reservoir characteristics and their effects on hydrocarbon accumulation in lacustrine turbidites in the jiyang super depression bohai bay basin china abstract a great difference exists between the hydrocarbon charging characteristics of different tertiary lacustrine turbidites in the jiyang super depression of the bohai bay basin east china based on wireline log data core observation and thin section analyses this study presents detailed reservoir property data and their controlling effects from several case studies and discusses the geological factors that govern the hydrocarbon accumulation in turbidite reservoirs the lacustrine fluxoturbidite bodies investigated are typically distributed in an area of 0 5 10 km2 with a thickness of 5 20 m the sandstones of the tertiary turbidites in the jiyang super depression have been strongly altered diagenetically by mechanical compaction cementation and mineral dissolution the effect of compaction caused the porosity to decrease drastically with the burial depths especially during the early diagenesis when the porosity was reduced by over 15 the effect of cementation and mineral dissolution during the late stage diagenesis is dominated by carbonate cementation in sandstones high carbonate cement content is usually associated with low porosity and permeability carbonate dissolution secondary porosity zone and primary calcite dissolution is believed to be related to thermal maturation of organic matter and clay mineral reactions in the surrounding shales and mudstone two stages of carbonate cementation were identified the precipitation from pore water during sedimentation and secondary precipitation in sandstones from the organic acid dissolved carbonate minerals from source rocks petrophysical properties have controlled hydrocarbon accumulation in turbidite sandstones high porosity and permeability sandstones have high oil saturation and are excellent producing reservoirs it is also noticed that interstitial matter content affects the oil bearing property to some degree there are three essential elements for high oil bearing turbidite reservoirs excellent pore types low carbonate cement 15 and average permeability 10 md

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 1 source rock characterization detailed mapping of the tertiary strata of the dongying depression bohai bay basin reveals that oil shales and dark mudstones in the es4 and es3 members of the eocene oligocene shahejie formation have excellent potential as petroleum source rocks regional distributions of total organic carbon content kerogen type and thermal maturation indicate that abundant mature source rocks are present in the niuzhuang sag whereas source rocks along the niuzhuang south slope are currently immature or marginally mature for the generation of conventional oils this study examined the molecular characteristics for a number of biomarker compound classes and related these to either source facies change or different burial and thermal maturation an important observation made during this study is the significant variation in the relative distributions and absolute concentrations of a wide range of aliphatic and aromatic hydrocarbon markers in the rock extracts as a function of burial depth this variation may potentially explain the uncertainty associated with the maturity assessment and genetic modeling for so called immature oils that are usually defined on the basis of alkane biomarker isomerization ratios and the presence of biomarkers with biological configurations

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

molecular and isotopic evidence for mixed source oils in subtle petroleum traps of the dongying south slope bohai bay basin abstract subtle traps have become an important petroleum play type for exploration in the dongying depression bohai bay basin eastern china the majority of the oil pools are in the middle interval of the es3 member e s 3 m of the eocene oligocene shahejie formation with the subtle traps being primarily in the lenticular basin floor turbidite sands enclosed within basin floor mudstones detailed geochemical investigation of 68 oil and rock samples from the depression reveals that in contrast to previous models the oils from the subtle traps correlate poorly with the surrounding e s 3 m source rocks while the high pristane phytane pr ph 1 and low gammacerane c30 hopane ratios in these source rocks represent a freshwater lacustrine setting the oils feature low pr ph ratios e s 4 u source rocks deposited in a brackish lacustrine setting the compound specific isotope ratios of n alkanes in the oils have intermediate values between those observed in extracts from the lower es3 e s 3 l and upper es4 e s 4 u source rocks consequently the oils in the e s 3 m subtle traps were most likely derived from mixed e s 3 l and e s 4 u sources with the contribution from the e s 4 u source rocks being predominant the oils generated from the e s 4 u source rocks must have migrated through a thick interval of the e s 3 l source rocks to reach the subtle traps in the e s 3 m through which there are no apparent structural nor stratigraphic pathways the traditional migration and accumulation model i e indigenous crude oil with short migration distance to lenticular oil pools should be revised to account for the charging of oils from e s 4 u source rocks

