the microbial input in carbonate anhydrite facies of a sabkha palaeoenvironment from guatemala a molecular approach abstract nine representative rock samplesincluding four anhydrites an oil stained dolomite and a laminated mudstone source rock from a sabkha type palaeoenvironment la felicidad 1 well guatemala have been compared in order to tentatively characterize each facies by a geochemical signature each sample has been studied by using basic parameters toc rock eval pyrolysis yields and analyses of alkanes and aromatics by computerized gc ms the following families of compounds have been reviewed n alkanes branched and cyclic alkanes n alkylbenzenes benzohopanes monoaromatic steroids d ring aromatic 8 14 secohopanoids alkylnaphthalenes alkylphenanthrenes alkyldibenzothiophenes and triaromatic steroids despite close geochemical relationships of all the sample a more in depth investigation taking into account molecular patterns and semi quantitative data reveals significant differences among the samples anhydrites may be differentiated from carbonates which illustrates the efficiency of organic geochemistry in environmental palaeoreconstruction even in organiccarbon lean sediments toc 0 04 0 08 in anhydrites in these anoxic marginally mature sediments the strong predominance of triterpanes over steranes tt to st 20 associated with other molecular features leads to the conclusion that the main contribution to the organic matter of all facies is by bacteria several prominent components including novel families iso c23 and iso c27 alkanes tetracyclic terpanes d ring aromatic 8 14 secohopanoids 1 phenylpentadecane undecylnaphathalene and their mono and dimethylated counterparts have been interpreted as derived from halophilic bacteria these conclusions may be extended to all crude oils from the same area which may be considered as true bacterially derived petroleums the la felicidad 1 well data are discussed with reference to other palaeosabkha type sequences from the sw aquitaine basin france in which the bacterial input is less important however in these sabkha sequences 1 phenylpentadecane undecylnaphthalene and related structures have also been identified

origin of crude oils in the jinhu depression of north jiangsu south yellow sea basin eastern china abstract the chemical compositions of 20 crude oils and the extracts of potential source rocks from the jinhu depression of the north jiangsu south yellow sea basin eastern china were studied in detail by geochemical methods in order to understand their genetic relationship the oil samples were collected from the major producing fields in the western slope ws and the biandong yangjiaba minqiao uplift belt bmy the rock samples studied selected after rock eval pyrolysis screening of a large suite of samples consist of 20 shale samples in the e 2 f 2 member of the paleocene funing formation from the oilfield areas ws and bmy and the sanhe sag all within the jinhu depression geochemical characteristics indicate only one single family of oils a number of biomarker features support deposition of the source rocks for these oils under conditions of enhanced salinity stratified water columns a wide thermal maturity range for the oils as indicated by sterane isomerization ratios was not substantiated by other maturity parameters the genetic relationships between the oils and the e 2 f 2 member of the paleocene funing formation present in the deeper parts of the sanhe and longgang sags were suggested using a wide range of molecular parameters variation in the sterane concentrations in source rocks with different maturity suggests that migrational contamination and or in situ extractions of organic matter from caprocks or intra reservoir shales by mature oils could potentially produce oils with apparent immaturity at the molecular level secondary alteration e g biodegradation of oils in the reservoir could also have a similar effect on the bulk oil compositions although we do not discount the possible presence of minor amounts of immature oils exploration focus in the jinhu depression as well as many other rift basins in eastern china should be on mature oils derived from the deep source kitchens

