bicadinanes and related compounds as maturity indicators for oils and sediments abstract biomarker maturity indices have proven useful in petroleum exploration to assess the thermal maturity of oils and sediments however their application to deltaic petroleum systems is often hindered by source and diagenetic interferences recently we have described several new maturity indices based on the catagenetic products of the plant biopolymer polycadinene these indices should be largely immune to biochemical effects during diagenesis since little microbial activity will remain at temperatures sufficient to dissociate the polymer here we report changes in five polycadinene related maturity indices through a marine fluvio deltaic depositional sequence in the south sumatra basin indonesia the results are compared with the maturity required for oil generation as estimated by kinetic modelling and with conventional maturity indicators such as sterane epimerisation and the methyl phenanthrene index the data confirm that the polycadinene indices are less subject to source and diagenetic interferences than those based on the sterane and aromatic hydrocarbon distributions values for several of the indices have also been measured for 17 tertiary oils from southeast asia papua new guinea new zealand and australia contrary to an earlier report the bicadinane maturity indicator bmi 1 continues to change into the oil window and hence may be useful in ranking the relative maturity of oils as well as sediments the bmi 1 values for two oils having unusually low sterane maturities are normal leading us to question whether the low sterane maturity of many tertiary age oils is due to their source rocks having been heated more rapidly than those of older oils

conflicting sterane and aromatic maturity parameters in neogene light oils eastern chepaizi high junggar basin nw china abstract the saturated and aromatic hydrocarbon maturity characteristics of crude oils from the eastern chepaizi high in the junggar basin of northwest china were analyzed in detail the results show that sterane maturity parameters for light oils from the neogene shawan formation differ from other maturity parameters sterane c 29 20s 20s 20r and c 29 ratios indicate low maturity while aromatic hydrocarbons indicate high maturity we infer that light oils from the shawan formation have higher maturity than cretaceous and jurassic crude oils and were generated at equivalent vitrinite reflectance of 0 9 1 2 it can be concluded that the shawan light oils originated mainly from deeply buried highly mature jurassic source rocks southeast of sikeshu sag southwest of shawan sag and west of huomatu anticline belt during upward migration crude oils generated from jurassic source rock dissolved less mature cretaceous bitumen resulting in a mixture with apparently conflicting parameters phase fractionation during migration also could have contributed to the anomalously low sterane maturity parameters

early generation of 20s 5α h 14α h 17α h and 5α h 14β h 17β h steranes in low salinity lacustrine shales abstract a quantitative sterane biomarker study was conducted on a series of paralic freshwater lacustrine shale samples ranging in maturity from immature to near oil window maturity taken from section 3 of the shahejie formation es3 in the liaohe basin n e china concentrations of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes remain nearly constant throughout the sample suite however the decrease in the absolute concentrations of the 20r 5 h 14 h 17 h c 29 steranes with increasing maturity results in an increase in the conventionally defined maturity parameters 20s 20 s 20r and sterane ratios in addition the data suggest that relatively early generation of 5 h 14 h 17 h 20s and 5 h 14 h 17 h steranes has occurred in lacustrine sediments with a vitrinate reflectance 0 3 r o the data provide strong support for the major importance of relative thermal stability of epimers but do not exclude the possibility of isomerization as a viable mechanism for production