oil charging history constrained by biomarkers of petroleum inclusions in the dongying depression china abstract free oils and inclusion oils were extracted from the third member of the eocene shahejie formation es3 reservoir sandstones of the wells chun 51 and liang 28 in the dongying depression china and then analyzed by gas chromatography mass spectrometry gc ms results show that biomarker distribution characteristics of the free oils and their associated inclusion oils are similar in each es3 reservoir sandstones of the two wells but the distributions of pr ph ratio gammacerane hopane series and c27 c29 steranes in well chun 51 oils are strikingly different from those of well liang 28 oils however the c29 sterane ts ts tm and c31 hopane 22s 22s 22r ratios of inclusion oils are higher than those of related free oils in all the samples this may indicate that maturity indicators decreased after reaching the maximum and relatively high mature oils were trapped in petroleum inclusions comparison with biomarkers of source rock extracts shows that oils in the es3 reservoir of well chun 51 were generated from the upper es4 source rocks whereas oils in the es3 reservoir of well liang 28 were derived from the lower es3 source rocks moreover the microthermometric data and burial history indicate one oil charging episode in the es3 reservoirs of the two wells during the late neogene it s concluded that different charging histories of these two reservoirs were attributed mainly to the sealing effect of the fault

origin and mixing of crude oils in triassic reservoirs of mahu slope area in junggar basin nw china implication for control on oil distribution in basin having multiple source rocks abstract the origin of crude oils and their varied geochemical features along the western and northern slope of the mahu depression in the junggar basin has been controversial based on the molecular and isotopic geochemistry of hydrocarbons from 46 drill stem test crude oil samples and 36 core samples three oil groups i ii iii and five subgroups i 1 i 2 ii iii 1 and iii 2 have been recognized and oil source correlations have been established the subgroup i 1 oils originated mainly from lower permian fengcheng p 1 f carbonate source rocks subgroup i 2 from p 1 f mudstone source rock and group ii oils from middle permian wuerhe p 2 w mudstone source rock whose potential was underestimated in the past group iii consists of mixed oils i e subgroup iii 1 received contributions from p 1 f carbonates and p 2 w mudstones and subgroup iii 2 is a mixture of oils from p 1 f mudstones and p 2 w generated oils in order to determine the main source rocks the laboratory oil mixing experiments were carried out tricyclic terpane biomarker parameters tts were used to quantify the source contributions whole oil carbon isotope ratios were also used to verify the proportions of different oils in each mixture the results show that subgroup iii 1 oils have diverse mixing ratios in different reservoir subgroup iii 2 oils are mainly from p 1 f mudstones and p 2 w source rock contributes little finally the accumulation process of oil fields along the northern slope of the mahu depression was analyzed and the contributions from different sources were revealed this study provides an effective quantitative method to identify contributions from different lacustrine source rocks to mixed oils in the mahu depression which could be helpful in predicting location and composition of undiscovered oils

correlation and migration studies of north central sumatra oils the central sumatra basin csb is a prolific petroleum producing basin and its petroleum systems have been extensively studied the widely occurring tertiary lacustrine shale brown shale has long been recognized as the main source rock for tens of billions of barrels of oil in place the oils produced from different fields display significant variation in source characteristics that have been attributed to variation in source facies despite this generalized recognition of the oil source the links between major oil accumulations and many possible source kitchens throughout the basin have not been established as detailed oil source correlation and oil migration routes are not well defined for continued exploration in the region detailed genetic grouping and migration routes of the oils were evaluated through geochemical characterization of numerous oils from various fields in the northern part of central sumatra biomarker and carbon isotopic data indicate that the oils are quite similar geochemically but form several genetic groups on the basis of subtle but persistent differences in source facies the groupings appear geographically meaningful and show association of the different oil groups with various troughs carbazole distributions show consistency in suggesting differences in relative migration distance among the oils within each genetic group by combining the oil grouping and carbazole distributions with geological data models of migration directions and pathways for oils in north central sumatra have been constructed

