integrated geochemistry organic petrology and sequence stratigraphy of the triassic shublik formation tenneco phoenix 1 well north slope alaska u s a abstract the tenneco phoenix 1 well recovered continuous core through the shublik formation allowing an uncommon opportunity to comprehensively study organic and lithostratigraphic facies variations in a known hydrocarbon source rock interval the lower portion of the cored shublik formation represents part of a transgressive systems tract tst and is characterized by alternating well laminated and bioturbated shales a pronounced condensed section occurs at the top of this interval the shublik formation above the maximum flooding surface mfs represents initial deposits of a highstand systems tract hst it contains coarser grained material and is more bioturbated than the base of the unit the distribution of oil prone facies within the shublik formation is dependent on stratigraphic position and is predictable within a sequence stratigraphic framework the transgressive portion is dominated by oil prone facies while the upper regressive portion is predominatly gas prone to non source well laminated organic rich oil prone intervals in the phoenix core correspond to uranium anomalies on the spectral gamma ray log an organic petrologic study of 54 core samples from the shublik formation is consistent with log analysis and source rock geochemistry both subtle and dramatic organic facies changes characterize the tst fluorescent amorphinite marine alginite and other exinites are the dominant kerogen macerals subtle variation in the maceral concentration of this oil prone organic debris is typical of this interval however there are four major changes in kerogen composition in this transgressive interval these changes include fluctuations in kerogen composition that reflect likely variations in those factors that controlled deposition and preservation of the organic matter in the shublik formation there is another significant reduction in the amount of oil prone kerogen in the condensed section at the top of the tst non fluorescent amorphinite is the dominant organic matter type in general fluctuations in kerogen composition are much less pronounced in the hst when compared with the tst fluorescent amorphinite is the dominant kerogen type but there is also 10 15 vitrinite with comparable amounts of inertinite the amount of these maceral types gradually increases stratigraphically upward in the hst because of this source rocks in this interval tend to be gas prone however there is no significant change in the apparent origin of the organic matter immediately across the mfs there is still considerable kerogen of marine origin in the hst

charging of the neogene penglai 19 3 field bohai bay basin china oil accumulation in a young trap in an active fault zone the penglai 19 3 pl19 3 oil field the largest offshore oil field in china was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl19 3 anticline was not finally formed until about 2 0 ma and is cut by densely distributed faults source rock and crude oil samples from the pl19 3 field were analyzed to determine the origin and formation mechanisms of this large oil field three organic rich oil prone source rock intervals exist in the bozhong subbasin each of which has a distinct biomarker assemblage oil samples from different wells have different biomarker associations and three source related oil classes were identified within the pl19 3 field based on biomarker compositions and multivariate analysis of the data the pl19 3 field displays considerable compositional heterogeneity the compositional heterogeneity within the field and comparison between oil samples from the pl19 3 field and those from nearby structures suggest three field filling directions which is consistent with the results of migration pathway modeling the pl19 3 field was charged in the north by oil generated from dongying formation source rocks in the eastern bozhong depression and bodong depression in the southeast by oil generated from shahejie formation source rocks in the miaoxi depression and in the northwest by oil generated from shahejie formation source rocks in the central bozhong depression oil charge from multiple source rock intervals and multiple generative kitchens and focusing of oil originating from a large area of the bozhong depression into the same trap resulted in rapid oil accumulation in the pl19 3 structure and the formation of this large oil field in a very young trap within an active fault zone

application of biologic markers in combination with stable carbon isotopes to source rock oil correlations prudhoe bay alaska abstract novel biologic marker parameters are applied to problems of geochemical correlation of crude oils and source rocks in the area of prudhoe bay field northern alaska the molecular structures used for fingerprinting the shale extracts the kerogen pyrolyzates and the crude oils are steranes terpanes and monoaromatized steranes the major sources of the principal oil accumulations are shown to be the shublik triassic kingak jurassic and the deep post neocomian shales in two of the three kingak and shublik the indigenous nature of the bitumen was proven by pyrolysis and quantitative biomarker data possible source rocks based on geologic reasoning and bulk geochemical data include the deep kayak mississippian shale the shallow post neocomian the neocomian a d the upper cretaceous shales however all of these are shown by biologic marker techniques not to have generated the petroleum accumulations studied of the nine oils investigated one kingak rises from a single source kingak shale the others have very similar source fingerprints using 10 different molecular and several bulk end page 990 parameters in combination these results are achieved by using a new quantitative approach based on concentrations and ratios of specific biomarkers by integration of mass chromatograms the assessment of all parameters in combination results in a well documented internally consistent picture permitting the above conclusions in addition these biomarker data permit in hindsight a reasonable interpretation of the wide range of carbon isotope data all results are consistent with the geologic setting the approach adds a new dimension in assisting the petroleum explorationist toward paleoreconstruction end of article last page 991

de convoluting crude oil mixtures from palaeozoic reservoirs in the tabei uplift tarim basin china abstract geochemical characteristics of 61 crude oil samples collected from palaeozoic reservoirs in the tarim basin 60 from the tabei uplift and one from the tazhong uplift were analyzed the samples proved to be mixed oils of different maturity from diverse source rocks concentrations of 40 biomarkers and carbon isotopic compositions for the whole oils were analyzed by alternating least squares als regression to de convolute the mixtures three endmember em oils were identified em1 is the minimum contributor to the mixed oils accounting for less than 10 of most oils em1 originated from cambrian lower ordovician source rocks in the early to peak oil window stage and experienced two phases of mixing and biodegradation em2 is the secondary contributor with proportions ranging from 10 to 40 in most oil samples em2 originated from middle upper ordovician source rocks at the early oil generation stage and underwent two phases of mixing and one stage biodegradation in the reservoirs em3 is the major contributor to most samples with proportions ranging from 13 to 95 em3 was generated from middle upper ordovician source rocks at the late oil generation stage and mixed with earlier emplaced mixtures in the reservoirs the final mixtures that were not biodegraded are currently exploited from palaeozoic reservoirs in the tabei uplift biomarkers in the crude oils reveal mixed characteristics including evidence for two phases of oil charge and severe biodegradation

implications of mesozoic and cenozoic tectonism for inner moray firth prospectivity the inner moray firth imf lies immediately adjacent to the sutherland coast in northeast scotland and contains the beatrice oil field mesozoic basin development of the imf has classically been regarded as being the result of accommodation to strike slip motion on the great glen fault zone ggf however a seismic interpretation consisting of over 5000 km of geco merlin seismic data which integrates all available well data and onshore exposures suggests that previous models of basin development are incorrect instead it is proposed that the ggf did not play a significant role in the mesozoic but that extensional dip slip motions on other faults controlled its basin geometry and sediment dispersal patterns the present expression of the ggf only attests to its cenozoic reactivation as an oblique slip fault the new model for basin development has considerable implications for the understanding of imf prospectivity particularly timing of structuration source rock maturation and hydrocarbon migration it is believed that the beatrice structure and its counterparts formed as extensional traps e g closures due to footwall uplift during late jurassic rifting they were probably charged by middle jurassic and older source intervals from a kitchen area that lays beneath a late jurassic cretaceous half graben depocenter to themore northwest subsequent cenozoic regional uplift and oblique slip motion on the ggf have served to raise and dissect the kitchen area tilt preexisting structures and reactivate several faults future exploration success may lie in the effective recognition of suitable unbreached paleostructures or stratigraphic traps less

chemometric identification of crude oil families and deconvolution of mixtures in the surrounding niuzhuang sag bohai bay basin china a total of 46 crude oil samples recovered from the surrounding niuzhuang sag were investigated to gain insight into the petroleum systems in the dongying depression chemometrics identified four genetically distinct oil families family 1 fails to match any of the source rocks that have been discovered thus far the candidate source rock must contain algal organic matter that could produce more negative carbon isotopic composition large quantities of wax c29 steranes and tricyclic terpenoids compared to the eocene shahejie es formation intervals es3 and es4 and deposited in a reducing stratified saline water environment family 2 is featured by high ratios of sterane hopane gammacerane hopane and c35 c34 homohopane and low pristane phytane ratios the source rock is the upper es4 interval family 3 is characterized by distinctive or even opposite features to family 2 the source rock is the lower es3 interval family 4 is a mixed oil derived from the lower es3 and upper es4 source rocks at different thermal maturation three end member oil samples em1 em2 and em3 were identified by alternating least squares as a minor contributor em1 has an average value of 10 as the main contributors em2 and em3 average 53 and 37 respectively oil samples from em1 and em2 are derived from the upper es4 source rock but em1 was generated at a lower thermal maturity than em2 oil from em3 was derived from the lower es3 source rock at peak hydrocarbon generation

