hydrocarbon generation migration alteration entrapment and mixing in the central and northern north sea abstract there is little doubt that sediments of upper jurassic to lowermost lower cretaceous age particularly those of the kimmeridge clay formation and its equivalents are the source of the vast bulk of the oil in the central and northern north sea this is true both of oil in conventional mesozoic plays and in tertiary clastic reservoirs the timing of oil generation and migration ranges from the late cretaceous through to the present the oil productivity of the kimmeridge clay formation in the central graben moray firth and south viking graben areas of the north sea is estimated to be in excess of 250 billion barrels of which about 25 is accounted for in accumulations discovered to date there is strong areal differentiation between oil trapped in mesozoic reservoirs as opposed to upper cretaceous chalk and tertiary reservoirs this paper is particularly concerned with hydrocarbons in tertiary reservoirs which have a wide range of compositions and appear to have complex accumulation and degradation histories migration to chalk and younger tertiary reservoirs occurs often through thick shale sequences the evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration mixing and degradation is proposed

charging of the neogene penglai 19 3 field bohai bay basin china oil accumulation in a young trap in an active fault zone the penglai 19 3 pl19 3 oil field the largest offshore oil field in china was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl19 3 anticline was not finally formed until about 2 0 ma and is cut by densely distributed faults source rock and crude oil samples from the pl19 3 field were analyzed to determine the origin and formation mechanisms of this large oil field three organic rich oil prone source rock intervals exist in the bozhong subbasin each of which has a distinct biomarker assemblage oil samples from different wells have different biomarker associations and three source related oil classes were identified within the pl19 3 field based on biomarker compositions and multivariate analysis of the data the pl19 3 field displays considerable compositional heterogeneity the compositional heterogeneity within the field and comparison between oil samples from the pl19 3 field and those from nearby structures suggest three field filling directions which is consistent with the results of migration pathway modeling the pl19 3 field was charged in the north by oil generated from dongying formation source rocks in the eastern bozhong depression and bodong depression in the southeast by oil generated from shahejie formation source rocks in the miaoxi depression and in the northwest by oil generated from shahejie formation source rocks in the central bozhong depression oil charge from multiple source rock intervals and multiple generative kitchens and focusing of oil originating from a large area of the bozhong depression into the same trap resulted in rapid oil accumulation in the pl19 3 structure and the formation of this large oil field in a very young trap within an active fault zone

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

source oil charging history and filling pathways of the ordovician carbonate reservoir in the halahatang oilfield tarim basin nw china abstract the ordovician reservoir in the halahatang depression is one of the most commercially prolific oil reservoirs in the tabei uplift of the tarim basin nw china for this study a total of 94 oil samples were collected from 88 exploration production wells in this oilfield all of the oils possess similar organic molecular compositions and belong to the same oil population oil to source correlation results indicate that oil accumulations discovered in halahatang oilfield were derived from the upper ordovician source rocks the homogenization temperatures of fluid inclusion in the ordovician reservoir in the halahatang oilfield range from 90 c to 100 c and from 140 c to 160 c the bimodal distribution pattern shown in a histogram of the homogenization temperatures indicates that the ordovician oil reservoir in the halahatang oilfield has been charged twice coupling this information with the reconstructed burial and geothermal histories by 1 d basin modeling the homogenization temperatures can be related to the relative geological ages of 419 ma to 410 ma and 16 ma to 8 ma namely the middle to late silurian and the middle miocene respectively representing the two phases of oil charging and entrapment the oil migration orientation and charging pathways can be traced using molecular indicators such as ts ts tm and tmnr parameters the overall oil migration orientation in the oilfield is generally from south to north therefore the source kitchen for the halahatang oilfield is predicted to be to the south side of the depression the southern part of the halahatang depression along the oil charging pathways is identified as the most promising region for oil exploration