test of climate leaf physiognomy regression models their application to two miocene floras from kenya and 40ar 39ar dating of the late miocene kapturo site abstract to test multiple regression models developed to predict seven variables of climate from leaf margin and size characters leaf character data were collected from modern woodland and rainforest plant communities in uganda these localities were chosen for their structural similarity to two fossil sites for which climate values were desired the test indicated that for these communities the model accurately predicts mean annual temperature however the multiple regression models overestimate seasonality of temperature and mean annual and seasonal precipitation amounts for the two modern communities reasons for the models inaccuracies may include no african analog in the non african database on which the model is based too much intraspecific variability in leaf size an important character in precipitation models and relationships between leaf form and climate that may not be well defined by multiple regression mean annual temperatures were reconstructed for two miocene paleobotanical localities from the tugen hills of the eastern rift valley kenya using leaf form data primarily margin characters the results indicate that mean annual temperatures at kabarsero 12 6 ma and kapturo 6 7 7 2 ma were essentially equivalent to temperatures at those localities today and differed little from one another the kapturo paleofloral assemblage is a deciduous woodland interpreted as indicating less available or more seasonal moisture than the kabarsero paleofloral assemblage a wet forest with west african floral affinities laser fusion 40 ar 39 ar dating of volcanic materials at kapturo provides the first control of this paleoflora bracketed by a 7 2 ma trachyte at the base of the sedimentary sequence and an age of 6 7 ma on a reworked tuff overlying the fossiliferous horizon the chronologic data places the paleofloral assemblage in stratigraphic context relative to other tugen hills units containing paleofloras and abundant vertebrate remains including hominoids

geochemical and petrological evidence for tertiary terrestrial and cretaceous marine potential petroleum source rocks in the western kamchatka coastal margin russia abstract rock eval pyrolysis and microscopic analyses of palaeogene terrestrial strata from the western kamchatka coastal margin russia indicate that good oil prone source rocks are present in both coals and shales hydrogen indices hi of up to 493 mg hc g toc are present in low maturity 0 45 r o vitrinite shale samples from the irgirninvayam river delta region whereas coals with 0 37 0 75 r o and hi of 270 310 mg hc g toc comprise potential oil gas and oil prone source rocks in the kvachincha bay tigel coastal and rassoshina napanskaya river areas the shales and coals with the highest petroleum potential were deposited in a freshwater paleo setting and consist of gelovitrinite cutinite suberinite sporinite resinite and matrix bituminite molecular geochemistry was also used to group genetically related oil samples and to postulate the likely petroleum systems in this area while the preliminary data confirm the origin of two families of oils from the palaeogene deltaic to marginal lacustrine source rocks the chemical composition of oils in two other families suggests the possible presence of marine source rocks in not yet penetrated upper cretaceous paleocene sequences of the basin

fault fracture mesh petroleum plays in the zhanhua depression bohai bay basin part 2 oil source correlation and secondary migration mechanisms abstract the chemical compositions of crude oils from over 20 oilfields in the zhanhua depression bohai bay basin were studied in order to understand their genetic relationships thermal maturity and biodegradation ranking molecular geochemical parameters indicate the presence of three possible oil families in reservoirs ranging from paleozoic basement to neogene a number of biomarker features support deposition of the source rocks for these oils under a wide range of depositional environments the majority of the oils discovered in the depression belong to the fl family and display characteristics consistent with a dominantly freshwater to slightly brackish water lacustrine source rock in the es 3 member of the shahejie formation the somewhat geographically restricted sl family oils are apparently linked to saline lacustrine carbonate evaporite source rocks distributed mostly in the upper es 4 member of the shahejie formation from the bonan gubei sag areas the thermally less mature bl family oils occur mostly within the es 1 es 2 or dongying formation reservoirs near the central sag areas and show close affinities to the interbedded or intercalating es 1 calcareous mudstones and oil shales deposited in a slightly saline to dominantly brackish water lacustrine setting the sl and fl family oils are generally mature whereas most of the bl family oils usually show low maturity oil source correlation demonstrates strong genetic relationships between the mature es 4 and es 3 source rocks of the eocene oligocene shahejie formation in the sag areas and the oils accumulated in the shallow neogene petroleum plays the geochemical data provide strong support for two sharply contrasting hydrocarbon migration scenarios 1 short distance lateral migration is dominant in the central sag areas and 2 the fault fracture mesh facilitated vertical migration and coupled with the regional porous guantao formation sand sheets makes the structural stratigraphic and lithological features over basement high blocks the focal points for petroleum accumulation therefore further exploration in this highly mature petroleum province should focus on heavy oils in the shallow neogene strata and light oils in the tight sandstones of the deep sag areas