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

north slope alaska source rock distribution richness thermal maturity and petroleum charge four key marine petroleum source rock units were identified characterized and mapped in the subsurface to better understand the origin and distribution of petroleum on the north slope of alaska these marine source rocks from oldest to youngest include four intervals 1 middle upper triassic shublik formation 2 basal condensed section in the jurassic lower cretaceous kingak shale 3 cretaceous pebble shale unit and 4 cretaceous hue shale well logs for more than 60 wells and total organic carbon toc and rock eval pyrolysis analyses for 1183 samples in 125 well penetrations of the source rocks were used to map the present day thickness of each source rock and the quantity toc quality hydrogen index and thermal maturity tmax of the organic matter based on assumptions related to carbon mass balance and regional distributions of toc the present day source rock quantity and quality maps were used to determine the extent of fractional conversion of the kerogen to petroleum and to map the original toc toco and the original hydrogen index hio prior to thermal maturation the quantity and quality of oil prone organic matter in shublik formation source rock generally exceeded that of the other units prior to thermal maturation commonly toco 4 wt and hio 600 mg hydrocarbon g toc although all are likely sources for at least some petroleum on the north slope we used rock eval and hydrous pyrolysis methods to calculate expulsion factors and petroleum charge for each of the four source rocks in the study area without attempting to identify the correct methods we conclude that calculations based on rock eval pyrolysis overestimate expulsion factors and petroleum charge because low pressure and rapid removal of thermally cracked products by the carrier gas retards cross linking and pyrobitumen formation that is otherwise favored by natural burial maturation expulsion factors and petroleum charge based on hydrous pyrolysis may also be high compared to nature for a similar reason

origin charging and mixing of crude oils in the tahe oilfield tarim basin china abstract forty eight crude oil samples collected from different reservoirs in the tahe oilfield of the tarim basin were investigated based on geochemical characteristics it is concluded that the oil samples originated from multiple marine source rocks deposited in various sedimentary environments and subsequently altered by different levels of thermal maturation these mixtures were de convoluted to three endmember oils em1 em2 and em3 by alternating least squares regression using 38 concentration parameters em1 is the minimum contributor with an average of 13 while em2 and em3 are the main contributors to the mixtures with averages of 52 and 35 respectively em1 oil originated from cambrian lower ordovician source rocks in the early to peak oil window and subsequently experienced two phases of mixing and biodegradation em2 and em3 oils originated from middle upper ordovician source rocks but em2 was generated at lower thermal maturity than em3 the em2 oil underwent two phases of mixing and one stage biodegradation while the em3 oil mixed with previous existing mixtures in the reservoirs the final mixtures that might be affected by secondary processes such as evaporative fractionation are currently produced from the tahe oilfield the general orientation of oil filling was from south to north and east to west based on variations in the relative contributions of ems and the total concentrations of dibenzothiophenes and dibenzofurans in the oils considering the histories of sedimentary tectonic evolution hydrocarbon generation and expulsion and the de convolution results a model of three stages of oil charge and two phases of mixing and biodegradation was established for the tahe oilfield oils

abstract biomarkers and carbon isotopes of oils and natural bitumens in the precambrian and paleozoic mesozoic formations of the siberian plafform russia

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

mixed marine and lacustrine input to an oil cemented sandstone breccia from brora scotland abstract a rounded cobble collected from a beach near brora scotland contains angular brecciated sandstone clasts cemented together by crude oil no oil occurs within the tight dolomite cemented clasts except along fractures provenance of the cobble is uncertain however the lithology and shape of the clasts suggests that they are fault gouge breccia composed of old red sandstone from the nearby helmsdale fault oil emplacement presumably along the fault cemented the breccia prior to transport and weathering of the cobble independent source and biodegradation parameters support mixing of two charges of oil like oil from the nearby beatrice field the oil cement contains 24 n propylcholestanes and carotane that indicate marine and lacustrine source rocks respectively the oil cement also contains pristane phytane residual n alkanes and a complete series of 25 norhopanes which indicate mild and heavy biodegradation respectively the first charge consisted of lacustrine devonian oil that was heavily biodegraded at shallow depth the origin of the second charge is unclear unlike beatrice oil the oil cement contains oleanane and shows a higher 24 24 27 nordiacholestane ratio suggesting input from a cretaceous or younger paralic marine shale source rock although cretaceous and paleocene source rocks are inferred to exist in various depocenters in the northeast atlantic margin subcrops of these rocks offshore brora are thermally immature alternately the second charge could originate from an effective middle jurassic source rock that contains oleanane this hypothesis is supported by mass spectrometric confirmation of oleanane in an extract from the marine equivalent of the middle jurassic brora coal in the nearby ukcs 11 30 2 well oleanane in crude oil is not positive proof of a cretaceous or younger source rock for the oil

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

families of miocene monterey crude oil seep and tarball samples coastal california biomarker and stable carbon isotope ratios were used to infer the age lithology organic matter input and depositional environment of the source rocks for 388 samples of produced crude oil seep oil and tarballs to better assess their origins and distributions in coastal california these samples were used to construct a chemometric multivariate statistical decision tree to classify 288 additional samples the results identify three tribes of 13c rich oil samples inferred to originate from thermally mature equivalents of the clayey siliceous carbonaceous marl and lower calcareous siliceous members of the monterey formation at naples beach near santa barbara an attempt to correlate these families to rock extracts from these members in the nearby cost continental offshore stratigraphic test ocs cal 78 164 well failed at least in part because the rocks are thermally immature geochemical similarities among the oil tribes and their widespread distribution support the prograding margin model or the banktop slope basin model instead of the ridge and basin model for the deposition of the monterey formation tribe 1 contains four oil families having geochemical traits of clay rich marine shale source rock deposited under suboxic conditions with substantial higher plant input tribe 2 contains four oil families with traits intermediate between tribes 1 and 3 except for abundant 28 30 bisnorhopane indicating suboxic to anoxic marine marl source rock with hemipelagic input tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher plant input tribes 1 and 2 occur mainly south of point conception in paleogeographic settings where deep burial of the monterey source rock favored petroleum generation from all three members or their equivalents in this area oil from the clayey siliceous and carbonaceous marl members tribes 1 and 2 may overwhelm that from the lower calcareous siliceous member tribe 3 because the latter is thinner and less oil prone than the overlying members tribe 3 occurs mainly north of point conception where shallow burial caused preferential generation from the underlying lower calcareous siliceous member or another unit with similar characteristics in a test of the decision tree 10 tarball samples collected from beaches in monterey and san mateo counties in early 2007 were found to originate from natural seeps representing different organofacies of monterey formation source rock instead from one anthropogenic pollution event the seeps apparently became more active because of increased storm activity

geochemistry and possible origin of petroleum in palaeozoic reservoirs from halahatang depression abstract the halahatang depression in the tabei uplift of the tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields geochemical analysis indicates that halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions the maturities for halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring tahe oils the halahatang oils feature low pr ph c 21 c 23 tricyclic terpane and c 28 c 29 sterane ratios high c 29 c 30 hopane and c 35 c 34 hopane ratios a v shape in the distribution of c 27 c 28 c 29 steranes and light carbon isotope ratios similar to the tahe oils and correlate well with the middle upper ordovician source rock however some source related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the tahe oils

source rock quality determination from oil biomarkers ii a case study using tertiary reservoired beaufort sea oils biomarkers molecular fossils in 26 beaufort sea mackenzie delta oils reveal three genetic oil groups and suggest descriptions of their probable sources group 1 21 tertiary reservoired oils was soured from tertiary deltaic sediments group 2 three cretaceous and one devonian reservoired oil and group 3 one lower cretaceous reservoired oil derive from two high quality sources deposited in open marine environments geographical variations in the geochemistry of the 21 group 1 oils suggest that their deltaic source was substantially more oil prone in the distal deltaic portions than in the region closer to the paleoshoreline although these data do not address source rock volumes they do indicate that poor source quality is not a cause of underfilled traps in the o fshore the map pable lateral variations in group 1 oil compositions illustrate how in basins with vertically drained sources lateral source rock facies changes can bc inferred from regional variations in the geochemistry of the overlying oils furthermore the data suggest that geochemical studies attempting to deduce genetic relationships between geographically separated oils should carefully consider the potential effects of source rock facies changes on the oil compositions

the petroleum geochemistry of canadian beaufort tertiary non marine oils abstract molecular isotopic and elemental data for a set of 28 paleogene and 3 cretaceous oils from the mackenzie delta and offshore canadian beaufort sea have been evaluated the depositional environment and organic matter characteristics of the source units for these oils have been predicted the paleogene oils of the canadian beaufort are molecularly distinctive and clearly contain a major land plant component oleanane and the 17 h and 17 h 24 28 bisnorlupanes are present as well as the following compound types 24 norlupanes and possibly higher homologues de a lupane noroleanenes norursene dehydroabietane 28 30 bisnorhopanes several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils the cretaceous oils are separately sourced from the paleogene oils the latter oils comprise two distinct land plant derived genetic families distinguished by the presence absence of 24 28 bisnorlupanes 24 norursene 24 norlupane and 24 noroleanenes the kugmallit richards family contains each of these compound types and is considered to originate from the eocene richards formation in contrast lupanoids and noroleanenes are absent in oils of the reindeer moose channel family the occurrence of 28 30 bisnorhopane and or oleanane in these oils suggests a paleocene origin although these source rock predictions are supported by the available data they must be considered speculative until detailed molecular isotopic and elemental compositional data are available regionally for potential source rocks of the eocene and paleocene source units in the canadian beaufort

the kingak shale of northern alaska regional variations in organic geochemical properties and petroleum source rock quality abstract the kingak shale a thick widespread rock unit in northern alaska that ranges in age from early jurassic through early cretaceous has adequate to good oil source rock potential this lenticular shaped rock unit is as much as 1200 m thick near the jurassic shelf edge where its present day burial depth is about 5000 m kingak sediment transported in a southerly direction was deposited on the then marine continental shelf the rock unit is predominantly dark gray shale with some interbeds of thick sandstone and siltstone the thermal maturity of organic matter in the kingak shale ranges from immature 2 0 r0 in the colville basin toward the south its organic carbon and hydrogen contents are highest in the eastern part of northern alaska south of and around the kuparuk and prudhoe bay oil fields carbon isotope data of oils and rock extracts indicate that the kingak shale is a source of some north slope oil but is probably not the major source

saturated hydrocarbon biomarkers in oils of late precambrian age from eastern siberia abstract large quantities of petroleum derived from source rocks of late precambrian early cambrian age have been discovered in the lena tunguska region of eastern siberia over the last twenty five years we have examined three oils with presumed late precambrian vendian source rocks from this region for c 15 saturated hydrocarbon biomarkers using gas chromatography gc and gas chromatography mass spectrometry gc ms our results show these oils to have many characteristics in common with other oils of similar age from eastern siberia and oman amongst the compounds detected in the three oils analyzed were 1 n alkanes which show a marine derived distribution 2 centrally branched monomethyl alkanes 3 acyclic isoprenoids pr ph 1 4 tricyclic and tetracyclic terpanes 5 hopanes 6 c 29 unrearranged steranes and 7 c 30 nuclear steranes all of these compounds with the exception of the 4 methylsteranes which on current biochemical knowledge are unexpected in oils of this age can be assigned a prokaryotic source this and other evidence such as the lack of diasteranes suggest microorganism were the major contributors to organic matter deposited as part of a carbonate source rock

