 5 ga c alkanes had gradually increasing concentrations from the surfaces to the center of the rock while the abundance of steranes hopanes and c 15 alkanes decreased with distance from the outer surfaces in samples from the fortescue group 2 7 ga hydrocarbons were overwhelmingly concentrated on rock surfaces two mechanisms are proposed that may have caused the inhomogeneous distribution diffusion of petroleum products into the rock contamination model and leaching of indigenous hydrocarbons out of host shales driven by pressure release after drilling live oil effect to test these models the hydrocarbon distributions in the archean shales are compared with artificially contaminated rocks as well as younger mudstones where leaching of live oil had been observed the results show that chromatographic phenomena associated with live oil escape and contaminant diffusion have strong effects on molecular ratios and maturity parameters potentially with broad implications for oil source rock correlation studies and paleoenvironmental interpretations for the archean shales the live oil effect is consistent with some of the observed patterns but only the contamination model fully explains the complex chromatographic fingerprints therefore the biomarkers in the pilbara samples have an anthropogenic origin and previous conclusions about the origin of eukaryotes and oxygenic photosynthesis based on these samples are not valid however the study also identified indigenous molecules the spatial distribution of particular aromatic hydrocarbons suggests they are syngenetic although devoid of biological information these aromatics now represent the oldest known clearly indigenous terrestrial liquid hydrocarbons

assessment of mesozoic and upper paleozoic source rocks in the south yellow sea basin based on the continuous borehole csdp 2 abstract being lack of core data and measured data although the marine oil gas exploration in the south yellow sea basin has been going on for 57 years no commercial hydrocarbon reservoirs have been found so far the quantitative source rocks evaluation based on geochemical data and fluid inclusions containing hydrocarbon benefits from the completion of borehole csdp 2 in 2016 a continuous coring well of the chinese continental shelf drilling program csdp which indicates that the marine origin oil gas exploration in the south yellow sea basin enters into a new stage as revealed by the well csdp 2 three sets of effective hydrocarbon source rocks in the mesozoic and upper paleozoic have been identified which are distributed in the lower triassic qinglong formation t1q upper permian longtan dalong formation p3l d and middle permian gufeng qixia formation p2g q respectively among them organic rich source rocks mainly concentrate in the lower part of the p3l d and the middle upper part of the p2g q and the p3d mudstone also works as good source rock the p3l d mudstone with high organic abundance is the chief source rock in the south yellow sea basin whose maximum hydrocarbon generating intensity may reaches up to 795 09 104 t km2 and hydrocarbon expulsing intensity remains at the level of 165 03 104 t km2 a noteworthy feature of the p2g q source rocks is the strong vertical heterogeneity with the hydrocarbon expulsing intensity of the upper part being 34 14 104 t km2 while that of the lower part being 18 07 104 t km2 in contrast the organic abundance of argillaceous limestone in the t1q is mainly poor to medium and its hydrocarbon expulsing intensity is the weakest one in the three sets of hydrocarbon source rocks only about 12 7 104 t km2 taking into consideration the joint influence of depositional environment organic matter parent source and biological productivity the overall quality of source rocks in the south yellow sea basin is at the similar level to the lower yangtze subei basin but lower than that of the upper yangtze sichuan basin the most significant oil gas information is that multiple direct oil indications and high value abnormalities of gas logging have been discovered in the well csdp 2 moreover the mesozoic and upper paleozoic marine strata in the south yellow sea basin have experienced three hydrocarbon charging stages indicating a broad prospect of marine oil gas exploration

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea ii molecular composition of alkylated naphthalenes phenanthrenes benzo and dibenzothiophenes abstract variations with depth in the quantitative distributions of di and tricyclic alkylaromatic hydrocarbons and sulfur heterocycles determined for a total of thirty two core samples from two thick shale intervals and thirteen thin interbedded shale layers of the upper jurassic age kimmeridge clay formation brae field area north sea reveal in part the effects of depletion with hydrocarbon expulsion trends of increasing depletion with approach to the nearest shale sandstone contacts as documented by a decrease in carbon normalized yields are more distinctive for the alkylnaphthalenes as compared to the alkylphenanthrenes and alkyldibenzothiophenes but less drastic than previously observed for long chain alkanes cf part i leythaeuser et al 1988 lowest yields consistently were encountered at the outermost 1 2 metres of the thick shale intervals and for the thin shale layers where the relative expulsion efficiencies were much higher for c15 to c30n alkanes 80 95 than for c2 and c3 alkylnaphthalenes 30 40 in contrast c2 and c3 alkylbenzothiophene yields were higher in these shale portions than further inside the thick shale which is interpreted to result from a post expulsion selective replenishment from the adjacent oil accumulation expulsion was not associated with any detectable fractionation among c1 and c3 alkylnaphthalenes or c1 and c2 alkylphenanthrenes as evidenced by a mass balance approach and concentration ratios of individual alkylaromatic isomers commonly used as maturity indicators based on a reconstruction of the quantitative distributions of aromatic hydrocarbons and sulfur aromatics expelled from thin shale layers from early mature through to mature stages of thermal evolution it was verified that the methylphenanthrene index mpi 1 and methyldibenzothiophene ratio mdr of the expelled oil reflects the average of the maturity levels during which the source rock has expelled petroleum