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

relationship between the fluorescence colour of oil inclusions and thermal maturity in the dongying depression bohai bay basin china part 2 fluorescence evolution of oil in the context of petroleum generation expulsion and cracking under geological conditions abstract abundant measured data from source rocks crude oils and oil inclusions in the dongying depression were used to identify the oil generation expulsion and cracking stages under geological conditions so as to build a fluorescence evolutionary model that considers all petroleum generation expulsion and cracking processes in the model oil generation consists of three successive processes bitumen generation bitumen decomposition into oil and oil cracking these three stages are strongly controlled by thermal stress in the dongying depression kerogen decomposition into bitumen occurs at around 85 c 0 42 ro while nso compounds in the bitumen begin to crack into oil at around 120 c 0 67 ro competition between bitumen generation and nso compound cracking leads to peak bitumen generation occurring at around 130 c 0 75 ro after that the main phase of oil generation from intense bitumen decomposition occurs a transition at approximately 160 c between bitumen decomposition into oil and the inferred start of oil cracking corresponds to 4000 m 0 98 1 11 ro during the bitumen generation and main oil generation stages the fluorescence colours of the expelled oils are mainly yellow and orange and a fluorescence blueshift of the oils only occurs during the main oil generation stage in the late oil generation stage 160 c the fluorescence colours of the oils may be close to blue with increasing burial once the source rock and reservoir temperatures reach the threshold conditions for oil cracking 160 c an intense blueshift of the oil occurs in both source rocks and reservoirs and even in oil inclusions this blueshift is shown by a decreased dispersion in the fluorescence colour distribution of oil inclusions with increasing burial from multiple colours at temperatures 160 c therefore in oil prone source rocks containing type i and ii kerogen a blue fluorescence colour of oil appears to be strongly related to the secondary cracking process blue fluorescent oil inclusions generally have higher thermal maturities than oil inclusions with green or yellow fluorescence for oil prone source rocks this relationship is based on the assumption that the oil was not from a gas prone source rock and that secondary alteration processes can be excluded including migration fractionation gas deasphalting trapping fractionation and phase separation furthermore blue fluorescent oil inclusions may be a good indicator for oil prone source rocks which is significant for evaluation of source rock quality in deepwater and ultra deepwater areas in offshore basins

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

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

oil source correlation in tertiary deltaic petroleum systems a comparative study of the beaufort mackenzie basin in canada and the pearl river mouth basin in china abstract biomarker distributions in crude oil have been routinely used to investigate source rock character thermal maturity of migrated oil and lateral facies changes in the underlying source rocks in vertically drained basins case studies from tertiary deltaic systems that contain mixed oils from multiple source rocks in the beaufort mackenzie and pearl river mouth basins indicate that oil source correlation using the common fingerprint approach tends to favour the source that contains higher biomarker concentrations so biomarker concentrations as well as concentration independent yet source definitive parameters are needed to address the mass balance issues

marine oil source of the yingmaili oilfield in the tarim basin abstract although a large amount of petroleum has been discovered in the tarim basin the origin of the oils is still disputed yingmaili oilfield was selected as a case study to further examine hydrocarbon generation and accumulation in the basin detailed geochemical studies were conducted to unravel the formation mechanisms the oils in the field correlate well with middle upper ordovician o 2 3 rocks or similar rocks oil oil and oil source rock correlation by maturity parameters of saturate and aromatic hydrocarbons suggest that the yingmaili and adjacent oils are primarily comparable to source rocks deeper than 6000 m the results also showed that carbonates might be important potential source rocks as indicated by a relatively high abundance of aromatic sulfur compounds and relatively high c 29 c 30 hopane and c 35 c 34 hopane ratios of the oils which are typical features of carbonate source rocks we suggest the oil from wells yg2 and yg2 1c are more suitable to be end members from the o 2 3 source rocks or similar rocks than the oil from well ym2 as previously suggested we also suggest that the previous model of hydrocarbon migration along the ordovician unconformity should be revised

