analysis of cyclical sedimentation in the lower permian mchuchuma coalfield south west tanzania a statistical approach by a modified markov process model was used to prove that the lower permian coal measures of the tanzanian mchuchuma basin developed distinct cyclicities during deposition from results the transition path of lithologic states typical for this coal sequence is as follows a coarse sandstone b medium sandstone c fine very fine sandstone d shale e mudstone f coal or e f and again a coarse sandstone the majority of cycles is are asymmetric abcdef abc but symmetrical cycles are present as well abcdefed the statistical results concur with observed sedimentological evidence of depositional environment fining upward cycles correspond to the development of basal channel bars changing into levees then into back swamps which are topped by coal swamps frequent interbedding of coal and mudstone in the upper part of the coal measures calls for periodic flooding and flushing of fine clastics into coal forming swamps causing interruption of peat formation cyclical deposition is explained by wandering channels in response to varying discharge and rate of deposition their lateral frequent shifting caused the formation of asymmetrical cycles in this fluviodeltaic depositional model

dibenzothiophenes in solid bitumens use of molecular markers to trace paleo oil filling orientations in the lower cambrian reservoir of the moxi gaoshiti bulge sichuan basin southern china abstract the moxi gaoshiti mg bulge of the sichuan basin in southwestern china is unique because of its enormous gas field in old cambrian and proterozoic marine strata where oils in carbonate reservoirs have been nearly completely cracked to solid bitumen and natural gas because of high to post mature thermal maturity levels numerous solid bitumen bearing dolomites obtained from boreholes in the mg bulge provide an ideal opportunity to trace the major filling orientations for the lower cambrian paleo oil reservoirs biomarker analysis was conducted on solid bitumens through quantitative detection with gas chromatography mass spectrometry results show that all solid bitumen samples in the mg bulge exhibit similar compositions of molecular markers thereby implying that they belong to the same oil population and that paleo oils should be derived from the same source kitchen bed low pristane phytane and dibenzothiophene dbt phenanthrene ratios as well as the predominance of dbt among dbt dibenzofuran and fluorene are observed in the solid bitumen samples which suggest that related paleo oil reservoirs likely originated from a highly reducing marine shale environment all isopleth maps of the dbt concentrations 4 methyldbt 1 methyldbt 4 6 dimethyldbt 1 4 1 6 dimethyldbt dmdbt and 2 6 3 6 dmdbt 1 4 1 6 dmdbt ratios consistently indicate that the overall orientation of oil migration in the mg bulge is primarily from the west to east direction with the strongest filling point located at approximately the mx12 well the north to west direction is an additional filling orientation these indicators show that those paleo oils that had been cracked to pyrobitumens mainly originated from a source kitchen in the western part of the mg bulge a hydrocarbon source kitchen in the northern part of the mg bulge may also have developed but further research on this is needed the recognition of these solid bitumen molecular signatures particularly the consistent results using dbt concentrations and alkyl dbt thermal maturity indicators suggests a potential approach that can be applied to the study of paleo oil reservoirs

chemical models of vitrinite reflectance evolution a global kinetic model of vitrinite reflectance evolution is developed to illustrate a new approach to vitrinite reflectance modelling the method utilizes quantitative pyrolysisgas chromatographic data from isolated vitrinite kerogens to derive the concentrations of structurally specific moieties alkylphenol precursors in vitrinite kerogens as a function of rank this data set is used to calibrate a gaussian distributed activation energy model for phenol precursor loss from vitrinites using published burial histories phenol yield is then correlated with vitrinite reflectance the predictive vitrinite reflectance model based on this phenol system is tested against a well from the us gulf coast area the results being compared with a lopatin model of the same well this type of vitrinite reflectance model is numerically compatible with current generation kinetic models of hydrocarbon production from source rock kerogens and has a better heating rate independence than lopatin s method

geochemical characterisation of middle devonian oils in nw alberta canada possible source and maturity effect on pyrrolic nitrogen compounds abstract molecular geochemical compositions of a suite of middle devonian sourced and reservoired oils from the rainbow zama shekilie sub basins in n w alberta canada reveal the presence of at least two oil families in the study area the distribution of each oil family is geographically restricted to a single sub basin consistent with the oils being sourced locally within a series of closed generation migration trapping systems the diversity in the biomarker distributions of the oils indicates the wide range of depositional environments and source materials existing in each sub basin rather than mixing of end member oils across different sub basins clear maturity differences are observed between the oils from the rainbow and zama subbasins pre cretaceous thermal anomalies along the reactivated regional precambrian basement faults are proposed as one of the major causes for the relatively high maturity levels for the middle devonian source rocks in the study area we infer that depositional environment and thermal maturity have had a strong impact on the geochemical characteristics of the saturated and aromatic hydrocarbons in the rainbow shekilie zama oils but may not influence the pyrrolic nitrogen compounds to a significant extent however recognition of possible source and maturity effects on pyrrolic nitrogen compounds in other studies suggests that these factors should be considered before the pyrrolic nitrogen compounds are used to characterize petroleum migration