identifying patchy saturation from well logs gassmann s 1951 equations relate the elastic bulk ksat and shear gsat moduli of a fully saturated rock to the elastic bulk and shear moduli of the dry rock frame kdry and gdry respectively porosity and the bulk moduli of the mineral phase ks and pore fluid kf

expulsion of petroleum hydrocarbons from shale source rocks there is compelling evidence that movement of petroleum from organic rich shales into sandstones and limestones occurs in the subsurface1 this expulsion of material must occur if crude oil accumulations are to form and it is termed primary migration2 earlier studies3 4 suggested that this movement occurs with chemical fractionation some components are more mobile than others one of the agents of expulsion at early maturity stages is compaction which is not only capable of forcing water but also organic components out of the pore network of a source rock2 5 6 because the fractionation effects associated with expulsion provide clues to the transport mechanisms involved we have made detailed quantitative comparisons of the hydrocarbons of shales of different thicknesses the centre and edges of thick shales and sandstones adjacent to shales from two cored interbedded shale and sandstone sequences from spitsbergen island svalbard norway these observations confirm considerable movement of hydrocarbons in the subsurface with lower molecular weight components being more mobile up to 90 the original amount of n pentadecane may be lost from very thin shales sandwiched between sandstone horizons and from shales close to a lithological boundary with sandstone

relationship between the fluorescence color of oil inclusions and thermal maturity in the dongying depression bohai bay basin china part 1 fluorescence evolution of oil in the context of hydrous pyrolysis experiments with increasing maturity abstract the fluorescence evolution of oils has been measured by simulation of petroleum generation and expulsion in a half closed system using hydrous pyrolysis based on four oil prone source rocks type i and ii kerogens from the dongying depression bohai bay basin china the results suggest that the fluorescence characteristics of expelled oil are independent of oil prone kerogen types but are strongly related to oil generation and expulsion processes which are controlled by thermal maturity of source rocks the fluorescence spectral parameters max q650 500 and qf 535 of expelled oils show no obvious variation or even show gradual redshifts when the highest max occurs at peak bitumen generation depending on the expulsion process a blueshift of fluorescence color occurs only during the main oil generation and expulsion stage which immediately follows the peak bitumen generation stage however the expelled oil mainly exhibits green to yellow fluorescence colors 500 nm

internal deformation and compaction of the makran accretionary wedge the makran accretionary wedge is one of the largest on earth a 7 km thick column of sands and quartzolithic turbidites are incorporated into this wedge in a series of deformed thrust sheets we present the results of prestack depth migration and focusing error analysis migration velocity analysis performed on a profile across the makran wedge the depth section shows the deformation style of the accreted sediments and the migration velocities allow us to estimate porosity variations in the sediments the thrust sheets show evidence of fault propagation folding with a long wavelength of deformation 12 km and secondary thrusting in the kink bands of the folds such that the central part of each thrust sheet is elevated to form an additional ridge this deformation style and the 15 steep surface slope of the first ridge suggest a high degree of consolidation porosities were calculated from the seismic migration velocities and the ratio of fluid pressure to lithostatic pressure was estimated for 5 locations along the profile rather than being undercompacted and overpressured as in most accretionary wedges the sedimentary input is normally compacted exponential porosity decay throughout almost the whole wedge however a slight increase in porosity and at depth with respect to the normal compaction curve indicates that the turbiditic sequence might be overpressured landward of the deformation front

effects of hydrocarbon expulsion from shale source rocks of high maturity in upper carboniferous strata of the ruhr area federal republic of germany abstract based on detailed geochemical analysis of closely spaced core samples from a sequence of interbedded source rock type shales and reservoir sandstones of upper carboniferous westphalian age certain effects of primary migration were recognized qualitatively expulsion of hydrocarbons from two high mature shale source rock units 1 1 r m has occured preferentially from their edges and is indicated by the following effects an overall decrease of the concentrations of total extract saturated and aromatic hydrocarbons and decreasing values for the production index from rock eval measurements from the centre portions of the shale units towards their outer edges these depletion trends are paralleled by systematic changes in the composition of the c 15 saturated hydrocarbons also evidence was obtained to suggest that preferential depletion has occurred into a local fracture zone the effects of hydrocarbon expulsion could be quantified on a molecular level for two thin source rock type shale layers interbedded in a reservoir sandstone for the n alkanes less than c 26 the expulsion efficiencies range between 70 and 80 despite the high maturity level and despite the resulting advanced migration stage some evidence for chromatography type compositional fractionation in the shale could still be observed in the c 27 range n alkanes and between pristane and its n alkane isomer pristane is preferentially retained in the source rock

appraisal of gas hydrate free gas from vp vs ratio in the makran accretionary prism abstract existence of gas hydrate in the marine sediments elevates both the p and s wave seismic velocities whereas even a small amount of underlying free gas decreases the p wave velocity considerably and the s wave velocity remains almost unaffected study of both p and s wave seismic velocities or their ratio v p v s for the hydrate bearing sediment provides more information than that obtained by the p or s wave velocity alone for the quantitative assessment of gas hydrate we estimate the p and s wave seismic velocities across a bsr interface between gas hydrate and free gas bearing sediments using the travel time inversion followed by a constrained ava modeling of multi channel seismic mcs data at two locations in the makran accretionary prism using this v p v s ratio we then quantify the amount of gas hydrate and free gas based on two rock physics models the result shows an estimate of 12 14 5 gas hydrate and 4 5 5 5 free gas of the pore volume based on first model and 13 20 gas hydrate and 3 3 5 free gas of the pore volume based on the second model respectively