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

pressure temperature time composition p t t x constraints of multiple petroleum charges in the hild field norwegian north sea abstract the brent reservoirs of the hild field situated at 3 8 4 3 km depth in the northern north sea show evidence of multiple episodes of diagenetic events fracturing and petroleum charging data from fluid inclusions and drill stem test samples characterise the petroleum filling history of the hild field two main types of petroleum inclusions occur type 1 inclusions which occur in two of the fault compartments of the field show a heavier composition than the present reservoir fluids from a comparison of fluid inclusion analyses and burial history onset of reservoir filling is most likely represented by type 1 inclusions and took place at 125 130 c in well 30 7 8r this temperature corresponds to a burial depth of 3 5 3 7 km which occurred 35 32 ma ago type 2 inclusions occur in all wells and are compositionally similar to the reservoir fluids suggesting recent trapping considerable differences in homogenisation temperature and phase behaviour of type 2 inclusions between the three wells of the hild field indicate the compartmentalised nature of the reservoir pvt modelling of fluid properties and trapping conditions was based on microthermometry gc data for type 1 inclusions and present day fluid compositional data for type 2 inclusions the results show generally good agreement between estimated pressure for type 2 inclusions and present day reservoir conditions and an increase in overpressure between trapping of types 1 and 2 inclusions we suggest that quartz cementation may continue after onset of reservoir filling and may exert major control on the pressure evolution in deep reservoirs

charging of the penglai 9 1 oil field bohai bay basin china functions of the delta on accumulating petroleum abstract the penglai 9 1 pl9 1 oil field which contains china s third largest offshore oil accumulation in place reserves greater than 2 28 10 8 ton or 1 49 10 9 bbl was found in shallow reservoirs 700 1700 m 2297 5577 ft within the most active fault zone in east china the pl9 1 field contains two oil bearing series the granite intrusions in mesozoic mz and both the sandstone reservoirs in neogene guantao ng and neogene minghuazhen nm formation the origins of the pl9 1 field both in terms of source rock intervals and generative kitchens were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples the mesozoic granite intrusions which hold more than 80 of the oil reserves in the field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression the neogene reservoirs of the pl9 1 field were charged in the west by oil generated from the third member es 3 of the shahejie formation in the bodong depression and in the south by oil generated from the first member es 1 of the shahejie formation in the miaoxibei depression interactive contact between the large fan delta and the mature source rocks residing in the es 3 formation of the bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the pl9 1 field which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east china

assessment of mesozoic and upper paleozoic source rocks in the south yellow sea basin based on the continuous borehole csdp 2 abstract being lack of core data and measured data although the marine oil gas exploration in the south yellow sea basin has been going on for 57 years no commercial hydrocarbon reservoirs have been found so far the quantitative source rocks evaluation based on geochemical data and fluid inclusions containing hydrocarbon benefits from the completion of borehole csdp 2 in 2016 a continuous coring well of the chinese continental shelf drilling program csdp which indicates that the marine origin oil gas exploration in the south yellow sea basin enters into a new stage as revealed by the well csdp 2 three sets of effective hydrocarbon source rocks in the mesozoic and upper paleozoic have been identified which are distributed in the lower triassic qinglong formation t1q upper permian longtan dalong formation p3l d and middle permian gufeng qixia formation p2g q respectively among them organic rich source rocks mainly concentrate in the lower part of the p3l d and the middle upper part of the p2g q and the p3d mudstone also works as good source rock the p3l d mudstone with high organic abundance is the chief source rock in the south yellow sea basin whose maximum hydrocarbon generating intensity may reaches up to 795 09 104 t km2 and hydrocarbon expulsing intensity remains at the level of 165 03 104 t km2 a noteworthy feature of the p2g q source rocks is the strong vertical heterogeneity with the hydrocarbon expulsing intensity of the upper part being 34 14 104 t km2 while that of the lower part being 18 07 104 t km2 in contrast the organic abundance of argillaceous limestone in the t1q is mainly poor to medium and its hydrocarbon expulsing intensity is the weakest one in the three sets of hydrocarbon source rocks only about 12 7 104 t km2 taking into consideration the joint influence of depositional environment organic matter parent source and biological productivity the overall quality of source rocks in the south yellow sea basin is at the similar level to the lower yangtze subei basin but lower than that of the upper yangtze sichuan basin the most significant oil gas information is that multiple direct oil indications and high value abnormalities of gas logging have been discovered in the well csdp 2 moreover the mesozoic and upper paleozoic marine strata in the south yellow sea basin have experienced three hydrocarbon charging stages indicating a broad prospect of marine oil gas exploration

