alkylbiphenyls in ancient sediments and petroleums abstract c 1 and c 2 alkylbiphenyls have been analysed in crude oils and sediment extracts by capillary gas chromatography after preliminary isolation procedures involving tlc and hplc the abundance of 2 methylbiphenyl relative to 3 methylbiphenyl has been measured in samples from two sedimentary sequences 2 methylbiphenyl decreases in relative abundance with increasing thermal maturity of the sediments in both sedimentary sequences these isomeric methylbiphenyls are potentially useful as thermal maturity indicators for crude oils

high diahopane and neohopane abundances in a biodegraded crude oil from the barrow sub basin of western australia abstract three crude oils from the barrow sub basin of western australia have been analysed for hopanoid biomarkers using gc ms techniques enhanced abundances of nordiahopane and diahopane and norneohopane relative to hopanes have been observed in the most severely biodegraded sample these differences have been attributed to the greater resistance of the diahopanes and norneohopane to microbial degradation

biomarker 17α h diahopane a geochemical tool to study the petroleum system of a tertiary lacustrine basin northern south china sea abstract relatively abundant c30 17 h diahopane has been detected in oils and rock extracts in the fushan depression a tertiary lacustrine basin of the northern south china sea c30 17 h diahopane c30 17 h diahopane c30 17 h hopane ratios di increase with increased burial depth of the source rocks di values of most oils from the upper unit e 2 l 3 1 of the third member of the eocene liushagang formation e2l3 in the huachang oil and gas field show a positive correlation with other molecular maturity indicators such as the dnr dimethylnaphthalene ratio mdr methyldibenzothiophene ratio 4 6 1 4 dmdbt 4 6 1 4 dimethyldibenzothiophene mpr methylphenanthrene ratios or the mpi 1 methylphenanthrene index the inflection of the di depth curve occurring at about 3200 m corresponds to 0 55 ro the oils of the huachang oil and gas field have higher di values than the extracts of in situ source rocks indicating the oils might be sourced from deeply buried source rocks two petroleum systems can be distinguished in the huachang field in terms of the relative concentration of diahopane and other maturity parameters the oils in the upper petroleum system consisting of the reservoirs in e 2 l 3 1 are mainly sourced from the e2l source rocks in the bailian sag and are characterized by relatively higher maturity higher oil and gas yields and lower contents of diahopane and oleananes the oils in the lower system consisting of middle e 2 l 3 2 and lower units e 2 l 3 3 of e2l3 have higher contents of diahopane higher contents of co2 gas and lower maturity and oil and gas yields the occurrence and geochemical characteristics of the petroleum system are mainly controlled by the double fault system in the huachang uplift the c30 17 h diahopane is an effective biomarker for oil source rock correlation oil oil correlation maturity assessment and petroleum system study in some terrestrial lacustrine basins

evidence for mixed and biodegraded crude oils in the socororo field eastern venezuela basin this work presents a geochemical study of crude oils from the socororo field socororo major area in the maturin sub basin of the eastern venezuelan basin the v ni total concentrations and v v ni ratios suggest the presence of two oil groups these oils are heavy aromatic asphaltic and according to their sulfur content api gravity and hydrocarbon compositions fall into the same two groups established from the v and ni proxies although the analyzed crude oils show evidence of biodegradation it was possible to determine based on various biomarkers parameters that the oils originated from marine organic matter in a marine carbonate or marine marl source rock deposited under anoxic to suboxic conditions the oils were generated near the peak of the oil window distributions of n alkanes isoprenoids hopanes and steranes combined with a prominent unresolved complex mixture ucm indicate that the oils are biodegraded moreover the presence of pristane and phytane along with alteration of hopanes and steranes and the presence of 25 norhopanes reveals that these oils are mixtures showing different levels of biodegradation sulfur content v and ni concentration and saturate aromatic resin and asphaltene sara composition provide additional evidence for oil mixing such mixed oils originate from several episodes of charging and biodegradation in the reservoirs the first charge was severely biodegraded and many biomarkers susceptible to degradation n alkanes acyclic isoprenoids terpanes methyl hopanes methyl steranes and steranes were extensively altered or completely removed the second oil charge was subjected to a lower degree of biodegradation and only the n alkanes show significant biodegradation both oil charges seem to come from the same source rock which was deposited under variable redox conditions moreover due to their similar maturity the generation and migration of these oils to reservoirs likely occurred close together in time

a geochemical reconstruction of oil generation in the barrow sub basin of western australia abstract a suite of crude oils and petroleum source rock extracts from the barrow sub basin of western australia have been analysed for biological marker compounds by capillary gc ms and for volatile hydrocarbons by whole oil capillary gc these analyses were used to calculate values for twenty three biomarker parameters in order to assess aspects of source type maturity migration and biodegradation of the hydrocarbons the crude oils had a source in the upper jurassic dingo claystone formation these hydrocarbons accumulated in the reservoir sands and in some cases were biodegraded several accumulation and biodegradation episodes have been recognised while the basin continued to subside which resulted in a suite of oils showing marked differences in composition

oligocene miocene source rocks of the zhongcang basin implications for hydrocarbon potential differentiation between lake basins in central tibet abstract the oligocene miocene dingqinghu formation is widely distributed in lake basins of the bangong nujiang suture zone bnsz central tibet and has been reported as an important source rock layer however limited works have been conducted in the zhongcang basin to gain knowledge on hydrocarbon potential of this area and further investigate the organic matter om accumulation mechanisms of source rocks in the bnsz basins samples collected along two measured sections from the zhongcang basin were subjected to sedimentological organic geochemical and petrographic analyses sedimentological analyses indicate that all samples were deposited in prodeltic to deep lake environments total organic carbon toc values and pyrolysis data suggest a poor to fair hydrocarbon source potential of the middle dingqinghu formation with the exception of om rich samples locate in a marker bed of the upper part vitrinite reflectance ro values of the upper part and middle lower part samples range from 0 41 to 0 50 and 0 52 to 0 61 indicating immature and marginal mature stages respectively these maturity levels were also supported by specific maturity indices of sample extracts such as ratios of c31 22s 22s 22r homohopanes and c29 steranes bulk geochemistry maceral composition of kerogen and extract biomarkers demonstrate that om rich samples were deposited in fresh to brackish waters with type ii iii kerogen mainly derived from algae and higher plants while poor to fair samples have less higher plant contribution but relatively high bacterial content that probably originated from more saline environments the paleoclimate induced environmental reorganization is likely responsible for the differential om accumulation in the zhongcang basin relatively wet climates would facilitate primary productivity of the lake as well as development of swamps on the delta resulting in deposition of mixed terrestrial and aquatic om with higher toc whilst dry conditions would restrict the development of river systems and promote the establishment of saline environments causing decreased total om input but increased proportion of halophilic bacterial om in addition we summarized published data of the dingqinghu formation in the bnsz basins and preliminarily reconstructed paleogeography of central tibet two types of drainage patterns were confirmed in this area a long lived hierarchical drainage system is developed in the lunpola area while single lake systems were prevalent in other basins including the zhongcang basin the hierarchical drainage pattern could minimize clastic dilution effects during tectonic active and or relatively wet periods and prevent the establishment of hypersaline environments during the dry period the drainage center in this kind of hierarchical system has lower sedimentation accumulation rate and could receive much more aquatic om at any climatic conditions we argue that tectonic induced drainage organization primarily controlled the hydrocarbon potential differentiation between lake basins of central tibet

hydrocarbon reserves of gachsaran oilfield sw iran geochemical characteristics and origin abstract biomarkers and carbon isotope data were used to depict geochemical properties and to delineate source of the crude oils from asmari and bangestan reservoirs of the giant gachsaran oilfield sw iran despite the distinct horizons of the reservoirs and severe petrophysical heterogeneity inside each reservoir all oil samples show an identical level of thermal maturity furthermore similar source related parameters reflect identical source rock for both reservoirs they indicate carbonate marl source deposited in a marine environment under anoxic suboxic conditions strong marine organic matter signatures of predominantly algal origin along with evidence of a terrigenous angiosperm plant contribution were detected geochemical evidence suggests that the gachsaran field asmari and bangestan oils being sourced from a mix of organic rich kazhdumi and pabdeh source rocks of albian and middle eocene early oligocene ages respectively carbon isotope composition and v ni ratio signatures indicate kazhdumi formation as the main source rock meanwhile significant presence of oleanane and less than unity values of c 29 c 30 hopanes ratio demonstrate a partial contribution of pabdeh formation this contradiction could be explained by two scenarios 1 incorporating very immature non expelled pabdeh oils into the mature kazhdumi oils during migration or 2 partial charge form low maturity pabdeh oils that is insufficient to impact a typical mixed signature over the geochemical fingerprint of the reservoired oils additionally geochemical similarities give rise to an assumption of reservoir and trap inter connection for this giant field

