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

geochemical effects of asphaltene separation procedures changes in sterane terpane and methylalkane distributions in maltenes and asphaltene co precipitates asphaltene precipitation either natural or artificial may be an important cause of observed compositional differences in oils of identical source and maturity we studied variations in both the bulk and molecular compositions of maltenes and asphaltene co precipitates prepared from six different oils using different procedures the first procedure used a single treatment with n pentane iptc to separate asphaltenes from maltenes the second procedure applied four sequential n pentane extractions of the iptc asphaltenes four times 4ptc analyses of resulting fractions included thin layer chromatography tlc gas chromatography gc and gas chromatography mass spectrometry gc ms these asphaltene separation processes resulted in changes in geochemical parameters previously considered to be influenced solely by source or thermal maturity maltene geochemical parameters not significantly affected by multiple n pentane extractions of the n pentane precipitated asphaltenes were the c 15 c 35 n paraffin distributions except for a small increase in higher n alkanes hopane and homohopane distributions tm ts ratios and c 27 c 28 c 29 sterane distributions maltene geochemical parameters which were affected by multiple n pentane washes of the n pentane precipitated asphaltenes were increases in the c 21 and c 22 sterane pregnane to c 27 c 28 c 29 and c 30 sterane and c 20 to c 24 tricyclic terpane to c 29 to c 35 hopane ratios the n pentane precipitated asphaltene co precipitates showed an increasing ratio of methylalkanes to n alkanes in the range from c 25 to c 36 following multiple extractions with n pentane these results suggest mechanisms of molecular interactions between maltenes and asphaltenes

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

biomarker maturity parameters for high maturities calibration of the working range up to the oil condensate threshold abstract in a study of oils and source rocks from the kimmeridge clay united kingdom and the hanifa qatar formations several biomarker maturity parameters with working ranges up to vr e vitrinite reflectance equivalent 1 0 oil condensate threshold have been identified and calibrated this represents a significant improvement compared to commonly used biomarker maturity tools sterane and hopane isomerisation with their maturity maximum of approximately vr e 0 7 early part of oil window these new parameters are 1 the absolute concentrations of steranes and hopanes decreasing gradually with increasing maturity 2 the ratio of tricyclic terpanes tricyclic terpanes hopanes increasing with maturity 3 the ratio of diasteranes 14 h 17 h steranes depending both on maturity and on source rock lithology and 4 the ratio of t s t m 22 29 30 trisnorneohopane 22 29 30 trisnorhopane increasing rapidly at very high maturities during artificial maturation experiments the biomarker maturities described in the natural samples were also known to be time temperature dependent up to rather severe laboratory heating conditions this corresponds with the working range up to high maturity levels as observed in the natural samples

geochemistry of asphaltenes abstract asphaltenes derived from both oil and source rocks have been studied by pyrolysis gas chromatography the pyrograms obtained at 450 and 550 c show that asphaltene structure is very close to the structure of the kerogen of the same sample they can be interpreted as kerogen moieties resulting from its early evolution therefore they can be used as substitutes of kerogen in genetic studies consequently asphaltenes pyrolysis appear to be a tool in correlation studies for oil oil correlation it can supplement and even replace in the case of degraded oils the information given by hydrocarbon distributions for oil source rock correlations the match between pyrograms of asphaltenes from both oil and source rocks offers more direct possibilities than usual techniques

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

recognition and quantification of the effects of primary migration in a jurassic clastic source rock from the norwegian continental shelf a detailed quantitative geochemical study was made of a mature jurassic clastic source rock sequence in order to attempt to recognize and quantify petroleum migration effects two different quantitative approaches were followed to monitor primary migration effects on both the bitumen 1 e g whole rock extract and the bitumen 2 e g isolated kerogen extract fractions these methods were a comparisons of toc normalized extract yields and quantified molecular compositions of petroleums from both tightly carbonate cemented zones and those from less cemented zones and b comparison of petroleums from shale laminae vs those from interbedded siltstone laminae on this basis it was possible to assess apparent primary migration efficiency relative expulsion efficiencies in certain shale samples and relative import efficiencies in siltstone bands ranged from 11 total extract to 85 saturated hydrocarbons and individual n alkanes no carbon number dependent fractionation effects were observed for n alkanes of bitumen 1 in the c15 to c35 range i e expulsion efficiencies were independent of carbon number suggesting bulk oil flow with chromatographic modification as the predominant transport mechanism

hydrous pyrolysis of monterey asphaltenes abstract hydrous pyrolysis of asphaltenes has been tested as a method to reconstruct the chemical composition of biodegraded oils and oil seeps the asphaltenes of three oils a nondegraded oil a biodegraded oil and a biodegraded oil seep from the monterey formation were studied results show that the aliphatic fraction generated by hydrous pyrolysis is very similar in chemical composition to the non degraded oil this makes the method very useful in correlation studies of biodegraded and nondegraded oils it also allows to roughly estimate the maturity of the source of the biodegraded oil or oil seep

