variable alteration in heavy crude oils of west central saskatchewan canada heavy crude oils occurring in the mississippian bakken and lower cretaceous mannville reservoirs in west central saskatchewan display variable geochemical composition in their light c 5 c 8 and medium c 12 c 30 molecular weight fractions all oils show a depletion of normal alkanes and to a lesser extent acyclic isoprenoids which appears to increase progressively southward as biodegradation seems to be the primary control of the n alkane distributions it appears that oils produced from deeper reservoirs in the south are more biodegraded than the oils in shallower mannville reservoirs in the north however several other compositional characteristics including gasoline range and aromatic fractions are inconsistent with the trend in biodegradation defined by the relative n alkane abundance oils from the shallower northern reservoirs are enriched in cycloalkanes show lower relative concentrations of isoheptane lower paraffin indices much higher kl ratios and lower relative concentrations of lower molecular weight naphthalenes moreover some oils show a persistent presence of lower homologs of n alkanes c 5 c 8 and light aromatics such as benzene and toluene when higher c 15 homologs are not present such compositional characteristics may indicate that some of the reservoirs containing biodegraded oil were subjected to a subsequent secondary charge of lighter unbiodegraded crude or to different post generative alteration mechanisms this later charge of light hydrocarbons suggests the timing of most biodegradation to be pre eocene destructive microbial action resulting in preferential removal of n alkanes isoprenoids alkylbiphenyls and methylated naphthalenes had little effect on higher molecular weight fractions therefore despite their apparently very low gravities average api of 14 most of these oils suffered only light to moderate biodegradation although generally similar biomarker signatures indicate an overall genetic affinity and the same source rock for these oils minor but systematic variations in the biomarker compositions likely reflect regional source organic facies variation or indicate a progressive change in oil maturity

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

geochemical characterization of selected western canada oils by c5 c8 compound specific isotope correlation csic abstract forty two oils condensates from the western canada sedimentary basin wcsb ranging in reservoir age from devonian to cretaceous are compared using the stable carbon isotopic ratio of individual hydrocarbons in the gasoline range fraction c 5 c 8 of these oils continuous flow isotope ratio mass spectrometry cf irms using a modified solid dilution purge and trap inletting system can provide reproducible isotopic ratios for the ca 26 dominant n iso and cyclo alkanes and aromatics in the gasoline range the resulting isotopic signatures or gasoline isotopograms for oils condensates provide a diagnostic geochemical technique for oil oil and oil source correlations in many instances the non straight chained hydrocarbons are more diagnostic than n alkanes hierarchical cluster analysis provides a non subjective approach to the treatment of individual isotopic information this study confirms that oils from similar or the same sources produce isotopic signatures that are highly correlated clear carbon isotopic relationships between individual hydrocarbon compounds in the oils suggest a steady state kinetic relationship for the generation of oil and gas as opposed to a thermodynamic equilibrium relationship this mechanism explains the consistent shift in isotopic ratios between similar compounds such as the methylalkanes and dimethylalkanes

application of the pyrolysis carbon isotope method for determining the maturity of kerogen in the bakken shale a maturity indexing procedure based on the isotopic difference between the total accumulated methane produced by exhaustive pyrolysis and the kerogen 13c and the mole ratio of methane to kerogen carbon cmr has been tested by applying a standardized technique i e exhaustive pyrolysis 600 c for 120 hr of extracted powdered samples and measurement of the amounts and isotopic composition of the methane and kerogen carbon on a suite of 15 bakken shale samples a linear relation was found between the carbon mole ratio of pyrolysis derived methane and total organic carbon and the 13c difference between the pyrolysis derived methane and total organic carbon r 0 79 and between the amount of ch4 generated from exhaustive pyrolysis and h c atomic ratios r 0 91

