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

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

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

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

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

deriving three dimensional reservoir bathymetry from multi satellite datasets abstract we evaluate different techniques that rebuild reservoir bathymetry by combining multi satellite imagery of surface water elevation and extent digital elevation models dems are processed in two distinct ways in order to determine 3 d reservoir bathymetry they are defined as a linear extrapolation and b linear interpolation the first one linearly extrapolates the land slope defining the bottom as the intersection of all extrapolated lines the second linearly interpolates the uppermost and lowermost pixels of the reservoir s main river repeating the process for all other tributaries a visible bathymetry resulting from the combination of radar altimetry and water extent masks can be coupled with the dem improving the accuracy of techniques a and b envisat and altika based altimetric time series is combined to a landsat based water extent database over the 2002 2016 period in order to generate the visible bathymetry and topography is derived from the 3 arcsec hydrosheds dem fourteen 3 d bathymetries derived from the combination of these techniques and datasets plus the inclusion of upstream and downstream riverbed elevations are evaluated over lake mead accuracy is measured using ground observations and show that metrics improve as a function of added data requirement and processing best bathymetry estimates are obtained when the visible bathymetry linear extrapolation technique and riverbed elevation are combined water storage variability is also evaluated and shows that best results are derived from the aforementioned combination this study contributes to our understanding and representation of reservoir water impoundment impacts on the hydrological cycle

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

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

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

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

a miocene polarity transition r n from the agno batholith luzon a geomagnetic reversal record has been obtained from the agno batholith 16 15 n 120 39 e in luzon island the philippines this body is a biotite hornblende quartz diorite dated at between 14 5 and 15 0 m y by the k ar whole rock method hysteresis properties show that the magnetic remanence is dominated by multidomain low titanium titanomagnetite a stable component of magnetization is isolated upon both thermal and alternating field demagnetization normal and reversed polarity zones within the batholith give tightly grouped results which when compared to other miocene poles from the baguio area allow a tilt correction to be made the resulting reversed to normal reversal sequence has a far sided vgp path and a decrease in intensity of magnetization of approximately a factor of 5 with a longer duration than the directional change the vgp path is confined in a longitudinal band 120 from the site and so differs from the characteristic reversed to normal transition paths in that it is not near sided intermediate field geometry cannot therefore always be the same for individual reversals the agno reversal record is consistent with a quadrupole field and reversal initiated in the northern hemisphere an octupolar intermediate field would require simultaneous flooding from both polar latitude bands

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

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

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

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

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

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

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

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

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