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

nonbiodegraded aromatic condensate associated with volcanic supercritical carbon dioxide otway basin implications for primary migration from terrestrial organic matter abstract liquid co 2 of magmatic origin is produced commercially from a petroleum exploration well caroline 1 in the otway basin south australia the well is located near a 4500 year old maar volcano production of this co 2 rich fluid 98 co 2 1 ch 4 0 5 n 2 from the late cretaceous waarre sandstone is accompanied by a small amount of heavy 15 api gravity low sulphur 0 2 aromatic condensate gasoline range hydrocarbons c 5 c 10 comprise less than 2 of this petroleum however there is no evidence of alteration by water washing or biodegradation whichmight otherwise explain its high specific gravity and unusual aromatic intermediate composition naphthalene and the methylnaphthalenes are the dominant individual components aspects of the condensate s biomarker geochemistry are consistent with its derivation from bacterially reworked terrestrial organic matter deposited in an oxic aquatic environment the methylphenanthrene index of the oil mpi 1 0 59 converts to a calculated vitrinite reflectance of 0 62 mature land plant derived crude oils and condensates usually have a primary paraffinic composition the highly aromatic character of the caroline 1 crude may reflect the involvement of co 2 in its origin in this case supercritical volcanic co 2 appears to have stripped aromatic and less abundant saturated hydrocarbons from marginally mature poor quality type iii iv kerogen in the reservoir rock this enigmatic condensate occurrence highlights the potentially important role played by co 2 in the mobilisation of liquid hydrocarbons from terrestrial organic matter in major petroleum provinces like the cooper basin central australia

marine to brackish depositional environments of the jurassic cretaceous suowa formation qiangtang basin tibet china abstract the late jurassic to early cretaceous depositional environments of the qiangtang basin in tibet have the potential to provide significant insight into mechanisms of black shale deposition organic matter accumulation and the timing of closure of the mesotethys ocean however the depositional setting has not been well constrained here we apply multiple geochemical proxies and petrologic analyses to representative samples of black shale marl and micrite collected from a section in the region these indicate a transitional marine continental environment with brackish to saline water redox conditions were weakly oxic to suboxic environments represented by the studied section varied over time the lowermost marls were deposited in a low salinity weakly oxic shore to shallow lake environment under a warm and humid climate regime the micrites in the middle part of the section were deposited in a lagoonal environment with intense evaporation high salinity and water column stratification the uppermost shales were deposited in a reducing semi enclosed lagoon environment during a marine transgression these results suggest that the late jurassic early cretaceous succession was deposited in a tidal flat or lagoonal environment

sedimentology and organic properties of lower tertiary lacustrine source rocks lunpola basin central tibetan plateau implications for hydrocarbon potential abstract the tertiary lacustrine niubao formation is well exposed in the middle western part of the lunpola basin central tibetan plateau where crude oil was once discovered during drilling campaigns sedimentological organic petrographic and geochemical work was performed on the upper and middle members of this formation in order to investigate its hydrocarbon source rock potential sedimentological analyses indicate that both members were deposited in relatively deep lake conditions away from the influence of big stream system with the upper niubao formation unf having higher sand content the two members contain abundant high quality type i kerogen derived mainly from plankton algae and bacteria compared with samples of the middle niubao formation mnf unf samples also contain more type ii and type iii kerogens of terrestrial origin biomarkers of source rock extracts suggest that a long standing anoxic stratified and saline ancient lake occupid the basin during deposition of the two members which was conducive to the preservation of organic matter however higher gammacerane content and the presence of carotane in mnf samples imply a more saline lake condition rock eval t max and biomarker parameters reveal marginal maturity and immaturity for samples from mnf and unf respectively therefore mnf has better source rocks of higher maturity might be the main hydrocarbon generating member of the basin similar diagnostic biomarkers and biomarker parameters reported in the crude oil also imply its affiliation with the source rocks of mnf

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

a geochemical appraisal of oil seeps from the east coast basin new zealand abstract oil seeps and stains from the east coast basin new zealand have been investigated using biomarker and stable carbon isotope analyses to determine oil oil correlations oils sampled from the raukumara peninsula northern east coast basin north island and marlborough southern east coast basin south island are derived from late cretaceous paleocene marine source rocks with a minor terrestrial content and are isotopically light in contrast oils sampled from hawke s bay and wairarapa central and southern east coast basin north island are derived from paleocene marine source rocks which contain high abundances of c30 regular steranes and 28 30 bisnorhopane and are isotopically heavier than the other group biomarkers and bulk carbon isotopes show that there are at least two distinct sources of hydrocarbons in the basin

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

organic geochemical and petrographical characteristics of coal bearing oligo miocene sequence in the oltu narman basin erzurum ne turkey abstract in the oltu narman erzurum tertiary basin coals occur in the oligo miocene lacustrine sequence in this study n alkane isoprenoid and saturated aromatic biomarker distributions of coals in the sutkans region are found in association with pyrolysis and petrographic data and detailed organic geochemical characteristics depositional environments and hydrocarbon potential of the coals are propounded huminite is the dominant maceral type in coals 51 84 telohuminite is in lesser abundance detrohuminite especially densinite and gelohuminite gelinite are in higher abundance groundwater influence index gwi and gelification index gi are quite high for the studied coals whilst tissue preservation index tpi and vegetation index vi are found to be extremely low according to the results of pyrolysis coal coaly claystone and clayey coal samples contain type ii kerogen although sutkans coals have high ash content 6 28 44 60 average 27 99 their calorific value is quite high 3947 7583 kcal kg random huminite reflectance values of coals vr are 0 4 048 average 0 44 indicating sub bituminous b rank tmax values of coal coaly claystone and clayey coal samples are between 413 and 437 c 20s 20r 20s sterane 22s 22r 22s homohopane ma i ma i ii ta i ta i ii and c28ta c29ma c28ta steroid mpi mpr and mdr ratios which reflect the maturity of coals are very low mpi 1 is intermediate and moretane hopane ratio is high according to petrographical palynological and geochemical data the coal sequence was formed in an environment changing in character from lacustrine to fluvial and coals were accumulated in a swamp area with high water level high ph and intense microbial activity represented by suboxic anoxic conditions

organic geochemistry of crude oils from the vienna basin and an assessment of their origin abstract a representative collection of oil samples and neogene rock samples from the vienna basin has been analyzed by organic geochemical methods the relatively high maturity of the crude oils and the characteristics of their hydrocarbon composition makes it unlikely that they are derived from the neogene sediments of the vienna basin furthermore investigation of the rock samples also showed that these sedimentary strata do not have the potential for generation of liquid hydrocarbons however there is some potential for gas generation even the deepest neogene sediments 4000 m depth just have reached the onset of the hydrocarbon generation zone from these results it has to be concluded that the bulk of the oil found so far in the vienna basin originated from pre tertiary sediments below the neogene basin