the influence of source depositional conditions on the hydrocarbon and nitrogen compounds in petroleum from central montana usa abstract the hydrocarbon and pyrrolic nitrogen compound compositions of 21 crude oils from reservoirs in the heath tyler amsden and swift morrison formations of central montana have been investigated by combined gas chromatography mass spectrometry the biomarker and aromatic hydrocarbon data enabled recognition of three composition types within the heath tyler amsden oils the swift morrison oils displayed different hydrocarbon characteristics and are classified as a separate oil group a number of geochemical parameters e g dibenzothiophene phenanthrene c 20 triaromatic steroid hydrocarbon c 20 c 28 triaromatic steroid hydrocarbons indicate strong variations in petroleum composition from north to south across the region oils from the central montana uplift with high relative c 27 diasteranes c 29 steranes and ts ts tm suggests increasing clay contribution to the source while abundant gammacerane indicates the development of hypersaline conditions with restricted circulation oils from the bull mountain basin represented by the amsden oils show relatively low c 27 diasteranes c 29 steranes and ts ts tm ratios indicating increasing carbonate contribution to the source while the decrease of a gammacerane contribution suggests decreasing salinity levels which may explain the dominance of tricyclic terpane and hence their precursors to the source organic matter while the changes recorded by the biomarker and aromatic hydrocarbon compositions show strong regional variations the nitrogen compounds do not respond so strongly however weak trends coinciding with source carbonate content were apparent in the following ratios 1 8 dimethylcarbazole 1 8 dimethylcarbazole 1 ethylcarbazole and carbazole sum of c 2 carbazoles the second parameter may be responding to variations in salinity since it co varies with the behaviour exhibited by the tricyclic terpanes the source information that can be extracted from biomarkers and aromatic hydrocarbons suggests that primary migration and compositional fractionation during expulsion has exerted little influence on this fraction of petroleum meanwhile primary migration and compositional fractionation during expulsion appear to effect the carbazole and benzocarbazole distributions thereby limiting their application as indicators for source rock facies composition

geosynthesis of dibenzothiophene and alkyl dibenzothiophenes in crude oils and sediments by carbon catalysis sediment extracts and crude oils have been shown to contain methyl substituted biphenyls and dibenzothiophenes with isomer distributions suggesting a geochemical relationship between the two compound classes laboratory simulation experiments have shown that carbon catalyses the reaction between surface adsorbed sulfur and biphenyl to form dibenzothiophene similarly the methyl substituted biphenyls reacted to yield corresponding methyl dibenzothiophenes we suggest that the widespread distribution of dibenzothiophene and alkylated dibenzothiophenes in sediments and crude oils is the result of a catalytic reaction of biphenyl ring systems and surface adsorbed sulfur on the surface of carbonaceous material

molecular correlation of crude oils and oil components from reservoir rocks in the tazhong and tabei uplifts of the tarim basin china molecular data from a large set of source rock crude oil and oil containing reservoir rock samples from the tarim basin demonstrate multiple sources for the marine oils in the studied areas of this basin based on gammacerane c31 hopane and c28 c27 c 28 c 29 sterane ratios three of the fifteen crude oils from the tazhong uplift correlate with cambrian lower ordovician source rocks while the other crude oils from the tazhong uplift and all 39 crude oils from the tahe oilfield in the tabei uplift correlate with middle upper ordovician source rocks these two ratios further demonstrate that most of the free oils and nearly all of the adsorbed and inclusion oils in oil containing reservoir rocks from the tazhong uplift correlate with cambrian lower ordovician source rocks while the free and inclusion oils in oil containing carbonates from the tahe oilfield correlate mainly with middle upper ordovician source rocks this result suggests that crude oils in the tazhong uplift are partly derived from the cambrian lower ordovician source rocks while those in the ordovician carbonate reservoirs of tahe oilfield are overwhelmingly derived from the middle upper ordovician source rocks the scatter of c23 tricyclic terpane c23 tricyclic terpane c30 17a 21b h hopane and c21 c21 rc29 sterane ratios for the free and inclusion oils from oil containing carbonates in the tahe oilfield possibly reflects the subtle organofacies variations in the source rocks implying that the ordovician reservoirs in this oilfield are near the major source kitchen in contrast the close and positive relationship between these two ratios for oil components in the oil containing reservoir rocks from the tazhong uplift implies that they are far from the major source kitchen