molecular memory effects recording the accumulation history of petroleum reservoirs a case study of the heidrun field offshore norway abstract the immobile portion of the oil occupying the pore space of reservoir sandstones which is mostly represented by visible impregnations is shown by the present study to contain geochemical signals that record their filling history the clue to unravelling these signals is sequential extraction of such impregnations of residual oil by a high pressure solvent flow through cell in which the solvent percolates through the intact and primary pore system of the rock sample gas chromatography mass spectroscopy gc ms analysis of residual oils extracted from samples of certain reservoir sandstones within the heidrun field offshore norway reveal significant contrasts in the chemical maturity of the first and the last fractions recovered as high as 0 69 versus 0 50 for the mpi 1 ratio corresponding to 0 79 versus 0 67 rc the hypothesis is proposed that by using this extraction technique oil impregnations from different portions of the pore system i e from large versus small pores are obtained separately this interpretation is especially supported by the regular occurrence of reservoir sandstones in which the residual oil exhibits maturity contrasts between those fractions extracted from large and small pores of the same rock within the heidrun field the distribution of reservoir sandstones with such maturity contrasts is strictly controlled by their position in the oil column and the location of their fault compartment these contrasts are interpreted to reflect the maturity levels of end members of the petroleum charges which have filled this trap during an extended period of geological time reservoir sandstone samples containing such end member charges are limited to the uppermost portion of the oil column lower in the oil column the pore system of all reservoirs contains oil impregnations of a uniform maturity level regardless of their pore size origin this distribution is believed to indicate an early stage of the accumulation history of the heidrun field characterised by the formation of a palaeo oil water contact well above the present one moreover the four fault compartments studied each controlled by bordering faults with different sealing capacities were not filled during the same stages of the accumulation history in summary the present study has shown that oil impregnations depending on their location within the pore system of individual reservoir sandstones can retain molecular memory effects which in turn allow the accumulation history of petroleum fields to be reconstructed

the petroleum characteristics and filling history of the froy field and the rind discovery norwegian north sea abstract the brent group reservoirs of the froy field and the rind discovery norwegian north sea show complex distributions of petroleum and aqueous fluids multiple fluid contacts are present in the rind discovery and the fields show various extent of compartmentalisation due to faulting geochemistry data of core extracts indicate that the two fields have different petroleum sources bhullar karlsen holm backer owe tran 1998 late diagenetic modifications of the reservoir quality consist of quartz cementation followed by carbonate and kaolinite cementation and dissolution of k feldspar fluid inclusion results indicate that filling of the reservoirs occurred after the main phase of quartz cementation at pressure temperature conditions close to the present differences in fluid properties between fault compartments in both fields have been identified fluid inclusion data have proved especially valuable for evaluation of the sealing capacity of faults through time and given evidence for the fault lineament north of both fields to be a time integrated pressure seal except for a lower gas condensate zone in the 25 2 13 compartment of rind the present reservoir fluids are volatile oils close to gas saturation the previous presence of an oil in the lower reservoir zone of 25 2 13 has also been demonstrated the fluid inclusion data indicate that the condensate in 25 2 13 represents a second episode of migration filling rather than phase separation

net subsidence and number of cycles their interrelationship in different permian gondwana basins of peninsular india abstract seven data sets were structured from subsurface lithologs of permian gondwana coal measures comprising the karharbari barakar and raniganj formations of the koel damodar and mahanadi basins of peninsular india all three formations are fluvial in nature and composed largely of fining upward cycles of clastic sediments capped by coal carbonaceous shale simple linear regression lines and correlation coefficients were computed for total thickness of strata net subsidence and number of cycles in each data set the strong positive relationships between total thickness of strata and number of cycles in permian coal measures suggest that the fluvial cycles of karharbari barakar and raniganj are formed by intrabasinal mechanisms of channel migration sedimentation and subsidence rather than tectonic events in the source area the slopes of linear regression lines fitted to the data sets vary more than has hitherto been supposed and are classified into two categories three out of seven regression lines exhibit steeper slopes and they are closely similar in this respect to other permian and upper carboniferous coal measures of australia great britain and germany the other four have gentler slopes these dissimilarities in the slopes of regression lines are attributed to the differential rate of increase in the number of cycles with respect to the total thickness of the strata net subsidence as well as the differential subsidence of the permian gondwana supergroup through space and time

a novel sequential extraction system for whole core plug extraction in a solvent flow through cell application to extraction of residual petroleum from an intact pore system in secondary migration studies abstract the rapidly developing field of reservoir geochemistry and studies into secondary migration require new methods and techniques to characterise the composition of organic fluids obtained from reservoir rock samples ideally the composition of residual petroleums should be compared with the mineralogical and petrophysical properties from the same sample this requires a non destructive extraction procedure that keeps the rock in its natural state we have developed a flow through extraction system capable of efficiently extracting core plugs while preserving the pore system of the sample extractions can be performed sequentially to obtain various oil phases present in the pore system i e free or mobile oil can be obtained separately from residual oils adsorbed onto mineral or organic matter surfaces the free and adsorbed residual oils exhibit marked compositional differences due to fractional adsorption effects and maturity variations monitoring the pressures at the inlet and outlet positions of the extraction cell allows the measurement of pressure gradients across the core enabling the calculation of the relative permeability of the sample according to darcy s law application of the sequential flow through extraction method gives a substantial increase in information on the rock sample allowing a better understanding of fluid flow and fluid rock interaction in the subsurface

temporal resolution of an oil charging history a case study of residual oil benzocarbazoles from the gidgealpa field reservoired oil is usually a mixture of multiple discrete petroleum charges unravelling the contribution and character of each charge is amongst the most daring challenges in petroleum geochemistry this paper describes an approach that involves the evaluation of both free and residual oils to reconstruct the history of petroleum accumulation within the multireservoir gidgealpa field located in the cooper and eromanga basins of central australia porewall coating residual oils form by reservoir wetting processes and grow continuously by adsorption of polar compounds retaining molecular information on the first oil that was present in the pore system such sequentially recovered residual oils proved useful in reconstructing the record of oil charges to the gidgealpa ridge using araucariacaean markers for source discrimination and the benzocarbazole a a c ratio bcr for identification of the source region five discrete charging events were distinguished in contrast to most previous studies benzocarbazole distributions were found to be independent of lithofacies organic facies and maturity however alkylated carbazoles did exhibit a pronounced facies dependency the application of alkylcarbazoles as source markers in the study area provides the first evidence of the expulsion of petroleum from cambrian marine source rocks in the underlying warburton basin 2007 elsevier ltd all rights reserved