re os geochronology of organic rich sediments an evaluation of organic matter analysis methods rhenium and osmium in organic rich sedimentary rocks are dominantly hydrogenous but any nonhydrogenous component will influence the accuracy and precision of the re os date obtained to minimize the influence of any nonhydrogenous re and os we evaluate analysis of isolated organic matter from the whole rock together with whole rock analysis using a cro3 h2so4 digestion medium instead of inverse aqua regia for a black shale unit of the exshaw formation canada this unit previously returned a whole rock re os date of 358 10 ma model 3 geochim cosmochim acta 2002 using inverse aqua regia dissolution organic matter isolated from the whole rock matrix using the hf bf3 technique org geochem 20 1993 249 yields scattered data and a re os date of 449 220 ma model 3 mswd 616 the organic matter analyses show similar 187os 188os values but significantly lower 187re 188os values in comparison to the whole rock analyses we show that the re os systematics of organic matter are altered during chemical isolation and as such we suggest that the hf bf3 method should not be used for re os analysis of organic matter whole rock re os analysis using a cro3 h2so4 digestion medium yields significantly better regression analysis compared with the inverse aqua regia method and the re os data identify two distinct initial 187os 188os values for the sample set separate regressions of these data yield precise dates 366 1 9 6 mswd 2 2 and 363 4 5 6 ma mswd 1 6 model 3 which are indistinguishable from the age constraints for this formation 363 4 0 4 ma u pb monazite comparison of the re os dates obtained from aqua regia and cro3 h2so4 methods suggests that the former may contain nonhydrogenous re and os whereas the cro3 h2so4 method dominantly liberates hydrogenous re os from organic matter allowing for better stratigraphic age determinations and evaluation of the os isotope composition of seawater

hydrocarbon potential of the zechstein main dolomite upper permian in western poland relation to organic matter and facies characteristics abstract the zechstein main dolomite ca2 in the area between grotow platform and western part of the gorzow platform in western poland represents the 3rd order sequence of the polish zechstein the deposits are mainly the hst carbonate facies totally fifteen hst microfacies associations were identified and they represent the carbonate platform shallow subtidal supratidal deposits the platform slope upper lower slope deposits and the basin environments the deposition of the ca2 was controlled by the pre zechstein paleomorphology and the systems of tectonic dislocations on this background the geochemical results are presented and their source nature characterized in the context of the facial model of the ca2 the results of geochemical analyses indicate that most of samples collected in the study area contain the epigenetic hydrocarbons in the ca2 carbonates the toc values range from near zero to 5 2 wt and these of hydrocarbons contents reach up to 9 6 mg g rock despite such significant variability the average values are low and do not exceed 0 5 toc and 2 5 mg hc g rock all geochemical parameters indicate that the ca2 carbonates from the study area represent poor to fair oil prone source rocks with local good and or excellent hydrocarbon potential the macerals composition reveals predominance of the oil prone type ii kerogen in all studied microfacies in the kerogen composition organic mineral associations and solid bitumens prevail the organic matter from the ca2 was deposited under anoxic conditions in the hypersaline depositional environment the maturity indicators vitrinite reflectance r o temperature t max and biomarker parameters indicate that the maturity of organic matter corresponds to the final phase of the oil window and to the early phase of the gas window

bakken madison petroleum systems in the canadian williston basin part 2 molecular markers diagnostic of bakken and lodgepole source rocks abstract the uppermost devonian mississippian bakken formation black shale and the mississippian lodgepole formation carbonate represent two of the most important source rocks in the canadian williston basin quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units among others the bakken shales are characterized by their high relative abundance of trimethyl aryl and diaryl isoprenoids likely derived from green sulfur bacteria chlorobiaceae in contrast the lodgepole carbonates at similar maturity levels display a c35 homohopane prominence and abundant benzohopanes ring d monoaromatic 8 14 secohopanes and a tetracyclic monoaromatic hydrocarbon the distinctive nature of molecular marker fingerprints diagnostic of the two source rocks is clearly related to their different organic inputs and depositional environments additionally the large difference in the absolute concentrations of these compounds observed in both source units may potentially lead to biased geochemical interpretations if strictly conventional saturate based biomarker approaches were used for oil oil and oil source correlation