evolution of alkanes and carboxylic acids in ancient sediments from the maracaibo basin abstract aliphatic hydrocarbons and carboxylic acids were analysed quantitatively in rock samples of different degrees of maturity from the icotea borehole eocene misoa formation maracaibo basin venezuela in order to compare their geochemical evolution in ancient sediments previously a double generation process for the carboxylic acids has been reported in which immature distributions of acids were generated at the highest maturities it was suggested that the generation of the organic acids was dependent on the nature of the binding in the kerogen and on steric factors by comparison the alkanes show different behaviour whilst a similar generation profile is observed for hopanes when compared to hopanoic acids no inversion of isomeric maturation parameters was observed in this case hopanes may be generated first by a release of hydrocarbons from the kerogen at low levels of thermal maturity r o 0 46 and secondly by cracking at higher temperatures the second generation being less significant than the first higher plant derived triterpanes behave similarly pristane phytane and n alkanes are generated at relatively high levels of thermal maturity r o 0 7 the generation profiles for the n alkanes are complicated by expulsion and cracking phenomena however these components are generated after the major release of n acids

amplitude versus offset modeling of the bottom simulating reflection associated with submarine gas hydrates abstract a bottom simulating seismic reflection bsr that parallels the sea floor occurs worldwide on seismic profiles from outer continental margins the bsr coincides with the base of the gas hydrate stability field and is commonly used as indicator of natural submarine gas hydrates despite the widespread assumption that the bsr marks the base of gas hydrate bearing sediments the occurrence and importance of low velocity free gas in the sediments beneath the bsr has long been a subject of debate this paper investigates the relative abundance of hydrate and free gas associated with the bsr by modeling the reflection coefficient or amplitude variation with offset avo of the bsr at two separate sites offshore oregon and the beaufort sea the models are based on multichannel seismic profiles seismic velocity data from both sites and downhole log data from oregon odp site 892 avo studies of the bsr can determine whether free gas exists beneath the bsr if the saturation of gas hydrate above the bsr is less than approximately 30 of the pore volume gas hydrate saturation above the bsr can be roughly estimated from avo studies but the saturation of free gas beneath the bsr cannot be constrained from the seismic data alone the avo analyses at the two study locations indicate that the high amplitude bsr results primarily from free gas beneath the bsr hydrate concentrations above the bsr are calculated to be less than 10 of the pore volume for both locations studied

simple kinetic models of petroleum formation part ii oil gas cracking kinetic schemes describing oil gas cracking are a required component of models which predict the masses compositions and phases of petroleum expelled from source rocks an additional application is in predicting the temperature zone over which reservoired oil deposits will be degraded to gas this simple first order kinetic model calibrated on closed system laboratory pyrolysis of 16 different source rock samples describes the bulk conversion of oil c6 molecular range to gas c1 5 molecular range cracking rates vary markedly between samples depending on the saturate to aromatic ratio of the generated oil the initial hydrogen index hl0 of the sample taken as an indirect measure of the saturate to aromatic ratio of the oil it generates correlates strongly with optimized rate constants for oil cracking in individual samples thus cracking rates are predictable using a simple routinely performed geochemical screening measurement source rocks with high hl0 tend to generate saturate rich oils with a high mean activation energy and a tight distribution of bond energies which crack relatively slowly over a high but relatively narrow temperature range source rocks with low hl0 generate aromatic rich oils with a low mean activation energy and a broad distribution of bond energies which crack relatively rapidly over a lower but relatively wide temperature range this is an important contributing factor in the observed gas proneness of type iii source rocks with low hl0 the projected cracking window defined limits at 10 90 of initial oil degraded reference heating rate 2 c ma 1 varies from 155 to 205 c in very high quality source rocks hl0 600 mg g c 1 to 115 205 c in very poor quality source rocks hl0 50 mg g c 1 an order of magnitude increase decrease in heating rate elevates depresses these temperature windows by ca 15 c the extrapolations to the geological subsurface are subject to a confidence limit no better than 7 c extrapolation to the reservoir environment requires caution because kerogen an important potential catalyst and hydrogen donor allowing 100 cracking efficiency in the source rock is absent furthermore fractionation during expulsion causes saturate enrichment of expelled ultimately reservoired oils thus in reservoir cracking should be at least as slow as cracking in good quality source rocks and coke or pyrobitumen formation is needed to conserve the hydrogen balance a case history based on deep petroleum pools of the uk central north sea confirms these projections demonstrating no positive evidence of significant in reservoir cracking at temperatures as least as high as 174 c and perhaps even 195 c previous studies have overestimated the importance of in reservoir cracking future studies aiming to predict petroleum composition in traps should concentrate on understanding the charge composition expelled from the kitchen