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 2 evidence for significant contribution of mature source rocks to immature oils in the bamianhe field the chemical compositions of 28 representative crude oils and oil sand samples collected from the bamianhe region of the bohai bay basin eastern china were studied in detail in order to understand their genetic relationships biodegradation ranking and thermal maturity level molecular geochemical parameters indicate the presence of one single oil family in the cenozoic reservoirs a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns the extremely low maturity levels of these immature oils as indicated by sterane isomerization ratios were not supported by other maturity parameters the genetic relationship between the oils and the es4 and es3 members of the eocene oligocene shahejie formation present in the deeper part of the niuzhuang sag but not those along the niuzhuang south slope was suggested using a wide range of molecular parameters variation in the sterane concentrations observed from potential source rocks with different maturity levels in the study area suggests a high probability of migration contamination of mature oils by immature bitumens along migration pathways or from intra reservoir shales variation in the level of oil biodegradation could also create anomalies in the use of gross oil compositions as an indicator of oil maturity although the recent rapid subsidence of the bohai bay basin and the saline depositional environment of one of the potential source rocks favor oil generation at relatively low maturity levels most of the economic oils discovered in the bamianhe region appear to have derived from conventionally mature source rocks but contain lower maturity fluids admixed with them

origin and quantitative source assessment of deep oils in the tazhong uplift tarim basin abstract a large amount of deep oil has been discovered in the tazhong uplift tarim basin whereas the oil source is still controversial an integrated geochemical approach was utilized to unravel the characteristics origin and alteration of the deep oils this study showed that the lower cambrian oil from well zs1c 1x was featured by small or trace amounts of biomarkers unusually high concentration of dibenzothiophenes dbts high 34 s of dbts and high 13 c value of n alkanes these suggest a close genetic relationship with the cambrian source rocks and tsr alteration on the contrary the middle cambrian oils from well zs1 2a were characterized by low 13 c of n alkanes and relatively high 34 s of individual sulfur compounds and a general v shape of steranes indicating a good genetic affinity with the middle upper ordovician source rocks the middle cambrian salt rock separating the oils was suggested to be one of the factors responsible for the differentiation it was suggested that most of the deep oils in the tazhong uplift were mixed source based on biomarkers and carbon isotope which contain tsr altered oil in varied degree the percentage of the oils contributed by the cambrian lower ordovician was in the range of 19 100 average 57 controlled by several geological and geochemical events significant variations in the 34 s values for individual compounds in the oils were observed suggesting a combination of different extent of tsr and thermal maturation alterations the unusually high dbts concentrations in the tazhong 4 oilfield suggested as a result of mixing with the zs1c oil 1x and lower ordovician oils based on 34 s values of dbt this study will enhance our understanding of both deep and shallow oil sources in the tazhong uplift and clarify the formation mechanisms of the unusually high dbts oils in the region

reconstruction of early triassic ocean redox conditions based on framboidal pyrite from the nanpanjiang basin south china abstract widespread oceanic anoxia has been implicated as an important factor in the ptb permian triassic boundary mass extinction and the delayed recovery of early triassic marine ecosystems an investigation of framboidal pyrite in the bianyang section nanpanjiang basin south china suggests that euxinia dysoxia peaked during the induan late smithian to earliest spathian and late spathian these anoxic episodes show a relationship albeit imperfect to major episodes of climatic warming during the early triassic that were associated with intensified oceanic stratification reduced marine productivity and organic carbon sinking fluxes as well as diminished burial fluxes of organic carbon and reduced sulfur in contrast intervals of better oxygenated marine conditions were associated with episodes of relative climatic cooling during the early to middle smithian and mid spathian the degree of ventilation of the thermocline region in particular had a profound effect on marine biotas with intervals of improved ventilation resulting in increased global diversity among ammonoids and conodonts and increased local abundance of foraminifera in the nanpanjiang basin these observations suggest that oceanic redox fluctuations played an important role in the delayed recovery of early triassic marine ecosystems and specifically that episodic expansion of oceanic oxygen minimum zones omzs resulted in repeated setbacks to the recovery process a pattern that persisted until the late spathian