hydrothermal zircon and baddeleyite in val d or archean mesothermal gold deposits characteristics compositions and fluid inclusion properties with implications fortiming of primary gold mineralization zircon and baddeleyite occur within quartz tourmaline veins at four gold deposits in the val d or district of the archean abitibi southern volcanic zone host rocks have experienced intense metasomatic enrichment of zr hf y and rare earth elements the zircons contain primary inclusions of quartz tourmaline pyrite albite k mica scheelite and gold and gold occurs in primary fluid inclusions in zircons magmatic zircons in host rocks do not have this suite of inclusions consequently a wall rock inheritance model for the vein zircons is implausible compositionally the zircons feature pronounced interzone and intergrain variations of hf y yb th and u and sporadic anomalous ce contents of 1100 ppm distinct from magmatic counterparts two principal types of primary fluid inclusion occur in the vein zircons type 1 h2o co2 inclusions have low salinities variable quantities of co2 and homogenization temperatures of 260 380 c and type 2 co2 rich inclusions contain minor h2o and ch4 the vei

a two dimensional regional basin model of williston basin hydrocarbon systems institut francais du petrole s two dimensional model temispack is used to discuss the functioning of petroleum systems in the williston basin along a 330 km long section focusing on four regional source intervals ordovician yeoman formation lower devonian winnipegosis formation upper devonianulower mississippian bakken formation and mississippian lodgepole formation thermal history calibration against present temperature and source rock maturity profiles suggests that the williston basin can be divided into a region of constant heat flow of about 55 mw m2 away from the nesson anticline and a region of higher heat flow and enhanced thermal maturity in the vicinity of the nesson anticline original kinetic parameters used in the calibration were derived or each of the four source rocks from rock eval yield curves bakken overpressures are entirely due to oil generation not compaction disequilibrium very low bakken vertical permeabilities range from 0 01 to 0 001 nd are matched against observed overpressures whereas bakken porosities based on the model and confirmed by measurements are inferred to be also unusually low around 3 mature bakken shales do not seem to have reached hydraulic fractionation thresholds except perhaps locally in regions of extensional tectonic stress hydraulic fracturing cannot be viewed as a pervasive mechanism driving bakken oil expulsion our expulsion model confirms the high residual bakken oil saturations and explains the low residual s1 toc by the low bakken shale porosities approximately 85 of the oil generated in the bakken shales is predicted to have been expelled out of bakken strata which agrees with observed s1 toc trends madison group accumulations at the subcrop edge are found to be fed by lodgepole sourced oil only in particular by the rich middle lodgepole interval these accumulations probably result from a three dimensional migration pattern madison accumulations in the nesson anticline are found to be fed mostly by lodgepole sourced oil mixed with minor amounts of bakken sourced oil the vast majority of the expelled bakken oils are lost in the madison group at very low saturations this explains the low conventional oil resource associated with bakken sources by recent geochemical studies expulsion and migration occurred no earlier than the atest cretaceous paleocene in the yeoman and no earlier than the eocene in other source rocks consistent with temporal controls on oil migration flow models show no restriction to expulsion and migration of yeoman oil this suggests a potential undiscovered oil resource in ordovician and silurian strata of williston basin northeast of the nesson anticline