post generative alteration effects on petroleum in the onshore northwest java basin indonesia northwest java basin oils largely derived from the fluvial deltaic to nearshore marine talangakar formation of oligocene to early miocene range from heavy oils to extremely light oils and retrograde condensates with api gravities of a suite of oils ranging from about 17 to 53 heavy oils with api gravities less than 22 all of which are in shallow reservoirs are biodegraded pristine oils concomitant with related derivative residual and retrograde condensate oil types indicate evaporative fractionation phenomena post generative alteration processes are widespread in this highly faulted region pristane to phytane biomarker ratios of retrograde condensates and residual oils have been shown to be severely affected by evaporative fractionation principal component analysis pca of isotope and biomarker data identified two oil families associated with source rocks of the talangakar formation one group is suggested to be derived from more marine influenced delta front to prodelta depositional settings while the second group is attributed to a higher plant rich delta plain to delta front depositional environment correlation of these oil families with the varied depositional environments of the talangakar formation has allowed a more refined approach to the identification of hydrocarbon migration pathways in the northwest java basin multivariate statistical analysis is shown to be an effective tool in correlating high gravity condensate oil types

bitumen accumulation in grosmont platform complex upper devonian alberta canada the upper devonian grosmont formation a broad carbonate platform complex in alberta canada contains an estimated 300 billion bbl of bitumen it has been suggested that these vast reserves are related to lower cretaceous athabasca oil sands detailed gas chromatographic mass spectrometric studies of a wide range of biologic marker compounds confirm this suggestion the grosmont formation contains bitumen of similar maturity and source to the athabasca deposit but it has been subjected to a greater degree of biodegradation and water washing possibly as a result of its reservoir rock characteristics the difference in the degree of biodegradation is manifested by the absence of bicyclic terpanes and by the reduced concentrations of the c30 and the 22r epimers of the extended hopanes in the grosmont bitumen also the greater degree of water washing of the grosmont bitumen is inferred from the observed distribution of the bicyclic tricyclic and tetracyclic terpenoid sulfides which shows a characteristic loss of the lower molecular weight members in the carbonate bitumen the correlation established here between the two deposits suggests that if the precursor oil has indeed undergone long distance migration the paleozoic carbonates could have acted as a path for migration finally the observed distribution of steranes in the grosmont bitumen corresponds to the suggestion that the mannville group shales were not the major source rocks of the oil sand and carbonate bitumen accumulations of northern alberta

the abundance and distribution of diamondoids in biodegraded oils from the san joaquin valley implications for biodegradation of diamondoids in petroleum reservoirs abstract the biodegradability of diamondoids was investigated using a collection of crude oil samples from the san joaquin valley california that had been biodegraded to varying extent in the reservoir our results show that diamondoids are subjected to biodegradation which is selective as well as stepwise adamantanes are generally more susceptible to biodegradation than other diamondoids such as diamantanes and triamantanes we report a possible pathway for the microbial degradation of adamantane this cage hydrocarbon possibly breaks down to a metabolic intermediate through the action of microbes at higher levels of biodegradation in petroleum reservoirs microbial alteration has only a minor effect on diamondoid abundance in oil at low levels of biodegradation our results suggest that most diamondoids with the exception of adamantane are resistant to biodegradation like the polycyclic terpanes e g c19 c24 tricyclic terpanes hopanes gammacerane oleananes ts tm c29 ts steranes and diasteranes microbial alteration of diamondoids has a negligible impact on the quantification of oil cracking achieved using the diamondoid biomarker method

the fram strait acoustic tomography system the deep and wide fram strait between greenland and spitzbergen is the main influx and efflux gate to the arctic basin although major resources are invested in measurements of current and temperature here http asof npoar no the flux estimates still have significant deficiencies and errors our objective is to build test validate and use an innovated integrated observing and modeling system including acoustic tomography for improved monitoring of volume heat and freshwater transports in the fram strait as part of the damocles ip developing arctic modeling and observing capabilities for long term environmental studies integrated project a first step acoustic tomography system is to be installed in the fram strait between east greenland and west spitzbergen in august 2008 the first step tomography system consists of one acoustic source near the svalbard shelf and one receiver array in the middle of the fram strait an extended acoustic system serving both tomography and glider navigation i

correlation alteration and origin of hydrocarbons in the gca bahar and gum adasi fields western south caspian basin geochemical and multivariate statistical assessments abstract geochemical as well as multivariate statistical analyses pca were carried out on 20 crude oil samples from middle pliocene production series mpps of guneshli chirag azeri gca bahar and gum adasi fields in the western south caspian basin scb pca analysis employed to source specific biomarkers distinguishes the oils into two types one being divided into two sub types type 1 gca oils type 2a bahar field oils and type 2b gum adasi field oils indirect oil to source rock correlations to available source rock data from previous studies suggest that type 1 oils located in the apsheron balkhans uplift area are derived from basinal shales of the oligocene lower miocene middle maikop formation type 2a and 2b oils located in the gum deniz bahar shakh deniz trend area are more likely derived from shelf edge shales of the upper maikop formation and the middle upper miocene diatom suite respectively biomarker maturity study reveals that type 1 oils mean rc 0 78 are more mature than type 2 oils mean rc 0 71 source rocks which generated these oils were at generation depth interval between 5200 m 112 c and 7500 m 153 c at the time of expulsion this indicates that the western scb oils experienced significant long range vertical migration along the deep seated faults to accumulate in the mpps reservoirs post accumulation biodegradation process was only observed in the guneshli field where bacterial alteration level 4 began between 4 2 and 2 6 mybp and stopped with the deposition of the overlying impermeable upper pliocene akchagyl formation subsequent light hydrocarbon c1 c16 charge into the guneshli fields caused precipitation of asphaltenes which is evidenced by high resin to asphaltene ratios for the present day guneshli oils evaporative fractionation examined using the scheme of thompson 1987 showed high correlations of the aromaticity b parameter toluene n c7 and parafinicity f parameter n c7 mch with the rc maturity and c27 c29 sterane ratio organic matter type this implies that thompson s approach should be used with caution in the scb among the several mechanisms rapid and thick deposition of pliocene sediments and subsequent high heating rate on the maikop formation and diatom suite is probably the most plausible way of explaining the origin of light hydrocarbons in the guneshli and bahar fields

compound specific isotope analysis as a tool for characterizing mixed oils an example from the west of shetlands area abstract the origin of an oil accumulation can be difficult to establish when the oil is a mixture from multiple sources or when multiple episodes of charging are involved in this study oils from the clair field west of shetland islands which are mixtures of nonbiodegraded oil added to biodegraded oil are characterized by comparing the carbon isotope ratios of the gasoline range hydrocarbons grh of the oil to the grh released from the pyrolysis of the asphaltenes in the oil this comparison allows characterization of the source of the first versus the second pulse of oil into the reservoir information useful in assessing the source potential of the basin

