a geochemical study of oil migration at source rock reservoir contacts stable isotopes abstract whereas organic geochemical analyses of oils and potential source rocks have enabled correlations to be drawn and have been utilized to suggest modes of migration only limited data has been published relating a known source rock in contact with an oil filled reservoir this paper presents initial results from the examination of an approximately 100 m continuous core through the kimmeridge shale of the north sea the variability in extractable source rock hydrocarbon contents kerogen toc asphaltene and their carbon isotopic contents are documented nitrogen isotopic content of kerogens and asphaltenes as well as kerogen and asphaltene ton are relatively constant carbon isotopic compositions of kerogen extractable hydrocarbons and asphaltenes covaried significantly as did nitrogen isotopic compositions of kerogen and asphaltenes average isotopic compositions of the asphaltene free extracts and asphaltenes were nearly identical to the oil in the primary reservoir small chemical differences are noted among extracts

the expulsinator versus conventional pyrolysis the differences of oil gas generation and expulsion simulation under near natural conditions abstract the expulsinator provides a new technique to simulate generation and expulsion of hydrocarbons under near natural conditions this is realized by application of lithostatic pressure onto an intact source rock disc with undisturbed mineral matrix and kerogen network and by hydrous pyrolysis conducted in open flow through mode conventional pyrolysis methodologies serve well in generation kinetics assessment but are only of limited use for investigation of primary migration and expulsion due to destructive sample preparation inappropriate pressure regimes and pyrolysis in closed mode and or in the absence of water however comparison of results generated with conventional pyrolysis with expulsinator experiments is important to assess the performance of the generation and expulsion simulation carried out with the expulsinator thus the generation and expulsion behaviour of this new methodology has been compared with established pyrolysis methodologies like hypy and closed small vessel pyrolysis csvp and has been assessed by rock eval pyrolysis expulsinator experiments released higher amounts of bitumen than csvp this has been attributed to increased cross linking reactions of bitumen in case of the classic pyrolysis favouring formation of pyrobitumen differences in yields and composition of n alkanes were controlled not by generation kinetics exclusively but also by expulsion effects in particular delayed expulsion caused by geochromatography expulsinator conversion rates of toc exceeded 81 whereas those of hydrous csvp remained at 65 higher expulsinator toc conversion was accompanied by lower gas generation compared to csvp this is attributed to the open setup of the expulsion experiment which by rapid removal of products generated prevents their secondary alteration particularly polymerization to pyrobitumen and oil to gas cracking at higher temperatures hypy of expulsinator pyrolysis residues verified a low generation potential remaining after the expulsion experiment the expulsinator device delivers oil and gas generation data which can be applied in numerical modelling exercises

ground based observations of volcanism on io in 1999 and early 2000 ground based observations of volcanism on io during the period of the 1999 and early 2000 galileo close flybys have detected several types of activity providing information which complements the spacecraft observations at loki a brightening began between august 25 and september 9 and continued through february on august 2 a major outburst was observed near 14 n 74 w whose brightness corresponds to an area of approximately 350 km 2 at a temperature of 1100 k observations of eruptions in late june 9906a and in late november 9911a at tvashtar provide temporal and photometric constraints on activity also seen by galileo high resolution adaptive optics images provide further information on the fainter sources distributed across the surface

volatile organic acids produced during kerogen maturation amounts composition and role in migration of oil abstract maturation dependent generation of organic compounds from north sea source rocks has been investigated by hydrous pyrolysis of powdered source rock samples the generation of water soluble organic acids is emphasised and their composition compared with oil field water samples similar compositions are found matrix adsorption effects are not found to be quantitatively important timing of acid generation relative to oil generation is discussed effects of realistic concentrations of a volatile organic acid in the water phase on interfacial tension is determined and effects on fluid flow of crude oil through water saturated sandstone is investigated using a long core flow rig