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

new quantitative palaeocolimate data for the late cretaceous arctic evidence for a warm polar ocean abstract physiognomic analysis of four taphofloras one from the coniacian of n alaska one from the coniacian of kamchatka one from the turonian of kamchatka and one from the turonian of novaya sibir island using the clamp technique of wolfe 1993 yielded quantitative data on the mean annual warm month mean and cold month mean temperatures the length of the growing season mean annual precipitation mean growing season precipitation mean monthly growing season precipitation and the precipitation during the three consecutive driest months these new results represent the first application of multivariate statistical analysis of foliar physiognomy to determine palaeoclimatic parameters clamp to arctic cretaceous floras and demonstrate its robustness even in the context of vegetation which has no living analogues these new estimates were comparable to those from previous quantitative or qualitative sedimentological or palaeobotanical data where they were available but offer greater measurable precision the results also suggest that an arctic ocean with a winter surface temperature of approximately 6 c maintained n alaska coastal temperatures above freezing locally reversing the equator to pole temperature gradient a phenomenon not seen in the northern proto pacific this anomalously warm arctic ocean could have been produced by marine poleward heat transport precipitation in alaska kamchatka and novaya sibir island was predicted to have been high e g 1760 mm yr in the coniacian of n alaska reflecting a very weak polar high pressure cell and substantially different precipitation patterns to present

geochemistry of petroleum systems in the niuzhuang south slope of bohai bay basin part 3 estimating hydrocarbon expulsion from the shahejie formation abstract based on the distribution and geochemical characteristics of potential source rocks in the niuzhuang and guangbei sags and the niuzhuang south slope bohai bay basin the quantities of hydrocarbons expelled from the eocene oligocene shahejie formation were evaluated using a mass balance approach the results confirm that most of the hydrocarbons in the study area were generated and expelled from the shahejie formation source rocks in the niuzhuang sag the algae rich saline brackish water lacustrine es 4 oil shales of the shahejie formation from the bamianhe to wangjiagang region along the niuzhuang south slope exhibit excellent potential for early hydrocarbon generation but they are not the major source for proven oil reserves in the bamianhe region the source rocks for most of the known oil reserves in the study area occur in the es 4 mudstones in the deep part of the niuzhuang sag thus the commonly assumed origin of so called immature oils from source rocks shallower than the conventional oil window in this area needs revision

using fossil leaves as paleoprecipitation indicators an eocene example estimates of past precipitation are of broad interest for many areas of inquiry including reconstructions of past environments and topography climate modeling and ocean circulation studies the shapes and sizes of living leaves are highly sensitive to moisture conditions and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations however when tested on extant forests this method has consistently overestimated precipitation we present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set the significant relationship that results in addition to having value for paleoclimatic reconstruction refines understanding of the long observed positive relationship between leaf area and precipitation seven precipitation estimates for the eocene of the western united states are revised as lower than previously published but remain far wetter than the same areas today abundant moisture may have been an important factor in maintaining warm frost free conditions in the eocene because of the major role of water vapor in retaining and transporting atmospheric heat

fault fracture mesh petroleum plays in the zhanhua depression bohai bay basin part 1 source rock characterization and quantitative assessment abstract in the prolific zhanhua depression of the bohai bay basin eastern china over 76 of the proven petroleum reserves occur in the neogene guantao and minhuazhen formations detailed geological and geochemical mapping of the phanerozoic strata in this area reveals that oil shales and dark mudstones in the es4 es3 and es1 members of the eocene oligocene shahejie formation have excellent potential as petroleum source rocks regional distributions of total organic carbon content kerogen type and thermal maturation indicate that abundant mature source rocks are present in several discrete sag areas bounded by extensive basement related fault networks in contrast source rocks along the paleo topographic highs are currently immature with respect to the generation of conventional oils this study examined the key molecular characteristics for the common isoprenoid hopanoid and steroid biomarkers in relation to source facies variations in lacustrine sediments the hydrocarbon source potential and expulsion efficiency for each of the source rock units were evaluated which integrated the source rock characteristics with regional thermal subsidence and sediment burial an important observation made during this study is the striking contrast between the source potential and proven oil reserves within each stratigraphic section illustrating how significant the migration of hydrocarbon fluids derived from deep mature source kitchens through over 2000 m of fine grained formations must have been to form several giant oil accumulations in the shallow strata these results support the concept of the neogene fault fracture mesh petroleum plays proposed by zhang et al 2004 marine petroleum geology 21 651 668 and the vital role that the faults and fracture systems have in controlling hydrocarbon migration conduits and accumulation habitat in this rift basin