distribution and isomerization of c31 c35 homohopanes and c29 steranes in oligocene saline lacustrine sediments from qaidam basin northwest china abstract the 22s 22s 22r ratios for c 31 c 35 homohopanes and the 20s 20s 20r ratio for c 29 steranes were measured by gas chromatography mass spectrometry gc ms on six oligocene saline lacustrine rock samples from a borehole located in the western qaidam basin northwest china these ratios vary significantly and irregularly with burial depth from 2831 m to 3054 m around the threshold of the oil generation window in addition 22s 22s 22r ratios also vary substantially among different homologs within the same sample generally decreasing from c 31 to c 35 homohopanes the distribution patterns of homohopanes for the six samples are unusual such as c 31 32 c 33 c 34 35 or c 31 c 32 c 33 34 35 or c 31 32 c 33 34 35 all of these observations can be mainly ascribed to the release of bound hopanes and steranes from kerogen and other macromolecules the 22s 22s 22r ratios of c 31 c 32 and c 33 homohopanes decreased while that of c 34 homohopanes increased for two samples yhs1 and yhs6 after pyrolysis at low temperatures 180 270 c a major reversal of 20s 20s 20r ratio for c 29 steranes was observed at 240 c for sample yhs1 but at 270 c for sample yhs6 the distributions of homohopanes for these two samples after pyrolysis changed from their original patterns toward the normal pattern c 31 c 32 c 33 c 34 c 35 these results reflect the influences of thermal degradation and direct isomerization of the free biomarkers and the release of bound biomarkers from kerogen and other macromolecules during pyrolysis

sterane isomerisation and moretane hopane ratios in crude oils derived from tertiary source rocks the extent of sterane isomerisation reactions and the moretane hopane ratios of 234 crude oils taken world wide from a wide variety of source rocks of differing geological ages have been measured this data indicates that in 78 crude oils derived from tertiary source rocks sterane isomerisation reactions as determined by the 20s 20s 20r ration of the c29 5 h 14 h 17 h normal steranes and the c29 iso iso normal ratio iso 5 h 14 h 17 h are mainly incomplete and sometimes considerably so in addition the same crude oils have 17 h 21 h moretane 17 h 21 h hopane ratios which are significantly greater predominantly in the range 0 10 0 30 than those of crude oils derived from older mature source rocks mainly less than 0 1 this data for crude oils lends support to the hypothesis proposed by mackenzie and mckenzie 1983 for source rock extracts that the time temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in tertiary sediments is generally insufficient despite generation of crude oil at relatively high temperatures an alternative hypothesis is that the incomplete sterane isomerisation of tertiary crude oils may be due to generation of these crude oils from their deltaic land plant containing source rocks under low heating conditions a third hypothesis proposes that the tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration although possible in particular instances such a mechanism does not appear to be generally applicable since in that case the phenomenon would then appear to be restricted to the tertiary the higher moretane hopane ratios of the tertiary crude oils could suggest that constraints similar to those applying in sterane isomerisation also operate in the conversion of moretane to 17 h hopane

geochemical evaluation of upper cretaceous fruitland formation coals san juan basin new mexico and colorado geochemical analyses of coal samples from the upper cretaceous fruitland formation in the san juan basin of new mexico and colorado were used to determine thermal maturity type of kerogen and hydrocarbon generation potential mean random vitrinite reflectance rm of the fruitland coal ranges from 0 42 to 1 54 rock eval pyrolysis data and saturated to aromatic hydrocarbon ratio indicate that the onset of thermal hydrocarbon generation begins at about 0 60 rm and peak generation occurs at about 0 85 rm several samples have hydrogen index values between 200 and 400 indicating some potential for liquid hydrocarbon generation and a mixed type iii and ii kerogen pentacyclic and tricyclic terpanes steranes aromatic steroids and methylphenanthrene maturity parameters were observed through the complete range of thermal maturity in the fruitland coals aromatic pentacyclic terpanes similar to those found in brown coals of australia were observed in low maturity samples but not found above 0 80 rm n alkane depleted coal samples which occur at a thermal maturity of approx 0 90 rm paralleling peak hydrocarbon generation are fairly widespread throughout the basin depletion of n alkanes in these samples may be due to gas solution stripping and migration fromthe coal seams coincident with the development of pressure induced fracturing due to hydrocarbon generation however biodegradation may also effect these samples

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

unusual biomarker maturation ratio changes through the oil window a consequence of varied thermal history abstract saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas condensate window to high vitrinite reflectances r o 1 16 in mature marine and lacustrine mesozoic clastic samples from a south african basin two of the ratios reverse above r o 0 9 these unusual maturation effects result from isolated periods of high rates of maturation increase the basin cooled regionally after the break up of gondwana but high heating rates prevailed during the late cretaceous early tertiary as africa moved across a hotspot and again in the late tertiary as a result of a possible hotspot and hydrothermal event