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 impact of severe biodegradation on the molecular and stable c h n s isotopic compositions of oils in the alberta basin canada abstract although the effects of biodegradation on the composition and physical properties of crude oil have been well studied effects of in reservoir petroleum biodegradation on molecular and isotopic compositions of crude oils are not yet clearly understood the alberta basin in western canada is one of the world s largest petroleum accumulations and constitutes an ideal example of a natural suite of sequentially biodegraded oils the basin hosts moderately to severely biodegraded petroleum regionally distributed and in single more or less continuous oil columns in this study a series of oil samples from the alberta heavy oil and oil sands provinces with varying degrees of biodegradation were analyzed to assess the impact of progressive biodegradation on the molecular and c h n and s isotopic compositions of oils the results of the molecular characterization of the hydrocarbon fraction of the studied oils show that the oils have suffered biodegradation levels from 2 to 10 toward the alberta saskatchewan border on the peters and moldowan scale of biodegradation abbreviated pm 2 to pm 10 and from tens to hundreds on the manco scale within single reservoirs increasing biodegradation was observed from top to bottom of the oil columns at all sites studied the whole oil stable isotopic compositions of the samples varied in the ranges 13 c 31 2 to 29 0 2 h 147 to 133 15 n 0 3 4 7 and 34 s 0 4 6 4 the maximum differences between values of samples within single oil columns were 13 c 1 4 2 h 7 15 n 1 7 and 34 s 1 0 regional variations in the isotopic compositions of oil samples from different wells averaged values from top to bottom were 1 2 for 13 c 12 for 2 h 4 1 for 15 n and 5 5 for 34 s and hence generally significantly larger variations were seen than variations observed within single oil columns especially for n and s it appears that even severe levels of biodegradation do not cause observable systematic variations in carbon nitrogen or sulfur isotope composition of whole oils this indicates that sulfur and nitrogen isotopic compositions may be used in very degraded oils as indicators for oil charge from different source rock facies

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

petroleum source rock evaluation of the alum and dictyonema shales upper cambrian lower ordovician in the baltic basin and podlasie depression eastern poland we present geochemical characteristics of the lower palaeozoic shales deposited in the baltic basin and podlasie depression in the study area this strata are represented by the upper cambrian lower ordovician alum shale recognized in southern scandinavia and polish offshore and a equivalent the lower tremadocian dictyonema shale from the northern estonia and the podlasie depression in poland geochemical analyses reveal that the alum shale and dictyonema shale present high contents of organic carbon these deposits have the best source quality among the lower palaeozoic strata and they are the best source rocks in the baltic region the bituminous shales complex has toc contents up to ca 22 wt the analysed rocks contain low sulphur oil prone type ii kerogen deposited in anoxic or sub oxic conditions the maturity of the alum and dictyonema shales changes gradually from the east and north east to the west and south west i e in the direction of the tornquist teisseyre zone samples located in the seashore of estonia and in the podlasie region are immature and in the initial phase of oil window the mature shales were found in the central offshore part of the polish baltic basin and the late mature and overmature are located in the western part of the baltic basin the alum and dictyonema shales are characterized by a high grade of radioactive elements especially uranium the enrichment has a syngenetic or early diagenetic origin the measured content of uranium reached up to 750 ppm and thorium up to 37 ppm

unusual crude oils in the canadian williston basin southeastern saskatchewan abstract the jedburgh well location 16 14 27 8w2 was drilled on a small salt dissolution structure in the williston basin the well lies near the cussed creek structure a complex feature involving both phanerozoic faults that offset the precambrian basement and the dissolution edge of the middle devonian prairie formation halite the chemical compositions of crude oils recovered from cores of devonian strata in this well are unique in the williston basin and unusual in a global perspective because they contain significant quantities of olefins with the n c 17 alk 1 ene alkane ratio ranging from 0 28 to 0 72 the gross chemical compositions and distributions of aliphatic biomarkers aromatic hydrocarbons and pyrrolic nitrogen compounds in the oils indicate that they were generated by high temperature short term pyrolysis of thermally immature organic matter their composition indicates that they were not generated in situ but accumulated in the jedburgh well after lateral migration from areas that were influenced by post devonian magmatic intrusions the inferred migration distance 10 km suggests that such intrusions occur within the cussed creek structure