geochemical characterization of qhd29 oils on the eastern margin of shijiutuo uplift bohai sea china insights from biomarker and stable carbon isotope analysis abstract toc and rock eval analyses were conducted on cutting samples 111 from various paleogene formations ed3 es1 and es3 in the qinnan sag the average values of total organic carbon toc content are 1 11 1 64 and 2 29 for ed3 es1 and es3 samples respectively the es1 and es3 source rocks are of relatively high s2 values ranging from 0 42 to 46 01 and 2 46 61 01mghc rock respectively the ed3 rocks have lower generative potential with s2 values ranging from 0 9 to 9 3 mg hc g rock moreover tmax values indicate that these source rocks are sufficiently mature for petroleum generation these analyses suggest that es1 and es3 are potential source rocks for oils produced from the qhd29 field eighteen oil samples from the qhd29 field were analyzed by gc and gc ms and 84 qhd29 oil 13 and source rock 71 samples were employed for stable carbon isotope analysis based on hierarchical cluster analysis of selected biomarker parameters the qhd29 oils can be identified into two groups group i and group ii oils are both derived from the eocene shahejie formation es1 and es3 displaying remarkable difference to the oligocene ed3 derived oils in comparison with group ii oils group i oils display relatively low 4msi and high g h indicating that group i oils have important contributions from es1 source rock deposited under more alkaline saline environment moreover these two group oils can be clearly separated by 13c values and group i oils are isotopically lighter than group ii oils difference occurs in stable carbon isotope distribution between es1 and es3 source rock extracts as well and es1 source rocks are characterized by relatively light carbon isotopic composition this implies that group i oil shares more es1 derived oil which is consistent with the results of biomarker analysis

alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments abstract we present the first sedimentary biomarker study encompassing the entire arctic ocean a large data set of organic markers for terrigenous petroleum and combustion inputs alkanes hopanes and steranes parent and alkyl polycyclic aromatic hydrocarbons pahs is examined for patterns in space and time using principal components analysis pca and partial least squares pls biomarker patterns reveal the central arctic ocean basin sediments to be compositionally distinct from those of the mackenzie river beaufort sea and barents sea but similar to those of the laptev sea pah distributions reflected in pah ratios and pca projections demonstrate that arctic ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion pahs are not significant we find only modest changes between the glacial and post glacial sediments for atmospherically transported hydrocarbon biomarkers while particle associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the post glacial period the orders of magnitude decreases in particle associated petrogenic alkanes and pahs in central basins during glacial times coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the pleistocene holocene central arctic basins the proximity of large coal deposits of various maturity levels along the lena river the overlap in pah and biomarker composition of the laptev sea and surficial sediments from the central arctic ocean and the location of the laptev sea at the origin of the main transpolar drift all point to eroded coals from the lena river laptev sea as the likely source of petrogenic hydrocarbons to the central arctic ocean the ubiquitous presence of allochthonous coal in arctic ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves

oil families and their potential sources in the northeastern timan pechora basin russia oil and rock samples collected throughout the northeastern timan pechora basin identify key oil families and correlate these oil families to stratigraphic units that sourced them based on distinctive molecular characteristics three distinctive hydrocarbon systems have been identified within the northeastern timan pechora basin hydro carbons both oil and gas are found in clastic and carbonate reservoirs from the lower silurian to the triassic three major oil families have been identified based on physical properties gas chromatography liquid chromatography and gas chromatography mass spectrometry family a oils are found in permian silurian reservoirs within the sorokin swell and upper devonian reservoirs within the eastern and western edges of the khoreyver depression this oil family is sourced from an upper devonian bitumen laminated carbonate mudstone informally known as the domanik facies family b oils are found only in upper devonian reservoirs within the central khoreyver depression this oil family is most likely sourced from upper devonian hypersaline marine mudstones with significant bacterial input many of the family b oils were generated at temperatures less than that for peak oil generation family c oils are found in carboniferous lower devonian reservoirs within the northern sorokin swell this family is sourced from marine mudstones that have gloecapsamorpha prisca as well as other marine algae present organic rich lower devonian and silurian shales contain similar molecular characteristics and are potential sources for the family c oils

geochemical characterization of source rocks and oils from northern iraq insights from biomarker and stable carbon isotope investigations abstract the origin of oil in the cretaceous tertiary reservoirs of northern iraq remains controversial consequently a detailed geochemical study including rock eval pyrolysis gas chromatography mass spectrometry and carbon isotope analysis was conducted on 65 source rock core and cuttings samples from the najmah chia gara and balambo formations northern iraq twenty four crude oils were also analyzed to provide new insights into source organic matter depositional environment and correlations between crude oils and their probable source rocks bulk geochemical analysis of candidate source rock samples indicates that the najmah formation has more petroleum potential than the chia gara and balambo formations these three candidate source rocks were deposited in slightly different environments and have different organic matter types as determined by screening analysis and biomarker data the najmah formation contains organic rich toc up to 4 2 wt oil prone type i ii kerogen deposited under anoxic conditions the chia gara and balambo formations contain mixed type ii iii and type iii kerogens oil and gas prone deposited under less reducing conditions with more terrigenous organic matter input unfortunately most of the rock samples contain less than 2 5 wt toc which likely excludes them as source rocks but more deeply buried equivalents may contain more organic matter biomarker and stable carbon isotope compositions suggest that cretaceous and miocene reservoired oils from the northern iraq basins although predominantly derived from marine carbonate organic matter constitute five genetically distinct oil families based on age specific biomarkers the oils were probably derived from three active petroleum systems in northern iraq jurassic jurassic early cretaceous and early to mid cretaceous biomarker maturity parameters indicate that most of the oils were generated in the early oil window similar to the extracts

depositional setting sequence stratigraphy diagenesis and reservoir potential of a mixed lithology upwelling deposit upper triassic shublik formation prudhoe bay alaska the upper triassic shublik formation within the prudhoe bay field unit north slope alaska is a potentially economic hydrocarbon reservoir comprised of mixed lithology and mineralogy its composition includes limestone phosphate shale siltstone and sandstone as well as accessory amounts of siderite glauconite pyrite kaolinite and dolomite within the prudhoe bay field unit the shublik has been subdivided into four zones lettered from base to top d through a which become thinner and show evidence of deposition under higher energy conditions toward the northeast the formation is truncated to the east by the regional lower cretaceous unconformity zones within the shublik comprise a basal transgressive systems tract conglomerate lag at the shublik formation ivishak formation contact through basal zone c shales and two highstand shallowing upward parasequences zones c through b and zone a respectively the parasequences are bounded by shales interpreted to represent deposition during periods of marine flooding the contact between the shublik and the overlying sag river formation juxtaposes comparatively deeper marine shublik with shallower water glauconitic sandstones of the sag river formation the contact is unconformable and is interpreted to represent a regional sequence boundary lithofacies of the shublik are interpreted to have been coeval depositional facies of an upwelling system relative sea level changes durin shublik deposition are interpreted to have caused the observed vertical and lateral variability in lithofacies via systematic changes between anaerobic dysaerobic and aerobic upwelling conditions dissolution of carbonate allochems resulted in the creation of moldic porosity that positively affected reservoir quality i e permeability in the carbonate packstone grainstone facies areas of highest porosity are in the northern and northeastern parts of the field which correspond to a combination of facies controlled reservoir quality improvement toward the northeast and carbonate dissolution along the lower cretaceous unconformity and the north prudhoe bay fault zone oil in place for the shublik within the prudhoe bay unit is estimated to be between 250 and 500 million bbl although permeabilities are generally low throughout the field area the shublik formation has the potential to add significant reserves to the prudhoe bay field unit

chemometric differentiation of crude oil families in the san joaquin basin california chemometric analyses of geochemical data for 165 crude oil samples from the san joaquin basin identify genetically distinct oil families and their inferred source rocks and provide insight into migration pathways reservoir compartments and filling histories in the first part of the study 17 source related biomarker and stable carbon isotope ratios were evaluated using a chemometric decision tree cdt to identify families in the second part ascendant hierarchical clustering was applied to terpane mass chromatograms for the samples to compare with the cdt results the results from the two methods are remarkably similar despite differing data input and assumptions recognized source rocks for the oil families include the 1 eocene kreyenhagen formation 2 eocene tumey formation 3 4 upper and lower parts of the miocene monterey formation buttonwillow depocenter and 5 6 upper and lower parts of the miocene monterey formation tejon depocenter ascendant hierarchical clustering identifies 22 oil families in the basin as corroborated by independent data such as carbon isotope ratios sample location reservoir unit and thermal maturity maps from a three dimensional basin and petroleum system model five families originated from the eocene kreyenhagen formation source rock and three families came from the overlying eocene tumey formation fourteen families migrated from the upper and lower parts of the miocene monterey formation source rocks within the buttonwillow and tejon depocenters north and south of the bakersfield arch the eocene and miocene families show little cross stratigraphic migration because of seals within and between the source rocks the data do not exclude the possibility that some families described as originating from the monterey formation actually came from source rock in the temblor formation