effect of a dolerite intrusion on triterpane stereochemistry and kerogen in rundle oil shale australia abstract stereochemical changes of triterpanes present in extracts from an immature oil shale sequence intruded by a 3 m dolerite sill have been studied by gas chromatography mass spectrometry gc ms the steric configuration of the hopanes was observed to change from one dominated by the thermally less stable 17 h 21 h configuration at some distance from the intrusion to one dominated by the thermally more stable 17 h 21 h and 17 h 21 h configurating in the immediate vicinity of the intrusion in addition severe alteration of the kerogen appeared to have taken place as a result of the contact metamorphism and high concentrations of extractable organic matter were observed below the intrusion characterization of the kerogens by curie point pyrolysis has enabled the effects of the intrusion on the shales to be monitored

organic geochemical evidence of late pleistocene holocene environmental changes in the lake balaton region hungary abstract this paper presents organic geochemical records and a combined interpretation of organic geochemical and palaeoecological data for a late pleistocene holocene shallow lake sequence abundance bulk chemical composition and sources of the organic matter om as well as the relative contribution of the labile and resistant bio and geo macromolecules were determined on 46 sediment samples lipids isolated from selected samples representing the lowest and highest water levels were analyzed integration of the organic geochemical and palaeoecological records suggests that climate exerted the primary control on the amount and quality of the om preserved the relative contribution of the labile fresh plant and litter and resistant lignin and cellulose bio macromolecules immature geo macromolecules humic substances and mature refractory geo macromolecules and the degree of preservation of the primary biomass calculated from mathematical deconvolution of rock eval pyrograms allowed the distinction of three and five zones related mainly to water level fluctuation within the late pleistocene and holocene sequences respectively

hydrocarbon distribution in coals and in dispersed organic matter of different maceral compositions and maturities more than 60 samples from 5 coal seams and adjacent siltstones and sandstones were selected from a well through westphalian b sediments from northern germany in order to study bitumen generation and migration the cores were drilled between 1200 und 1530 metres depth in this interval vitrinite reflectance rr is increasing from 0 70 to 0 92 results reveal high hydrocarbon generation potentials for all coal samples but not for adjacent clastic rocks although maceral compositions of both are quite similar yields and compositions of thermal extracts from the coals depend on maceral compositions and rank however the bulk of the already generated bitumen has not been removed during natural coalification and is not easily releasable by thermovaporisation a mass balance based on elemental composition of dull coals indicates that in the rather narrow rank interval 0 70 0 92 rr a total mass loss of 20 may have occurred by migration this is evidenced by a loss of about 20 of the original hydrogen the rest being stored in the coals

primary migration by diffusion through kerogen ii hydrocarbon diffusivities in kerogen abstract laboratory experiments were performed to assess diffusion through kerogen as a mechanism of liquid hydrocarbon transport through fine grained rocks such transport can be important in primary migration within source rocks and in leakage through seals previous work with organic coated model cores has shown that hydrocarbon diffusion through organic matter networks can be substantially greater than hydrocarbon diffusion through aqueous pore space in the present work natural kerogen networks were evaluated experiments with five natural source rocks showed that kerogen increased the experimental hydrocarbon flux over the calculated hydrocarbon flux through pore water in only one of these source rocks the richest 2 2 toc carbonate sample effective diffusivities through kerogen were calculated for the two experimental hydrocarbons through this sample the results were extended with the wilke chang correlation to yield diffusivities of several other hydrocarbons through similar source rocks

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

evidence for a thick free gas layer beneath the bottom simulating reflector in the makran accretionary prism abstract seismic reflection data from the makran continental margin indicate the presence of a strong and widespread bottom simulating reflector bsr we apply a nonlinear full waveform inversion technique to multichannel reflection data from this area to investigate the detailed velocity structure and hence the origin of the bsr our result shows an abrupt decrease in the compressional wave velocity from 2 2 to 1 3 km s at a depth of 500 m below the sea bed the low velocity zone is unusually thick 200 350 m and may contain large quantities of free gas similar to some of the recently drilled blake ridge sites of odp leg 164 the voluminous free gas may have been generated by the dissociation of gas hydrates as a consequence of the upward movement of the base of gas hydrate stability field relative to the sediment column due to uplift and sedimentation in the accretionary wedge

petroleum generation and migration in coal seams of the carboniferous ruhr basin northwest germany a series of 64 coal and clastic rock samples of westphalian age was taken from five narrow 3 m depth intervals between 1200 and 1530 m depth and studied by geochemical and petrological methods maturity increases regularly with increasing depth as indicated by several maturity parameters the influence of organic facies is evident in the uppermost coal seam 0 70 rr where a hand picked vitrinite contains less total extract and less saturated long chain hydrocarbons than a directly adjacent sporinite rich coal extracts from deeper and more mature coals are less affected by facies changes probably due to enhanced petroleum redistribution in the seams total yield and gross composition of extracts in the deepest seam 0 92 rr which is directly overlain by sandstone seem to be influenced by the preferential expulsion of saturated hydrocarbons