geochemical comparison of core extracts and oil samples in reservoir abstract a geochemical study was undertaken to compare the geochemical parameters obtained from the analysis of different sample types of oils collected from the same horizons in particular produced oil samples and oil extracted directly from reservoir cores in the laboratory and analysed by slightly different methods it is not easy to carry out a major comparison because of the scarcity of horizons from which both dst oil samples and cored reservoir samples are available bp was only able to locate such samples from three wells kirklington 2 onshore england qusahwira 1 middle east and 26 28 1 offshore ireland the composition and concentration petroleum rock percentage of the oil in these three wells varied widely some molecular maturity parameters e g methylphenanthrenes and sterane isomerisation ratios suggest that the extraction process mobilises lower maturity material from the cores in some cases the parameters contradict one another possibly indicating measurement of different components of the petroleum or inherent uncertainties in the analysis source type indicators are observed for some of the oils and their respective core extract samples from the same intervals in the same wells which suggest derivation from different types of organic material the results show that it is not possible to characterise an oil definitively by examination of the core extract that the differences may not be systematic and that comparison of oil and extract data from different wells or horizons may be misleading this study demonstrates some of the differences that need to be taken into account during interpretation

degradation and maturity controls on oil field petroleum column heterogeneity in the gullfaks field norwegian north sea abstract a geochemical mapping of the gullfaks reservoir petroleum column based on 226 reservoir core extracts and 23 drill stem test dst and repeat formation test rft oil samples indicates the presence of statistically testable lateral compositional heterogeneities in the petroleum column these different petroleum populations can be related to lateral filling of the field from two source basins and a more pervasive subsequent episode in reservoir biodegradation petroleum maturity gradients within the field were detected using conventional biomarker gc ms methods on saturated hydrocarbon fractions the degree of biodegradation was monitored by quantitative gc of n alkanes in whole oil samples using a squalane internal standard the observed compositional differences in the gullfaks petroleum column are consistent with diffusion being the primary mixing process thermal convection being eliminated on both compositional and modeling grounds compositional differences between core extracts and dst samples from the same intervals suggest that fractionation of petroleum might occur during testing and that interpretation of reservoir petroleum columns from mixed sample sets should be treated cautiously

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

fractionation of azaarenes during oil migration abstract a comparative study of alkylbenzoquinolines in crude oils and rock extracts bitumens from japan and sumatra shows that the ratios of nitrogen masked isomers nmis to nitrogen exposed isomers neis and the ratio of higher homologs to lower homologs is higher in crude oils than in corresponding bitumens also a regular increase in the ratios of nmis to neis with increasing migration distance is observed for a series of crude oils from the sarukawa oil field northeastern japan these results are attributed to the preferential migration of nmis caused by their weak adsorption on clay minerals and or their low solubility in interstitial water and the selective removal of lower honologs caused by their irreversible adsorption onto clays during oil migration which are regarded as geochromatographic phenomena it is suggested that those ratios can be used to estimate the degree of fractionation of oils during primary and secondary migration

biomarker analysis of oils and source rocks using a thermal extraction gc ms abstract gc ms analysis of thermally extracted hydrocarbons on sediments has been tried in practice only in the last few years it allows rapid acquisition of data normally only obtained after elaborate work up processes have been performed an oil an oil stained sandstone and source rocks 4 have been selected for this study both saturated and aromatic hydrocarbon biomarkers were monitored using mid of selected ions the machine used in this study has been developed at our laboratories the methodology is the same for both oils and source rocks so that rapid hydrocarbon characterisation and oil source rock correlations are possible

sedimentological synthesis of permian fluviatile sediments of east bokaro basin bihar india abstract the early permian karharbari and barakar formations of east bokaro basin comprise the following lithofacies lithofacies a consisting of monomictic cobble and pebble conglomerate including pebbly sandstone with faint crossbeds deposited mainly by high velocity aqueous currents as channel lag deposit or longitudinal bars lithofacies b coarse to medium sandstone profusely crossbedded interpreted as channel facies formed by downcurrent migration of sand bars in low sinuosity streams lithofacies c mainly fine sandstone with interbedded siltstone characterised by small scale ripple lamination formed in a low energy environment such as swale fill and or overbank deposits lithofacies d including carbonaceous shale and coal with lack of current structures indicating quiet water deposition interpreted as backswamp and lacustrine deposits the overall context of the karharbari and barakar assemblage with relative abundance of pebbly coarse sandstone in the former and fine clastics in the latter the presence of fining upward cycles widespread development of tabular and trough crossbedding and sample to sample variation of foreset azimuths all suggest a generally alluvial environment analysis of crossbedding dip azimuth and dimensional fabric suggest that the sediment milieu in either case consisted of streams flowing persistently from the south southeast to north northwest direction it is inferred that the unidirectional system of streams flowing across the east bokaro basin changes systematically in channel sinuosity through time