origin of tar mats in petroleum reservoirs part i introduction and case studies abstract three case studies of petroleum reservoirs containing tar mats oseberg field and ula field both from the north sea and a north american field have been studied using a variety of organic geochemical techniques with special emphasis on the geochemistry of the asphaltenes the results were evaluated in combination with the available geological data and with numerical simulations to evaluate possible mechanisms of tar mat formation part ii wilhelms and larter 1994 in part i the petroleum geochemistry of three sets of tar mats is described the tar mat extracts were characterized by a sharp increase in the asphaltene content 20 60 wt compared with the oil leg extracts 1 5 wt the extract yields kg eom t rock in the tar mats ca 4 46 for the oseberg field 8 18 for the ula field and 8 43 for the north american case study are significantly higher than in the corresponding oil leg extracts which have extract yields of ca 1 14 kg t rock the tar mat extracts are geochemically related to the pooled oil as revealed by geochemical fingerprinting including biomarker analysis the tar mats are situated in high porosity and high horizontal permeability sandstone layers above permeability barriers several zones of low extract yield and immature petroleum geochemical characteristics were observed within the oil legs and between tar mats which might represent minor amounts of petroleum generated locally from indigenous organic matter

inversion of submesoscale patterns from a high resolution solomon sea model feasibility assessment a high resolution realistic numerical model of the solomon sea which exhibits a high level of variability at mesoscales and submesoscales is used to explore new avenues for data assimilation image data assimilation represents a powerful methodology to integrate information from high resolution observations such as satellite sea surface temperature or chlorophyll or high resolution altimetric sea surface height that will be observed in the forthcoming swot mission the present study investigates the feasibility and accuracy of the inversion of the dynamical submesoscale information contained in high resolution images of sea surface temperature sst or salinity sss to improve the estimation of oceanic surface currents the inversion method is tested in the context of twin experiments with sst and sss data provided by a model of the solomon sea for that purpose synthetic tracer images are built by binarizing the norm of the gradient of sst sss or spiciness the binarized tracer images are compared to the dynamical image which is derived from the finite size lyapunov exponents the adjustment of the dynamical image to the tracer image provides the optimal correction to be applied on the surface velocity field the method is evaluated by comparing the result of the inversion to the reference model solution the feasibility of the inversion of various images sst sss both sst and sss or spiciness is explored on two small areas of the solomon sea we show that errors in the surface velocity field can be substantially reduced through the inversion of tracer images

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

sequential extraction a useful tool for reservoir geochemistry abstract little is known about the microscale distribution and potential molecular fractionation of bitumen residing in reservoir rocks few data exist on the comparative organic geochemistry of hydrocarbons in authigenic inclusions formed in reservoir rocks and the bitumen in the pore space a three step sequential extraction technique has been applied to clastic petroleum reservoir samples using a suite of solvents with increasing polarity in order to address these questions in the analyzed samples the following main trends were observed i the first extract represents 95 of the total extract ii the relative polar compound content increases going from the first to the last extract iii the last extract has generally a slightly lower apparent maturity as assessed using biomarker parameters additionally a reduction in the degree of biodegradation from the first to the last extracts was observed implying tentatively that biodegradation takes place dominantly in the center of the pores fluid inclusion extracts show distinct source characteristics however the last extract appears to approach the fluid inclusion extract signature in some aspects the use of sequential extraction as a routine tool in the reservoir geochemical context is judged to be limited however it may help to solve specific problems

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

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

application of biological markers in the assessment of paleoenvironments of chinese non marine sediments abstract in this study we employ molecular organic geochemical data for 22 representative sediment samples from chinese non marine sedimentary basins in an attempt to characterize and assess the non marine depositonal paleoenvironments the samples investigated include oilshale shale mudstone and sodium sulphate rich sediments ranging in age from cretaceous to tertiary it is evidenced by geological and geochemical data that those sediments studied originate from lacustrine environments ranging from freshwater brackish fresh water to hypersaline the aliphatic fractions of the sediment extracts were analyzed by gc and gc ms and relative abundance of compounds and compound classes of normal acyclic and cyclic alkanes were measured from mass chromatograms the results reveal significant differences in the chemical features of the various sample groups which enable them to be characterized and identified in terms of source and or environment related parameters the diagnostic parameters that allow this assessment are the relative abundances of n alkanes acyclic isoprenoid alkanes and 4 methyl steranes hopane sterane ratio gammacerane and homohopane indexes etc in this study data interpretation was also assisted by pattern recognition through principal component analysis the results show that the sample groups of different environmental origin could be unambiguously distinguished on scores plot

primary migration by diffusion through kerogen i model experiments with organic coated rocks abstract laboratory experiments were performed to assess diffusion through kerogen as a mechanism of hydrocarbon transport through fine grained rocks such transport can be important in primary migration within source rocks and in leakage through seals to test the concept of diffusion through organic matter networks model experiments were performed in which hydrocarbon diffusion was measured through austin chalk cores that had been coated with a monolayer of fatty acids hydrocarbon fluxes through the coated cores were compared to hydrocarbon fluxes through uncoated austin chalk cores results showed that the organic coating enhanced transport through the core by a hundredfold over diffusion through its water filled pore space alone

a comparison of organosulphur compounds produced by pyrolysis of asphaltenes and those present in related crude oils and tar sands abstract asphaltenes and nso fractions from a variety of oils and tar sands have been characterized by pyrolysis gas chromatography py gc using both flame ionization and flame photometric detectors organosulphur compounds were not always produced by pyrolysis of the asphaltenes isolated from the biodegraded tar sand extracts although pyrolysis of the nso fractions produced a series of thiophenes from all of the samples examined these observations suggest that under certain conditions asphaltene fractions may be affected by biodegradation leading to preferential removal of the sulphur containing compounds in addition it was observed that py gc of asphaltenes permitted oils to be differentiated on the basis of their source rock lithology oils derived from carbonate source rocks produced thiophene benzothiopene ratios 1 for oils derived from shales thiophene dibenzothiophene ratios could be used in a similar manner

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