seismic velocity structure at a gas hydrate reflector offshore western colombia from full waveform inversion seismic reflection profiles across many continental margins have imaged bottom simulating reflectors bsrs which have been interpreted as being formed at the base of a methane hydrate stability field such reflectors might arise either from an impedance contrast between high velocity partially hydrated sediments and water saturated sediments or from a contrast with partially gas saturated sediments these alternatives may be hard to distinguish by conventional amplitude versus offset or waveform modeling approaches here we investigate the origin of a high amplitude bsr in the accretionary wedge offshore of western colombia by seismic waveform inversion the inversion procedure consists of three steps firstly determination of root mean square velocities and hence estimates of the interval velocities between major reflectors by a global grid search for maximum normalized energy along elliptical trajectories in the intercept time slowness domain secondly determination of accurate interval velocities between these reflectors by a monte carlo search for maximum energy and thirdly a waveform fit in the frequency slowness domain using differential reflectivity seismograms and a conjugate gradient optimization algorithm to minimize the sample by sample waveform misfit between data and synthetic at two locations near a structural high we find a 30 m thick low velocity zone beneath the bsr with the properties of a partially gas saturated zone while at a third location where the bsr amplitude is lower we find no evidence for anomalously low velocities the preferential development of the bsr in structures that would tend to intercept fluid flow or migrating gas and the presence of free gas beneath the bsr indicate a mechanism of bsr formation in which free methane gas migrates upward into the hydrate stability field or is carried there in advecting pore water

small angle neutron scattering signature of oil generation in artificially and naturally matured hydrocarbon source rocks abstract we have demonstrated for the first time the application of a small angle neutron scattering sans technique for the precise determination of the onset of hydrocarbon transport primary migration in shaly source rocks we used a sequence of rocks pyrolysed in the laboratory under nitrogen at temperatures in the range 310 370 c these rocks contained several percent of dispersed marine type ii organic matter geochemical analysis indicated a peak of the hydrocarbon generation in the middle of the temperature range at 340 c we observed a sharp decrease of sans intensity in a narrow maturity range within the geochemically determined region of the onset of hydrocarbon generation this decrease was a direct consequence of the sans contrast variation caused by the invasion of the pore space by bitumen during the primary migration of hydrocarbons a similar phenomenon was observed for a natural maturity sequence of source rocks originating from the same location

recognizing and quantifying expulsion of oil from the woodford formation and age equivalent rocks in oklahoma and arkansas accumulations of oil in fractures stylolites burrows sandstone lenses and chert nodules deeply embedded within organic rich mature oil source beds of late devonian early mississippian age are considered prima facie evidence of internal migration and expulsion most oil migrated internally and was expelled as a separate phase within a given section in which chert and black shale are interbedded contain the same type of organic matter and have reached the same level of thermal maturity black shales typically contain less hydrocarbons per weight percent toc than cherts the observed differences represent the amount of oil expelled from the black shales and range from 10 to 15 mg g toc for total bitumen 7 to 8 mg g toc for saturated hydrocarbons and 11 mg g toc for volatile hydrocarbons approximately 27 33 of the oil generated in these source rocks was calculated to have been expelled in the main oil producing region of central and southern oklahoma 22 billion bbl of bitumen and 16 billion bbl of saturated hydrocarbons were estimated to have been expelled from the woodford formation relatively efficient separate phase oil expulsion may be characteristic of very rich oil source rocks like those reported here such rocks would reach effective oil saturation and begin to expel oil as a separate phase at a relatively early stage of generation timing and efficiency of oil expulsion must then be influenced by the concentration and type of organic matter in the source rock because these factors determine the volume of oil generated and hence the time when a source rock becomes oil saturated

geochemical effects of petroleum migration and expulsion from toarcian source rocks in the hils syncline area nw germany for mature oil prone source rocks of toarcian age in the hils syncline area nw germany the geochemical effects of primary migration of petroleum are shown expulsion has occurred at high efficiencies primarily via a network of macro and micro fractures the effects of this fracture controlled expulsion with respect to gross and molecular composition of c15 soluble organic matter are documented samples from fractured intervals have expelled total c15 soluble organic matter more efficiently than adjacent unfractured intervals a systematic comparison of samples taken at cm intervals away from macro fractures reveals compositional gradients which are interpreted to reflect preferential depletion of saturated and aromatic hydrocarbons from the source rock shale into the fractures extracts of shale samples directly at fracture walls are enriched in nso compounds and highly polar asphaltene like fractions the composition of residual petroleum fluids extracted from the fracture fill materials is variable in some cases there is a close match with that of the shale at some distance away from the fractures in other cases there is geochemical evidence to suggest that petroleum fluids were chemically altered during lateral flow along the fractures based on available geological and geochemical evidence a conceptual model is proposed to explain fracture development and fluid flow processes rapid heating by a nearby intrusive body at shallow depths when the toarcian sediments still contained about 15 20 pore water has played an important role overpressuring of aqueous pore fluids with abundant dissolved carbonate caused intense fracturing of the rich intervals in the mature toarcian sections finally the closely interdependent relationships between petroleum generation and petroleum migration processes are documented especially the evolution of these relationships with maturity progress from immature 0 48 rm to mature 0 68 and 0 88 rm and overmature 1 45 rm stages is shown for example in the maturity interval from 0 68 to 0 88 rm most of the measured shale compaction and porosity decrease is achieved by expulsion of petroleum for some samples there is an inverse relationship between kerogen quality and extractable hydrocarbon yields suggesting that expulsion efficiencies were higher from the better quality intervals because the petroleum achieved higher saturations and hence higher relative permeabilities