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

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

the organic geochemistry of petroleum reservoirs abstract the organic constituents of petroleum reservoirs frequently show measurable compositional variations both laterally between wells and vertically within a single well the pattern of variation is controlled by the geological setting of the reservoir which influences the way in which migrating petroleum fills the reservoir from one or more source kitchens having achieved a high petroleum pore saturation the reservoir fluids may then redistribute themselves at rates are often comparable to geological time periods mass transfer by diffusion and density driven convection must be considered and their timescales compared with the elapsed time since the accumulation was filled in many cases the compositional variations inherited from the filling process persist to the current day this paper outlines the mechanisms by which reservoirs fill and mix and describes how this can lead to observable lateral differences in composition the relationship between certain engineering parameters particularly the gas oil ratio and reservoir fluid density reservoir rock description and geochemical parameters will be stressed the goal being to improve the characterisation of petroleum reservoirs by combining geochemical and engineering data into a scientifically consistent framework many aspects of the geochemistry of petroleum reservoirs have only recently begun to be researched it is hoped that the recent advances in the geochemical characterisation of oils and gases will be increasingly applied to the problems of reservoir and petroleum engineering this should lead to improvements in the efficiency with which petroleum is recovered from the subsurface

analysis of petroleum fractions by tlc fid applications to petroleum reservoir description abstract thin layer chromatography and flame ionization detection iatroscan tlc fid offers a rapid and accurate method for quantifying saturated and aromatic hydrocarbons and resin asphaltene fractions in solvent extracts of petroleum source rocks reservoir rocks and crude oils while the instrument is superficially simple special precautions need to be taken in calibration and parameter setting due to complexities arising from the operational characteristics of the detector system nevertheless the technique offers superior speed and precision to conventional mplc analysis of petroleum fractions this paper describes the choice of operational parameters provides comparison with the traditional group type analysis technique mplc and presents some geochemical applications

effect of artificial maturation on carbazole distributions as revealed by the hydrous pyrolysis of an organic sulphur rich source rock ghareb formation jordan abstract hydrous pyrolysis experiments were performed on the ghareb formation upper cretaceous jordan a carbonate and organic rich toc 19 6 source rock using a temperature range of 200 to 360 c 72 h the original sediment contains only low amounts of carbazoles maximum 2 2 g g bitumen for 1 methylcarbazole with increasing thermal maturation intense generation begins at temperatures only in excess of 300 c reaching a maximum at 360 c likewise during natural maturation generation occurs at later stages of maturity e g for tithonian source rocks at 0 81 rr and for posidonia shale at 0 88 rr some isomeric changes during hydrous pyrolysis do not resemble those in nature whereas others do the relative abundances of selected c1 and c2 alkylcarbazoles on ternary diagrams reveal differences whereas the benzo a carbazole benzo a carbazole benzo c carbazole ratio is closely similar the latter result supports the contention that maturation plays a key role in controlling carbazole distributions in source rocks however the results for alkylcarbazoles especially the c2 carbazoles are not easy to interpret

cyclicity in early permian fluviatile gondwana coal measures an example from giridih and saharjuri basins bihar india abstract the karharbari and barakar coal measures of giridih and saharjuri basins of bihar eastern india comprise an interbedded assemblage of sandstone shale and coal in variable abundance the lithofacies composition records a progressive decrease in sandstone and enrichment of shale and coal from karharbari up to barakar application of first order embedded markov chain statistics to subsurface data of karharbari 52 borehole logs and barakar 10 borehole logs reveals that deposition in both the coal measures followed a markovian mechanism with variable probability to yield a sequence of upward transition from sandstone through shale to coal the repetitive fining upward cycles are asymmetrical i e sandstone shale coal sandstone in the case of karharbari but symmetrical as sandstone shale coal shale in barakar the abundance of sandstone and the asymmetrical nature of karharbari cycles are attributed to abrupt shifting of channel bars in low sinuosity anabranching streams by contrast the subequal amount of sandstone shale and coal forming symmetrical cycles in the overlying barakar formation is due perhaps to a slow and gradual shift of the stream channels over and across the adjacent subenvironments of the flood plain

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

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

geochemical characterization of free versus asphaltene sorbed hydrocarbons in crude oils implications for migration related compositional fractionations based on the existing petroleum migration models that focus on the role of organic sorption a laboratory study has been performed to simulate the migration effects on the various fractions of oil in this study one free oil fraction defined as bitumen 1 existing outside of or loosely attached to asphaltene and three to four absorbed oil fractions defined as bitumens 2 3 4 and 5 more strongly attached to asphaltene macromolecules that were obtained from three oil samples collected from the bohai bay basin east china were analyzed in detail based on the laboratory partition of oil components between the solvent phase oil and the asphaltene phase petroleum migrationrelated effect on saturate fraction was re evaluated our observation indicates that the compositional variation from bitumen 1 to bitumen 4 or 5 includes the following 1 the resin content increases while the saturate content and saturates aromatics ratio decrease 2 the relative abundance of short chain n alkanes decreases while that of the long chain n alkanes increases 3 pr nc17 ph nc18 and pr ph ratios stay virtually unchanged while the relative abundances of terpanes to n alkanes and steranes to n alkanes decrease 4 the ratios of c21 c21 c29 steranes and c23 c23 c30 terpanes in the free oil fraction are similar to or even lower than those in the whole absorbed fraction suggesting relatively stronger affinities of these smaller terpane and sterane molecules to asphaltenes in contrast to the relatively larger ones and 5 the isomerization parameters of c27 and c29 steranes are slightly higher in the free fraction than in the whole absorbed oil fraction large variations were observed in the distributions of steranes among the four bitumen fractions of the x52 oil and were considered to be related to the heterogeneity of the source rocks in addition to the partition of these compounds between the asphaltene phase and the solvent phase q 2002 elsevier science ltd all rights reserved