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

upper mantle seismic anisotropy and lithospheric decoupling the lithosphere underlying stable continental shield regions is thought to extend to a depth of 200 km compressional wave velocity models derived from a recent approximately ns refraction profile in northern australia include a pronounced high velocity zone at a depth of around 200 250 km conventional petrological interpretations in terms of mineralogical or compositional changes cannot readily explain this feature calculated velocities for the garnet pyrolite model using a derived geotherm fit the velocities above and below this high velocity zone but cannot account for the high velocity 8 6 km s 1 zone itself this feature is explained in terms of velocity anisotropy which might reflect mechanical decoupling of the continental lithosphere from the underlying mantle

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

identifying multiple sources of petroleum fluids in browse basin accumulations using diamondoids and semi volatile aromatic compounds abstract hydrocarbon fluid correlation studies often rely on compounds that are source specific but only represent a minor fraction of the bulk fluid e g steranes the correlation in the present study utilises compounds that represent a significant proportion of the bulk fluid namely semi volatile aromatics sva and diamondoids comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry gc gc tofms was used to analyse diamondoids and sva in whole oil condensate samples from the browse basin north west shelf australia together with aromatic maturity ratios and the stable carbon isotopic composition for selected diamondoids and alkylbenzenes these analyses demonstrate that numerous accumulations within the browse basin contain hydrocarbons from mixed sources the diamondoid and sva data provides further information on the current hydrocarbon fluid discrimination which is primarily based on saturated biomarker compositions results of this study reveal a complex fill history by identifying the presence of a high maturity fluid s in the biodegraded accumulations on the yampi shelf i e in the greater cornea field and at gwydion 1 this high maturity fluid is most likely derived from the lower middle jurassic plover formation j10 j20 supersequences in the greater cornea area and in the case of gwydion 1 additional hydrocarbons may also be derived from the upper jurassic vulcan formation j30 k10 supersequences other accumulations that comprise mixtures include mimia 1 and concerto 1 st1 deep located to the north of the ichthys field and could represent charge from several jurassic source rocks the most mature fluids analysed in this basin are family ii plover sourced and reservoired condensates from kronos 1 dinichthys north 1 and gorgonichthys 1 as demonstrated by their elevated concentrations of the methyladamantanes and methyldiamantanes the dinichthys north 1 and gorgonichthys 1 condensates also show a significant enrichment in the 13c compound specific values of the di tri and tetra methylbenzenes whereas the kronos 1 condensate does not suggesting derivation from different source kitchens

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

assessment of fluid contacts and compartmentalization in sandstone reservoirs using fluid inclusions an example from the magnus oil field north sea location of an oil water contact is crucial for estimating reserves and for designing production strategies identifying hydrodynamic barriers or baffles is also important for optimizing both recovery and flow rates in some oil fields identifying fluid contacts and barriers is not always possible using conventional wireline and formation testing methods