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

intraformational migration of petroleum insights into the development of sweet spot in the cretaceous niobrara shale oil system denver basin abstract the cretaceous niobrara formation is one of the latest unconventional exploration targets in north america in this paper an overall type ii marine organofacies with some variability is present within a core which consists of alternating marls and chalks covering a maturity range of 0 8 1 0 rc calculated vitrinite reflectance enhanced oil saturation index osi values have previously been reported for the chalk and here a positive trend r2 0 92 between the osi and the percentage of saturates in gross fractions is present thus the saturate fraction gradually increases from 40 to above 60 as the osi increases from 40 to 550 mg hc g toc total organic carbon extremely high osi values 300 mg hc g toc are characteristic of niobrara chalks therefore the chalk intervals represent primary sweet spots using a combined analytical approach petroleum has been shown to migrate from the organic rich marls into juxtaposed chalks and that this has fractionated oils into higher quality liquids extractable organic matter in the chalks is clearly enriched in saturate hydrocarbons while the nso containing polar compounds are preferentially retained in the shale and marl units compared with the significant fractionation effects between these gross fractions fractionation within a given compound class is nevertheless indistinct

a novel approach for recognition and quantification of hydrocarbon migration effects in shale sandstone sequences a detailed organic geochemical study of over 150 samples from two cores with a total combined length of 320 m 1 050 ft through sequences of interbedded source rock type shales 0 84 rm maturity and reservoir sandstones allowed recognition and quantitation of a number of migration effects detailed gas chromatography mass spectrometry of steranes and triterpanes was used to insure that samples being compared to investigate migration effects contain organic matter of a similar type thin shales interbedded in sands and the edges of thick shale units are depleted in petroleum range hydrocarbons to a much higher degree than the centers of thick shale units for the alkanes expulsion occurs with pronounced compositional fractionation effects shorter chain length n alkanes are expelled preferentially and isoprenoid alkanes are expelled to a lesser degree than their straight chain isomers based on material balance calculations expulsion efficiencies were determined and found to be very high in certain instances for thin interbedded shales they decrease from about 80 around c15 to near zero in the c25 region there is no evidence for significant redistribution of steranes and triterpanes in the two sequences compared to c15 to c25 n alkanes they appear relatively immobile the composition of the hydrocarbons impregnating parts of the reservoir sandstones is in agreement with expulsion occurring with pronounced fractionation based on molecular chain length hence consideration of bulk expulsion efficiencies gives an unrealistic picture furthermore the impregnation of a siltstone cap rock from an underlying hydrocarbon accumulation seems to have occurred by bulk oil migration and without significant fractionation the degree of hydrocarbon depletion of some of the shales of both sequences appears to be controlled by compaction and the primary migration process appears to have occurred with chromatographic separation the migration phenomena observed in both sequences lead us to propose that the main phase of expulsion can be preceded by an earlier sta e during which the edges of thick shales and thin interbedded shales appear to be slowly and continuously depleted by the chromatographic processes the composition of the hydrocarbon product accumulating in the reservoirs at this stage appears to be controlled primarily by physical processes rather than by the type and maturity of the organic matter in the generating source rock by this mechanism the origin of accumulations of light oils and gas condensates in low mature sequences bearing predominantly terrestrial derived organic matter can be explained finally the migration effects documented in this study have some consequences for interpretation of geochemical data e g the pristane n c17 ratio a commonly accepted maturity parameter has been shown to be also controlled by the degree of hydrocarbon expulsion

migration of hydrocarbons in carbonate source rocks of the stasfurt member ca2 of the permian zechstein borehole aue 1 germany the role of solution seams abstract the effects of petroleum migration from carbonate source rocks through preferential expulsion of hydrocarbons from stylolites is investigated this type of expulsion is associated with compositional fractionation saturated hydrocarbons and nso compounds are expelled preferentially pristane and phytane show higher relative expulsion efficiencies than n c 17 and n c 18 alkanes aromatic hydrocarbons especially trimethylnaphthalenes are fractionated by the expulsion processes triterpanes and steranes are not fractionated by expulsion from solution seams and could be valuable tools for oil source rock correlation in carbonate rocks

migration of c1 c8 hydrocarbons in marine sediments abstract light hydrocarbon c 1 c 8 profiles are compared for three wells of varying maturities two immature dsdp wells site 397 near the canary islands and site 530a near the walvis ridge in the south east atlantic and a mature well the east cameron well in the texas gulf coast primary migration of c 1 and c 2 appears to be occurring in all of the sedimentary rocks examined primary migration of c 3 components becomes important only as fine grained sedimentary rocks enter the catagenetic hydrocarbon generation zone or over short distances in more permeable sections lateral migration along bedding planes was more important than vertical migration in sedimentary rocks of all maturities the lightest methane ethane and propane gases hydrocarbon show greater fractionation than do the c 4 c 8 alkanes which generally show minimal fractionation during the migrational process subsurface diffusion coefficients for these p p b quantities of c 2 c 5 alkanes from immature sediments from dsdp site 530 are estimated to be several orders of magnitude less than values reported in the literature for diffusion of much larger amounts of these compounds from mature water wet sediments into air or sandstones since our calculations suggest light hydrocarbons are present in amounts less than their reported solubilities in pure water at 25 c we postulate that the sediment organic matter has a substantial effect on retarding the movement of these light hydrocarbons