evidence for biodegradation and evaporative fractionation in west sak kuparuk and prudhoe bay field areas north slope alaska abstract oils from the west sak kuparuk and prudhoe bay fields on the north slope of alaska display geochemical evidence for a complex petroleum filling history that includes multiple sources and alteration by evaporative fractionation and biodegradation source specific biomarkers in west sak oils indicate generation from the same source rocks in approximately the same proportions as prudhoe bay field oil consistent with the hypothesis that oil spilled from the deeper prudhoe accumulation and remigrated about 10 miles laterally and 5000 feet vertically into the west sak field west sak oils are moderately biodegraded but exhibit anomalously high concentrations of gasoline range saturate and aromatic compounds interpreted as a secondary gas condensate charge that arrived after biodegradation of the spilled prudhoe oil the shallowest west sak oils have less secondary gas condensate charge lower api gravities and reduced concentrations of methylcyclopentane benzene cyclohexane 3 methylhexane heptane methylcyclohexane and toluene relative to the deepest west sak zone a oils the carbon isotopic compositions of these c6 and c7 compounds in the shallowest west sak reservoirs are heavier than those of the deepest west sak oil reservoirs by up to 3 and the isotopic compositions of saturate compounds are altered more than those of aromatic compounds the heavier isotopic compositions of c6 and c7 compounds in the shallow west sak reservoirs are interpreted to result from a kinetic isotope shift caused by light biodegradation of the secondary gas condensate charge west sak field solution gas is also interpreted as biodegraded based upon its dryness 98 methane relatively high isobutane n butane ratio the presence of isotopically heavy carbon dioxide and isotopically light methane and propane that is isotopically heavier than either ethane or butane the isotopic compositions of methane and carbon dioxide in west sak gas suggest that biogenic methane was generated during co2 reduction under anaerobic conditions the isotopic compositions of c6 and c7 compounds in the deepest least biodegraded west sak oils are nearly identical to those of the underlying oils from the kuparuk field but differ from the prudhoe bay field oils the kuparuk field is therefore postulated as the source of the secondary gas condensate charge observed in oils from the west sak field ratios of toluene heptane and heptane methylcyclohexane in kuparuk oils provide independent evidence for loss of gas and condensate from the kuparuk reservoir by the process of evaporative fractionation and the oils subjected to the most evaporative fractionation are isotopically heavier in the c6 c7 range the isotopic compositions of west sak zone a c6 and c7 hydrocarbons suggest that a slight 0 8 isotopic fractionation resulted from evaporative fractionation of the gas condensate charge from the kuparuk field oil accumulation north northeast striking faults that connect the kuparuk and west sak reservoirs provide a potential migration pathway for the secondary gas condensate charge through 3000 feet of intervening shale this model of west sak oil biodegradation subsequent secondary gas condensate charge and further biodegradation has implications for development of north slope west sak oil reserves because heavily biodegraded west sak oils that lack a secondary gas condensate charge may be too viscous to develop by conventional waterflooding methods

alteration of natural gas during leakage from a north sea salt diapir field oil and gas are leaking from a salt diapir field in the norwegian sector of the central north sea the gas is being biodegraded as it migrates to the surface the seeping gas is pervasive in the sediments above the diapir and clearly visible on shallow and deep seismic records and on wireline logs an exploration well was drilled to test a cretaceous chalk reservoir above the diapir and provided an opportunity to sample the gas along the seepage pathway carbon isotope ratios of gases released from sealed cuttings taken from the gas cloud interval above the diapir were determined to test the hypothesis that biodegradation of leaking hydrocarbons produces secondary methane with a biogenic isotope signature generally high but variable concentrations of co2 were detected all the way from the surface to the salt diapir this results from biodegradation of hydrocarbons and particularly oil the source of oxygen for this process is problematic since most of the migration takes place through shales and there is no obvious aquifer source of dissolved oxygen the effect of biodegradation of gases escaping from this structure results in a comparable increase in 13c for both methane and ethane up to 10 with a lesser effect on propane and less still for butane and pentane this conflicts with published data on such effects which suggest that methane and propane should be most affected with little effect on ethane isotopically light methane was found only in the very deepest samples within the salt of the diapir itself and this is thought to be biogenic gas trapped in the salt at the time of deposition no evidence was found that any secondary biogenic methane is being produced during gas seepage and biodegradation at this site