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

geochemical characterization of source rocks and crude oils in the upper cretaceous qingshankou formation changling sag southern songliao basin abstract the upper cretaceous qingshankou formation is one of the main exploration target in the changling sag southern songliao basin however the origin of source rock deposition and crude oils remains undiscovered a comprehensive geochemical study including rock eval pyrolysis gas chromatography mass spectrometry and carbon isotope analysis on fifteen crude oils and twenty two source rock samples from the qingshankou formation were performed in order to provide new insights into source organic matter depositional environment and correlation between crude oils and source rocks bulk geochemical analysis on source rock samples indicates that the lower member of the qingshankou formation has more hydrocarbon generating potential than the middle member these two potential source rock members were interpreted to be deposited in slightly different environments and have different sources of organic matter determined by biomarker assemblages the lower member is organically rich average toc 1 27 wt oil prone mature and deposited under anoxic conditions with more contribution from sapropelic organic matter the middle member is organically poor average toc 0 78 wt gas prone less mature and deposited under less anoxic conditions with more terrigenous organic matter input biomarker fingerprints and carbon isotope compositions suggest that all the crude oils were genetically related and could be classified into one oil family which has significant contribution from the lower member source rocks and minor contribution from the middle member source rocks

palaeogeography of radiolarite and organic rich deposits in mesozoic tethys siliceous and marine organic rich deposits are sometimes associated sometimes separate in space and time however both are generally accepted to be the result of high planktonic productivity among the siliceous marine deposits the phtanite family facies is distinguished from the radiolarite family facies by several characteristics they contain organic material and as a result are blackish vs red green for radiolarite facies their time of deposition corresponds with strong faunal modifications and they are deposited generally in shallower environments a palaeogeographic analysis of locations of tethyan biosiliceous and marine organic rich rocks both resulting from a high planktonic palaeoproductivity for three mesozoic high sea level intervals toarcian kimmeridgian and cenomanian show a during jurassic times these tethyan deposits were dissociated the siliceous deposits being closer to open ocean waters than the organic rich ones this is a common disposition in modern upwelling systems and suggests a common process b during cretaceous times these tethyan deposits were often associated i e both occur at the same site and are probably the result of a different process from that in the jurassic

origin of oils in the eastern papuan basin papua new guinea the geochemical characteristics of 16 oils condensates seep oil oil shows collectively called oils from the eastern papuan basin epb and one seep oil from the western papuan basin wpb are integrated with data from previous studies of oils fluid inclusion oils and solid bitumens from the epb and wpb papua new guinea the combined set of samples can be divided in two major families of hydrocarbons the family a oils mostly occurring in the wpb region were generated from clay rich marine source rocks containing predominantly terrigenous higher plant derived organic matter om deposited in a sub oxic to oxic environment source rock s for family a oils are likely to be of middle to upper jurassic e g the upper jurassic imburu formation the family b oils distributed mainly in the epb region were generated from cretaceous or younger marine carbonate source rock s deposited under anoxic to sub oxic conditions and containing predominantly prokaryotic om with some terrigenous higher plant inputs the epb natural gases analyzed in this study may be co genetic to the co occurring family b oils in the epb both family a and b oils were generated at similar thermal maturities of 1 0 1 3 vitrinite reflectance equivalent although no source interval to date has been firmly identified in the epb post jurassic strata are a viable option because 1 late cretaceous and paleogene carbonate and clastic marine sediments including possible source lithologies are present and 2 this section of the papuan basin sustained rapid sedimentation and tectonic loading particularly in the cenozoic

complex series of pentacyclic triterpanes in a lacustrine sourced oil from korea bay basin abstract gc ms analysis was undertaken of a waxy paraffinic low sulphur oil from korea bay basin apparently deriving mainly from bacterially reworked terrestrial organic matter deposited in a lacustrine environment in addition to the regular c27 35 hopanes a number of pentacyclic triterpanes was identified in the range c29 c32 these components appeared to be members of at least two homologous series one of which has been previously postulated to be 18 h neohopanes a further previously unreported series is characterized by a relatively intense molecular ion response during gc ms analysis a bacterial origin is suggested for these pentacyclic triterpane series the presence of which may reflect a particular set of sedimentological conditions

geochemistry of crude oils from eastern indonesia high resolution geochemistry shows genetic relationships among 27 crude oils from eastern indonesia and suggests the ages and paleoenvironments of their source rocks oils inferred to originate from tertiary and triassic jurassic source rocks in the study occur north and south of 2is latitude respectively twenty oils mainly from irian jaya and sulawesi originated from tertiary marine marlstone source rocks that contained type ii iii kerogen deposited under suboxic conditions probably the upper miocene klasafet formation these low sulfur oils show high oleanane c26 24 nordia cholestane and pristane phytane ratios and 13c rich carbon isotope compositions high oleanane and 24 nordiacholestane ratios are diagnostic of tertiary oils and source rocks these oils account for about 16 of the estimated ultimate recoverable reserves in eastern indonesia

comparative study between rock eval pyrolysis and biomarkers parameters a case study of ypresian source rocks in central northern tunisia abstract sedimentary rock samples from the ypresian basin in central northern tunisia were analyzed by two well proven organic geochemical methods rock eval re pyrolysis and gas chromatography mass spectrometry gc ms analysis these techniques were uses to obtain independent parameters on organic matter composition its thermal maturity and environment of deposition this study reveals a close concordance between rock eval pyrolysis data and polycyclic biomarkers parameters such as hopanes and steranes re pyrolysis in conjunction with gc ms analysis show that the ypresian basin sediments contain a variable but notable organic rich facies during the ypresian and prove an unequivocal evidence for type ii organic matter which lies dominantly prior to the peak stage of the conventional oil window end of diagenesis beginning of catagenesis the case study from the ypresian basin shows that these methods remain undoubtedly suitable for a good assessment of the petroleum potential of source rocks and rapid geochemical characterization of sedimentary organic matter

geochemical application of sterane and triterpane biomarkers to a description of oils from the taranaki basin in new zealand abstract the distributions of sterane and terpane biomarkers in a suite of 25 oils from onshore and offshore regions of the taranaki basin of new zealand have been determined by gc ms features of these distributions include the presence of relatively high concentrations of a number of c 24 tetracyclic terpanes the virtual absence of tricyclic terpanes a predominance of c 29 normal iso and dia steranes and the presence of a number of non hopanoid triterpanes in one member of the suite urenui 18 h oleanane is the most abundant component m z 191 ion chromatogram of the terpane class of biomarkers based upon the distributions of 18 h oleanane the mckee and moturoa families of oils can be delineated these terpane distributions are qualitatively similar to those encountered in crude oils from a number of far eastern basins and from the handil field of the mahakam delta indonesia the taranaki oils are of approximately the same thermal maturity maturity parameters calculated from the distributions of c 29 steranes and of 17s h 21 h and 17 h 21s h hopanes confirm recent findings of incomplete nuclear isomerisation in oils derived from tertiary sediments an attempt has been made to correlate the mckee 1 and maui 4 crude oils with potential source rocks from depths of 3708 m and 3825 m respectively the rocks studied have attained insufficient maturity to have been the sources of these oils

the jurassic petroleum system north and west of britain a geochemical oil source correlation study abstract recent significant oil discoveries have focused exploration attention on the atlantic margin areas north and west of britain in particular the west of shetlands area these discoveries the foinaven and schiehallion fields each have reserves of 250 to 500 million barrels 39 8 to 79 5 106 m3 of 24 27 api oil while an earlier heavy oil discovery the clair field is the largest undeveloped oil discovery on the u k continental shelf with resources estimated in the range 3 5 billion barrels 477 to 795 106 m3 other discoveries include suilven the very heavy oil in well 204 28 1 and the quadrant 205 strathmore and solan fields potential source rocks in areas adjacent to the west of shetlands include the upper jurassic kimmeridge clay formation equivalent the middle and lower jurassic and the middle devonian the results of geochemical studies of the oils reservoir core extracts and source rocks from released wells from these west of shetlands discoveries show them to be genetically related to north sea oils sourced from the kimmeridge clay formation equivalent detailed geochemical analysis biomarkers source rock reaction kinetics compound specific isotope analysis and fluid inclusion crush leach analysis of the clair field and foinaven complex oils showed that at least two episodes of charging from different source facies within the kimmeridge clay formation took place with an intervening biodegradation event oil charging from middle jurassic lacustrine source rocks is also indicated in the foinaven complex oils the source rocks are shown to exhibit variations in organic facies from very oil prone to mixed oil and gas with a corresponding range of kinetic parameters this complex generation migration and trapping scenario is directly linked with the tectonic evolution of the west of shetlands with major oil generation from very oil prone kimmeridge clay and middle jurassic lacustrine facies into shallow buried reservoirs biodegradation of the oils appears to have occurred shortly after migration into the traps followed later by a second charge of unaltered oil this appears to have been from a different source facies with more terrestrial slower reacting type ii iii kerogens similar to those seen in the kimmeridge clay formation or heather formation in wells on the basin margins kinetics studies show the middle and upper jurassic kerogens to be fast reacting and very oil prone with little potential for later gas generation this finding appears crucial in the understanding of the west of shetlands petroleum system as it explains the lack of large gas accumulations in a basin of such high thermal maturity