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

geochemistry and correlation of crude oils from reservoirs and source rocks in southern biyang sag nanxiang basin china abstract the paleogene hetaoyuan formation a sequence of gray to dark calcareous mudstone and dolomitic mudstones is the main source rock and reservoir in the biyang sag nanxiang basin eastern china organic geochemical analysis study performed on 57 source rock samples from the hetaoyuan formation demonstrates poor to abundant organic matter content ranging from 0 24 5 4 wt toc content characterized by oil prone type ii kerogen eleven crude oil samples from the hetaoyuan formation in southern biyang sag were analyzed using bulk properties and molecular methods to determine their maturity and origin the results suggest that the crude oils exhibit different maturity and source organic matter three groups of oils were identified by integrated analysis of gas chromatography gas chromatography mass spectrometry stable carbon isotope physical properties and gross composition of crude oil group a oils defined as low mature oil are characterized by high density viscosity sulfur content and low saturated hydrocarbon content this group of oils has relatively high values of ph n c 18 c 24 c 26 and gammacerane index indicating that the original organic matter had more contribution from terrigenous plants and was deposited in saline and stratified water columns under anoxic conditions group b oils defined as normal maturity oil are characterized by moderate density viscosity sulfur content and moderate saturated hydrocarbon content this group of oils has relatively low values of ph n c 18 c 24 c 26 and gammacerane index and displays a slight predominance of c 29 steranes indicating that the original organic matter had more contribution from marine algae and was deposited under sub oxic to anoxic conditions with low salinity group c oils defined as light oil are characterized by low density viscosity and abundant saturated hydrocarbons representative source rock samples were selected for further correlation the results of oil source rock correlation suggest that crude oils from the eh 2 member of hetaoyuan formation are mixture derived from source rocks in the eh 2 member and upper layer of the eh 3 member while oils from the upper and lower layer of the eh 3 member correlate with source rocks in the upper and lower layers of the eh 3 member respectively

geochemistry and possible origin of petroleum in palaeozoic reservoirs from halahatang depression abstract the halahatang depression in the tabei uplift of the tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields geochemical analysis indicates that halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions the maturities for halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring tahe oils the halahatang oils feature low pr ph c 21 c 23 tricyclic terpane and c 28 c 29 sterane ratios high c 29 c 30 hopane and c 35 c 34 hopane ratios a v shape in the distribution of c 27 c 28 c 29 steranes and light carbon isotope ratios similar to the tahe oils and correlate well with the middle upper ordovician source rock however some source related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the tahe oils

palaeoenvironmental conditions during deposition of the upper cretaceous oil shale sequences in the songliao basin ne china implications from geochemical analysis abstract excellent hydrocarbon source rocks oil shales containing type i organic matter om were deposited in the continental songliao rift basin during the late cretaceous a major contribution of aquatic organisms dinoflagellates green algae botryococcus and minor input from macrophytes and land plants to om accumulation is indicated by n alkane distribution steroid composition and 13 c values of individual biomarkers microbial communities included heterotrophic bacteria cyanobacteria and chemoautotrophic bacteria as well as purple and green sulfur bacteria the presence of methanotrophic bacteria is indicated by 13 c depleted methyl hopane the sediments were deposited in a eutrophic alkaline palaeolake highly reducing saline bottom water conditions and a stratified water column existed during om accumulation of the qingshankou formation and member 1 of the nenjiang formation this is indicated by low pristane phytane gammacerane index and mttc ratios and the presence of carotane and aryl isoprenoids however an abrupt change in environmental conditions during deposition of member 2 of the nenjiang formation is indicated by significant changes in salinity and redox sensitive biomarker ratios a freshwater environment and suboxic conditions in the deep water prevailed during this period higher input of terrigenous om occurred during deposition of the upper nenjiang formation good oil to source rock correlation was obtained using biomarker fingerprints of oil stained sandstone from the quantou formation and oil shales from the qingshankou formation based on the extent of isomerisation of c 31 hopanes the oil was most probably derived from oil shales of the qingshankou formation in deeper parts of the basin