fractionation of dibenzofurans during subsurface petroleum migration based on molecular dynamics simulation and reservoir geochemistry abstract dibenzofurans oxygen containing heterocyclic aromatics are ubiquitous in crude oils their geochemical implications in petroleum geochemistry have been studied in numerous previous publications here we present the distribution of dibenzofuran and its methylated homologues and calculate the polarity and solubility of methyldibenzofuran isomers based on the connolly surfaces and molecular dynamics simulation the results show that the geo chromatographic fractionation effect is evident due to absorption onto the water silica matrix carrier bed during the oil migration process two potential molecular indicators relative to dibenzofurans i e the total content of dibenzofurans and the relative abundances of 1 methyldibenzofuran to 4 methyldibenzofuran are proposed for tracing the oil migration orientation and filling pathways these two indicators were applied successfully in paleozoic marine carbonate and tertiary lacustrine sandstone reservoirs the variations of source input depositional environment and maturity for oils from same source bed kitchen appear to have no significant effect on these two indicators it suggested that these two dibenzofuran indicators are potentially effective molecular tracers for orientation and filling pathways in oil migration

controls on hydrocarbon properties in a paleozoic petroleum system in saudi arabia exploration and development implications the unpredicted discovery of downdip oil in permian carboniferous unayzah sandstone reservoirs along the southern flank of the predominantly gas condensate ghazal field in saudi arabia highlighted the need for a thorough assessment of controls on hydrocarbon properties with the aim to improve prediction and reduce uncertainty primary controls on hydrocarbon property variations condensate to gas ratio here appear to be compartmentalization multiple charging presumably from a lower silurian qusaiba kitchen to the south and east within the late oil to wet gas generation window and dysmigration to the north and west gas on production represents mostly unmixed thermogenic accumulations of variable maturities with no sign of biodegradation or thermal cracking light oil 1 06 1 21 calculated vitrinite reflectance rc in the southern part of the field represent late mature accumulations that apparently escaped flushing by subsequent gas condensate charges generated near the wet gas generation window 1 41 1 55 rc and currently occupying the field to the north constant maturity variations for both gasoline range and heavier components in each sample testify to a lack of mixing between the hydrocarbon phases petroleum inclusions similarly comprise either light oil or gas condensate that coexist with significantly overlapping homogenization temperatures suggesting considerable overlap in their trapping history 135 35 ma less mature petroleum has not been identified in the field possibly because of a lack of trap closure or migration focus prior to the inferred late jurassic filling or because of displacement to updip structures thereby high grading the probability of undiscovered oil west and northwest of ghazal if thermal generation instead of retrograde condensation or phase separation controls this petroleum system then the potential for deeper oil accumulations is limited

millimeter scale concentration gradients of hydrocarbons in archean shales live oil escape or fingerprint of contamination abstract archean shales from the pilbara in western australia contain biomarkers that have been interpreted as evidence for the existence of cyanobacteria and eukaryotes 2 7 billion years ga ago with far reaching implications for the evolution of earth s early biosphere to re evaluate the provenance of the biomarkers this study determined the spatial distribution of hydrocarbons in the original drill core material rock samples were cut into millimeter thick slices and the molecular content of each slice was analyzed in core from the hamersley group 2 5 ga c alkanes had gradually increasing concentrations from the surfaces to the center of the rock while the abundance of steranes hopanes and c 15 alkanes decreased with distance from the outer surfaces in samples from the fortescue group 2 7 ga hydrocarbons were overwhelmingly concentrated on rock surfaces two mechanisms are proposed that may have caused the inhomogeneous distribution diffusion of petroleum products into the rock contamination model and leaching of indigenous hydrocarbons out of host shales driven by pressure release after drilling live oil effect to test these models the hydrocarbon distributions in the archean shales are compared with artificially contaminated rocks as well as younger mudstones where leaching of live oil had been observed the results show that chromatographic phenomena associated with live oil escape and contaminant diffusion have strong effects on molecular ratios and maturity parameters potentially with broad implications for oil source rock correlation studies and paleoenvironmental interpretations for the archean shales the live oil effect is consistent with some of the observed patterns but only the contamination model fully explains the complex chromatographic fingerprints therefore the biomarkers in the pilbara samples have an anthropogenic origin and previous conclusions about the origin of eukaryotes and oxygenic photosynthesis based on these samples are not valid however the study also identified indigenous molecules the spatial distribution of particular aromatic hydrocarbons suggests they are syngenetic although devoid of biological information these aromatics now represent the oldest known clearly indigenous terrestrial liquid hydrocarbons