glacier fed sandstone sheets in the weller coal measures permian allan hills antarctica abstract the upper member of the weller coal measures permian at allan hills victoria land antarctica consists of repetitive coal layers separated by sheetlike bodies of predominantly sandstone and subordinate siltstone and conglomerate all of fluvial origin investigation of the lowermost inter coal sheet wc1 reveals abrupt planar basal contacts persistent upward fining and a strong westward palaeocurrent trend three lithofacies are recognized in the wc1 sheet a small scale cross bedded pebbly sandstone which occupies most of the basal portions of the sheet b large scale cross bedded medium coarse sandstone confined to a linear ne sw belt overlying or locally replacing facies a and c siltstone and rippled fine grained sandstone which drapes and overlaps facies a and b and contains glossopteris leaves and vertebraria root traces facies distribution patterns indicate the wc1 body initiated as an abrupt sheetlike incursion of coarse sediment over a low lying mire facies a followed by entrenchment and confinement of flow as the sheet extended distally facies b facies c represents low energy floodplain sedimentation co existing with and later succeeding facies b as deposition evolved toward abandonment and eventual renewal of peat deposition relatively rapid deposition of the sandstone sheet is implied by the lack of any significant hiatus markers outsized clasts up to 45 cm in diameter one observed to display prominent striations occur sporadically throughout the wc1 including within siltstone beds of facies c these are inferred to be ice rafted deposits which together with other evidence suggest meltwater influence possibly glacial on sediment transport and deposition preliminary examination of other sandstone sheets in the upper weller indicates attributes similar to the wc1 including abrupt bases upward fining character and predominantly westward palaeocurrent patterns the allan hills exposures are believed to represent a succession of low lying mire complexes interrupted by abrupt but infrequent incursions of coarse sediment possibly by extreme meltwater floods

cretaceous arc volcanism of palmer land antarctic peninsula zircon u pb geochronology geochemistry distribution and field relationships abstract the cretaceous marks an episode of enhanced magmatism sedimentation and tectonic processes along the entire proto pacific convergent margin of west gondwana cretaceous magmatism across the antarctic peninsula is dominated by the intrusive lassiter coast intrusive suite which developed as episodic flare up events during the mid cretaceous at a time of increased convergence volcanic rocks of this age are poorly defined as a consequence of limited field observations and an absence of accurate geochronology recent field mapping combined with unpublished field observations has identified a region 10 000 km2 of dominantly subaerial rhyolitic pyroclastic and epiclastic successions from northern palmer land of the antarctic peninsula volcanic successions up to 1500 m in thickness consist of dominantly silicic ignimbrites lavas heterolithic breccias and lahar deposits fed by caldera forming eruptions the volcanic rocks of this region were widely considered to be early cretaceous in age based on field relationships and early geochronology new u pb zircon ages identify three distinct volcanic episodes during the late cretaceous early cenozoic at 108 ma 93 ma and 64 ma lu hf data indicate significant proportions of ancient crust in the petrogenesis of the volcanic rocks and the slightly negative ehf values are consistent with a mid position 120 km within the magmatic arc relative to more juvenile compositions close to the trench

molecular markers carbon isotopes and rare earth elements of highly mature reservoir pyrobitumens from sichuan basin southwestern china implications for precambrian lower cambrian petroleum systems abstract the moxi gaoshiti bulge of the sichuan basin in southwestern china is unique because it provides insights into the geochemistry of lower cambrian reservoir bitumens and their geological significance for paleo oil reservoirs analyses of biomarkers carbon isotopes trace elements te and rare earth elements ree were conducted on reservoir bitumens and the associated source rocks to constrain sedimentary environments and bitumen paleo oil sources based on biomarkers carbon isotopes te ratios and ree distribution patterns both of the cambrian qiongzhisi 1q and sinian dengying z2dn source rocks can be hydrocarbon sources for the cambrian longwangmiao 1l bitumens in the mg bulge lower cambrian doushantuo formation not discussed here abundant n alkanes relative to isoprenoids significant c21 and c22 steranes predominance of dibenzothiophene dbt and low ratios of biomarkers such as pr ph dbt p c22tt c21tt and c35h 22s c34 h 22s indicated that the source rock was characterized as shale from an overall highly reducing marine depositional environment the average 13c values from the compositions of the solid bitumens show an abnormal order saturate hydrocarbons

geostatistical cross association method used for the lithostratigraphic correlation of coal measure profiles abstract the case study from the early permian coal bearing barakar formation in the east bokaro sub basin of jharkhand india demonstrates that the non parametric geostatistical method of cross association can give a reliable lithostratigraphic correlation of borehole or outcrop profiles at a confidence level of at least 95 the inclusion of lithofacies details in the stratigraphic criteria does not necessarily enhance the correlation and may actually render it less reliable because the main lithological units vary internally on a local scale and their lateral variability is virtually irrelevant to basin scale correlation

the factors controlling the abundance and migration of heavy vs light oils as constrained by data from the gulf of suez part ii the significance of reservoir mass transport processes abstract reservoir flow processes have a major impact on the oil quality and distribution of heavy vs light oils both within reservoirs and on the petroleum system scale in the gulf of suez gos gravitational segregation of black oil columns is a common phenomenon an understanding of the mass transport processes in these reservoirs is important for evaluating their impact on the composition of migrating petroleum 2d simulation results show that pressure diffusion is a too slow process to be the main cause for the vertical compositional gradients a reservoir filling model which is a refined version of the geological model of gussow linked to the composition of the gos expelled petroleum fluids and their pvt behaviour and constrained by the gos oil field data is presented this model gives viable explanations for a formation of gravitationally segregated oil columns b tar mat occurrences and their affinity to low maturity heavy oils and c wide spread occurrences of heavy oils and their relationship with light oils in this model continuous density overturning by compositionally controlled bulk flow is the prime cause for the formation of gravitationally segregated columns occurring when a the charge to the reservoir displays a maturity related decrease in density with time and b the reservoir volume relative to the charge volume is large enough for the reservoir to retain a wide maturity range lateral compositional variability in many reservoirs is today interpreted to image the initial filling of the reservoirs it is demonstrated that such lateral gradients can form effectively from re orientation of vertical gradients via ordinary diffusion these gradients have symmetry elements relative to the petroleum mass distribution in the reservoir fill and spill from gravitationally segregated columns enhance the efficiency of the migration of heavy oils