the origin and charging directions of neogene biodegraded oils a geochemical study of large oil fields in the middle of the shijiutuo uplift bohai sea china abstract two large oil fields qhd32 6 and qhd33 1 located in the middle part of the shijiutuo uplift have generally suffered mild biodegradation based on multivariate statistical analysis of the biomarker parameters this study discussed the origin and charging directions for these two oil fields in contrast to ed 3 derived oil all available oil samples from these two large oil fields displayed low c 19 c 23 c 24 c 26 and high g h and 4 msi which are attributed to the mixtures of oils derived from the shahejie es 1 and es 3 source rocks oils in qhd32 6 which contain relatively more es 3 derived oil are called group i oils and most oils in qhd33 1 which share relatively more es 1 derived oil are called group ii oils our mixed oil experiments reveal the predominant es 3 and es 1 derived oil contribution for group i and group ii oil groups respectively however the selection of end member oils warrants further research based on comparisons of biomarker parameters the qhd32 6 oil field was mainly charged in the north by oil generated from shahejie formation source rocks in the bozhong depression however oils from the north of qhd32 6 field display a remarkable difference to the oils in the south of this field which may indicate that a charging pathway exists from the qhd33 1 field considering the variations in biomarker compositions in the west to east and northwest to southeast sections across the qhd33 1 and qhd32 6 oil fields it can be deduced that es 3 sourced oil migrated westward to the qhd32 6 traps and then charging by es 1 oil from the bozhong sag resulted in the qhd33 1 oil field being characterized by the mixture of es 3 and es 1 sourced oil moreover migration of es 1 derived oil from the qinnan sag was not identified implying that the qhd33 1 oil field is mainly charged from the northeast of the bozhong sag

oil source rock correlation using carbon isotope data and biological marker compounds cook inlet alaska peninsula alaska rock and oil samples from the cook inlet alaska peninsula area were analyzed to determine the source of the commercial hydrocarbons produced in the cook inlet basin from lower tertiary nonmarine sandstone reservoirs rock eval hydrogen index analysis and organic carbon content were used to identify the most favorable rock samples for solvent extraction and carbon isotope gas chromatographic gc and gas chromatrographic mass spectrometric gcms analyses on the basis of organic matter richness five nonmarine tertiary coal and shale samples and 12 marine mesozoic upper triassic and middle jurassic shale samples were selected a total of 28 oil and condensate samples from producing wells oil stem tests field separators and seeps were used for oil oil and oil source rock correlation on the basis of biomarker and carbon isotope data four of the shallower oils and condensates are from nonmarine source rocks and 24 of the deeper oils are sourced from marine shales geochemical and regional geologic considerations indicate the following conclusions the upper tertiary nonmarine oils and condensates associated with commercial microbial gas accumulations are geochemically similar to the immature organic matter in the tertiary nonmarine rocks in the upper cook inlet marine oils in lower tertiary nonmarine reservoirs originated from middle jurassic rocks that matured during themore pliocene to holocene in the lower cook inlet alaska peninsula area oils migrated from both upper triassic and middle jurassic source rocks during the late cretaceous to early tertiary although three petroleum systems are identified this study on the petroleum potential in a convergent margin setting indicates that only one of these three systems was responsible for the 1 2 billion bbl of recoverable oil in the lower tertiary nonmarine reservoirs less

mississippian bakken and equivalent formations as source rocks in the western canadian basin abstract the organic rich bakken formation of mississippian age has previously been identified as the source rock for mississippian reservoired oils in the williston basin north dakota examination of c15 hydrocarbon data including biomarker distributions steranes triterpanes and diterpanes and stable carbon isotope ratios of bakken formation core samples from williston basin and those of equivalent formations from western canadian basin alberta reveals similar types of extractable organic matter stable carbon isotope and biomarker data support strong positive correlations between the bakken formation core samples and mississippian oils from both basins in addition a positive correlation is found between bakken core samples and lower cretaceous heavy oil deposits from athabasca cold lake and peace river areas in alberta thus the mississippian bakken and equivalent formations are also important source rocks in the western canadian basin

the occurrence of petroleum in sedimentary rocks of the meteor impact crater at lake siljan sweden abstract during the devonian large parts of sweden were covered by sandstones shales and limestones of precambrian to upper silurian age at the end of the devonian 360 m yr b p a meter struck causing a large impact crater at lake siljan with a diameter of 50 60 km annular depression was formed which is still preserved today this depression contains undisturbed as well as tilted paleozoic rocks numerous sedimentary occurrences of asphalts and seep oils are reported from quarries in the sedimentary rocks and some shallow boreholes contain a thin layer of free oil floatingon arterian groundwater a representative set of paleozoic shales and limestones found in the siljanarea was analyzed with respect to organic richness type and thermal maturity three intervals of organic rich and oil prone source rocks 2 10 toc were distinguished and extracts of these rocks were geomically compared with the seep oils using stable carbon isotopes and terpenoid biomarkers even though these low maturity oils were altered by biodegradation a correlation with ordovician source rocks was established all the analyzed organic rich rocks are on the verge of oil generation as determined by 20s 20r 5 h c 29 sterane ratios in addition burial history indicates insufficient overburden available for oil generation the seep oils however are more mature and within the oil window yet below peak generation levels thus it appears that the heat effect of meteor impact locally matured the source rock allowing for geologically instantaneous hydrocarbon generation and expulsion resulting in the formation of seep oils

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

the nature of porosity in organic rich mudstones of the upper jurassic kimmeridge clay formation north sea offshore united kingdom abstract analyses of organic rich mudstones from wells that penetrated the upper jurassic kimmeridge clay formation offshore united kingdom were performed to evaluate the nature of both organic and inorganic rock constituents and their relation to porosity in this world class source rock the formation is at varying levels of thermal maturity ranging from immature in the shallowest core samples to mature in the deepest core samples the intent of this study was to evaluate porosity as a function of both organic macerals and thermal maturity at least four distinct types of organic macerals were observed in petrographic and sem analyses and they all were present across the study area the macerals include in decreasing abundance 1 bituminite admixed with clays 2 elongate lamellar masses alginite or bituminite with small quartz feldspar and clay entrained within it 3 terrestrial vitrinite fusinite semifusinite grains and 4 tasmanites microfossils although pores in all maceral types were observed on ion milled surfaces of all samples the pores largely nanopores with some micropores vary as a function of maceral type importantly pores in the macerals do not vary systematically as a function of thermal maturity insofar as organic pores are of similar size and shape in both the immature and mature kimmeridge rocks if any organic pores developed during the generation of hydrocarbons they were apparently not preserved possibly because of the highly ductile nature of much of the rock constituents of kimmeridge mudstones clays and organic material inorganic pores largely micropores with some nanopores have been observed in all kimmeridge mudstones these pores particularly interparticle i e between clay platelets and intraparticle i e in framboidal pyrite in partially dissolved detrital k feldspar and in both detrital and authigenic dolomite are noteworthy because they compose much of the observable porosity in the shales in both immature and mature samples the absence of a systematic increase in organic porosity as a function of either maceral type or thermal maturity indicates that such porosity was probably unrelated to hydrocarbon generation instead much of the porosity within mudstones of the kimmeridge appears to be largely intraparticle and interparticle adjacent to inorganic constituents so the petroleum storage potential in these organic rich mudstones largely resides in inorganic pores

petroleum isotopic and biomarker composition related to source rock organic matter and depositional environment abstract a multivariate approach has been developed that separates oils derived from organic matter in nonmarine shales marine shales and marine carbonates some or all of the following analyses were completed on 43 oils from known source rocks 1 c30 sterane and monoaromatic steroid biomarker ratios and 2 stable carbon and hydrogen isotope compositions of whole oil saturates and aromatics three group discriminant analysis of the 28 oils whereall biomarker and isotopic data are available results in no misclassifications at a significance level of 99 using only carbon and hydroogen isotopic data for whole oils saturates and aromatics results in correct classifications of 82 for oils derived from marine shale organic matter and 100 for oils from the other two sources triangular plots probabilities can be used to distinguish oils derived from the three source rock organic matter end members several publications describe classifications of marine vs nonmarine oils using stable carbon isotope ratios of the whole oil or the saturate and aromatic fractions our results confirm that these methods do not completely differentiate oils by source

circum arctic petroleum systems identified using decision tree chemometrics source and age related biomarker and isotopic data were measured for more than 1000 crude oil samples from wells and seeps collected above approximately 55n latitude a unique multitiered chemometric multivariate statistical decision tree was created that allowed automated classification of 31 genetically distinct circum arctic oil families based on a training set of 622 oil samples the method which we call decision tree chemometrics uses principal components analysis and multiple tiers of k nearest neighbor and simca soft independent modeling of class analogy models to classify and assign confidence limits for newly acquired oil samples and source rock extracts geochemical data for each oil sample were also used to infer the age lithology organic matter input depositional environment and identity of its source rock these results demonstrate the value of large petroleum databases where all samples were analyzed using the same procedures and instrumentation

geochemistry of selected oils and rocks from the central portion of the west siberian basin russia six analyzed oils produced from middle jurassic to upper cretaceous strata in the middle ob region of the west siberian basin show biomarker and stable carbon isotope compositions indicating an origin from the upper jurassic bazhenov formation the chemical compositions of these oils are representative of more than 85 of the reserves in west siberia kontorovich et al 1975 bazhenov sourced oil in cenomanian strata in the van egan field underwent biodegradation in the reservoir resulting in a low api gravity an altered homohopane distribution and the appearance of 25 norhopanes without alteration of the steranes high api gravity oil from the salym field has surpassed the peak of the oil window consistent with abnormally high temperatures and pressures in the bazhenov source rock from which it is produced the remaining oils are very similar including samples from valanginian and bathonian callovian intervals in a sequence of stacked reservoirs in the fedorov field bazhenov rock samples from the study area contain abundant oil prone marine organic matter preserved under anoxic conditions organic matter in a bazhenov core from the pokachev 58 well was compared with the oils because it is thermally mature and shows total organic carbon toc 13 8 wt and hydrogen index values hi 489 mg hc g toc representative of the average for the formation 10 7 wt for 840 samples 420 mg hc g toc for 75 samples other rocks in the middle ob region are far less likely to have generated these oils than the bazhenov formation no prospective source rocks older than middle jurassic were available geochemical analyses indicate a lack of thermally mature hauterivian or younger source rocks in the study area core samples from the lower cretaceous frolov formation either are thermally immature hauterivian or show little oil generative potential berriasian valanginian the upper jurassic vasyugan formation shows lower oil generative potential than the bazhenov formation the average toc for vasyugan rocks is 3 20 wt 240 samples average atomic h c ratios for vasyugan and bazhenov kerogens are 0 90 10 samples and 1 13 25 samples respectively the vasyugan formation cannot be excluded as a source rock because insufficient sample was available for biomarker analysis core from the lower to middle jurassic tyumen formation in the yemyegov 15 well was compared with the oils because it is thermally mature and shows toc and hi values 2 78 wt and 137 mg hc g toc respectively indicating slightly more favorable oil generative characteristics than the average for the formation 2 75 wt for 720 samples 95 mg hc g toc for 25 samples the core contains terrigenous gas prone organic matter that shows no relationship with the analyzed oils