volcanic activity at tvashtar catena io abstract galileo s solid state imager ssi observed tvashtar catena four times between november 1999 and october 2001 providing a unique look at a distinctive high latitude volcanic complex on io the first observation orbit i25 november 1999 resolved for the first time an active extraterrestrial fissure eruption the brightness temperature was at least 1300 k the second observation orbit i27 february 2000 showed a large 500 km 2 region with many small hot regions of active lava the third observation was taken in conjunction with cassini imaging in december 2000 and showed a pele like annular plume deposit the cassini images revealed an 400 km high pele type plume above tvashtar catena the final galileo ssi observation of tvashtar orbit i32 october 2001 revealed that obvious to ssi activity had ceased although data from galileo s near infrared mapping spectrometer nims indicated that there was still significant thermal emission from the tvashtar region in this paper we primarily analyze the style of eruption during orbit i27 february 2000 comparison with a lava flow cooling model indicates that the behavior of the tvashtar eruption during i27 does not match that of simple advancing lava flows instead it may be an active lava lake or a complex set of lava flows with episodic overlapping eruptions the highest reliable color temperature is 1300 k although higher temperatures cannot be ruled out they do not need to be invoked to fit the observed data the total power output from the active lavas in february 2000 was at least 10 11 w

keck ao observations of io in and out of eclipse abstract we present adaptive optics ao observations of io taken with the w m keck ii telescope on 18 december 2001 ut before the satellite went into eclipse and while it was in jupiter s shadow making these kind of io in eclipse observations as well as the associated data reduction and analysis are challenging hence one focus of the paper is to explain the methods and tools used for these data sets for the sunlit images io itself was used as the wavefront reference source while nearby ganymede was used as reference star when io was in eclipse observations were obtained in k l and m bands the sunlit images have been deconvolved using mistral the io in eclipse data were deconvolved with idac and mistral the former gives better results both in absolute photometry and in matching the original images we determined the flux densities of the hot spots from the original io in eclipse data with starfinder as well as from the deconvolved images by integrating the intensity over the relevant areas we determined the highly anisoplanatic psf via a fft method from the original data and used this in starfinder and as a starting psf for idac and mistral we derived temperatures and areal coverage of all 19 spots detected in both k and l band images of io in eclipse we also determined temperatures and areal coverage of the hot spots visible on the l and m band images of sunlit io most volcanoes contain a compact hot core 10 km2 at 600 800 k within a larger area at lower temperatures e g 102 104 km2 at 300 500 k the total heat flow contributed by these active volcanoes is 0 2 w m 2 8 of the average global heat flow measured at 5 20 m by veeder et al j geophys res 99 1994 17095

some aspects of the organic geochemistry of petroleum fluids the most important influences on the compositions of petroleum fluids are in many cases the composition of a petroleum sample may allow the depositional environment of its source rock and its temperature history before and after expulsion to be determined this information assists the search for more petroleum in a region we suggest that this approach should be used more frequently to validate models of petroleum generation and migration in the second part of the paper we discuss the origin and nature of the differences in petroleum composition which are frequently found within individual petroleum reservoirs petroleum accumulations in permeable reservoirs are normally found to be inmechanical equilibrium and verticalchemical equilibrium this is manifested by constant subsurface fluid density at any given depth across the accumulation and increases in subsurface density with depth known as gravitational segregation however even in permeable reservoirs lateral differences in composition inherited from the reservoir filling process are not totally eliminated by mixing processes such as diffusion and convection thus lateral chemical equilibrium is often not achieved and lateral compositional variations are observed in present day oil and gas reservoirs these observations are justified in terms of order of magnitude estimates for the rates at which reservoirwide mixing occurs a case history is presented