geochemical and petrophysical characteristics of permian shale gas reservoirs of raniganj basin west bengal india abstract thick shale horizons of permian age emerged as the potential source of gas through primary investigation and resulted into the first indian pilot scale gas recovery demonstration project in the raniganj basin however the relation of geochemical properties with shale pore matrix porosity and permeability mechanism are yet to be evaluated for better dealing the phenomena of diffusion transport and gas recovery in this study the analyses like proximate rock eval toc vro low pressure n2 sorption porosity permeability sem edx and image processing have been carried out the values of s1 s2 toc and tmax indicated fair to excellent source rock potential of the shales having type iii iv kerogens prone to thermal gas genesis the low pressure n2 desorption curve of raniganj formation shales shows the type h3 hysteresis comprising slit shaped pores the barren measures shales have type h2 and h3 hysteresis patterns specifying to ink bottle shaped pores and slit shaped pores whereas the oldest barakar formation shales are having ink bottle shaped pores caused due to blocking effect the slit shaped pores favour the pore network and characteristically excellent for the flow of gas the results of sem edx are indicating alteration stability in the order of o the increasing tmax values with a centric decrease in porosity and permeability specifying the role of devolatilization disintegration and blocking of pore spaces openings is a function of the thermal gradient the linear evolution of multipoint bet surface area with increasing porosity suggests that the porosity values from 2 0 to 6 5 mainly corresponds to pore size of 3 0 11 0 nm similarly the inverse relationship between average pore size and porosity attributed to a greater contribution of smaller pores in total porosity the pore network model derived through the sem image processing has shown two types of connectivity i various pore sizes of diverse pore throats with dual opening directions and ii interlinked large and small pores obeying similar normal distributions the barren measures shales have shown higher pore connectivity than the raniganj and barakar formation shales

application of pyrolysate carbon isotope and biomarker technology to organofacies definition and oil correlation problems in north sea basins abstract detailed sampling of apparently homogeneous potential source rock intervals frequently indicates unsuspected variations in organic facies which may or may not be reflected in the wireline logs carbon isotope analyses of pyrolysates provide a useful technique in these investigations which are essential for valid oil to source correlations in the jurassic of a north sea viking graben well the rich source shales at the top of the draupne formation are significantly depleted in 13 c and correlate with the oils from this area thus suggesting that this interval has acted as the primary source of the viking graben crudes a quite different pattern is evident in a well from the central graben and the data not only explain why the oils of the greater ekofisk area are relatively enriched in 13 c but also demonstrate that the variations within these oils are facies controlled pyrolysate carbon isotopes provide an excellent correlation between the middle devonian upper caithness flagstones of the inner moray firth and the beatrice crude oil this correlation is supported by the biomarker data and there is no need to appeal to a contribution from either an upper or middle jurassic source to achieve a match with the beatrice oil

pvt and phase behaviour analysis in petroleum exploration abstract this paper describes the application of pvt data routinely determined for almost all conventional oil tests with respect to petroleum exploration in a broader context the use of pvt and phase behaviour analysis focuses on phase envelope evolution as a function of source rock maturity and secondary migration using both laboratory analyses and natural examples from the ekofisk eldfisk and snorre fields as well as data from the tampen spur area and barents sea in general pvt analysis is demonstrated to be applicable for relative maturity estimation recognition of mixing effects volumetric evaluation of complex reservoir filling histories and as a screening tool for oil population characterisation pvt analysis is used in this paper as a tool complementary to organic geochemistry allowing the integration and interpretation of data reflecting fluid response to geological conditions on a regional scale

the evolution of the geothermal gradient from lambert graben and mahanadi basin a contribution to the indo antarctic rift debate abstract the east antarctic lambert graben and the indian mahanadi basin are considered to represent segments of an intra gondwanan rift structure that was active at least since the paleozoic fission track analyses of apatites from a comprehensive data set across the shoulders of both grabens were used to compare their low temperature history and to estimate the paleo geothermal gradients before the onset of the last denudation rifting stage late jurassic the paleo geothermal gradients of both juxtaposed gondwana margins similarly increase from the basement towards the respective rift shoulder from 15 20 ckm 1 to 25 30 ckm 1 this trend of increasing paleo geothermal gradients together with a denudation episode commencing in the early cretaceous and coeval igneous activity indicates a common rifting stage accompanying the breakup of gondwana in the india antarctica sector

fluvial architecture of the upper permian raniganj coal measure in the damodar basin eastern india abstract the upper permian raniganj formation of the damodar basin consists of an interbedded assemblage of sandstone shale carbonaceous shale and coal facies the trough cross bedded sandstone bodies st facies formed by migration of dunes in sand bar point bars are widely developed in the lower part of raniganj formation the planar cross bedded facies sp of transverse and diagonal bars and massive sandstone of longitudinal bars abound in the upper part of the eastern raniganj and jharia coalfields the succeeding ripple cross laminated sr facies with or without reactivation surface alternating with thick beds of fine clastics suggestive of flood deposits is widespread in the western bokaro and north karanpura coalfields markov chain statistics reveals a fining upward cyclical order of superposition throughout the raniganj sequence the integrated results of paleocurrent channel morphology texture and petrography suggest that the raniganj sedimentation was brought about in an extensive unified alluvial plain drained by a system of west northwest flowing streams whose channel sinuosity increased and depth decreased progressively in a downcurrent direction from east to west post gondwana faulting and subsequent erosion account for the disconnected disposition of the coalfields