relative role of accommodation zones in controlling stratal architectural variability and facies distribution insights from the fushan depression south china sea in sedimentary basins a better understanding of the controlling effect of accommodation transfer zones on stratal architecture and facies distribution can improve the success rate of locating hydrocarbon reservoirs the fushan depression is a half graben rift sub basin located in the southeast of the beibuwan basin south china sea in this study comparative analysis of seismic reflection palaeogeomorphology fault activity and depositional facies distribution indicates that three different types of inner basin slopes i e multi level step fault slope in the western area slope flexure zone in the accommodation zone area and gentle slope in the eastern area were developed along the southern slope of the fushan depression together with a large scale accommodation zone located at the intersection of the western and eastern fault systems further analysis shows that the accommodation zone played an important role in controlling not only stratal architectural variability in the southern slope but also depositional facies distribution in the accommodation zone area during the high stand stage the deposition of depositional systems was mainly controlled by sediment supply and the nw trending transfer faults major drainage systems entered the fushan depression through the accommodation zone along the direction of sediment supply and sedimentary flow paths were parallel to the accommodation zone axis with sedimentary flows constrained to the adjacent areas of the nw trending transfer faults by contrast during the low stand stage the transfer faults had little control over depositional facies distribution and the sublacustrine fan sediments diverted away from the accommodation zone and flew down along the northeast oblique to the accommodation zone axis the flow division in the lowstand stage might be greatly influenced by flow type and topography in addition the accommodation zone area demonstrated unique hydrocarbon accumulation models different from the western and eastern areas suggesting that the future exploration should be conducted at different levels in the fushan depression

fault fracture mesh petroleum plays in the jiyang superdepression of the bohai bay basin eastern china abstract based on the results of laboratory simulation experiments and field observations the concept of fault fracture mesh petroleum play is proposed to explain the secondary petroleum accumulations in the neogene reservoirs of the jiyang superdepression bohai bay basin eastern china a well defined fault fracture mesh petroleum play usually contains three basic elements an oil source network at the base a transient storage for migrating hydrocarbons in the middle and a petroleum accumulation network at the top the oil source network provides fairways for hydrocarbons generated in a deep source to migrate vertically upward to shallow strata often consisting of primary faults and fracture zones and or regional unconformities in direct contact with mature petroleum source beds and secondary faults intercepting lenticular fluvial sandstones the transient storages for migrating hydrocarbons include the thick porous mat or sheet like sandstones deposited under the fluvial braided stream setting and occurring over relatively large geographic areas these sandstones serve as temporary storage spaces through which deep sourced petroleum fluids migrate further either laterally or vertically into shallower reservoirs the upper petroleum accumulation network provides suitable habitats for oil and gas accumulation comprising structural lithologic stratigraphic and combination traps the jiyang superdepression of the bohai bay basin hosts several excellent examples of the fault fracture mesh petroleum play where hydrocarbons in the neogene reservoirs were derived either directly from eocene oligocene source rocks or from the redistribution of pre existing oil accumulations in the deeper reservoirs reactivation of basement involved faults and regional unconformities provided conduits for channeling the pre neogene hydrocarbons into the shallow strata the magnitudes and frequencies of the faulting activities and their relative timings to those of peak oil generation and expulsion were critical factors for controlling the quantities of hydrocarbons transmitted to the neogene strata the thick sandstones and conglomerates in the lower guantao formation acted as excellent transient storages for the deep sourced oils which were then trapped to form accumulations in the shallow structural lithologic stratigraphic and combination traps of the guantao ng minhuazhen nm formations with the recent discovery of several giant oilfields in the shallow neogene reservoirs both onshore and offshore bohai bay basin the proposed fault fracture mesh petroleum play concept helps the exploration geologists to modify and clarify long held traditional concepts of petroleum play types in this basin and expand upon the new exploration horizons of the shallow subtle petroleum traps