microbial cycling migration and leakage of light alkanes in the nile delta tertiary fan abstract we present a geochemical dataset which helps unravel the complex set of processes by which light alkanes are sourced charged mixed leaked and altered in the plio pleistocene nile delta thermogenic gas derives from a sub messinian source and mixes with microbial hydrogenotrophic methane rich gas in the plio pleistocene section there is strong isotopic evidence for both microbial generation and microbial degradation of ethane and propane but these signals are only recorded where the rates of biological processes outstrip the rate of thermogenic charge high resolution gas geochemistry profiles through four 500 1100 m sequences of mixed channel channel levee mass flow deposits and hemipelagites shed light on migration and leakage pathways we see limited geochemical evidence for migration along or across faults which cross cut mud rich sequences lateral migration along sands silts delivers gas to structural highs where leakage occurs vertically along focussed pathways through heterogeneous mud rich sediments we propose that in situ generation of microbial gas within mud rich sequences facilitates percolation of migrating gases that replenishes c2 components and sustains the biodegradation pathway in syntrophic microbial communities high resolution changes in gas composition suggest an unequilibrated system which is being actively charged in some structures rates of charge and of microbial alteration of gas are broadly similar in others rates of charge exceed rates of microbial alteration our results have important implications for the understanding of both basin wide fluid flow and the ecology of the deep biosphere

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

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

carbon and hydrogen isotopic variations of natural gases in the southeast columbus basin offshore southeastern trinidad west indies clues to origin and maturity natural gas can have two distinct origins biogenic and thermogenic sources this paper investigates the types and maturities of natural gas present in the se columbus basin offshore trinidad the chemical composition and the isotope ratios of c and h were determined for approximately 100 samples of natural gas from eight areas within the se columbus basin these compositions and isotopic data are interpreted to identify the origins of gas biogenic thermogenic and maturity the data showed that the gases in the se columbus basin are of both biogenic and thermogenic origin with a trend of mainly thermogenic to mixed to biogenic when moving from sw to ne across the basin this trend suggests differential burial of the source rock the presence of mixed gas indicates there was migration of gas in the basin resulting in deeper thermogenic gas mixing with shallow biogenic gas

detection of petroleum heterogeneity in eldfisk and satellite fields using thermal extraction pyrolysis gc gc ms and isotope techniques abstract eldfisk field is one of several oil producing chalk fields of the north sea analysis was performed on core samples from 11 wells from the palaeocene cretaceous chalk reservoir analyses performed on cores included various pyrolysis techniques conventional gc ms was performed on 27 oils from the 2 7 block stable carbon isotope analysis was performed on bulk and n alkane fractions of the oils pyrolysis data could be used to detect the main producing section of the reservoir and show that there appear to be sections of the reservoir rich in waxes biomarker and pyrolysis data indicate that there are differences in maturity of the petroleum of eldfisk alpha and bravo structures and that there are lateral and vertical variations in composition within each structure based on both biomarker and isotopic data there is evidence for at least two phases of reservoir filling

mechanisms for oil depletion and enrichment on the shijiutuo uplift bohai bay basin china the shijiutuo uplift is a major uplift to the north of the bozhong depression the largest generative kitchen in the bozhong subbasin bohai bay basin although the n35 2 trap on this uplift contains a medium size oil accumulation and the q32 6 trap contains china s third largest offshore oil accumulation the q31 1 trap between the n35 2 and q32 6 traps with very similar evolution history was confirmed to be dry biomarker associations of crude oil and source rock samples were analyzed and three dimensional migration pathway modeling was conducted to investigate the origin of oils and mechanisms for oil enrichment and depletion on the uplift multiple parameter oil source correlation and hierarchical cluster analysis using 10 selected biomarker parameters allowed the identification of four source related oil classes almost all oils from the shijiutuo uplift are derived from the eocene shahejie formation whereas oils found between the shijiutuo uplift and the bozhong depression either are derived from or have important contributions from the oligocene dongying formation variations in oil classes and biomarker parameters suggest sequential migration of oil generated from the shahejie and then dongying formations in the bozhong depression which is reasonably supported by petroleum migration pathway modeling oil charge from two oil prone source rock intervals and more importantly focusing of oil originating from a large area of the bozhong generative kitchen into the same trap accounted for oil enrichment and formation of china s third largest offshore oil field in the q32 6 structure the complexity and primary control of the sealing surface top surface of the carrier bed morphology on the positions of migration pathways caused the q31 1 trap to be shielded from migration of oil originating from the bozhong depression resulting in oil depletion in this trap shadows to petroleum migration may occur because of the three dimensional behavior of petroleum migration and two dimensional migration modeling may be misleading in predicting petroleum occurrences