charging of oil fields surrounding the shaleitian uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract this paper discusses origin and charging directions of oil fields on the shaleitian uplift bohai bay basin the shaleitian uplift is a footwall uplift surrounded by three sags containing mature source rocks the origins of the four oil fields on the shaleitian uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions for 61 source rock samples and 27 oil samples hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and or depositional conditions allowed the identification of six oil types or classes these six oil classes could then be linked to three distinct source rock intervals ranging in age from 43 0 ma to 30 3 ma the third member 43 0 38 0 ma in age and first member 35 8 32 8 ma of the eocene shahejie formation and the third member of the oligocene dongying formation 32 8 30 3 ma each sourced one class of oil the other three classes represent mixtures of oil generated from multiple source rock intervals traps on the shaleitian uplift were charged in the east by oil generated from the eocene shahejie formation in the bozhong sag in the southeast by oil generated from the eocene shahejie and then oligocene dongying formations in the southwestern part of the bozhong sag and or in the eastern part of the shanan sag and in the southwest by oil generated from the eocene shahejie formation in the western part of the shanan sag the estimated migration distances range from less than 5 km to about 20 km the compositional heterogeneity within fields and multiple parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist

phanerozoic history of the mahanadi region india the mahanadi basin is a nw se stretching gondwana basin perpendicular to the east coast of india the metamorphic basement to the basin mainly comprises rocks of the eastern ghats mobile belt egmb which experienced a complex thermotectonic evolution involving several episodes of deformation and magmatism it can be inferred from 40ar 39ar ages on hornblende 845 ma and biotite 622 and 593 ma from basement rocks that the last high grade metamorphism in the western part of the egmb i e the western khondalite zone occurred during the late grenvillian with any pan african overprint only reaching anchimetamorphic conditions only pseudotachylite intrusions and their related thermal imprint with ages around 515 ma display a direct pan african signature fission track analyses on nine zircon 419 313 ma and 49 apatite 443 119 ma samples indicate a rift related formation of the mahanadi basin as an asymmetrical half graben in two stages during the permo carboniferous and the middle triassic moreover the gondwana breakup in eastern india is signified by dyke intrusions and the thermal overprint of thrusts and faults in the mahanadi region and the onset of ocean floor production in the mahanadi offshore basin at around 120 ma

geochemical characteristics and implications of hydrocarbons in reservoir rocks of junggar basin china abstract a practical sequential extraction approach has been applied to two core samples collected from oil zones of triassic sandstones in junggar basin northwest china five bitumen fractions were obtained from each sample using this approach these fractions are free oil components in inter granular pores bitumen 1 adsorbed oil components on grain surfaces and liberated by hcl treatment bitumen 2 oil bearing fluid inclusions hosted by grains bitumen 3 and adsorbed oil components on clay mineral surfaces and liberated by hcl and hcl hf treatments bitumens 4 and 5 striking differences have been observed both in bulk compositions and in aliphatic biomarker distributions e g terpanes and steranes among the five bitumen fractions this phenomenon is ascribed to the indigenous compositional variations and differential maturation behaviors between adsorbed oil components in a network of polar compounds resins and asphaltenes and free oil components in even a same oil charge in addition to fractional adsorption effects and compositional changes of the oil charges in reservoir rocks during filling process the molecular compositions and homogenization temperatures of oil bearing fluid inclusions in these two samples indicate that trapping of these types of inclusions apparently ceased in sample a while continued in sample b after the initial oil charge suggesting that the relative content of polar components in the initial oil charge compared to the later oil charges plays a dominant role controlling the trapping of oil bearing fluid inclusions in an oil saturated zone sequential extraction studies are important and useful for reservoir geochemistry especially in the cases where only limited samples of oil and reservoir rocks are available and or where compositional heterogeneity of free oils has disappeared in a reservoir karlsen d a nedkvitne t larter s r bjorlykke k 1993 hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history geochim cosmochim acta 57 3641 3659

dibenzothiophenes and benzo b naphthothiophenes molecular markers for tracing oil filling pathways in the carbonate reservoir of the tarim basin nw china abstract dibenzothiophenes dbts and benzo b naphthothiophenes bnts are the main sulfur containing heterocyclic aromatic compounds in crude oils and sedimentary rock extracts because of the relatively higher electronegativity and an unshared pair of electrons in the outer shell orbital of the sulfur atom hydrogen bonds can be formed between the sulfur and hydrogen atoms of the surrounding medium in carrier beds therefore dbts and bnts are potential geochemical markers for tracing oil filling pathways a correlation of oils in the halahatang oilfield of the tabei uplift in the tarim basin nw china shows that the molecular marker compositions of all oils are quite similar implying that these oils have been sourced from the same source kitchen and belong to a same oil family using molecular indicators relative to dbts and bnts namely 4 1 mdbt 4 1 methyldibenzothiophene 4 6 1 4 1 6 dmdbt 4 6 1 4 1 6 dimethyldibenzothiophene 2 6 3 6 1 4 1 6 dmdbt 2 6 3 6 1 4 1 6 dimethyldibenzothiophene and 2 1 bnt 2 1 bnt 1 2 bnt benzo b naphtho 2 1 d thiophene benzo b naphtho 2 1 d thiophene benzo b naphtho 1 2 d thiophene this paper traces the oil migration orientation and filling pathways in this oilfield the isopleth maps of these molecular indicators unequivocally reveal an overall oil migration filling points and preferred filling pathways orientation from south to north based on this a potential source kitchen is predicted in the southern part of the halahatang depression most probably at the manxi shuntuoguole low uplift just between the awati and manjiaer depressions the southern part of the halahatang depression along the oil charging pathways is predicted to be the most promising region for oil exploration