petroleum geochemistry of oil and gas from barbados implications for distribution of cretaceous source rocks and regional petroleum prospectivity petroleum produced from the barbados accretionary prism at woodbourne field on barbados is interpreted as generated from cretaceous marine shale deposited under normal salinity and dysoxic conditions rather than from a tertiary source rock as previously proposed barbados oils correlate with some oils from eastern venezuela and trinidad that are positively correlated to extracts from upper cretaceous la luna like source rocks three distinct groups of barbados oils are recognized based on thermal maturity suggesting petroleum generation occurred at multiple levels within the barbados accretionary prism biodegradation is the most significant process affecting barbados oils resulting in increased sulfur content and decreased api gravity barbados gases are interpreted as thermogenic having been co generated with oil and show mixing with biogenic gas is limited gas biodegradation occurred in two samples collected from shallow reservoirs at the woodbourne field the presence of cretaceous source rocks within the barbados accretionary prism suggests that greater petroleum potential exists regionally and perhaps further southeast along the passive margin of south america likewise confirmation of a cretaceous source rock indicates petroleum potential exists within the barbados accretionary prism in reservoirs that are deeper than those from woodbourne field

steranes and triterpanes in the beacon supergroup samples from southern victoria land in antarctica steranes and triterpanes in beacon supergroup samples sedimentary rock and silicified wood from allan hills and carapace nunatak of southern victoria land in antarctica were studied to elucidate sources of organic materials sedimentary paleoenvironment and thermal history after deposition relative abundances of c27 c28 and c29 steranes and visual kerogen results of beacon supergroup samples from allan hills imply that organic materials in the sedimentary paleoenvironments are contributed mainly by vascular plants with some influence of microorganisms while those of the carapace nunatak sample may be largely due to fern spores the pristanephytane and pristaneheptadecane ratios of the samples were generally close to unity and between 0 50 and 0 99 respectively suggesting that the sedimentary paleoenvironment was shallow lacustrine with alternating oxic and anoxic conditions the 22s22r 17 h 21 h c31 c33 triterpane ratios are approximately at thermal equilibrium values ca 1 5 in most samples while the 20s20r 5 h 14 h 17 h c29 sterane ratios and the 20r 20s 5 h 14 h 17 h 5 h 14 h 17 h c29 sterane ratios vary from 0 0 to 1 1 and from 0 0 to 1 4 respectively most of the 20s20r 5 h 14 h 17 h c29 sterane ratios did not reach thermal equilibrium values the correlation coefficient between the 20s20r 5 h 14 h 17 h c29 sterane ratios and 20r 20s 5 h 14 h 17 h 5 h 14 h 17 h c29 sterane ratios is very high 0 96 these variable maturities probably reflect thermal effects of basaltic dikes on the beacon supergroup at allan hills and carapace nunatak during jurassic time thermal stresses on the beacon supergroup prior to basaltic intrusion have been estimated to be quite low so the paleotemperatures of this formation have been quite low

geochemical characteristics and genetic origin of crude oil in the fushan sag beibuwan basin south china sea abstract the fushan sag is an important petroleum bearing unit in the beibuwan basin south china sea however genetic relationship between oil and source rocks has not been well understood in this work 43 mudstone samples and 22 crude oil samples in the sag were collected for molecular geochemical and isotopic analyses to investigate this relationship the geochemical data shows that the mudstones in liushagang formation have poor to good oil generation potential with toc ranging from 0 45 to 2 19 wt and the kerogen is mainly type two types of crude oils were identified in this study the first type of group a oils including the subgroup a1 and subgroup a2 has the characteristics of low maturity with low saturated hydrocarbon content and lighter 13c values in the huachang uplift the source rocks for the group a oils were deposited under suboxic to oxic and freshwater environment containing more terrestrial higher plant and less angiosperm the subgroup a1 oils in els11 reservoirs are separated from subgroup a2 in the els12 reservoirs by relatively lower maturity the subgroup a1 and subgroup a2 oils are closely related to the els1 to els21 and els12 to els21 source rocks respectively while the second type of oils including group b and group c oils has higher level of maturity with higher saturated hydrocarbon content and heavier 13c values the source rocks of group b oils were deposited in a freshwater environment with lower salinity and more angiosperms and terrestrial higher plants input than those of group c oils two subgroups are divided in the group b oils of which subgroup b1 oils have higher maturity and their source rocks were deposited in lower salinity with more terrestrial higher plant input than that of subgroup b2 oils the subgroup b1 oils occurring in the els31 reservoirs from the huachang uplift are likely related to els31 source rocks while subgroup b2 oils in the els22 reservoirs from the southern slope area of the bailian subsag is linked with mixed source of els22 and els31 mudstones the group c oils are distributed in els22 and els31 reservoirs in the huachang uplift and their oil source are from els32 mudstones two petroleum plays are likely divided by the mfs in els2 based on the oil source correlation in the sag group b and group c oils belong to the lower play and group a oils only occur in the upper play the distribution and accumulation of different groups of oils are mainly controlled by the special two layered tectonostratigraphic framework and the transport ability of fault zone in the sag this study clarifies the types of oils as well as the oil source correlation and the spatial distribution of different groups of oils the results could benefit the further petroleum exploration and resource evaluation in the sag

microbial degradation of aromatic components of crude oils a comparison of laboratory and field observations abstract small aliquots of crude oil brent north sea were incubated aerobically for periods of up to 14 days with an inoculum of recent sediment the saturated and aromatic hydrocarbon components were then isolated and the latter were compared by capillary gas chromatography with similar fractions isolated from four oils from the barrow sub basin of western australia which had experienced different degrees of biodegradation biodegradation of the aromatic hydrocarbons of brent oil produced a series of altered oils whose compositions were comparable to those of the naturally reservoir degraded oils compounds such as naphthalene phenanthrene and alkylated homologues of these hydrocarbons were oxidised but individual isomers were oxidised to different extents

ketones in hydrothermal petroleums and sediment extracts from guaymas basin gulf of california the polar compound nso fractions of seabed petroleums and sediment extracts from the guaymas basin hydrothermal system have been analyzed by gas chromatography and gas chromatography mass spectrometry the oils were collected from the interiors and exteriors of high temperature hydrothermal vents and represent hydrothermal pyrolysates that have migrated to the seafloor by hydrothermal fluid circulation the downcore samples are representative of both thermally unaltered and thermally altered sediments the survey has revealed the presence of oxygenated compounds correlated with samples exhibiting a high degree of thermal maturity several homologous series of related ketone isomers are enriched in the interiors of the hydrothermal vent samples or in hydrothermally altered sequences of the downcore sediments dsdp holes 477 and 481a the n alkanones range in carbon number from c11 to c33 with a cmax from 14 to 23 distributions that are similar to those of the n alkanes the alkan 2 ones are usually in highest concentrations with lower amounts of 3 4 5 6 7 and higher alkanones and they exhibit no carbon number preference there is an odd carbon number preference of alkanones observed for downcore samples the alkanones are enriched in the interiors of the hydrothermal vent spires or in downcore hydrothermally altered sediments indicating an origin at depth or in the hydrothermal fluids and not from an external biogenic deposition minor amounts of c13 and c18 isoprenoid ketones are also present simulation of the natural hydrothermal alternation process by laboratory hydrous pyrolysis techniques provided information regarding the mode of alkanone formation hydrous pyrolysis of n c32h66 at 350 c for 72 h with water only or water with inorganic additives has been studied using a stainless steel reaction vessel in each experiment oxygenated hydrocarbons including alkanones were formed from the n alkane the product distributions indicate a reaction pathway consisting of n alkanes and olefins as primary cracking products with internal olefins and alkanones as secondary reaction products hydrous pyrolyses of messel shale spiked with molecular probes have been performed under similar time and temperature constraints to produce alkanone distributions like those found in the hydrothermal vent petroleums