hydrocarbon potential of the zechstein main dolomite in the western part of the wielkopolska platform sw poland new sedimentological and geochemical data abstract the results of identification of facies and microfacies of highstand systems tract hst deposits in the zechstein main dolomite ca2 are presented followed by a critical analysis of the existing views on the paleogeography and facies architecture of the wielkopolska platform eastern part of the fore sudetic monocline sw poland the authors discuss and question the existence in zones that have been treated as basinal flat in the analysed area and an extensive platform margin ooidal barrier in general the facies architecture of the study area resembles the block built of the paleozoic basement on this background analytical geochemical results are presented and their source nature characterized in the context of a new revised model of the ca2 basin paleogeography a new facies classification of carbonates which has not been applied for the polish part of the ca2 basin yet was presented the geochemical characteristic of ca2 rocks indicates that good oil prone source rocks are present only locally and are connected with calcisiltites and dolomudstones of facies ii and dolobindstones of facies iv these facies are mainly present in the slope and toe of slope zones the microbial algal facies abundant in the carbonate platform have a weaker residual potential however the thermal maturity stays within the entire range of the oil window the rocks should be re labeled as good source rocks the presence of oil prone kerogen type ii and locally even type i makes the ca2 beds in this part of the wielkopolska platform a very efficient source rock the character of which is confirmed by numerous hydrocarbon accumulations related to the course of tectonic zones and morphology of the basement the proposed characteristic of source rocks in the new paleogeographic facies system enables their better petroleum evaluation and shall enable future prospecting of the perspective zones

carbon isotope composition of marine crude oils 1 a histogram of isotope 13 c values of 621 post ordovician marine oils shows a trimodal distribution within this distribution four groups of oils can be recognized on the basis of isotope 13 c values in conjunction with pristane phytane ratios and sulfur contents oils with isotope 13 c values of 32 0 to 28 0 o oo are mainly marine shale oils older than oligocene oils with isotope 13 c values of 28 0 to 23 5 o oo are mainly deltaic oils of varying geologic age or mesozoic carbonate oils and oils with isotope 13 c values heavier than 23 5 o oo are mainly marine shale oils of miocene age the isotope 13 c variation among oil groups is explained primarily by different factors that control the fractionation of carbon isotopes during primary production of rganic carbon miocene and younger marine shale oils are isotopically heavier than older marine shale oils because of decreased atmospheric co 2 concentration since 25 ma which has resulted in decreased isotope fractionation by marine plankton during photosynthesis deltaic oils are mostly derived from terrestrial organic matter and their isotope 13 c values reflect the time invariant average isotope 13 c value of land plant carbon at about 25 o oo mesozoic carbonate oils are isotopically heavy due mainly to salinity and temperature effects during primary production in restricted environments from which terrestrial organic matter is excluded processes that occur after oil generation generally have smaller effects on isotope 13 c values of oils as a result isotope 13 c val es of oils are useful for determining oil oil and oil source rock relationships and in conjunction with other geochemical properties can indicate the possible age and depositional environment of source rocks

further evaluation of the re os geochronometer in organic rich sedimentary rocks a test of hydrocarbon maturation effects in the exshaw formation western canada sedimentary basin abstract re os isotopic analyses of a single organic rich sedimentary rock unit ors of known depositional age and at three levels of regional hydrocarbon maturity show that hydrocarbon maturation does not affect the ability the 187re 187os chronometer to yield a depositional age for such rocks we present re os isotope analyses from the late devonian exshaw formation in the subsurface of the western canada sedimentary basin alberta and obtain a re os isochron age of 358 10 ma 2 model 3 1 666 10 11 a 1 for samples ranging from hydrocarbon immature to overmature this age is within uncertainty of the established absolute age for the exshaw formation hydrocarbon immature and mature plus overmature samples show no significant age differences if regressed individually indicating that hydrocarbon maturation did not greatly disturb the re os isotope system in the exshaw formation as such we propose that the re os geochronometer may be used as a reliable tool for measuring the depositional ages of ors regardless of their level of hydrocarbon maturity we find that minimizing natural variation in the initial 187os 188os ratio is more important than avoiding hydrocarbon maturation in obtaining precise re os ages in particular the exshaw formation appears to contain a nonhydrogenous component of unradiogenic os in addition to the hydrogenous os load a subset of exshaw formation samples with 5 total organic carbon toc which should best reflect the hydrogenous os load alone yields a very well fitted isochron having a depositional age of 358 9 ma 2 1 666 10 11 a 1 with an initial 187os 188os ratio of 0 59 0 05 model 3 mean square of weighted deviates mswd 1 8 the initial 187os 188os ratio of this regression may provide an estimate of the os isotopic composition of local seawater at the time of deposition