a biomarker study of depositional paleoenvironments and source inputs for the massive formation of upper cretaceous lacustrine source rocks in the songliao basin china abstract the abundance and composition of total organic carbon aliphatic and aromatic hydrocarbons including biomarkers and the 13c composition of total organic matter and individual compounds in core samples of the nenjiang formation from the sk 1 borehole of the songliao basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the upper cretaceous the distribution of n alkanes and their 13c composition and 4 methylsteranes and dinosteranes in the first member of the nenjiang formation k2n1 indicate that the organic matter largely originated from algal organisms and is dominated by types i and ii kerogen the occurrence of gammacerane aryl isoprenoids isorenieratane and low pristane phytane and diasterane sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters as well as possible photic zone oxygen depletion conditions during major source rock deposition of the k2n1 the organic geochemical data also indicate significantly different depositional environments for the second member of the nenjiang formation k2n2 sediments which are interpreted to have been deposited under a uniform salinity non stratified oxic water column consequently although the organic matter in the k2n2 sediments was largely derived from algal and bacterial sources the kerogen types are dominantly iib and iii due to the oxidative degradation of organic matter combined with a gradual increase in land plant input furthermore the occurrence and shift of two saw toothed distribution patterns of the 13c composition of c29 to c33 n alkanes with w and m patterns being isotopically heavy odd and even numbered alkanes respectively is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation in particular the heavy even carbon numbered high molecular weight n alkanes is rare and needs further investigation

recent advances in petroleum isotope geochemistry abstract organic matter is isotopically heterogeneous lipids tend to be depleted in the heavy carbon and hydrogen isotopes as compared to carbohydrates and lignite the c and h isotopic composition of kerogens is determined by many factors such as environmental conditions during formation and deposition and variability of sources of organic matter stable isotope concentrations in mature kerogens are not significantly altered during maturation and hence reflect the variability of the organic matter during deposition isotope variations in kerogens therefore reflect to some extent the paleogeographic situation and can be used for paleoreconstruction a basin facies with anoxia and a marginal facies with detrital input can be differentiated isotopically in the toarcian of central europe coals are isotopically heterogeneous due to different isotopic composition of macerals inertinite and vitrinite tends to be enriched in deuterium as compared to exinite also boghead coals tend to be depleted in dueterium which possibly reflects various lipid contents of respective precursor materials petroleums can be genetically classified through the patterns of covariance of their compound classes carbonate and shale sourced petroleums may be additionally differentiated through their deuterium content the general world wide applicability of such genetic differentiations needs still to be proved carbon and hydrogen isotope variations in methane are genetically controlled bacterial methane in freshwater environments is characteristically depleted in deuterium even complex origins of natural gases can be unraveled using compositional and isotopic variations new analytical developments led to the application of carbon isotope analyses of gaseous hydrocarbons desorbed from sediments for geochemical surface exploration a discussion reveals that processes such as isotope effects during degassing and bacterial oxidation as well as indigenous formation of hydrocarbons may completely obscure the results

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

pyrite morphology in the first member of the late cretaceous qingshankou formation songliao basin northeast china abstract the study of sedimentary pyrite morphological characteristics provides useful information on depositional environments and early diagenic processes and can be used as an indicator of redox conditions in ancient lake bottom waters the results of this study in the songliao basin in northeastern china show that euhedral crystals and framboids are the dominant pyrite forms in the mudstones of the first member of the qingshankou formation k2qn1 the framboidal size distribution indicates that during the deposition of k2qn1 redox conditions in the bottom water fluctuated from oxic dysoxic to euxinic anoxic to oxic dysoxic the presence of euxinic anoxic bottom water suggests that an anoxic event developed in the songliao ancient lake and continued for 196 ka the development of an anoxic bottom environment was the most important factor in hydrocarbon source rock formation in the songliao basin

spontaneous onset of a madden julian oscillation event in a cloud system resolving simulation 1 spontaneous onset of a madden julian oscillation mjo event in november 2006 was reproduced at a proper location and time by a global cloud resolving model crm used with a relatively coarse horizontal grid preconditioning of moisture was simulated about 4 days prior to the onset in the indian ocean which agreed with data obtained in an in situ observation to investigate influence of zonal sea surface temperature sst gradient in the indian ocean we conducted a sensitivity study comparing composites made from five ensemble simulations it was found that the eastward moving signal of this mjo event could be obscured if sst were zonally uniform in the western indian ocean zonal sst gradient has not been considered important in the previous studies about the mjo onset but sst distribution locating cooler sst in the west side possibly help enhance convection in slow eastward moving envelopes of the mjo