organic geochemistry of marine source rocks and pyrobitumen containing reservoir rocks of the sichuan basin and neighbouring areas sw china abstract three bitumen fractions were obtained and systematically analysed for the terpane and sterane composition from 30 paleozoic source rocks and 64 bitumen containing reservoir rocks within the upper sinian lower cambrian lower silurian middle carboniferous upper permian and lower triassic strata in the sichuan basin and neighbouring areas china these bitumen fractions include extractable oils bitumen i oil bearing fluid inclusions and or closely associated components with the kerogen or pyrobitumen mineral matrix released during kerogen or pyrobitumen isolation and demineralization bitumen ii and bound compounds within the kerogen or pyrobitumen released by confined pyrolysis bitumen iii in addition atomic h c and o c ratios and carbon isotopic compositions of kerogen and pyrobitumen from some of the samples were measured geochemical results and geological information suggest that 1 in the central sichuan basin hydrocarbon gases in reservoirs within the fourth section of the upper sinian dengying formation were derived from both the lower cambrian and upper sinian source rocks and 2 in the eastern sichuan basin hydrocarbon gases in middle carboniferous huanglong formation reservoirs were mainly derived from lower silurian source rocks while those in upper permian and lower triassic reservoirs were mainly derived from both upper permian and lower silurian marine source rocks for both the source and reservoir rocks bitumen iii fractions generally show relatively lower maturity near the peak oil generation stage while the other two bitumen fractions show very high maturities based on terpane and sterane distributions tricyclic terpanes evolved from the distribution pattern c20 c23 finally to c20 c21 c23 during severe thermal stress the concentration of c30 diahopane in bitumen iii the bound components released from confined pyrolysis is substantially lower than in the other two bitumen fractions for four terrigenous upper permian source rocks demonstrating that this compound originated from free hopanoid precursors rather than hopanoids bound to the kerogen

a ramm study of thermal maturity of dispersed organic matter in marine source rocks abstract the raman maturity method ramm is a non graphical technique for thermal maturity determination based on the multi linear regression analysis of parameters derived from carbon raman spectra of humic macerals it is calibrated against vitrinite reflectance with a suite of australian mostly permian coals in a previous communication an equation to cover the range 0 4 1 2 equivalent vitrinite reflectance was derived in this report we extend the range with a second equation for the range 1 0 2 5 and validate its use by testing a series of australian permian and german carboniferous coals the special features of the technique are that it is equally applicable to vitrinite and inertinite it corrects internally for the suppression of vitrinite reflectance effect grains as small as 5 m are suitable and it does not require well depth information to be available the technique has been applied to two wells cape range 2 and dampier 1 from the rift margin of the north west shelf of australia both wells intersect large thicknesses of fine grained marine jurassic and cretaceous sediments including the major source rock formation of the carnarvon basin there are no terrestrial sediments for control there is good agreement between ramm and vr results for vr 1 2 for cape range 2 however within the oil window in both wells ramm results indicate the vitrinites in many of the samples have reflectance suppression to such a degree that the vr results would be misleading or useless for maturity modeling it is likely that this problem which is well documented for marine influenced coals to some degree affects organic matter in marine source rocks worldwide

irradiation of organic matter by uranium decay in the alum shale sweden the alum shale of sweden contains black shales with anomalously high uranium concentrations in excess of 100 ppm syngenetic or early diagenetic origin of this uranium indicates that organic matter within these shales has been irradiated by decaying uranium for approximately 500 ma radiation induced polymerization of alkanes through a free radical cross linking mechanism appears to be responsible for major alterations within the irradiated organic matter specific radiation induced alterations include generation of condensate like oils at reduced yields from hydrous pyrolysis experiments decrease in atomic h c ratios of kerogens decrease in bitumen organic carbon ratios and a relative increase in low molecular weight triaromatic steroid hydrocarbons conversely stable carbon isotopes of kerogens reflectance of vitrinite like macerais oil generation kinetics and isomerization of 20r to 20s c29 steranes were not affected by radiation the radiation dosage needed to cause the alterations observed in the alum shale has been estimated to be in excess of 105 mrads with respect to organic carbon this value is used to estimate the potential for radiation damage to thermally immature organic matter in black shales through the geological rock record high potential for radiation damage is not likely in cenozoic and mesozoic black shales but becomes more likely in lower paleozoic and precambrian black shales

correlation of different maturity parameters in the ahmedabad mehsana block of the cambay basin abstract the potential use of organic matter maturation parameters in assessing the diagenetic catagenetic transition zone with the help of various known molecular parameters has been investigated in the ahmedabad mehsana block of the cambay basin a set of 24 conventional cores from the eocene shales covering a depth regime of 922 2500 m has been studied the oil generation threshold i e the boundary between the diagenetic and catagenetic maturation regimes is assessed to be at 1800 m based on a combination of parameters including percent hydrocarbons in eom saturate aromatic hydrocarbon ratio in eom and the rock eval production index the pr n c17 ratio rock eval hi and oi were not suitable for reliable maturation profiling nor for independently indexing the stages of maturation the extent of the catagenetic regime is distinguished by ph n c18 ratios

geochemical characterisation of migrated hydrocarbons reveals insights into the source rocks of the bight basin abstract the ceduna sub basin in the offshore bight basin of southern australia is under explored with no significant hydrocarbon discoveries validation of potential petroleum systems is limited to geochemical data from minor shows fluid inclusion fi analysis was used to investigate the possibility of hydrocarbon migration throughout the penetrated sedimentary sections low abundances of fis were identified in sandstones from several intervals in the gnarlyknots 1a and greenly 1 wells indicative of oils trapped along migration pathways the trace quantities of oils contained within fis were successfully analysed by the molecular composition of oil inclusions mci technique the gnarlyknots 1a fi oil provides the first geochemical characterisation of oil generated in the central ceduna sub basin it originated from source rocks that contain both terrestrial and algal organic matter deposited in a sub oxic environment the biomarker signature of the greenly 1 fi oil reflects its derivation from a fluvial deltaic clay rich source rock containing predominantly terrestrial higher plant detritus deposited under oxic conditions these results reveal that several lower to upper cretaceous source rock intervals in the tiger blue whale and white pointer supersequences have potentially generated hydrocarbons a finding which significantly enhances the petroleum prospectivity of the bight basin

geochemical significance of 17α h diahopane and its application in oil source correlation of yanchang formation in longdong area ordos basin china abstract relatively high abundance of 17 h c30 rearranged hopane has been detected in some oils and rock extracts from yanchang formation of longdong area southwestern ordos basin oil shale silty mudstone and carbonaceous mudstone extracts from yanchang formation all have low abundance of c30 rearranged hopane while high concentrations of c30 rearranged hopane were observed in the dark mudstone extracts analysis on the geochemical parameters of the organic matter origin thermal maturity and sedimentary organic facies were carried out the result showed that the depositional redox environment and lithology may be the critical factors for the rearrangement of hopanes which usually occurred in suboxic condition with clay catalyzed reactions as is consistent with the viewpoint of peters and moldowan 1993 according to the relative abundance of diahopane three oil classes can be identified class 1 oil with low abundance of diahopanes was originated from oil shale of chang 7 member while class 2 oil and class 3 oil with middle to high abundance of diahopanes were derived from dark mudstones of chang 4 5 to chang 9 members of yanchang formation of the 151 analyzed oil and extracts samples from different stratigraphic intervals 105 samples belong to class 1 oil coming from oil shale while 46 samples belong to class 2 and class 3 oil derived from mudstones so oil shale of chang 7 member is the main effective source rock of longdong area and dark mudstones of chang 4 5 to chang 9 member are also important source rocks