sediment compaction and fluid migration in the makran accretionary prism the makran continental margin in the gulf of oman forms the seaward extremity of an accretionary sediment prism which extends several hundred kilometers inland a recently acquired multichannel seismic reflection profile shot across the margin imaged the structure of the prism in greater detail than was previously possible and allowed us to investigate the relationship between deformation and pore fluid motion in the region velocity analyses of the common midpoint gathers reveal a marked change in velocity structure at the toe of the accretionary wedge as seen in previous sonobuoy wide angle data accreted sediments show significantly higher vertical velocity gradients than those of sediments entering the prism this change is interpreted as due to porosity reduction as pore fluids are squeezed out of the compacting sediment a prominent bottom simulating reflector appears 500 800 m beneath the sea bed several lines of evidence suggest that this reflector represents the base of a gas hydrate zone underlain by widespread free gas which may be exsolved from pore water migrating from deep within the sediment pile up permeable fault planes imaged in the profile the hydrate reflector appears to shallow in the region of some faults suggesting a temperature anomaly due to the presence of warm pore fluids a heat flow profile derived from the depth of the hydrate reflector does not show the expected landward decrease as the sediment pile thickens simple thermal modeling suggests that advective heat flow within the prism may explain this anomaly the inferred presence of overpressured pore fluids in the makran suggests that accreted sediments have a low permeability the seismic evidence suggests a two stage compaction process with rapid initial dewatering through intergranular permeability as sediment enters the prism followed by a buildup of pore pressure as the permeability decreases and fluid migration is restricted to fault zones

efficiency of petroleum expulsion from shale source rocks the limited data available on the mechanism and the efficiency of the processes by which petroleum is expelled in the subsurface from source rocks into adjacent reservoir rocks are mostly qualitative1 2 we present here material balance type comparisons of sample series extending from the centre portions of two adjacent hydrocarbon source rock units towards their outer edges3 which enable expulsion efficiencies to be determined in certain parts of the shale the expulsion efficiencies for total extract and its saturated and aromatic hydrocarbon fractions have much higher values than previously thought reaching up to 80 for the total extract which increase towards possible secondary migration avenues the expulsion is associated with fractionation effects such as those based on polarity differences also expulsion efficiencies were found to be related to the degree of hydrocarbon saturation of the pore system they are higher for a rich oil prone source rock unit compared with a poorer quality one which had generated less hydrocarbons

3d thermobaric modelling of the gas hydrate stability zone onshore central spitsbergen arctic norway abstract dissociation of onshore natural gas hydrates nghs could lead to the release of methane directly to the atmosphere especially in arctic regions such as svalbard where enhanced climate warming has the capacity to promote rapid methane evasion to the atmosphere following the decay of permafrost and glacier ice here we present the first assessment of the ngh stability zone ghsz in central spitsbergen a climate sensitive part of svalbard where thermobaric conditions appear favourable for onshore ngh formation we developed an approach incorporating regionally constrained 3 dimensional parameterisation of temperature pressure and phase boundary 93 methane 7 ethane 35 ppt salinity to define the ghsz this resulted in an up to 650 m thick mean 308 m ghsz covering 74 8 of the study area thickening significantly in the east where the climate is colder perturbation of the base case parameters was undertaken to quantify the sensitivity of the ghsz to the variation in environmental conditions across the study area we present 26 examples of these deterministic scenarios and show that the largest changes in the ghsz were observed when either the ethane content to 20 or the regional pore water pressure to 125 hydrostatic were increased the ghsz also increased markedly when the geothermal gradient was reduced from 33 to 26 c km 1 but was almost completely inhibited by a dry gas 100 methane greater salinity 50 ppt or exposure to an increase in surface temperatures relative to the mean annual air temperature e g by 2 c most parameters affected both the upper and the lower stability boundary of the ghsz with the exception of the geothermal gradient which impacted primarily upon the latter given that svalbard is host to a proven petroleum system we conclude that nghs almost certainly exist onshore svalbard

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

capillary fluid dynamics within unconventional rocks investigated by scanning electron microscopy abstract fresh cores from tight rock samples of subsurface hydrocarbon reservoirs retain mobile fluids these fluids have complex chemical compositions and a large spectrum of molecules with different diameters and polarities when investigated using high resolution field emission scanning electron microscopy sem the imposed vacuum over hours of time causes pore fluids trapped in the rock sample to flow and interact with the mineral matrix this paper reports the capillary fluid dynamics effect observed on freshly milled cross sections of tight chalk at high resolution multiphase fluid dynamic simulations confirm the aggregation of heavier fluid molecules on the geometrical irregularities of the pore space as a consequence of this pitfall the differentiation of solid organic matter versus variably viscous hydrocarbons from sem data is subject to a fundamental revision