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

tectonic and climate control of oil shale deposition in the upper cretaceous qingshankou formation songliao basin ne china oil shales were deposited in the songliao basin ne china during the upper cretaceous period representing excellent hydrocarbon source rocks high organic matter om contents a predominance of type i kerogen and a low maturity of om in the oil shales are indicated by bulk geochemical parameters and biomarker data a major contribution of aquatic organisms and minor inputs from terrigenous land plants to om input are indicated by n alkane distribution patterns composition of steroids and organic macerals strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane phytane ratios high c14 aryl isoprenoid contents homohopane distribution patterns and high v ni ratios enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values low mttc ratios high carotene contents low toc s ratios and high sr ba ratios the stratified water column with anoxic conditions in the bottom water enhanced preservation of om moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations in this study environmental conditions in the paleo lake leading to om accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics the first member of the qingshankou formation k2qn1 in the songliao basin containing the oil shale sequence encompasses a third order sequence that can be divided into three system tracts transgressive system tract tst highstand system tract hst and regressive system tract rst enrichment of om changed from low values during tst i to high moderate values during tst ii iii and hst i ii low om enrichment occurs during rst i and rst ii therefore the highest enrichment of om in the sediments is related to stages of mid late tst and early hst

source rock heterogeneity of the upper jurassic draupne formation north viking graben and its relevance to petroleum generation studies abstract the upper jurassic draupne formation in the north viking graben north sea has been studied to identify lateral and vertical variations in source rock characteristics and their effect on the timing of petroleum generation fourteen source rock samples from the western flank of the graben and five from the eastern flank were analysed using rock eval analysis microscopy open system pyrolysis gas chromatography and kinetic experiments two major organic facies with different petroleum generation characteristics were identified a stratigraphically higher thermally less stable facies corresponding to a type ii kerogen with hi hydrogen index values of 350 mg hc g toc and a stratigraphically lower more stable type ii iii facies with hi values

managed coastal retreat reducing flood risks and protection costs dungeness nuclear power station uk abstract the two reactors of dungeness nuclear power station the station were built in the late 1950 s on the southern eroding coast of dungeness which is the largest coastal shingle feature in europe the site was chosen because of its proximity to deep fast flowing water but local erosion was up to 1 5 m annually the station has been protected from erosion throughout its life by beach feeding the shingle for beach feeding has been taken from the accreting downdrift eastern shore annually during winter months for the last 30 years the suitability of this method of coast and the flood protection it offered has been regularly reviewed and has always been found to be considerably less expensive than the more formal options such as rock revetments and concrete seawalls however the amount of shingle required to maintain the beach has been increasing rapidly as the main feed point became more and more out of regime consequently a new policy was adopted that allowed the coast locally to retreat producing considerably cost savings allowing the level of flood protection offered to the power station to be increased and reducing the impacts of shingle extraction this change in policy was developed from a number of studies and has been in operation for 3 years not only has there been a considerable reduction in the amount of shingle required but the beach stability has improved in the critical areas