environmental control of carbon isotope variations in pennsylvania black shale sequences midcontinent u s a abstract a reversal of the conventional carbon isotope relationship terrestrial lighter than marine organic matter has been documented for two pennsylvanian desmoinesian cyclothemic sequence cores from the midcontinent craton of the central united states deep water organic rich phosphatic black shales contain a significant proportion of algal derived marine organic matter as indicated by organic petrography rock eval hydrogen index and c 27 c 29 sterane ratios and display the lightest 13c values max 27 80 for kerogen while shallower water more oxic facies e g fossiliferous shales and limestones contain dominantly terrestrial organic matter and have heavier 13ckerogen values to 22 87 for a stratigraphically adjacent coal 13c values for extract fractions were relatively homogeneous for the organic rich black shales with the lightest fraction often the aromatics being only 1 or less more negative than the kerogen differences between extract fractions and kerogens were much greater for oxic facies and coals e g saturates nearly 5 lighter than the kerogen a proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent extremely widespread pennsylvanian peat swamps which were rapidly submerged by transgression of the epicontinental seas in this setting marine organisms drew upon a co2 reservoir which was in a state of disequilibrium with the atmosphere being affected by isotopically light recycled co2 derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments

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

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

texture mineralogy and rock strength in horizontal stress related coal mine roof falls abstract geologic structures can represent planes of preferential weakness that by dismembering the roof beam may contribute to the failure of roof spans however beam deflection and roof failure also occur in rocks where no visible geologic discontinuities are present this suggests that roof failure may depend on rock strength which in turn depends on intrinsic textural properties inherent to the rock in this study rock samples were collected from horizontal stress related roof fall material in coal mines for petrographic characterization and compressive strength testing brittle stress failure prone rock types include thinly interlaminated siltstone and shale and black shale that had been lightly recrystallized samples exhibit a narrow range of density values between approximately 2 5 3 0 g cm3 but exhibit a wide range of unconfined compressive strength values between approximately 20 70 mpa results of laboratory observations suggest that for samples of coal mine immediate roof shale compressive strength is not well correlated with density grain size sutured grain boundaries or quartz content these results for shale are generally at odds with the results of similar studies for sandstone the great variability of strength texture and mineralogy documented in these samples may be an indication of their complexity and the need for specialized methodology in the study of shale strength

organic geochemistry depositional history and hydrocarbon generation modelling of the upper permian kupferschiefer and zechstein limestone strata in south west poland abstract the upper permian zechstein limestone carbonates in the south western part of the polish zechstein basin contain small quantities of organic matter usually less than 0 1 wt toc and have poor hydrocarbon potential in contrast the kupferschiefer shales have excellent hydrocarbon potential with toc as high as 10 8 wt predominantly algal type ii kerogen generally thermal maturity of the organic matter is 0 6 0 9 vitrinite reflectance while locally is as high as 1 45 the kimmerian and laramian tectonic events significantly influenced the regional burial and thermal history the main subsidence of the kupferschiefer zechstein limestone complex took place during the late permian late triassic period with additional burial during the jurassic and late cretaceous hydrocarbon generation from the kupferschiefer source rocks occurred from middle triassic to late jurassic times reaching maximum rates during the jurassic the cretaceous subsidence had only a minor influence on the maturity and transformation of organic matter expulsion started between late triassic in the western part of the study area and early jurassic in the eastern part then ceased by the late jurassic early cretaceous erosion the total amount of generated and expelled hydrocarbons from source rocks was small because their thickness was limited therefore kupferschiefer shales cannot be considered as source rocks for liquid hydrocarbons but may be a potential source for gas accumulated in the zechstein limestone and rotliegend reservoirs