spatial 87sr 86sr variations in formation water and calcite from the ekofisk chalk oil field implications for reservoir connectivity and fluid composition abstract the 87 sr 86 sr ratios of formation waters from the chalk of the ekofisk oilfield were measured using a new technique extracting salt residues from the interstices of core samples in the danian ekofisk formation the chalk matrix itself has 87 sr 86 sr and 13 c values characteristic of danian seawater even though 18 o data indicate the presence of varying quantities of diagenetic carbonate cement in the ekofisk formation porewater 87 sr 86 sr values are very constant range 0 70786 0 70810 the formation water probably contains locally derived sr from carbonate plus a small contribution from noncarbonate minerals with higher 87 sr 86 sr in the underlying tor formation chalk samples containing a mixture of primary chalk and later cement have 87 sr 86 sr values that rise with depth to a maximum of 0 70865 much higher than contemporaneous seawater porewater 87 sr 86 sr values increase even more dramatically with depth to a maximum of 0 70988 both cement and waters have been influenced by sr with a high 87 sr 86 sr probably derived from underlying sedimentary rocks comparison with waters brought to the surface together with produced oil indicates that the depthwise increase in 87 sr 86 sr reflects an increase in salinity from 50 000to 140 000 mg l total solute content this suggests that zechstein evaporites may be the source of the radiogenic sr in the tor formation the difference in isotope composition between carbonates and waters in the ekofisk and tor formations indicates that their hydrochemical systems have evolved differently during diagenesis this is due to the barrier effect of the ekofisk tight zone a hardground at the base of the ekofisk formation which effectively splits the reservoir vertically into two this study thus provides a new way of determining the positions of permeability barriers in oil reservoirs also demonstrated for the first time is the existence of vertical variations in salinity of water in oil such variations could have important implications for the calibration of resistivity logs and calculation of the amount of oil in place

carbazole distributions in carbonate and clastic source rocks abstract carbazole the benzocarbazoles and their alkyl derivatives have been studied from rock extracts to assess the contribution of facies and maturity in controlling their distribution carbonates from the keg river formation elk point group middle devonian western canada consisting of two different facies reflecting deposition under trangressive and regressive events were used to assess facies influences to study maturation a uniform organo facies of organic rich posidonia shale lower toarcian jurassic northern germany from 0 48 to 1 45 r r was used the organic rich lower keg member deposited under photic zone anoxia contained predominantly c 4 c 5 carbazoles by contrast the upper keg river member deposited under regressive higher salinity environment contains predominantly carbazole itself 1 methylcarbazole and a high abundance of benzo c carbazole relative to benzo a carbazole the distribution of the c 1 to c 3 carbazoles was seen to vary with facies an examination of the carbazole derivatives within the posidonia shale reveals that maturation strongly influences the distribution of carbazole methylcarbazoles 1 8 dimethylcarbazole 1 ethylcarbazole benzo a carbazole and benzo c carbazole quantitative determination of these compounds indicates a maximum yield at 0 88 r r for all derivatives with the exception of carbazole which displays as a maximum at 0 53 r r a systematic variation of compound ratios with maturity to 0 88 r r suggests that selective isomerisation destruction generation of carbazole derivatives may occur in contrast to earlier publications which stress the importance of carbazoles as migration markers in migrated oils the results presented here indicate that facies and maturation do play a significant role in controlling the distribution of carbazole derivatives in source rocks and other sediments

r mode factor analysis of lithologic variables from cyclically deposited late paleozoic barakar sediments in singrauli gondwana sub basin peninsular india abstract the quantitative relationships between lithological variables from the late paleozoic coal bearing cycles have been investigated using factor analysis in an attempt to analyze net subsidence during the deposition of these cycles the results suggest that there are only two non zero eigenvalues in varimax matrix which indicate that the hyper ellipsoid enclosing the data points have seven axes of zero length and exists an ordinary two dimensional ellipsoid the data points can be located with reference to two mutually perpendicular axes loading on thickness of sandstones thickness of shale number of sandstone beds and number of shale beds are extremely high on rf i and low on the other factor this would lead to the interpretation that a balance was maintained throughout the barakar sedimentation between the rate of deposition and the rate of subsidence on the other hand loading on number of coal beds is high on suggesting that the development of peat swamps coal beds is not a normal feature during the late paleozoic barakar sedimentation in this gondwana sub basin

migration of hydrocarbons in the tampen spur area norwegian north sea a reservoir geochemical evaluation abstract this paper describes the application of reservoir geochemical protocols to a study of oil field and regional petroleum compositional variations in the major fields in the tampen spur area the tampen spur high is located in the middle of several oil mature to gas mature source rock kitchens and most of the structures might receive petroleum from several different directions based on the definition of several different petroleum populations within the tampen spur area we define five major petroleum charging systems correlating the petroleum population variations with geological information allows us to derive likely migration fill scenarios for many of the oil fields and requires us to invoke a new upper jurassic carrier system in parts of the area connecting brent group reservoirs across major faults based on this hypothesis two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures an understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest because most of the smaller substructures are marginally economic thus it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling this study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the tampen spur is more complicated than suggested earlier