improved understanding of the petroleum systems of the niger delta basin nigeria biomarker and n alkane compound specific stable carbon isotope analyses csia were carried out on 58 crude oil samples from shallow water and deepwater fields of the niger delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks using a source organofacies prediction approach from oil geochemistry the presence in the western deepwater oils relatively abundant c27 steranes c30 24 n propyl cholestane low oleanane index relatively low pr ph ratios gammacerane and positive to nearly flat c12 c30 n alkane compound specific stable carbon isotope profiles suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub oxic and stratified water column conditions this contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water niger delta oils oils in the shallow water accumulations can be separated into terrigenous and mixed marine terrigenous families the terrigenous family indicates expulsion from source rock s containing overwhelmingly higher plant source organic matter average oleanane index 0 48 high c29 steranes as well as having negative sloping n alkane isotope profiles oxic source depositional conditions pr ph 2 5 and non stratified conditions absence to low gammacerane content are inferred for the terrigenous family the mixed marine terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils bitumen extracts of the sub delta late cretaceous araromi formation shale in the dahomey basin are comparable both molecularly and isotopically to the studied western deepwater oil set but with an over all poor geochemical correlation this poor geochemical match between araromi shale and the western deepwater oils does not downgrade the potential of sub delta cretaceous source rock contribution to the regional oil charge in the deepwater niger delta

compound specific carbon isotope analysis of natural and artificially generated hydrocarbons in source rocks and petroleum fluids from offshore mid norway stable carbon isotope signatures of individual hydrocarbon components provide important information on the source rock facies of oils as well as their asphaltene fractions despite maturity variations and secondary processes such as phase fractionation and biodegradation our study is based upon petroleum fluids and source rock samples from offshore mid norway where the main source rock is the marine shales of the upper jurassic spekk formation an alternative source is provided by coals and coaly shales of the lower jurassic are formation in terms of maturity the source rock samples are distributed throughout the main phase of oil generation in this study compound specific carbon isotope analysis has been performed on thermal extracts and kerogen pyrolysates of the source rocks as well as on the oils and the pyrolysis products of their asphaltenes we demonstrate that trends of absolute isotope data and specific isotopic fingerprints after normalizing the data are useful for petroleum source rock correlations the carbon isotope ratios of the n alkanes separate the are from the spekk formation samples in both thermal extracts and kerogen pyrolysates becoming less negative with increasing terrestrial input the spekk samples also tend to become isotopically heavier with increasing maturity while the are samples do not show any systematic difference with increasing maturity the carbon isotope ratios of the n alkanes also discriminate between the oils as well as the asphaltenes from the fluids the individual components generated by pyrolysis of kerogens are isotopically heavier than those from the thermal extracts this is expected from models of kinetic isotope effects which predict that the isotopically lightest products are generally released at an earlier stage in the maturation process a similar isotopic difference is also observed between the pyrolysis products of asphaltenes and the original oils derived from the same source rock type however in a sample where the oil and its asphaltene fraction originate from two different source rocks the opposite relationship between the carbon isotope composition of the oil and its asphaltene fraction is observed bulk isotope data of kerogen concentrates pyrolysates and the residue after pyrolysis of the source rock samples as well as bulk isotope data of whole oils are also presented we show that besides separating are from spekk the bulk carbon isotope values of the spekk samples are considerably heavier than the n alkanes from the thermal extracts whereas those of the are samples are almost equal

marine incursion events in the late cretaceous songliao basin constraints from sulfur geochemistry records abstract songliao basin in ne china developed the most productive oilfield in the world sourced from terrestrial rocks the main source rock of the basin includes member 1 of the qingshankou k2qn1 and members 1 and 2 of the nenjiang formation k2nj1 2 however the exact reasons for the formation of the source rock especially the k2qn1 are still controversial former paleontological and organic geochemical research suggested that organic matter was deposited during marine incursion events of k2qn1 but further geochemical evidence is needed this paper explores the distinct sulfate levels that distinguish marine from fresh waters of the songliao paleo lake we undertook a systematic investigation the sulfur geochemistry of the sediments from top of member 4 of the quantou formation k1q4 to top of member 1 of the qingshankou k2qn1 the ratio of organic carbon to the pyrite sulfur toc pys proved the previously suggested saline conditions during the deposition of k2qn1 and the pyrite sulfur isotope indicated that marine incursion may not only have occurred for k2qn1 but also for top of k1q4 the exact time for the beginning of marine incursion is to be determined the marine incursion within k2qn1 is not strong and partially controlled by the fluctuation of paleo lake level the present study will be helpful for understanding the contribution of marine incursion events to the burial of organic carbon in the songliao paleo lake although further studies are still needed