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

a forward modeling strategy for balancing cross sections 1 a strategy to balance cross sections of complex structures is documented and illustrated by the interpretation of a compressional structure in the deep water gulf of mexico the strategy is applicable to structures formed in sedimentary rocks under low temperatures in both compressional and extensional environments and involves the comparison of the observed structure with simple balanced forward models forward models generated using fault related fold theory help in understanding the processes and kinematics involved in the deformation further forward models are completely constrained and easy to balance whereas it is difficult to balance data therefore forward models are useful in evaluating ideas without completely solving the structure models are constructed assuming parallel behavior preservation of layer thickness no net distortion where layers are horizontal and conservation of bed length unmetamorphosed sedimentary rocks are generally observed to deform obeying the assumptions of parallel behavior in field map well and seismic data

estimating kinetic parameters for organic reactions from geological data an example from the gippsland basin australia abstract an examination has been made of strategies to estimate kinetic parameters activation energy and pre exponential factor for organic reactions from geological data least squares regression and a direct search algorithm were applied to a set of sterane isomerization data from volador 1 an oil exploration well in the gippsland basin australia the best fit kinetic parameters depend on the number and quality of data points used as well as the thermal history because both the data and thermal history have intrinsic uncertainties a range of kinetic parameters can explain the data to a specified level of misfit for reasonable variations in the thermal history the effective kinetic parameters for the data from volador 1 are e 75 100kj mol and a 10 1 10 5 s it is observed that the range of acceptable parameter pairs has a linear relation of the form ln a a be and the slope b is dependent on the thermal history small departures of either parameter from this relation lead to significant variations in the predicted values for the reaction progress

biomarker signatures of sinian bitumens in the moxi gaoshiti bulge of sichuan basin china geological significance for paleo oil reservoirs abstract chen et al precambrian research 296 1 19 2017 presented a biomarker study on solid bitumens and associated source rock extracts from the moxi gaoshiti bulge of the sichuan basin sw china biomarker characteristics revealed that the solid bitumens and related paleo oils belong to the same group and are well correlated to source rocks of the neoproterozoic dengying and lower cambrian qiongzhusi formations the thermal maturity of solid bitumens and their migration direction have been assessed it appears that these interpretations are internally inconsistent and are also inconsistent with much published geochemical data and the biomarker data are over interpreted and flawed

geochemical characteristics of oils from the sirikit oilfield phisanulok basin thailand abstract twelve oils from the sirikit field of the phisanulok basin thailand have been examined to determine the nature of their source materials depositional environment relative maturity and extent of biodegradation the geochemical analyses performed in this study suggested that all of the oils were derived from similar types of organic source matter consisting of a mixture of bacterial algal and higher plant material the sterane contents of the oils were relatively low and conventional maturity parameters based on sterane ratios suggested the oils were relatively immature extensive strike slip faults in the phisanulok basin may have led to rapid burial of the sediments during deposition preventing these ratios from having attained their equilibrium ratios

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

eohimalayan fold and thrust belt implications for the geodynamic evolution of the nw himalaya india 1 in the himalayas the eocene deformation phase is called the eohimalayan event by means of a forward and backward balanced cross section along a classical traverse through the tethyan himalaya we constrain eohimalayan sw vergent folding and sw directed thrusting in a belt above a basal thrust at 10 km depth this thrust is located at the structural position of the southern tibetan detachment system with a ne directed normal sense displacement suggesting miocene reactivation of a major eocene contractional fault stepwise palinspastic restoration demonstrates that this eocene contractional fault has been subsequently openly folded due to southwestward propagation of the himalayan thrust system