chemometric differentiation of crude oil families in the southern dongying depression bohai bay basin china abstract fifty seven crude oil samples from the southern dongying depression were selected for detailed geochemical analysis high c26 c25 tricyclic terpanes 0 81 1 26 and low c31 homohopane r c30 hopane 0 15 0 26 ratios indicate that the oils are from lacustrine source rocks the presence of c30 4 methyl 24 ethylcholestanes and c30 tetracyclic polyprenoids imply the contribution of microalgal organic matter large variations of depositional environment related biomarker parameters suggest differences in organofacies and water environment four genetically distinct oil families were differentiated by chemometrics of hierarchical cluster and principal component analyses using the parameter dataset of three isotope ratios and 15 molecular parameters all related to source and depositional environment family i is mature and does not match any available source rocks the inferred source rock contains microalgal material that could produce large quantities of wax c29 steranes and tricyclic terpenoids in a reducing salinity stratified water column family ii is characterized by a strong phytane dominance relatively high gammacerane and c35 homohopanes and low diasterane and 4 methyl sterane contents it has high values of sterane hopane s h 1 67 4 14 c35 c34 homohopane c35h c34h 0 81 1 66 and gammacerane c30 hopane g c30h 0 57 1 13 and low pristane phytane pr ph 0 30 0 59 suggesting that the inferred source rock is the upper es4 interval family iii has characteristics distinct from families i and ii low s h 0 15 0 27 c35h c34h 0 39 0 49 and g c30h 0 03 0 12 ratios and high pr ph 0 48 1 90 c30 4m c29 20r 0 54 1 18 and c30 tetracyclic polyprenoid 0 54 0 66 ratios suggesting that the source rock is the lower es3 interval the family iv oils are compositionally in between the ranges of families ii and iii oils and in line with them in plots of geochemical parameters we suggest that family iv consists of mixed oils derived from the upper es4 and lower es3 intervals family ii has a relatively low thermal maturity and the inferred source rock may be located in the niuzhuang sag and or the southern gentle slope zone family iii is mature and its inferred source rock may be situated in the lijin and boxing sags the upper es4 and lower es3 source rocks in the three sags contribute the crude oils of family iv that occurs in the middle and eastern parts of the southern dongying depression

quantitatively predicting the thermal maturity of oil trapped in fluid inclusions based on fluorescence and molecular geochemical data of oil inclusions in the dongying depression bohai bay basin china the fluorescence characteristics of individual oil inclusions and molecular composition analysis of oil inclusions in 20 eocene sandstone samples from the dongying depression were used to assess the relationship between the fluorescence colors of the oil inclusions and their thermal maturity the oil inclusions from the shahejie formation member iii middle submember member iii lower submember and member iv upper submember samples primarily have yellow fluorescence colors 500 nm wavelength of the maximum intensity max 590 nm whereas the oil inclusions in the shahejie formation member iv lower submember reservoir sample only have blue fluorescence 440 nm max 500 nm the molecular maturity parameters from steranes hopanes and aromatic hydrocarbons showed that the oil inclusions with yellow fluorescence colors have relatively low thermal maturities within a narrow range 0 75 0 82 vitrinite reflectance equivalent requ which is significantly lower than that of the sample containing oil inclusions with blue fluorescence colors 1 26 requ the yellow fluorescent oil was interpreted to be related to the main oil generation and expulsion process whereas the blue fluorescent oil was mainly controlled by the thermal cracking process of c14 aromatic hydrocarbons in source rocks reservoirs and oil inclusions this study demonstrates that the fluorescence colors of oil inclusions may be good indicators of thermal maturity in oil systems charged from oil prone source rocks and for the first time makes it possible to quantitatively predict the thermal maturity of oil inclusions based on their fluorescence characteristics however biodegradation water washing phase separation and trapping fractionation should be considered before using this correlation because these processes can also influence fluorescence colors

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