characterization of petroleum source rocks and shales by pyrolysis gas chromatography mass spectrometry multiple ion detection abstract a number of organic rich shales and potential source rocks from australia and alaska have been examined by pyrolysis gaschromatography mass spectrometry multiple ion detection attempts have been made to observe variations in the distributions of biomarkers released from the samples by pyrolysis particular emphasis has been placed on the release of pentacyclic triterpanes to evaluate whether or not a one step pyrolysis method can be used to determine relative maturity of the samples immature shales are observed to produce c27 and c29 hopenes not present at higher levels of maturity as well as number of hopanes and moretanes variations in the distributions of alkylbenzenes alkanes alkenes sesquiterpenoids and diterpenoids can also be monitored during the pyrolysis reaction and provide information on the nature of the source material in the samples

oil source correlation for the paleo reservoir in the majiang area and remnant reservoir in the kaili area south china abstract there are different viewpoints on the oil source correlation of the majiang paleo reservoir and the neighbouring kaili remnant reservoir in the southern guizhou depression of china three potential source rocks in this depression could be inferred the lower cambrian marine mudstone lower silurian shale and lower permian mudstone most of the potential source rocks are of high maturity the solid bitumens and oil seepages in the southern guizhou depression suffered severe secondary alterations such as thermal degradation and biodegradation the solid bitumens of the majiang paleo reservoir are also of high maturity the oil seepages and soft bitumen of the kaili remnant reservoir were severely biodegraded all these secondary alterations may obscure oil source correlations by routine biomarkers thus it is very important to select appropriate biomarker parameters for the oil source correlation in this work biomarkers resistant to thermal degradation and biodegradation and the data of organic carbon isotopic compositions were used for the correlation the 13c values of n alkanes in asphaltene pyrolysates were also used to make oil oil and oil source correlations between severely biodegraded oils the results indicate that the lower cambrian marine mudstones are the main source for the ordovician silurian o s solid bitumens of the majiang area and the ordovician silurian oil seepages and soft bitumens of the kaili area remnant reservoir in the eastern kaili area might have been charged at least twice by the oil generated from the lower cambrian marine source rocks

geochemistry origin and correlation of crude oils in lower cretaceous sedimentary sequences of the southern mesopotamian basin southern iraq abstract thirty one crude oil samples from lower cretaceous reservoirs in southern iraq were analyzed using bulk property and molecular methods to determine their maturity and biomarker characteristics as well as to obtain information on their respective source rocks all the oils are unaltered non biodegraded have high sulfur content and api gravity is in the range for light to heavy oil 19 40 api they are characterized by low pr ph values even odd predominance and front end biased n alkane distributions based on these parameters the oils were generated and expelled from a marine carbonate source rock bearing type ii s kerogen compositional similarities of hopane and sterane biomarkers with those from potential source rocks allowed identification of the upper jurassic lower cretaceous sulaiy and yamama carbonate succession as the effective source beds a similar composition of normal and isoprenoid hydrocarbons among the oils suggests an origin from a common source rock however biomarker maturity ratios indicate a wide range of maturity this appears to result from the type of burial history of the source rock characterized by a slow passage through the liquid window interval during an extended period of geologic time

the occurrence of bisnorhopane trisnorhopane and 25 norhopanes as free hydrocarbons in some australian shales abstract the triterpenoid hydrocarbons of some west australian shales have been examined by gc ms in addition to the common 17 h 21 h hopanes 17 h 21 h hopanes and 17 h 21 h moretanes 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes were identified in the organic extracts in contrast pyrolysates of the solvent extracted sediments contained only the common hopane and moretane series indicating that 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes are not bonded to kerogen but rather are present in the sediments as free hydrocarbons

trimethylnaphthalenes in crude oils and sediments effects of source and maturity abstract three sedimentary sequences and a number of crude oils have been analysed for trimethylnaphthalenes tmns using gas chromatography the sediments were found to contain enhanced relative abundances of 1 2 5 tmn and 1 2 7 tmn in samples of cretaceous age and younger this was especially pronounced in lower maturity sediments containing type iii organic matter older samples containing type iii organic matter were found to contain enhanced relative abundances of 1 2 5 tmn and lower relative abundances of 1 2 7 tmn 1 2 7 tmn appears to be derived directly from the structural degradation of oleanane type triterpenoids present in angiosperms and as such is proposed as a marker for this class of plant and indirectly therefore also for samples deposited since the early cretaceous the crude oils have been classified according to their trimethylnaphthalene compositions this classification enables crudes of higher plant origin to be identified and to be further classified according to whether the organic matter pre dated or post dated the evolution of angiosperms

molecular parameters of maturation in the toarcian shales paris basin france iv laboratory thermal alteration studies abstract an immature toarcian shale from the paris basin semecourt reported maximum burial depth 700m was heated in the laboratory under reduced pressure at different temperatures 201 257 285 c for different times 6 91 days we measured in the resulting extracts by gas chromatography or combined gas chromatography mass spectrometry 1 a extent of configuational isomerisation at i c 6 and c 10 in pristane ii c 20 and c 14 and c 17 in 5 h 14 h 17 h steranes iii c 17 and c 22 in hopanes 2 b extent of aromatisation in aromatic steroid hydrocarbons both configurational isomerisation and aromatisation occur during heating but the latter process is accelerated relative to the former in comparison with the maturation effect experienced by the toarcian shales as a result of burial depth and the associated temperature rise the results suggest that it may be possible to distinguish the thermal histories of sedimentary sequences by comparison of the relative extents of isomerisation at c 20 in steranes with the extent of aromatisation in aromatic steroid hydrocarbons

extreme summer convection in south america abstract tropical rainfall measuring mission trmm precipitation radar pr and national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data are used to indicate mechanisms responsible for extreme summer convection over south america the three dimensional reflectivity field is analyzed to define three types of extreme echo deep convective cores wide convective cores and broad stratiform regions the location and timing of these echoes are sensitive to midlatitude synoptic disturbances crossing the andes at the leading edges of these disturbances the nocturnal south american low level jet sallj transports moisture along the eastern edge of the andes from the tropical to the subtropical part of the continent where the sallj rises over lower but steep mountains on the east side of the southern central andes deep and wide convective cores are triggered in the evening when the sallj withdraws to the north as the disturbance passes nocturnal trig

constraining the oil charge history of the south pepper oilfield from the analysis of oil bearing fluid inclusions abstract the south pepper oilfield located in the barrow sub basin on the nw margin of the australian continent has experienced a multi phase charge history abundant oil bearing fluid inclusions are present in samples from within the current gas cap suggesting that an oil column existed prior to gas this palaeo oil gas leg fi oil has ts tm and c29 c30 hopane ratios of 1 and the c35 homohopanes are a significant proportion of the extended homohopanes it has lower pr ph and diasterane sterane ratios than the currently reservoired live oil and contains gammacerane a series of peaks tentatively identified as c30 to c34 17 h 30 norhopanes and a large amount of 2 methylhopanes collectively geochemical analysis of the gas leg fi oil suggests that it was generated from a less mature more calcareous source rock deposited under more reducing conditions than the upper jurassic dingo claystone the main source of the live oil in addition the presence of c30 dinosteranes in the gas leg fi oil provides a triassic or younger age constraint this makes palaeozoic carbonates an unlikely source possible source intervals for the gas leg fi oil are thin lower jurassic limestones and marls which occur at the base of the lower dingo claystone or a thin limestone unit the cunaloo member at the base of the triassic locker shale samples from within the present oil leg also contain abundant oil inclusions consistent with high oil saturations at the present day however these oil inclusions exhibit different fluorescence colours suggesting they represent a second oil charge geochemically the oil leg fi oil has an intermediate composition between the live oil and the gas leg fi oil suggesting that gas charge displaced the first oil charge samples of which were preserved as fluid inclusions in the oil leg sample biodegradation of the first oil charge indicated by the presence of 17 h 25 norhopanes in the currently reservoired live oils can be attributed to the ingress of meteoric waters probably during sub aerial exposure of the basin margin during miocene wrenching changing environmental conditions curtailed bacterial activity and allowed unaltered oil sourced from the dingo claystone to accumulate below the gas cap and mix with the biodegraded residues of the first oil charge to achieve the live oil composition the biodegradation event must have preceded the second charge as the live oil contains compounds such as n alkanes which would have been removed had alteration occurred after the second charge complex charge histories are common and the analysis of palaeo oils trapped within fluid inclusions provides the opportunity to achieve a more comprehensive assessment of hydrocarbon charge