confocal microscopy of fluid inclusions reveals fluid pressure histories of sediments and an unexpected origin of gas condensate we present two examples of how fluid inclusion data can be used to determine geologic pressure histories and to quantify the compositional evolution of petroleum in oil reservoirs volumetric liquid vapor ratios generated with a confocal laser scanning microscope are used along with pressure vapor temperature p v t modeling software to estimate the composition p t phase envelope and isochore of single petroleum inclusions in the north sea9s judy and alwyn fields in both cases the gas condensates currently in the reservoirs formed by the emplacement of gas into preexisting oil accumulations pressure histories of individual units in each field are also revealed providing the kind of data needed to determine the permeability and fluid flow histories of sedimentary basins

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

floodplain deposits a geochemical archive of flood history a case study on the river rhine germany abstract based on the correlation between discharge and carbonate content of the suspended load of the river rhine germany a systematic geochemical mineralogical and granulometric study was carried out to verify whether this geochemical signal is transferred to floodplain deposits and in what way these sediments and their chemostratigraphic characterization can be used as a tool for the reconstruction of the river flood history the analysis of the time resolved changes in the composition of particulate matter during a flood event revealed that the increase of carbonate content represented by cao sr with discharge was coupled to a simultaneous decrease in the relative amount of siliciclastics k 2 o rb the association of these two groups of diametrical parameters with specific grain size fractions carbonates with 40 200 m siliciclastics with 200 m were found to be slightly shifted relative to each other and showed different gradients during the surging and fading flood wave this together with the covariance of elements pertaining to minerals with different density e g carbonate and heavy minerals suggests a chemical response to the changes in discharge which is controlled primarily by hydraulic equivalence rather than grain size there is also a time lag between the amount of suspended load and discharge with a maximum in suspended load shortly after the peak discharge when the flood has already started to abate the flood plain sediments have similar composition to the suspended load suggesting the direct transfer of the geochemical flood signal to the floodplain sediments three lithological units could be distinguished in a 240 cm long sediment core collected from the floodplain grain size and geochemical composition indicate that only the top of the section 20 70 cm represents sediments deposited in an abandoned channel of the river and may have preserved the geochemical flood signals as identified during actual flood events the comparison of the chemostratigraphy of this part of the section estimated with optical stimulated luminescence to be deposited between ca 1650 and 1920 with a record of historically documented inundations however yielded only poor agreement the possible reasons for this inconsistency are discussed and suggestions are made for continuing investigations

charging of carboniferous volcanic reservoirs in the eastern chepaizi uplift junggar basin northwestern china constrained by oil geochemistry and fluid inclusion substantial amounts of petroleum were recently discovered in the carboniferous andesite tuff breccia and basalt reservoirs of the chepaizi uplift in the western junggar basin however the charging history of the carboniferous petroleum reservoir is poorly understood oil oil correlation studies indicate that all of the oils were mainly derived from the middle permian wuerhe formation source rocks possibly mixed with a small contribution from carboniferous baogutu formation source rocks in the neighboring changji sag based on the petrographic and microthermometry of fluid inclusions two hydrocarbon charging episodes are defined these episodes were characterized by a low peak range homogenization temperature th distribution 80 c 90 c and high salinity 13 22 13 42 wt nacl and a high peak range th distribution 120 c 130 c and low salinity 4 89 11 72 wt nacl respectively through one dimensional basin modeling and pressure volume temperature composition simulation the burial thermal histories for wells p61 p66 p668 and p663 were reconstructed and their trapping temperatures of the hydrocarbon inclusions were calculated to be higher than their corresponding highest paleotemperature i e 56 8 c 53 7 c 60 9 c and 58 1 c respectively implying fast hydrocarbon charging processes promoted by deep hydrothermal fluids associated with the hydrocarbon generation history sealing process of the hongche fault and regional tectonic evolution these two hydrocarbon charging events were deduced as the adjustments of oils previously accumulated along the hongche fault zone because of the tectonic extension in the paleogene and regional tilting in the neogene respectively the general direction of oil charging was traced from south to north and from east to west as indicated by the molecular parameters of nitrogen bearing compounds and c20 c21 triaromatic steroids c20 c21 c26 c28 triaromatic steroids ta i ta i ii which roughly coincided with the active fracturing