suppression of thermal maturity indicators in lacustrine source rocks a case study of dongying depression eastern china abstract the paleogene shahejie formation of the dongying depression in eastern china is a unique region and can offer insights into the suppression of thermal maturity in a large set of successive lacustrine shales this study focuses on the paleogene shahejie formation of n 38 well in the dongying depression the unusual distribution of thermal maturity indicators such as vitrinite reflectance vro and c29 sterane thermal parameters was investigated through geochemical analysis the research interval 2770 3376 m was divided into three parts the upper part of es32 2770 2990 m the lower part of es32 2990 3190 m and the es31 3190 3376 m the es31 mainly contained organic matter type i and some type ii which included mostly good and excellent source rocks meanwhile the upper es32 mainly contained organic matter type iii which included mostly poor and moderate source rocks the parameters g c30h c35h c31 35h c31m c31h c29 20s 20s 20r c31 22s 22s 22r and c32 22s 22s 22r showed a different distribution corresponding to the different lake sedimentary environments various organic facies were developed at the different evolution stages of the lake basin which showed a noticeable influence on the parameters the thermal maturity indicator vro and molecular thermal parameters such as c29 20s 20s 20r c31 22s 22s 22r c32 22s 22s 22r and c31m c31h presented abnormal distributions in the large set of lacustrine shales especially in the es31 this observation suggested suppression of several thermal maturity indicators vro suppression positively correlated well with the corrected hydrogen index and alginite content in maceral composition the high content of alginite group was considered to be the primary reason behind the evident negative vro anomaly

the effects of varying tissue preservation on the aliphatic hydrocarbons within a high volatile bituminous coal detailed petrographic analyses of the barrett coal an upper permian high volatile bituminous coal in the hunter coalfield australia reveal cycles of peat formation defined by the tissue preservation index these cycles correspond to coal plies that are separated by dirtbands the petrographic cyclicity is also manifested by a corresponding stratigraphic cyclicity in the biomarker composition of the extracted aliphatic hydrocarbons higher amounts of hopanes and lower carbon preference index values n c22 to n c30 show greater bacterial contribution in samples characterised by low values of tissue preservation index the inherited biodegradation signal from the diagenetic stage has now been partially diluted by the generation of new hydrocarbons from the macromolecule the c31 22s22s 22r hopane and c29 20s20s 20r sterane ratios show least variation through the seam the homohopane epimer ratios have attained equilibrium whilst the hopane moretane ratios are typical of coals with unsupressed vitrinite reflectance of 0 65 however other hopane and sterane maturity ratios appear slightly affected by the degree of preservation of organic matter the c29 and c29 20s20s 20r sterane ratios were not found to be useful for maturity comparisons with other coals because of the low values average 0 18 and 0 43 respectively due to heating rate effects these and other biomarker distributions are syndepositional features of the coal precursor and therefore are controlled by the environmental conditions during the stage of peat accumulation and its subsequent coalification all these changes are evident in a coal member only 2 2 m in thickness the petrographic and geochemical evidence suggest that the environmental affinity of the barrett coal is that of a delta plain depositional setting

biomarker and n alkane isotope profiles for tertiary oils relationship to source rock depositional setting abstract biomarker and n alkane isotope profiles have been measured for 29 late cretaceous tertiary oils from se asia china papua new guinea new zealand and the u s a the results are interpreted with respect to six kinds of source rock depositional setting fluvio deltaic fd freshwater transitional tr lacustrine lac saline lacustrine sal marine deltaic md and marine carbonate mc a comparison of biomarker and n alkane isotope results suggests that parameters such as the oleanane hopane ratio may overestimate the higher plant contribution to marine oils the abundance of bicadinanes is much more variable than that of oleanane probably because of a specific association with the highly resinous dipterocarp hardwoods of se asia however traces do occur in an oil from outside the paleogeographic range of the dipterocarp family confirming that there is also a more general angiosperm source the bicadinane isomeric distribution is shown to depend on maturity leading to new maturity parameters which are resistant to even very heavy biodegradation retention indices based on the regular hopane series are provided for the main bicadinane and methyl bicadinane isomers and for a group of oleanane related triterpanes of unknown structure the presence of the latter compounds may indicate locally deposited as opposed to transported higher plant matter in the source source rock depositional setting is the primary control on the shape of the n alkane isotope profile with negatively sloping curves being characteristic of fd and tr oils and flat or positively sloping curves typical of marine oils the difference is probably related to the bacterial reworking of higher plant matter in the fd environment a slight isotopic anomaly at n c 17 correlates with the abundance of algal derived steranes and may indicate a minor marine contribution to the source of an fd oil

biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of opalinus clay and posidonia shale in northern switzerland abstract samples from two argillaceous formations opalinus clay and posidonia shale of near identical maturity from northern switzerland were subjected to a geochemical characterisation of organic matter and to confined system pyrolysis experiments throughout the study area the characteristics of organic matter are similar indicating a spatially homogeneous sedimentary facies posidonia shale contains marine organic matter deposited in a reducing environment while a predominantly terrigenous source and a more oxidising environment of deposition was identified for opalinus clay in the western and central parts of the study area organic maturity is close to the onset of oil generation in the easternmost part a higher maturity has been reached due to a deeper burial below thick tertiary molasse deposits isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 c over 24 h bitumen yields increase along similar pathways for both opalinus clay and posidonia shale but the maximum values are displaced by 10 20 c data pertaining to maturity were determined from gc ms analyses of saturated hydrocarbons and specific attention was given to c 29 sterane and c 32 hopane isomerisation ratios the evolution of these parameters with rising temperature is slightly different in the two formations which is attributed to the contrasting organic facies the pyrolysis data together with literature data from natural basins were used to calculate kinetic parameters for c 29 sterane and c 32 hopane assuming a single step isomerisation scheme according to the arrhenius law the resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data activation energies are similar in both formations while the frequency factors are up to one order of magnitude higher for posidonia shale when compared to opalinus clay for the benken site maximum temperature during cretaceous burial was calculated on the basis of the kinetic data using the tti approach the resulting temperatures of 75 80 c are 5 10 c below those derived in the literature from apatite fission track analysis vitrinite reflectance and basin modelling

biomarker geochemistry of crude oils and lower paleozoic source rocks in the tarim basin western china an oil source rock correlation study abstract in order to select biomarker parameters that have potential to quantitatively distinguish between the cambrian lower ordovician and upper ordovician source rocks in the tarim basin with a total organic carbon content 0 5 42 lower paleozoic shale samples were collected from a number of wells and outcrops in the tarim basin northwestern china the biomarkers in the extracts of the source rocks were analyzed by gas chromatography mass spectrometry the results show that c23 and c30 were dominant in the tricyclic terpanes and pentacyclic triterpanes respectively and c27 and c29 were both dominant in c27 29 steranes of the source rock samples the distribution of n alkanes isoprenoids and terpanes indicate that the source rock samples have been slightly to moderately biodegraded and they originated from a reducing depositional environment with considerable marine algal input in comparatively upper ordovician source rock samples presented lower values of c28 c29 regular steranes and higher values of c29 20s 20s 20r and c29 abnormally lower values of c29 20s 20s 20r and c29 were observed in the cambrian lower ordovician strata the set of data in this study show that homohopane index including c31homohopane c30hopane c31 35homohopanes c30hopane and the ratios related to the triaromatic steroids including c26 20s c28 20s tas c27 20r c28 20r c26 20r c27 20s c28 20s and c28 c26 c27 tas could serve as potential biomarker parameters to distinguish between the two groups of source rocks in the tarim basin the values of those parameters in above order in cambrian lower ordovician source rocks were 0 3 0 5 0 85 and 0 8 1 9 1 2 respectively the correlation between the source rock samples and 19 oils obtained from the tadong tabei and tazhong uplifts in the tarim basin show that most of the oils in tabei uplift are probably from upper ordovician source rocks the oils in tadong uplift are more likely from cambrian lower ordovician source rocks and the tazhong uplift is more like a mixed oil region with oils from both of the two groups of source rocks