the role of calcareous and shaly source rocks in the composition of petroleum expelled from the triassic shublik formation alaska north slope abstract for nearly thirty years the triassic marine carbonate shublik formation has been suggested and confirmed as a key source rock for hydrocarbons in the north slope of alaska the formation accounts for roughly one third of the oil in the supergiant prudhoe bay field and for nearly all of the oil in the second largest kuparuk river field recent studies of oil types in the vicinity of the northstar field suggested presence of shaly organofacies of the shublik formation based on the likely triassic age and marine shale biomarker signatures of some analyzed oil samples the current work fills the gap between biomarker analysis of predicted calcareous and shaly oil types and source rock geochemistry biomarker based oil source rock correlation confirms the presence of two genetically distinct organofacies and related oil families both groups were deposited under a similar redox condition anoxic to suboxic with dominantly marine algal input but in either 1 a clay rich or 2 a clay poor depositional setting chemometric evaluation of multivariate biomarker data reveals mixtures with variable degrees of mixing between end members analysis of diamondoids confirms mixed oil types and establishes diamondoid signatures of source rock end members this allows for correlation of biomarker poor overmature shublik source rock samples to oils and extends these interpretations over large areas of the north slope

oil source correlation in the slope of the qikou depression in the bohai bay basin with discriminant analysis abstract the commonly used tools for oil source correlation such as mass chromatograms of biomarkers and bivariate cross plots of geochemical parameters cannot deal with multiple geochemical parameters and plenty of samples simultaneously leading to uncertainties in the results and even failures sometimes in this paper the discriminant analysis da is selected from supervised machine learning algorithms as it is superior to the commonly used tools as well as other multivariate statistical methods with the accumulation of geochemical data of source rocks and oils in the slope of the qikou depression the main source rocks in the third es3 and first members es1 of the paleogene shahejie formation were deposited in similar depositional environments the source rocks cannot be distinguished with the commonly used tools we firstly extended geochemical parameters and then used stepwise da to select informative parameters and to develop a discriminant model for oil source correlation the 22 selected parameters are supported by geochemical characteristics of the source rocks in the study area the da of these parameters for oil source correlation achieved a high correct rate of original validation 96 8 and leave one out cross validation 89 4 indicating a sufficient discriminatory power the oil source correlation results with high posterior probabilities showing strong similarity between the sources and oils coincide with geological conditions and illustrate that there is still much exploration potential in the study area especially for the es3 petroleum system all these illustrate that da is one of the most useful tools for oil source correlation with the accumulation of geochemical data of source rocks and oils

mechanisms for oil depletion and enrichment on the shijiutuo uplift bohai bay basin china the shijiutuo uplift is a major uplift to the north of the bozhong depression the largest generative kitchen in the bozhong subbasin bohai bay basin although the n35 2 trap on this uplift contains a medium size oil accumulation and the q32 6 trap contains china s third largest offshore oil accumulation the q31 1 trap between the n35 2 and q32 6 traps with very similar evolution history was confirmed to be dry biomarker associations of crude oil and source rock samples were analyzed and three dimensional migration pathway modeling was conducted to investigate the origin of oils and mechanisms for oil enrichment and depletion on the uplift multiple parameter oil source correlation and hierarchical cluster analysis using 10 selected biomarker parameters allowed the identification of four source related oil classes almost all oils from the shijiutuo uplift are derived from the eocene shahejie formation whereas oils found between the shijiutuo uplift and the bozhong depression either are derived from or have important contributions from the oligocene dongying formation variations in oil classes and biomarker parameters suggest sequential migration of oil generated from the shahejie and then dongying formations in the bozhong depression which is reasonably supported by petroleum migration pathway modeling oil charge from two oil prone source rock intervals and more importantly focusing of oil originating from a large area of the bozhong generative kitchen into the same trap accounted for oil enrichment and formation of china s third largest offshore oil field in the q32 6 structure the complexity and primary control of the sealing surface top surface of the carrier bed morphology on the positions of migration pathways caused the q31 1 trap to be shielded from migration of oil originating from the bozhong depression resulting in oil depletion in this trap shadows to petroleum migration may occur because of the three dimensional behavior of petroleum migration and two dimensional migration modeling may be misleading in predicting petroleum occurrences

characteristic of source rocks and origin of crude oils in the raoyang sag and baxian sag bohai bay basin china insights from geochemical and geological analyses abstract three potential source rock intervals were evaluated based on the results of rock eval pyrolysis on nearly 700 rock samples and the origin of the twenty two oil fields was studied by the biomarker analysis on 62 source rock samples and 93 oil samples in the raoyang sag and baxian sag bohai bay basin the first member of the shahejie formation es was deposited in an anoxic and salted water column with the dominant contribution of algal organic matters reflected by its rock samples with high gammacerane c30 hopane high etr high c35 c34 hopane high steranes hopanes low pristane phytane low c27 diasterane c27 sterane and low c19 c23 tricyclic terpane characterized by higher c19 c23 tricyclic terpane higher pristane phytane lower steranes hopanes and lower c35 c34 hopane than the es1 rock samples the biomarkers of rocks suggest that the third and forth members of the es were deposited in the sub oxic to anoxic environments with a significant terrestrial organism input further studies suggest that the best source rock interval for oil generation is the es1 source rock interval in the raoyang sag and is the es3 source rock interval in the baxian sag by organic facies analysis of source rocks three source related oil groups have been identified there are two oil groups for the discovered oils in the raoyang sag group i oil dominated by the es1 derived oils has been found in all the oil fields in the raoyang sag and group ii oil mainly derived from the es3 source rock interval only distributes in the north east area and in the south end of the raoyang sag however the three oil groups have been found in the baxian sag but the es3 derived oils are dominant in them and have been found in the major oil fields in the east area and the wen an slope in the west area furthermore the es4 derived oils group iii oil mainly distribute in the baxian sag without any findings in the raoyang sag because of the absence of the es4 source rocks as our studies oils almost accumulate near their source rocks without a long distance migration except the slope areas in the raoyang sag and baxian sag therefore the source rock distribution is a key factor to oil accumulations in the raoyang sag and baxian sag especially the efficient source rock distributions which mainly developed in the organic facies a and b based on the geochemical and geological researches

secular episodic changes in stable carbon isotope composition of crude oils abstract stable carbon isotopic compositions of c15 saturate and aromatic hydrocarbon fractions from 514 crude oils from known source rocks were examined for secular episodic variations the oils have been correlated by means of biomarker analyses and or geological inferences to their respective source rocks and were further categorized into seven source rock types based on geochemical and petrologic indicators of depositional environments thus these oil samples represent a wide range of source paleoenvironments from thirteen age divisions riphean to neogene the stable carbon isotopic compositions of both fractions become enriched in 13 c with decreasing geologic age three major abrupt shifts toward 13 c enrichment occurred at the precambrian cambrian ordovician triassic jurassic and paleogene neogene boundaries analysis of smaller scale isotopic shifts reveals four distinct groups of oils generally independent of organic facies and secondary alteration processes comparison of evolutionary changes in the biosphere to episodic changes in stable carbon isotopic compositions throughout the phanerozoic indicates that isotopic shifts of crude oils may generally be related to the diversity of preserved phytoplankton

holocene ooids of aitutaki atoll cook islands south pacific although oolitic sands are widespread throughout the phanerozoic carbonate rock record and they are abundant in some modern shallow marine carbonate systems recent ooids have not been recognized from any locality in the pacific basin on aitutaki atoll cook islands south pacific oolitic sands occur in water depths of 2 1 6 3 m within the lagoon and less abundantly on shallower reef aprons most ooids are between 150 and 300 m in diameter have between 1 and 25 concentric to irregular laminae and occur with peloids and skeletal grains cortical laminae include mg calcite crystals with radial tangential and random orientations the occurrence and distribution of oolitic sands on aitutaki are facilitated by a convergence of hydrodynamic and chemical factors wave driven currents combined either with flow separation over a sharp increase in depth at the reef apron lagoon interface or with oceanward flow in the lee of islands serve to transport ooids without flushing them from the system here ph alkalinity and carbonate supersaturation are at some of the highest levels in the tropical pacific the restricted occurrence of holocene oolitic sands in areas of the pacific and atlantic basins with elevated ph and total alkalinity reflects the importance of carbonate saturation thresholds in limiting the spatial distribution of these sands in modern shallow marine settings these recent examples are consistent with interpretations of the importance of these variables in determining the distribution abundance and cortical mineralogy of oolitic sands throughout the phanerozoic stratigraphic record of carbonate accumulation