vitrinite reflectance and molecular geochemistry of jurassic sediments the influence of heating by tertiary dykes northwest scotland vitrinite reflectance measurements from sedimentary rocks adjacent to six dykes from sites across the inner hebrides indicate that the lateral extent of thermal alteration is reasonably similar and proportional to dyke thickness d t with alteration starting to take effect at 70 d t detailed sampling of a jurassic siltstone adjacent to a 0 9 m dyke reveals that the zone of maximum extractable organic matter eom wt g rock equivalent to the oil window is relatively narrow ca 25 of the d t the position of this oil window relative o the vitrinite reflectance profile is comparable with that from burial maturation gas chromatograms of the aliphatic hydrocarbon fractions reveal i a shift from branched and cyclic dominated hydrocarbons to an increasing predominance of straight chain components and ii the carbon number distribution of the n alkanes shifts towards the shorter chain homologues with decreasing distance from the dyke contact apart from the methylphenanthrene index mpi1 changes in each of the molecular maturity parameters are initiated by the the thermal effects of the dyke between 80 and 70 d t from the contact the mpi1 parameter was the most sensitive maturity indicator in that it responded to the dyke emplacement even in the distal samples i e distance from dyke contact 140 d t a significant reduction in toc at the dyke contact suggests that the synthesis gas reaction may have occurred i e the reaction of organic matter with steam resulting in the formation of carbon monoxide this reaction may be associated with the vitrinite reflectance reversal this study suggests that these particular dykes have had only a local effect on the maturity of the intruded sediments

recent advances in petroleum geochemistry applied to hydrocarbon exploration this paper presents a critical review of recent advances in the study of generation maturation and migration of petroleum the different source potentials for generating hydrocarbons depend on the type of kerogen in addition to the classic types i ii and iii a residual oxidized organic matter is also observed which has no potential for hydrocarbon generation coal is widely considered as a potential source for gas but some coals may generate sizeable amounts of oil as well the development of routine analytical tools particularly pyrolysis makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses among optical techniques the major subjects of discussion concern the nature of amorphous organ c matter which may encompass different chemical types of kerogen and the applicability of vitrinite reflectance techniques to type i and ii kerogens following important advances in identification of biological markers in sediments and crude oils these markers are used for oil source rock correlation and proposed for reconstruction of depositional environment and subsequent thermal evolution migration of hydrocarbons is now better understood and the importance of a hydrocarbon phase migration is widely recognized overpressuring of pore fluids is mainly responsible for expulsion of petroleum geologic models of basin evolution subsidence compaction thermal history and geochemical models hydrocarbon generation and migration become progressively available their integration int a comprehensive model should be one of the major developments in future petroleum exploration

charging of oil fields surrounding the northern end of liaoxi uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract the liaoxi uplift one of the most petroliferous uplifts in the bohai bay basin is sandwiched by two sags containing multiple mature source rocks the origins of oil located on the northern end of this uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions from 75 source rock extracts and 15 oils two oil families have been identified using 4 biomarker parameters and could be linked to the source rocks of the first and second members of the shehejie formation e 2 s 1 2 and the third member of the dongying formation e 3 d 3 respectively e 2 s 1 2 derived oils were found in the liaoxi sag and on the liaoxi uplift and were interpreted to originate primarily from the liaoxi sag e 3 d 3 derived oils were found in the liaozhong sag and originated from the liaozhong sag the liaoxi uplift have not been charged by e 2 s 3 drived oils from the liaoxi sag mainly because it departed from the dominant migration direction of e 2 s 3 drived oils the liaoxi uplift have not been charged by e 2 s 3 e 2 s 1 2 and e 3 d 3 drived oils from the liaozhong sag mainly because there were no delta sandstones developed on the slope between the liaoxi uplift and the liaozhong sag to serve as migration channels from source rocks to uplift in all three formations the sandstone up dip pinch out traps in e 2 s 3 formation in the liaoxi sag traps within the liaozhong sag and traps on the slope between the liaozhong sag and the liaodong uplift have a better chance to accumulating petroleum

hydrocarbon evaporative loss evaluation of lacustrine shale oil based on mass balance method permian lucaogou formation in jimusaer depression junggar basin abstract hydrocarbon evaporative loss evaluation is important for shale oil resource assessment we propose a mass balance model to evaluate the hydrocarbon evaporative loss s1 loss in this study the proposed method is applied to a large rock eval pyrolysis dataset on source rock samples from the lucaogou formation in the jimusaer depression of the junggar basin nw china as a case study to evaluate the s1 loss the results indicate that the s1 loss can range from 0 12 to 7 25 mg g rock corresponding to 11 89 loss of the generated hydrocarbons s1 loss s1 s1 loss due to evaporation before lab analysis it appears that when ro 1 3 s1 loss and s1 loss toc decreases gradually with increasing ro likely corresponding to increasing oil density as results of heterogeneous source rock compositions and increased accommodation space via the creation of organic pores of large specific surface for heavy and large hydrocarbon molecules in oil window when ro 1 3 s1 loss toc begins to increase with increasing ro as more oil crack to gaseous and light hydrocarbons that are more susceptible to evaporative loss in the case of similar ro the relative s1 loss toc varies little among the samples but the absolute s1 loss amount increases with increasing toc restricted by regional geological conditions in this study we focused on the s1 loss for lacustrine type i kerogen only and quantification of evaporative loss for other kerogen types remains a subject for further study

the pristane n heptadecane ratio as an indicator for recognition of hydrocarbon migration effects a simple scheme is proposed for type iii kerogen source rocks which uses pristane n heptadecane concentration ratios for recognition of hydrocarbon expulsion effects within the maturity interval 0 82 1 03 rm this scheme can be applied from gas chromatography data routinely obtained by most petroleum geochemistry studies in exploration exploration of this scheme to oil prone type ii source rocks appears very promising

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