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

trends in thermal maturity indicators for the organic sulfur rich eagle ford shale abstract thermal maturity is critical to evaluate petroleum systems and to interpret biomarker results for paleoenvironmental and geobiology studies many thermal maturity indices were developed for marine source rocks containing type ii kerogen but their behavior in organic sulfur rich source rocks requires more investigation here we present geochemical analyses of whole and extracted rock isolated kerogen and extractable organic matter across a natural thermal maturity sequence of the upper cretaceous eagle ford shale to evaluate the behavior of maturity parameters in organic sulfur rich source rocks the samples have similar mineralogy and trace element composition minimizing potential facies effects on thermal maturity parameters atomic h c ratios of isolated kerogen extractable organic matter yield and programmed pyrolysis results show that the samples range from the pre oil through dry gas generation windows programmed pyrolysis data and kerogen elemental ratios show that the immature samples host both type iis atomic sorg c 0 04 and sulfur rich type ii kerogen kerogen sorg c 0 03 0 04 while samples with lower kerogen sorg c ratios kerogen sorg c

tertiary deltaic and lacustrine organic facies comparison of biomarker and kerogen distributions abstract biological marker and kerogen compositional data in tertiary deltaic and lacustrine settings were compared and contrasted the two settings are represented by a coals and organic carbon rich shales in a ick deltaic sequence from the far east constituting three distinct organic facies and b humic coals and spropelic oil shales in a restricted intermontane freshwater lacustrine sequence from western montana u s a constituting two distinct organic facies wedistinguish the organic facies in each depositional setting by systematic differences in gross compound class distributions kerogen and infrared spectral characteristics molecular character of pyrolyzates sterane carbon number distribution and sterane hopane ratios the kerogens of the three deltaic organic facies are characterized by varying quantities of vitrinite resinite sporinite cutinite and fluorescent amorphinite triterpane distributions reveal numerous terrigenous compounds including oleanane oleanenes and unidentified c 30 presumably resin derived components the two organic facies of the freshwater lacustrine setting are distinguishedased upon either a vitrinite or an alganite fluorescent amorphinite predominance in the kerogen numerous characteristics facies related markers are also present including dehydroabietane land plant resins and 4 methylsteranes perhaps from freshwater dinoflagellate input the available molecular and petrographic data are evaluated and characteristics are proposed for distinguishing five organic facies of these two depositional settings the successful simultaneous use of molecular geochemistry and organic petrography in this study provides a format for refining the organic facies concept

confined pyrolysis of tertiary lacustrine source rocks in the western qaidam basin northwest china implications for generative potential and oil maturity evaluation abstract the parameter s 1 s 2 genetic potential of rock eval analysis is widely used as an evaluation of the genetic potential for the source rocks oligocene miocene saline lacustrine source rocks in the western qaidam basin have low total organic c contents toc most around 0 5 with a few exceptions 1 0 mineral matrix effects are substantial for source rocks with low toc resulting in relatively low s 1 and s 2 peaks based on the results of confined pyrolyses sealed au capsules on 6 oligocene miocene source rocks from the western qaidam basin with toc ranging between 0 48 and 2 22 the relationship between the s 1 s 2 parameter and the maximum amount of extracted bitumen or saturated and aromatic hydrocarbons sa after the confined pyrolysis has been established as follows bitumen mg g rock 1 4924 s 1 s 2 0 3201 r 0 987 or sa saturates aromatics mg g rock 0 7083 s 1 s 2 0 4045 r 0 992 based on these formulas the amounts of hydrocarbons generated from source rocks can be reasonably estimated the typical crude oils with low biomarker maturities in this region appear substantially different to the pyrolysates of these six rocks at 180 300 c but comparable to the pyrolysates at 320 c and higher temperatures based on molecular parameters this result in combination with the physical and gross compositions of the crude oils suggests that the majority of these crude oils were generated from the source rocks during the main oil generative stage possibly at a maturity higher than r o 0 74