a magnus opus helium neon and argon isotopes in a north sea oilfield this study of the magnus oilfield located in the east shetland basin northern north sea represents the most detailed investigation of noble gas isotope systematics in a liquid hydrocarbon reservoir yet undertaken samples from nine producing wells across this middle jurassic field were taken and the helium neon and argon isotopic ratios and abundances in the oil were determined both the helium and the neon isotope systematics require a contribution from a mantle source if the mantle endmember is modeled using mid ocean ridge mor values 2 3 4 5 of the 4he and 4 3 6 2 of the 21ne is mantle derived the remainder of the 4he and 9 0 12 0 of the 21ne is crustal radiogenic and the remaining 21ne is atmosphere derived the resolved mantle derived he ne ratio is quite distinct from upper mantle values estimated from mor samples but indistinguishable from values resolved in other regions of continental extension this result provides strong evidence that the subcontinental lithospheric mantle not only has a different noble gas inventory to the convecting mantle under mors but also has a near uniform composition the quantity of radiogenic noble gas associated with the magnus oil groundwater system can only be accounted for by production predominantly from outside the volume of the magnus sandstone aquifer reservoir drainage area and the associated kimmeridge clay source rock formation and together with the mantle derived noble gases provides strong evidence for cross formational communication with deeper regions of the crust the 20ne and 36ar must have been input into the oil phase by interaction with an air equilibrated groundwater noble gas partitioning between a seawater derived groundwater and the oil phase at the average magnus sandstone aquifer temperature requires a subsurface seawater oil volume ratio of 110 40 to account for both the 20ne and 36ar concentrations in the central and southern magnus samples the volume of groundwater which has equilibrated with the magnus oil is indistinguishable from the static volume of water estimated to be in the down dip magnus aquifer reservoir drainage volume this suggests that the magnus oil has obtained complete equilibrium with the groundwater in the reservoir drainage volume probably during secondary migration and further suggests that concurrent cementation of the magnus sandstone aquifer has occurred with little or no large scale movement of air equilibrated groundwater through the aquifer system higher concentrations of 20ne and 36ar in the n magnus oil cannot be accounted for by equilibration with a seawater derived groundwater this is qualitatively consistent with the earlier and more mature oil in this section equilibrating with freshwater which is known to have been trapped in the crest of the reservoir structure

secondary migration of petroleum along syncline axes a case study of the southern kuqa foreland basin tracing petroleum migration pathways for petroleum exploration in a sedimentary basin is challenging paleo uplifts are generally considered to represent the primary migration directions of petroleum here we propose a model for the kuqa foreland basin in which petroleum migrates along the axes of synclines between paleo uplifts based on an integrated analysis of seismic geochemical and production data interpretation of detailed seismic data indicates that petroleum is unlikely to migrate to the paleo uplifts because of their relatively low positions fault disruptions or a lack of mesozoic reservoirs geochemical parameters including the ratios of alkyl dibenzothiophenes and the gas wetness parameter show that petroleum maturity gradually decreases along the axes of synclines between paleo uplifts from northeast to southwest petroleum production data and gas oil ratios also show decreasing trends from northeast to southwest this evidence suggests that petroleum is likely to migrate along the ax