two case studies of thermal maturity and thermal modelling within the overpressured jurassic rocks of the barrow sub basin north west shelf of australia abstract thermal maturity within the jurassic thick overpressured source rocks of the bambra 2 and barrow deep 1 wells barrow sub basin western australia was investigated and modelled using a temperature time related kinetic model the aim of this study is to investigate whether overpressure has a determinable influence on thermal maturation repeat formation tests rfts drill stem tests dsts and mud weights indicate that the jurassic section in the barrow sub basin is highly overpressured it appears that the overpressured zone is associated with high sonic transit times and low resistivity values in the jurassic fine grained rocks anomalously low measured vitrinite reflectance r o values in the overpressured zone appear to be due to either r o suppression or inaccurate identification of vitrinite anomalously low t max values are found to be caused by contamination from drilling mud additives a good correlation is found between the reliable maturity data including biomarker maturity and predicted maturity values r o between 0 8 and 2 2 and suggests that the anomalously low r o and t max values are probably not related to the overpressuring fluid pressure about 40 80 mpa at 3000 4600 m these results demonstrate that the true maturity level in the jurassic overpressured section probably depends on temperature and time alone we therefore conclude that overpressure is not an important factor in thermal maturity and hydrocarbon generation in this region

evaluation of sedimentary features and biomarkers in the paleogene niubao formation in the lunpola basin tibetan plateau implications for the oil source rocks and exploration the paleogene niubao formation is mainly exposed in the central part of the lunpola basin in the hinterland of the tibetan plateau and has high potential for oil and gas exploration and development the biomarkers of source rocks are systematically studied by selecting representative samples the middle and upper niubao formation contain rhythmically inter bedded mudstone and sandstone that show periodic variations characteristic of the lake water environment additionally the large volumes of muddy dolomite in the upper niubao formation unf are associated with high salinity in the lake environment under a hot and arid climate the organic geochemical analysis shows that the middle niubao formation mnf and unf have high organic abundance total organic carbon toc contents of 1 48 8 96 in the mnf and 1 52 12 83 in the unf and type i ii kerogen the analysis shows that the unf was deposited in a persistent anoxic stratified and highly saline paleo lake environment which was beneficial to the preservation of organic matter the high phytoalkane and paraffin contents in the unf indicate a strongly reducing and highly saline lacustrine depositional environment the high pregnane contents and ascending sterane in the source rocks in the mnf indicate high maturity and the distribution of n alkanes and regular sterane indicates the input of some terrestrial organic matter the high maturity indicates that the source rock in the mnf may represent the main hydrocarbon generating layer in the basin

the occurence of unusual c27 and c29 sterane predominances in two types of oman crude oil abstract two types of oman crude oils reveal unusual sterane distributions type a which is the more common 74 examples is characterised by a predominance of c 29 iso and normal steranes and generally none or only very low relative concentrations of rearranged steranes the triterpanes are characterised by the predominance of the c 29 17 h 21 h norhopane over the c 30 17 h 21 h hopane and non predominant c 20 c 30 tricyclic terpanes the c 29 steranes of this type of crude were not derived from the c 29 sterols of land plant origin frequently proposed as the source of c 29 steranes since there is good geological evidence that these crudes were generated from a pre cambrian source rock a geological period when land plants did not exist the type b crude oil 11 known examples is characterised by a strong predominance of c 27 iso normal and rearranged steranes relatively lower concentrations of 17 h 21 h hopanes and relatively high concentrations of c 20 c 30 tricyclic terpanes the remarkably different biomarker characteristics of these crude oils imply that the organisms active in the depositional environment of the respective source rocks were significantly different

biological marker distribution and significance in oils and rocks of the monterey formation california abstract the biological marker distributions of several oils core extracts and solid bitumens of the monterey formation of california have been studied sterane terpane and monoaromatic steroid hydrocarbons were analyzed in samples from the san joaquin los angeles ventura and santa maria basins the sterane patterns of both oils and extracts are characterized by 1 a low relative concentrations of diasteranes 2 b low 20s 20r 5 14 17 ethylcholestane ratios 3 c relatively high concentrations of cholestane vs methyl and ethylcholestane isomers san joaquin basin samples contain significant amounts of the 5 isomer which is generally absent in samples from other basins the carbon number distribution of 5 14 17 20r steranes is similar for all oils regardless of api gravity depth or basin location and is suggestive of open marine depositional conditions for the source material involved 17 h l8 h 21 h 28 30 bisnorhopane is present in almost all samples certain san joaquin basin oils and extracts contain 1 a a series of 25 nor hopanes including 25 28 30 trisnorhopane 2 b a distinctive monoaromatic steroid hydrocarbon distribution 3 c an aliphatic hydrocarbon fraction devoid of n paraffins biological marker characteristics suggest that the monterey oils examined originated early in the maturational sequence from elastics poor source material api gravities of the monterey formation oils examined vary monotonically with 1 a bisnorhopane hopane ratios 2 b aromatized regular sterane ratios and 3 c the concentration of monoaromatized steranes relative to terpanes and regular steranes these oil gravity correlations exist regardless of sample depth or basin location

diamondoid hydrocarbon ratios as indicators of biodegradation in australian crude oils the effect of biodegradation on diamondoid distributions in petroleum has been investigated on a series of crude oils reservoired in two australian sedimentary basins the gippsland basin and the carnarvon basin the ratio of methyladamantanes to adamantane rises with increasing biodegradation significant changes in the ratio occur at extreme levels indicating that diamondoids can be indicators of petroleum biodegradation especially when most other hydrocarbons have been removed the methyladamantane adamantane ratio can also be used to assess the composition of crude oils that are comprised of a mixture of severely biodegraded and non biodegraded oil

geochemical investigation of oils from cretaceous to eocene sedimentary sequences of the abadan plain southwest iran abstract oil samples from lower cretaceous to eocene reservoirs in southwest iran were analyzed using gas chromatography mass spectrometry and gas chromatography isotope ratio mass spectrometry for genetic classification of oil families and determining their maturity the studied oil samples are non biodegraded and their gravity range from 18 3 to 37 api the slight even odd n alkane predominance coupled with low pr ph values suggests their likely source rocks with a predominance of algal organic matter type iis kerogen deposited under strongly reducing marine environments the biomarker distribution of investigated oils is characterized by high concentration of both c29 and c30 hopanes and ratios of c29 c30h are generally greater than unity there is a marked predominance of c29 regular sterane over c27 and c28 homologs in our studied oils high sterane hopane values and cross plot of the 13c sat versus 13c aro show contribution of marine organic matter medium value of gammacerane index and other salinity indices show water density stratification and high salinity conditions of the environment of deposition it can be concluded that the studied reservoirs due to their variable maturity have different api gravity and contain two oil families types a and b with latter being deeper and comprising more mature oils