predicted and measured petrophysical and geochemical characteristics of the egret member oil source rock jeanne d arc basin offshore eastern canada abstract the log r wireline log technique has been used to predict high vertical resolution geochemical profiles for 17 well penetrations of the upper jurassic egret member source rock of the jeanne d arc basin offshore newfoundland the predictions are compared with rock eval data obtained from the same interval high resolution comparison of the computed total organic carbon toc curves with gamma ray logs implies that the source rock layers in the egret member are mainly shale claystone and the non source rock layers are limestone marl to the south and siltstone sandstone to the north these comparisons also indicate that in the mature area some coarse grained non source rock layers are filled with hydrocarbons implying primary migration of oil gas using the average computed toc value the thickness of the egret member and the average formation density the mass of organic carbon was calculated at 19 well locations and regional variations examined areas with a great mass of organic carbon were identified the present mass of organic carbon is primarily related to the amount of organic matter being deposited and preserved but the expulsion of oil gas may also exert a control using 1 wt as the lower limit for a source rock it was observed that the percentage of non source rock in the egret member is generally higher in immature wells lom 7 than in mature wells probably as a result of hydrocarbon migration expulsion after maturation

geochemistry of crude oil from bent horn field canadian arctic archipelago and its possible paleozoic origin abstract geochemical analysis shows that oil from devonian reservoirs at bent horn field in the canadian arctic archipelago is non biodegraded and has a maturity corresponding to the mid late part of the oil window it is characterized by a smooth n alkane profile low concentration of acyclic isoprenoids and saturated hydrocarbon biomarkers with some variability in sterane composition compared with oil from mesozoic strata of the canadian arctic islands the bent horn oil shows higher paraffin indices and aromatic hydrocarbon maturity indicators mpi mdr dominant tricyclic terpanes and different distribution of regular steranes geological evidence suggests a paleozoic source rock for the oil rock eval pyrolysis and total organic carbon toc data indicate good source rock potential for the silurian basinal facies and upper silurian lower devonian clastics of the boothia uplift these intervals are enriched in type ii oil prone organic matter commonly 2 0 5 0 toc maximum 13 6 and are mature with respect to petroleum generation based on preliminary biomarker analysis maturity and stratigraphic and geographic proximity to the bent horn oil field the cape phillips formation appears to be the most likely source rock for the hydrocarbon accumulation at bent horn

multiple oil families in the west siberian basin two major oil families are identified in the west siberian basin twenty six of 32 analyzed oils occur in jurassic and cretaceous reservoirs and are derived from anoxic marine upper jurassic bazhenov source rock based on geochemical comparison of oils and source rock extracts these oils are widely distributed both north and immediately south of the ob river and their biomarker ratios indicate a wide range of source rock thermal maturity from early to middle oil window van egan russkoye samotlor sovninsko sovyet olyenye ozynornoye and kogolym to peak oil window srednekhulym yem yegov vostochno surgut khokhryakov fedorov and urengoi to late oil window salym some of these oils have been mildly e g fedorov 75 to heavily e g russkoye biodegraded n the reservoir the bazhenov sourced oils show different compositions that support regional variations of organic facies in the source rock for example the anoxic marine bazhenov facies which generated the oils in the samotlor fedorov and nearby fields was particularly clay poor and sulfur rich six nonbiodegraded highly mature oils show geochemical characteristics that suggest they were derived from clastic rich lacustrine or nearshore marine source rocks dominated by terrigenous higher plant input like those in the lower to middle jurassic tyumen formation although no correlation was observed between the oils and a single rock sample yem yegov 15 from the formation the six oils occur in the tyumen taitym geologiche and cheremshan and fractured basement paleozoic gerasimov yagyl yakh and verchnekombar reservoirs in positions readily accessible to any oil migrating from the tyumen source rock for example at the gerasimov location the tyumen formation lies unconformably on weathered basement paleozoic reservoir rocks most of the probable tyumen sourced oils ar from south of the ob river but the occurrence of geologiche oil to the north suggests that related oils may be widespread in the basin

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

prediction of source rock characteristics based on terpane biomarkers in crude oils a multivariate statistical approach abstract the distributions of eight tricyclic and eight pentacyclic terpanes were determined for 216 crude oils located worldwide with subsequent simultaneous rq mode factor analysis and stepwise discriminate analysis for the purpose of predicting source rock features or depositional environments five categories of source rocks are evident nearshore marine i e paralic deltaic deeper water marine lacustrine phosphaticrich source beds and ordovician age source rocks the first two factors of the rq mode factor analysis describe 45 percent of the variation in the data set the tricyclic terpanes appear to be twice as significant as pentacyclic terpanes in determining the variation among samples lacustrine oils are characterized by greater relative abundances of c 21 diterpane and gammacerane nearshore marine sources by c 19 and c 20 diterpanes and oleanane deeper water marine facies by c 24 and c 25 tricyclic and c 31 plus c 32 extended hopanes and ordovician age oils by c 27 and c 29 pentacyclic terpanes although thermal maturity trends can be observed in factor space the trends do not necessarily obscure the source rock interpretations also since bacterial degradation of crude oils rarely affects tricyclic terpanes biodegraded oils can be used in predicting source rock features the precision to which source rock depositional environments are determined might be increased with the addition of other biomarker e g steranes and stable isotope data using multivariate statistical techniques

oil source and charge in the wuerxun depression hailar basin northeast china a chemometric study abstract one hundred fifty four samples collected from the wuerxun depression hailar basin northeast china were analyzed using gc ms the k1n formation including k1n2 and k1n1 members consists mainly of argillaceous rock with relatively abundant organic matter and is considered to be the best source rock in the study area whereas the k1t formation and k1d1 member damoguaihe formation provide a limited contribution to the wuerxun oils chemometric methods i e principal component analysis pca and multidimensional scaling mds were used for oil oil and oil source rock correlations in this study based on pca and geological evidence the oils from northern wuerxun originated primarily from source rocks of the k1n1 member that were charged ca 100 ma whereas those in the southern wuerxun form separate genetic groups i and ii when combined with trend surface analysis the mds technique also revealed variations in the depositional conditions and the maturity of the source rocks and oils group i oils which have relatively higher maturity are characterized by relatively high saturate aromatic hydrocarbon ratios high pr ph ratios 1 high ts ts tm ratios a slight predominance of c29 regular steranes and more positive 13c values of saturated and aromatic hydrocarbon fractions whereas the lower maturity group ii oils have relatively low saturate aromatic hydrocarbon ratios low pr ph ratios

late devonian and early mississippian bakken and exshaw black shale source rocks western canada sedimentary basin a sequence stratigraphic interpretation the late devonian and early mississippian bakken and exshaw formations are a continuum of regionally correlated organic rich up to 35 total organic carbon black shale source rocks covering much of the western canada sedimentary basin the bakken formation is composed of 1 a black mudstone lower member 2 a gray mudstone sandstone middle member and 3 a black mudstone upper member the exshaw formation beneath the alberta plains and in exposures in the foothills and front ranges of the rocky mountains is composed of 1 a lower black shale member and 2 an upper siltstone member the basal black shale unit of the lower mississippian banff formation overlying the exshaw formation is a second organic rich interval these black shales are regionally significant hydrocarbon source rocks and local reservoirs the middle bakken member is a locally important reservoir rock with substantial economic potential the bakken and exshaw formations and the basal banff black shale are divisible into three systems tracts 1 a transgressive systems tract 2 a lowstand systems tract and 3 a second transgressive systems tract lodgepole and banff formation carbonates overlying the bakken and exshaw formations are part of a highstand systems tract a sequence boundary occurs between the lower and middle bakken members the conformable equivalent of this sequence boundary is within the exshaw black shale member variations in the internal composition of these systems tracts imply that two depocenters 1 the williston basin and 2 the prophet trough and the western margin of the north american craton were affected differently by relative sea level rise and fall during bakken and exshaw deposition because of differences in water depth and sediment accommodation spatial and temporal changes in black shale and gray mudstone sandstone as highlighted by this sequence stratigraphic interpretation may have significant impacts on source rock potential and hydrocarbon reservoir size location and quality

application of pyrolysate carbon isotope and biomarker technology to organofacies definition and oil correlation problems in north sea basins abstract detailed sampling of apparently homogeneous potential source rock intervals frequently indicates unsuspected variations in organic facies which may or may not be reflected in the wireline logs carbon isotope analyses of pyrolysates provide a useful technique in these investigations which are essential for valid oil to source correlations in the jurassic of a north sea viking graben well the rich source shales at the top of the draupne formation are significantly depleted in 13 c and correlate with the oils from this area thus suggesting that this interval has acted as the primary source of the viking graben crudes a quite different pattern is evident in a well from the central graben and the data not only explain why the oils of the greater ekofisk area are relatively enriched in 13 c but also demonstrate that the variations within these oils are facies controlled pyrolysate carbon isotopes provide an excellent correlation between the middle devonian upper caithness flagstones of the inner moray firth and the beatrice crude oil this correlation is supported by the biomarker data and there is no need to appeal to a contribution from either an upper or middle jurassic source to achieve a match with the beatrice oil

origin and mechanism of the formation of the low oil saturation moxizhuang field junggar basin china implication for petroleum exploration in basins having complex histories the moxizhuang field is a small oil field in the central junggar basin containing several low saturation low resistivity oil reservoirs which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs biomarker associations of crude oil and grains containing oil inclusions gois of both the present day water bearing zones water zones and the oil and water bearing zones low oil saturation pay zones were analyzed to investigate the mechanisms for the formation of the low saturation low resistivity oil accumulations the biomarker assemblage and hierarchical cluster analysis indicate that oil in the moxizhuang field was mostly generated from permian source rock deposited in brackish to hypersaline anoxic environments the pay zones and several water zones display goi values as much as 38 greater than the generally accepted threshold goi value for an oil column 5 these goi values are similar to those for high saturation oil reservoirs in the bohai bay basin and oil zone samples from australian basins suggesting that both pay zones and water zones were high saturation oil reservoirs in the geologic past geologic history analysis shows that the moxizhuang field was located on the north wing of a paleoanticline during oil charge in the late cretaceous to paleogene this anticline has gradually evolved into a south dipping monocline since the neogene causing northward remigration of accumulated oil differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high goi values completely drained reservoirs and the low saturation low resistivity pay zones partially preserved reservoirs and caused the complex correlation between oil saturation and porosity and permeability compared with other postaccumulation physicochemical alteration processes lateral leakage has rarely been recognized recognizing differential lateral leakage of accumulated petroleum with the existence of high quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories

origin and migration pathway of biodegraded oils pooled in multiple reservoirs of the chepaizi uplift junggar basin nw china insights from geochemical characterization and chemometrics methods abstract the chepaizi uplift possesses three sets of oil bearing reservoirs six sets of source intervals multiple episodes of hydrocarbon charging and variable physical properties of crude oils in this study based on geochemical characterization source intervals and the biodegradation rank of the crude oils four oil populations named as group a b c and d d1 d2 were defined the combined results of q cluster analysis qca and discriminant analysis da indicate that group a occurred mainly in lower neogene shawan formation n1s in the western chepaizi uplift and were primarily derived from the middle lower jurassic xishanyao badaowan sangonghe formations j2x j1b j1s and a little of paleogene anjihaihe formation e2 3a of the sikeshu sag group b occurred essentially in upper carboniferous xibeikulasi formation c2x of the western chepaizi and originated mainly from the j1b mudstone of the shawan sag in addition the crude oils of group c occurred mainly in the lower cretaceous tugulu group k1tg of the eastern chepaizi and were primarily derived from carboniferous sourced oil from the chepaizi uplift the crude oils of groups d d1 and d2 are mixed with permian p1f and p2w of shawan sag and carboniferous sourced oil from the chepaizi uplift based on the reconstruction of the migration history the oils of group a in the n1s formation of western chepaizi migrated predominantly from the south sikeshu sag to the north and northeast with wells su1 2 and c27 as the initial filling points the oils of group b in the n1s formation of the western chepaizi travelled predominantly from the southeast shawan sag to the north and northwest the oils of group d1 in the c2x formation of eastern chepaizi migrated mainly from the northeast and southeast shawan sag to the west with well p661 as the initial filling point wells sm011 and c64 are the initial filling points of the k1tg group in the hongche fault belt crude oils of group c in the k1tg group travelled predominantly from the southeast shawan sag and northeast to the west into the eastern chepaizi and from well p68 to the southwest according to the paleo oil preferential filling orientations and paleogeomorphology some favourable targets for petroleum exploration of the chepaizi uplift are forecast in this study

kuparuk oil field alaska a mixture of kekiktuk gas condensate and shublik oil kuparuk river is a giant oil field located on the colville high west of prudhoe bay field on the north slope of alaska the kuparuk oils have values greater than 0 5 for the aromaticity b parameter toluene n c7 and less than 1 for the paraffinicity f parameter n c7 mch using two parameters in isolation one would interpret kuparuk as the residue from repeated episodes of phase segregation and gas cap leakage this process termed evaporative fractionation is experimentally proven to concentrate naphthenic and aromatic hydrocarbon with low fugacity in the parent oil phase while enriching the daughter gas condensate phase in alkanes reassessment of the geochemistry of the kuparuk field within the context of a regional evaluation of north slope petroleum systems suggests a very simple charge and filling model where the kuparuk accumulation remained a single phase throughout its history oil and solution gas derived mainly from the shublik formation together with gas and very light naphthenic aromatic condensate derived from kekiktuk conglomerate coals shared a common migration path into kuparuk field this study illustrates that the b f plot must be used with caution because factors other than evaporative fractionation such as source input can influence these ratios based on data from southeast asia alberta and north slope basins this study also suggests that the sohio 1 mukluk well did not successfully result from the presence of kuparuk thief sands thus petroleum migration continued to the kuparuk field

charging of oil fields surrounding the shaleitian uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract this paper discusses origin and charging directions of oil fields on the shaleitian uplift bohai bay basin the shaleitian uplift is a footwall uplift surrounded by three sags containing mature source rocks the origins of the four oil fields on the shaleitian uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions for 61 source rock samples and 27 oil samples hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and or depositional conditions allowed the identification of six oil types or classes these six oil classes could then be linked to three distinct source rock intervals ranging in age from 43 0 ma to 30 3 ma the third member 43 0 38 0 ma in age and first member 35 8 32 8 ma of the eocene shahejie formation and the third member of the oligocene dongying formation 32 8 30 3 ma each sourced one class of oil the other three classes represent mixtures of oil generated from multiple source rock intervals traps on the shaleitian uplift were charged in the east by oil generated from the eocene shahejie formation in the bozhong sag in the southeast by oil generated from the eocene shahejie and then oligocene dongying formations in the southwestern part of the bozhong sag and or in the eastern part of the shanan sag and in the southwest by oil generated from the eocene shahejie formation in the western part of the shanan sag the estimated migration distances range from less than 5 km to about 20 km the compositional heterogeneity within fields and multiple parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist

identification of genetically distinct petroleum tribes in the middle magdalena valley colombia six distinct oil tribes were established using multivariate statistical analysis of source related biomarker and isotopic ratios for 73 crude oil samples from the middle magdalena valley mmv colombia these six tribes show a systematic distribution by both basin location and reservoir rock age and may originate from different source rocks or different organofacies of the same source rock biomarker and isotopic data further differentiate the tribes with respect to source rock depositional environment lithology organic matter type and thermal maturity the thermal maturity and reservoir interval for the northernmost tribe 5 suggest a middle cretaceous tablazo formation source rock in contrast tribes 1 through 4 are likely derived from the primary regional source rock the upper cretaceous la luna formation however we observe regional differences in bulk properties thermal maturity terrigenous input and oxicity between the four la luna derived oil tribes in addition tribe 3 appears to result from end member mixing between tribes 2 and 4 finally the southernmost tribe 6 is the only oil with terrigenous character diamondoid analysis shows the presence of significant secondary cracking in the tribe 6 oil with low levels of cracking present in oil samples from tribes 1 and 2 in the central mmv this suggests a more deeply buried nonmarine source along the western flank of the andean eastern cordillera the integration of chemometric biomarker and diamondoid analyses have improved our understanding of the mmv petroleum system and advocate for the presence of three or more source rock intervals within the basin

impacts of source input and secondary alteration on the extended tricyclic terpane ratio a case study from palaeozoic sourced oils and condensates in the tarim basin nw china abstract a suite of oils and condensates from cambrian ordovician sources in the cratonic region of the tarim basin nw china has been characterized by gas chromatography mass spectrometry with a focus on factors affecting the extended tricyclic terpane ratio etr c28 c29 tt ts these oils and condensates show etr values ranging from 0 3 to 12 4 suggesting variable source contributions deposited under different environmental conditions coupled with tri and tetracyclic terpane distributions etr can be used as an organofacies discriminator most of the samples have high etr values 2 0 a low relative abundance of the c19 tricyclic terpane c19tt and the c24 tetracyclic terpane c24tet characteristic of a clastic marine depositional environment possibly with upwelling conditions a specific organofacies for a few samples is characterized by low etr values 0 8 and c24tet c26tt 1 0 ratios reflecting deposition under dysoxic conditions however various other alteration processes such as thermal maturity thermochemical sulfate reduction tsr biodegradation and in reservoir mixing probably have a significant impact on this parameter which makes understanding the meaning of the etr complicated the effect of thermal maturity on etr is minimal in the oil generation window but the etr values decrease dramatically at the post oil generation stage tsr seems to preferentially lead to the loss of the c28tt and c29tt before the 18 h 22 29 30 trisnorneohopane ts and thus the etr value decreases as tsr progresses while the dibenzothiophene phenanthrene ratio can help to differentiate tsr alteration from thermal cracking processes the etr is no longer a valid geochemical parameter when these two processes occur etr also increases with biodegradation the c28 and c29tt are more resistant to biodegradation than ts supporting evidence can be derived from a positive correlation between etr and c29 25 norhopane to c30 hopane ratio in reservoir mixing is another important alteration process which normally results in lower etr values after a fresh charge is mixed with a biodegraded charge in a reservoir evaporative fractionation may also have an impact on etr values some unusually high etr values might be attributed to evaporative fractionation the etr values from our case study suggests that the etr parameter is much more complicated than just being an age diagnostic parameter maturation and secondary alteration processes need to be fully accounted for before the etr can be properly applied to interpretations of depositional environment conditions such as upwelling