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

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

petroleum geochemistry of the froy field and rind discovery norwegian continental shelf implications for reservoir characterization compartmentalization and basin scale hydrocarbon migration patterns in the region abstract petroleum geochemistry provides an excellent tool for understanding reservoir characteristics with respect to oil flow and tracing out elements of basin scale migrational patterns and reservoir compartmentalization organic geochemical characterization has been carried out on 580 core extracts and 9 oils from 11 wells of the froy field and rind discovery in the south viking graben two different drainage areas and source rock systems have been identified for the hydrocarbons in the froy field and the rind discovery on the basis of differences in maturity and gas to oil ratio in addition to facies differences like c 28 sterane content and the ratio of bisnorhopane to bisnorhopane plus norhopane results show that the rind discovery contains oil of higher maturity compared to the oil from froy field the petroleum in the rind discovery has a more terrestrial character and is interpreted to have been derived from source rocks other than the draupne formation in its typical anoxic distal development a likely candidate is the heather formation in addition a small contribution of immature oil has been identified in a separate small sub compartment in the froy field the petroleum in this sub compartment shows a high pristane to phytane ratio and a very prominent odd to even predominance well 25 14 drilled northeast of the froy field penetrates a water bearing hydrostatic structure the detailed geochemical characterization including petroleum inclusion studies have shown that this structure never received oil or gas nor did it have any communication with the froy field hence it is inferred that this structure never communicated with the hydrocarbon producing basin one of the two compartments in the rind discovery is hydrostatic and contains petroleum of a comparatively large maturity span whilst residual core bitumen in a high pressured neighboring compartment has a very small maturity span and contains presently only water as producible phase the ratios of the 20s to 20s 20r isomers of c 29 steranes the ratio of c 20 to c 20 c 28 triaromatic steroids and the c 28 triaromatic steroid to c 28 triaromatic steroid c 29 monoaromatic steroid ratio in the latter compartment have almost uniform values indicating a single oil pulse i e a short filling history whereas in the other compartment these ratios vary over a large range indicating a longer filling history as both compartments contain petroleum with the same source rock facies signatures it is suggested that these at some time were part of the same migration system communication between these compartments is inferred to have been disrupted before seal failure occurred in the structure which was penetrated by well 25 15r2 the analyses carried out indicate a high degree of chemical homogeneity in the petroleum of the froy field reservoir which in comparison with the rind discovery is more similar to extracts from typical anoxic developed distal shales of the upper jurassic source rock in the viking graben i e the kimmeridge equivalent draupne formation however the upper reservoir units in the northern well 25 5 a7 contain extracts with lower maturity and more terrestrial characteristics compared with the extracts in the deeper reservoir sections in addition well 25 5 1 which penetrates the highest point of the froy structure contains petroleum of slightly higher maturity than found elsewhere in the froy field the results further suggest that the faults in the froy field including the main e w trending fault separating the northern and the southern parts of the of the froy field did not adversely affect lateral communication during filling to conclude there is no petroleum geochemical evidence to suggest that intra reservoir faults have caused significant compartmentalization of the froy field except for the n s trending fault which separates a small block to the west from the froy field main reservoir thus with respect to petroleum production it is concluded that primary sedimentological features are more important in terms of exerting a first order control for determining the vertical and lateral flow of hydrocarbons in this reservoir than faults

charging of oil fields surrounding the northern end of liaoxi uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract the liaoxi uplift one of the most petroliferous uplifts in the bohai bay basin is sandwiched by two sags containing multiple mature source rocks the origins of oil located on the northern end of this uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions from 75 source rock extracts and 15 oils two oil families have been identified using 4 biomarker parameters and could be linked to the source rocks of the first and second members of the shehejie formation e 2 s 1 2 and the third member of the dongying formation e 3 d 3 respectively e 2 s 1 2 derived oils were found in the liaoxi sag and on the liaoxi uplift and were interpreted to originate primarily from the liaoxi sag e 3 d 3 derived oils were found in the liaozhong sag and originated from the liaozhong sag the liaoxi uplift have not been charged by e 2 s 3 drived oils from the liaoxi sag mainly because it departed from the dominant migration direction of e 2 s 3 drived oils the liaoxi uplift have not been charged by e 2 s 3 e 2 s 1 2 and e 3 d 3 drived oils from the liaozhong sag mainly because there were no delta sandstones developed on the slope between the liaoxi uplift and the liaozhong sag to serve as migration channels from source rocks to uplift in all three formations the sandstone up dip pinch out traps in e 2 s 3 formation in the liaoxi sag traps within the liaozhong sag and traps on the slope between the liaozhong sag and the liaodong uplift have a better chance to accumulating petroleum