changes in hydrocarbon maturity indices with coal rank and type buller coalfield new zealand abstract the buller coalfield south island new zealand is an inverted late paleogene basin that contains middle eocene bituminous coals which exhibit considerable variation in both coal rank across basin and coal type in seam twenty two fractionated bitumen extracts of brunner coal measures coal samples from 12 drillholes were analyzed by gc and gc ms to characterize the effect of coal rank and type on conventional hydrocarbon maturity indices at the beginning and end of the oil window 0 56 1 26 ro max the carbon preference index pristane phytane and isoprenoid n alkane ratios evolve throughout the high volatile bituminous b rank stage while other biomarker ratios 18 h 22 29 30 trisnorneohopane 17 h 22 29 30 trisnorhopane ts tm 18 h 21 h 30 norneohopane c 29 ts 17 h 21 h 30 norhopane and c 30 diahopane hopane do not show appreciable change in value until medium volatile bituminous rank various aromatic based ratios appear to be more effective in delineating rank throughout the entire oil window in particular the methylphenanthrene index and vitrinite reflectance are positively correlated over the entire bituminous rank range however subtle changes in depositional conditions variable coal type complicate these rank estimates within a given coal seam variation in cpi isoprenoid n alkane and hopane sterane ratios appear to be related to the hydrogen content of the coal while the homohopane index and the oleanane hopane ratio covary with sulfur content as with depressed vitrinite reflectance values mpi is similarly lowered in the perhydrous samples the mechanisms that control these hydrocarbon parameters during deposition and diagenesis are complex and convoluted however changes in bacterial activity and community with marine incursion appear to play an important role due to these anomalies none of the hydrocarbon maturity indices calculated can be singularly used to constrain coal rank

biomarker maturity parameters the role of generation and thermal degradation abstract the effects of burial maturation upon seven molecular maturity parameters and the concentrations of individual biomarkers employed in these parameters have been studied in a well in the barents sea the depth interval between 1400 and 3000 m comprises homogenous eocene claystones with effectively uniform organic carbon content 0 4 0 6 and kerogen type hi of 100 200 mg hc g toc the quantitative biomarker data thus contain minimal interference from organic facies hydrocarbon expulsion effects and the presence of migrated hydrocarbons bulk geochemical data define the hydrocarbon generation threshold or oil window at around 2300 m molecular maturity parameters proceed to equilibrium and in some cases demonstrate inversion at high maturity these molecular changes are associated with major changes in biomarker concentrations the hopane 22 s c 31 hopane and 20 s c 29 sterane parameters proceed as a result of the balance between the relative rates of generation and thermal degradation of the different isomers increased concentrations of the individual isomers are interpreted to be the result of biomarker generation from the kerogen mainly and other macromolecular polar fractions the c 29 sterane parameter and the three parameters involving rearranged hopanes ts 29ts and diahopane operate at higher maturity levels and proceed as a result of the relative rates of thermal degradation of the compound pairs isomerisation in the bitumen may also influence the operation of the parameters involving stereoisomers but must be a relatively minor contribution

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

constraints upon the use of 24 ethylcholestane diastereomer ratios as indicators of the maturity of petroleum abstract we have measured the ratio 20 s 20 s 20 r the relative abundances of the 24 ethylcholestane diastereomers in nine pairs of closely adjacent samples of coals and shales which represent a range of geological ages and different sedimentary basins within some sample pairs the values were similar in others they were very different the differences between the values for coal and shale members of pairs are attributed to effects of sediment matrix type upon the processes which cause the changes in the ratio the kinetic parameters e and s for the changes in the 20 s 20 s 20 r ratio have been estimated using previously published measurements for the hod 1 well shale and jupiter 1 well coal and these values were found to be very different the process in the coal sequence has a much lower activation energy and is therefore less responsive to differences in heating rate regimes than is the case for the shale sequence values of the 20 s 20 s 20 r ratio in two other sequences are shown to be consistent with this explanation and the implications of these observations for the practice of using sterane isomer ratios for assessment of maturity of sediments and crude oils are discussed