sulfur isotope ratios in petroleum research and exploration williston basin the three major types of crude oil in the williston basin the type i oils of the winnipeg red river system the type ii oils of the bakken madison system and the type iii oils of the tyler pennsylvanian system can be distinguished by their sulfur isotope compositions they have characteristic dgr34s values of 5 8 1 2 parts per thousand ppt 2 8 0 8 ppt and 4 0 0 7 ppt respectively highly mature oils have less typical values type ii oils which have migrated over a distance of some 150 km beyond the region of generation have maintained their characteristic dgr34s values even though sulfur may have been lost this indicates little or no interaction with reservoir sulfates under normal circumstances on the periphery of the basin type ii oils altered by water washing and biodegradation have altered dgr34s values which increase from 2 9 to 9 4 ppt with the increasing degree of crude oil degradation the bakken shales source of the type ii oils have dgr34s distribution patterns in the reduced sulfur typical of marine sediments the dgr34s values for the type ii oils match most closely the dgr34s value of organic sulfur in the black bituminous shales of the lower bakken

source rock contributions to the lower cretaceous heavy oil accumulations in alberta a basin modeling study the origin of the immense oil sand deposits in lower cretaceous reservoirs of the western canada sedimentary basin is still a matter of debate specifically with respect to the original in place volumes and contributing source rocks in this study the contributions from the main source rocks were addressed using a three dimensional petroleum system model calibrated to well data a sensitivity analysis of source rock definition was performed in the case of the two main contributors which are the lower jurassic gordondale member of the fernie group and the upper devonian lower mississippian exshaw formation this sensitivity analysis included variations of assigned total organic carbon and hydrogen index for both source intervals and in the case of the exshaw formation variations of thickness in areas beneath the rocky mountains were also considered all of the modeled source rocks reached the early or main oil generation stages by 60 ma before the onset of the laramide orogeny reconstructed oil accumulations were initially modest because of limited trapping efficiency this was improved by defining lateral stratigraphic seals within the carrier system an additional sealing effect by biodegraded oil may have hindered the migration of petroleum in the northern areas but not to the east of athabasca in the latter case the main trapping controls are dominantly stratigraphic and structural our model based on available data identifies the gordondale source rock as the contributor of more than 54 of the oil in the athabasca and peace river accumulations followed by minor amounts from exshaw 15 and other devonian to lower jurassic source rocks the proposed strong contribution of petroleum from the exshaw formation source rock to the athabasca oil sands is only reproduced by assuming 25 m 82 ft of mature exshaw in the kitchen areas with original total organic carbon of 9 or more

bakken madison petroleum systems in the canadian williston basin part 3 geochemical evidence for significant bakken derived oils in madison group reservoirs there have been two different definitions of the upper devonian mississippian bakken madison petroleum systems in the canadian williston basin early studies proposed the bakken shales as the source for oils in both the bakken formation and madison group reservoirs more recent studies suggested two separate sources for these oils thus the bakken oils were interpreted to be derived from the bakken formation shales and the madison group oils from a carbonate source within the madison group the present study utilized quantitative results of molecular markers across gasoline range light hydrocarbons saturated and aromatic hydrocarbon fractions in 122 oil samples to re evaluate the oil oil and oil source relationships the steroid and hopanoid parameters collected in this study have confirmed the diagnostic features for end member bakken and lodgepole sources whereas a range of other molecular markers revealed compositional continuums occurring between the two oil families the recognition of more extensive mixing of bakken derived oils in madison group reservoirs along a sw ne trending fault fracture zone in southeastern saskatchewan indicates focused migration pathways for bakken oils and thus upward resource potentials the results also suggest caution with the use of conventional biomarker data in oil oil and oil source correlation when the different sources concerned contain biomarkers in drastically different concentrations