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

chemometric classification and geochemistry of oils in the iranian sector of the southern persian gulf basin crude oil samples collected from several oilfields across the southern persian gulf basin from jurassic to cretaceous reservoirs were chemometrically classified into two genetically distinct oil families family a oils occurring in the western areas are restricted to the jurassic series family b oils mostly occurring in the eastern areas were generated from a younger homogeneous marine carbonate source rock an improved geochemical understanding of family a oils is achieved in this study and a refined paleo depositional model for their source rock is presented these high maturity oils were generated from a middle jurassic carbonate source rock formed within a shallow anoxic intra shelf basin that was connected to the neo tethys marine environment an initial phase of biodegradation is suggested to have affected family a oils during their initial accumulation phases but the imprint has likely been masked with mixing of multiple charges or phase fractionation similarly family b oils appear to be controlled by mixing of at least two separate charges or phase fractionation processes although the trap charging dynamics of the cretaceous accumulations agrees with a stronger probability for secondary alteration processes based on these findings we conclude that the present day geochemistry of both oil families is the result of a complicated sequence of events including mixing of at least two separate charges with varying maturities or phase separation these new insights can have practical implications for assessing volumetric mass balance relationships in advanced hydrocarbon generation models identifying low risk plays and ranking prospects

geostatistic recognition of genetically distinct shale facies in upper triassic chang 7 section the ordos basin north china abstract the ordos basin in north china may be one of the nonmarine basins with highest hydrocarbon generation per volume of sedimentary fill it has great potential for unconventional oil and gas exploration especially shale oil when evaluating and predicting shale oil resources the difference between different regions and different layers of shale is very obvious so it cannot be calculated simply by average a geostatistic decision tree was constructed based on a training set of 22 parameters geochemistry petrology and sedimentology for 110 shale samples from the basin which can be used to implement genetic classification of subsequently collected shale samples three shale facies are identified by the decision tree the properties of each facies are different such as toc kerogen type and sulfur content genetic properties indicate formation conditions and provide base for the geostatistic assignments the differential distribution of shale facies in the basin reflects their origins from different formation mechanism elements ratios isotopes and biomarkers can be used to infer the sedimentary environment for each shale facies facies 1 mainly occurs in the upper chang 7 section and shows evidence of quartz rich source rock deposited under suboxic anoxic condition facies 3 occurs at the lower chang 7 section and shows evidence of clay rich and pyrite rich shale deposited under reducing dysoxic conditions with numerous higher plants input facies 1 and 2 constitutes the upper chang 7 with interactive thick layers facies 2 and 3 constitute the lower chang 7 with interactive thin layers petrology geochemistry and sedimentology of the shale facies suggest facies 1 represents the suboxic anoxic upper chang 7 proximal quartz rich shale which has lower toc and sulfur content than other facies the organic lamina is straight but rare kerogen is type i and dominated by sapropel the content of saturated hydrocarbon in chloroform asphalt a extract is the highest facies 2 has higher toc value sulfur content and soluble hydrocarbon content than facies 1 it was formed in unstable hydrodynamic environment under weak anoxic condition it is characterized by abundant laminas with various deformation structures and more alginite and vitrinite in kerogen anoxic lower chang 7 distal sulfur rich shale source rock make up organic rich facies 3 7 0 17 0 wt toc this facies received more higher plant input than the other facies well preserved algae shells are common in numerous and flat laminas the content of chloroform asphalt of facies 3 is higher than that of other facies but among which the saturated hydrocarbon content is the lowest the aromatic non hydrocarbon and asphalt are the highest suggesting the fluidity of hydrocarbon is the worst compared to others this facies was formed in the environment where temperature is relative lower water is relative deeper productivity and salinity are relative higher and the reducibility is relative stronger a deeper understanding of shale classification and distribution is important for the accurate resource evaluation and optimal exploration planning of shale oil

oil families and their inferred source rocks in the barents sea and northern timan pechora basin russia a geochemical study of 34 oil samples was conducted to understand the types and distributions of effective source rocks and evaluate the geographic extent of the petroleum systems in the barents sea and northern timan pechora basin taxon specific age related and source related biological markers biomarkers and isotope data provided information on the depositional environment of the source rock source input and source age of the oil samples a relationship between biomarker and diamondoid concentration was used to identify mixed oils having both oil window and highly cracked components compound specific isotope analyses of diamondoids and n alkanes were used to deconvolute cosourced oils and identify deep source rocks in the basin results suggest five major source rocks in the barents sea and the northern timan pechora basin upper jurassic shale lower middle jurassic shale triassic carbonate and shale devonian marl and devonian carbonate the upper and lower middle jurassic source rocks are dominant in the barents sea triassic source rock consists of carbonate in the onshore part of northern timan pechora basin and marine shale in the barents sea the devonian domanik formation carbonate source rock extends offshore into the southern barents sea the high maturity domanik formation could also be a secondary source rock for most of the mixed oils in the northern timan pechora basin this detailed geochemical study provides a new and detailed understanding of petroleum systems in the barents sea and northern timan pechora basin

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

new upper paleozoic and lower mesozoic stratigraphic units central and western brooks range alaska the sequence of rocks described lies primarily in the delong and endicott mountains in the western and central parts of the brooks range northern alaska new names are given to dominantly siliceous and shaly sedimentary rocks of mississippian through early middle jurassic age the kuna formation new name consists dominantly of black bedded chert shale limestone and dolomite within the lisburne group some beds are phosphatic and mafic extrusive igneous rocks occur in a few areas paleontologic data suggest an early mississippian to early or middle pennsylvanian age for the kuna formation because the formation intertongues eastward with light colored shallow water carbonate rocks of the wachsmuth and alapah limestones of the lisburne group it is also assigned to t e lisburne group light colored shallow water carbonate rocks of other formations of the lisburne group were apparently also deposited on the south but have been telescoped northward by thrust faulting over the darker kuna formation the formation ranges up to 100 m in thickness the etivluk group new name is composed of dominantly siliceous beds of the previously named siksikpuk formation and overlying otuk formation new name new paleontologic data suggest that the siksikpuk is of pennsylvanian permian and early triassic age the otuk formation consists of up to 100 m rhythmically interbedded chert silicified limestone and shale previously assigned in this area to the shublik formation a thin but distinctive zone of early middle jurassic organic shale and dolomitic limestone ocally present within the top of the otuk constitutes the blankenship member new name which is up to 7 m thick paleontologic data indicate that the otuk formation ranges in age from late early triassic to early middle jurassic these dominantly siliceous stratigraphic units appear to be limited to the allochthons of the western and central brooks range they are not known to be present on the autochthonous complex of the northeastern brooks range and subsurface arctic slope

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

recent deceleration of oceanic pco2 increase in the western north pacific in winter 1 recent changes in oceanic co2 partial pressure pco2sea have attracted increasing interest as they relate to the increase in atmospheric co2 and climate change we report decadal changes in the growth rates of pco2sea in latitudinal zones from 3 n to 33 n along the repeat hydrographic line at 137 e in the western north pacific in winter the growth rates of pco2sea for 1999 2009 0 3 0 9 mean 1 to 1 7 0 5 atm yr 1 were lower than those for 1984 1997 0 7 0 3 to 2 2 0 6 atm yr 1 at most latitudes indicative of the recent notable deceleration of pco2sea increase for latitudes around 10 20 n we attribute the reduction in the growth rate of pco2sea for 1999 2009 primarily to the reduction in the contribution from dissolved inorganic carbon dic originating from a reduction in carbon accumulation associated with the expansion of the western subtropical gyre towards the south

chemometric recognition of genetically distinct oil families in the los angeles basin california the prolific los angeles basin in california may be the most petroliferous province on earth per volume of sedimentary fill however because most exploration in the basin occurred prior to the advent of modern geochemical methods genetic relationships among the various petroleum accumulations and their source rocks have remained speculative a training set of 24 source related biomarker and stable carbon isotope ratios for 111 non or mildly biodegraded oil samples from the basin was used to construct a chemometric multivariate statistics decision tree the decision tree allows genetic classification of additional oil or source rock extract samples that might be collected the decision tree identifies 6 tribes and a total of 12 genetically distinct oil families the families have different bulk properties such as api gravity and sulfur content which were previously explained as resulting from secondary processes including thermal maturity or biodegradation however the chemometric assignments are based on genetic properties that reflect distinct organofacies the oil families occur in different locations and reservoir intervals in the basin consistent with their origins from different organofacies of active source rock the source rock depositional environment for each oil family can be inferred using biomarker and isotope ratios the samples show stable carbon isotope ratios for saturate and aromatic hydrocarbons that indicate different organofacies of miocene marine source rocks tribes 1 and 2 straddle the central trough mainly occur east of the newport inglewood fault zone nifz and show evidence of proximal clay rich source rock deposited under suboxic conditions with elevated angiosperm input tribes 3 6 occur west of the nifz and show evidence of more distal clay poor source rock deposited under anoxic conditions geochemistry and stratigraphy of the oil tribes 1 6 below suggest the following source rock organofacies

de convoluting mixed crude oil in prudhoe bay field north slope alaska abstract seventy four crude oil samples from the barrow arch on the north slope of alaska were studied to assess the relative volumetric contributions from different source rocks to the giant prudhoe bay field we applied alternating least squares to concentration data als c for 46 biomarkers in the range c19 c35 to de convolute mixtures of oil generated from carbonate rich triassic shublik formation and clay rich jurassic kingak shale and cretaceous hue shale gamma ray zone hue grz source rocks als c results for 23 oil samples from the prolific ivishak formation reservoir of the prudhoe bay field indicate approximately equal contributions from shublik formation and hue grz source rocks 37 each less from the kingak shale 26 and little or no contribution from other source rocks these results differ from published interpretations that most oil in the prudhoe bay field originated from the shublik formation source rock with few exceptions the relative contribution of oil from the shublik formation decreases while that from the hue grz increases in reservoirs along the barrow arch from point barrow in the northwest to point thomson in the southeast 250 miles or 400 km the shublik contribution also decreases to a lesser degree between fault blocks within the ivishak pool from west to east across the prudhoe bay field als c provides a robust means to calculate the relative amounts of two or more oil types in a mixture furthermore als c does not require that pure end member oils be identified prior to analysis or that laboratory mixtures of these oils be prepared to evaluate mixing als c of biomarkers reliably de convolutes mixtures because the concentrations of compounds in mixtures vary as linear functions of the amount of each oil type als of biomarker ratios als r cannot be used to de convolute mixtures because compound ratios vary as nonlinear functions of the amount of each oil type

the origin and distribution of crude oil in zhu iii sub basin pearl river mouth basin china abstract the origin of thirteen major oil fields in zhu iii sub basin pearl river mouth basin was studied by using the results of rock eval pyrolysis on 340 samples and biomarker analysis on 18 source rock samples and 33 oil samples the two possible source rock intervals have different biomarker assemblages and were deposited in different environments the eocene wenchang formation e2w 49 5 35 ma is characterized by high hopane sterane ratio 37 84 high 4 methyl sterane index 0 28 1 06 low gammacerane index 0 10 high bicadinane c30 hopane up to 73 62 but low hopane sterane ratio