molecular correlation of free oil adsorbed oil and inclusion oil of reservoir rocks in the tazhong uplift of the tarim basin china the free adsorbed and inclusion oils were recovered by sequential extraction from eleven oil and tar containing reservoir rocks in the tazhong uplift of tarim basin the results of gas chromatography gc and gc mass spectrometry analyses of these oil components and seven crude oils collected from this region reveal multiple oil charges derived from different source rocks for these oil reservoirs the initially charged oils show strong predominance of even over odd n alkanes in the range n c12 to n c20 and have ordinary maturities while the later charged oils do not exhibit any predominance of n alkanes and have high maturities the adsorbed and inclusion oils of the reservoir rocks generally have high relative concentrations of gammacerane and c28 steranes similar to the cambrian lower ordovician source rocks in contrast the free oils of these reservoir rocks generally have low relative concentrations of gammacerane and c28 steranes similar to the middle upper ordovician source rocks there are two interpretations of this result 1 the initially charged oils are derived from the cambrian lower ordovician source rocks while the later charged oils are derived from the middle upper ordovician source rocks and 2 both the initially and later charged oils are mainly derived from the cambrian lower ordovician source rocks but the later charged oils are contaminated by the oil components from the silurian tar sandstones and the middle upper ordovician source rocks

pvtx characteristics of oil inclusions from asmari formation in kuh e mond heavy oil field in iran incorporating pvt properties and compositional evolution of oil inclusions into reservoir engineering simulator protocols can enhance understanding of oil accumulation reservoir charge history and migration events microthermometry and volumetric analysis have proven to be useful tools in compositional reconstitution and pt studies of oil inclusions and were used to determine composition thermodynamic conditions physical properties and gas to oil ratios of heavy oil samples from asmari carbonate reservoir in kuh e mond heavy oil field in iran pvt properties were predicted using a pvt black oil model and an acceptable agreement was observed between the experiments and the simulations homogenization temperatures were determined using microthermometry techniques in dolomite and calcite cements of the asmari formation as well based on the homogenization temperature data the undersaturated hydrocarbon mixture prior to formation of the gas cap migrated with a higher gas to oil ratio from a source rock according to the oil inclusion data the onset of carbonate cementation occurred at temperatures above 45 c and that cementation was progressive through burial diagenesis pvt black oil simulator results showed that the reservoir pressure and temperature were set at 100 bar and 54 c during the initial stages of oil migration compositional modeling implies that primary and secondary cracking in source rocks were responsible for retention of heavy components and migration of miscible three phase flow during hydrocarbon evolution the pt evolution of the petroleum inclusions indicates changes in thermodynamic properties and mobility due to phenomena such as cracking mixing or and transport at various stages of oil migration

modelling of thermal convection in sedimentary basins and its relevance to diagenetic reactions abstract mathematical calculations of thermal convection have been carried out using a porous three player model to simulate pore water flow in a sedimentary basin with layers of different permeabilities the calculated flow lines demonstrate that even very thin layers eg around salt domes and igneous or hydrothermal intrusions analyses of formation waters from sedimentary basins like the north sea often show evidence of a crude stratification of the pore water with respect to salinity and isotopic composition this is evidence suggesting that large scale convection or other types of mixing does not take place and positive salinity depth gradient may help to physically stabilize the formation water the fact that many of the shallow reservoir rocks from the north sea have formation water with low salinity and negative 18 o values suggest that this is modified meteoric water and that migration of petroleum from deeper parts of the basin occurred as a separate phase along restricted migration pathways and was not associated with a high flux of pore water in the absence of thermal convection the total pore water flux through sandstones will be rather small except locally where we may have focused compactional flow through small cross sections diagenetic reactions will therefore normally be relatively isochemical during deeper burial