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

a history of high temperature io volcanism february 1995 to may 1997 ground based observations of io s infrared thermal emission between february 1995 and may 1997 show several discrete brightenings for which we can constrain locations fluxes and durations several of these were brief high temperature events with temperatures up to at least 1500 k similar to but often smaller than the rare outbursts seen previously loki io s most powerful volcano was relatively active before and probably during galileo s december 1995 io flyby was faint during most of 1996 and began a major long lived brightening between february 20 and march 12 1997 thermal emission was not seen from ra patera site of an active plume in galileo images major outbursts were seen on march 2nd and september 27 1995

flow through extraction of oil and gas shales under controlled stress using organic solvents implications for organic matter related porosity and permeability changes with thermal maturity abstract four core plugs from the lower jurassic posidonia shale of the hils syncline in northern germany have been subjected to flow through extraction tests with dichloromethane dcm under controlled stress conditions in a tri axial flow cell the samples represent a maturity sequence from 0 53 to 1 45 vrr the bitumen sequentially extracted from the natural pore space of the shale plugs was analyzed for its geochemical composition changes in rock matrix density porosity and permeability resulting from the removal of soluble organic matter were determined the relative porosity increase of the plugs after extraction ranged from 6 to 13 and correlated with the extract yield klinkenberg corrected permeability coefficients measured with helium increased by a factor of 17 0 for the immature early mature sample and 26 6 for the overmature sample petrographical investigations after extraction indicate that fluid flow occurred predominantly parallel to bedding as evidenced by open fractures and fractures bearing residues that apparently precipitated from the dcm solution compositional variations of the extracts over time are interpreted in terms of the organic geochemical inventory of bitumen associated with the natural pore system and its accessibility at different maturity levels these patterns deviate strongly from the bulk rock extracts of the powdered samples

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

relationship between the fluorescence colour of oil inclusions and thermal maturity in the dongying depression bohai bay basin china part 2 fluorescence evolution of oil in the context of petroleum generation expulsion and cracking under geological conditions abstract abundant measured data from source rocks crude oils and oil inclusions in the dongying depression were used to identify the oil generation expulsion and cracking stages under geological conditions so as to build a fluorescence evolutionary model that considers all petroleum generation expulsion and cracking processes in the model oil generation consists of three successive processes bitumen generation bitumen decomposition into oil and oil cracking these three stages are strongly controlled by thermal stress in the dongying depression kerogen decomposition into bitumen occurs at around 85 c 0 42 ro while nso compounds in the bitumen begin to crack into oil at around 120 c 0 67 ro competition between bitumen generation and nso compound cracking leads to peak bitumen generation occurring at around 130 c 0 75 ro after that the main phase of oil generation from intense bitumen decomposition occurs a transition at approximately 160 c between bitumen decomposition into oil and the inferred start of oil cracking corresponds to 4000 m 0 98 1 11 ro during the bitumen generation and main oil generation stages the fluorescence colours of the expelled oils are mainly yellow and orange and a fluorescence blueshift of the oils only occurs during the main oil generation stage in the late oil generation stage 160 c the fluorescence colours of the oils may be close to blue with increasing burial once the source rock and reservoir temperatures reach the threshold conditions for oil cracking 160 c an intense blueshift of the oil occurs in both source rocks and reservoirs and even in oil inclusions this blueshift is shown by a decreased dispersion in the fluorescence colour distribution of oil inclusions with increasing burial from multiple colours at temperatures 160 c therefore in oil prone source rocks containing type i and ii kerogen a blue fluorescence colour of oil appears to be strongly related to the secondary cracking process blue fluorescent oil inclusions generally have higher thermal maturities than oil inclusions with green or yellow fluorescence for oil prone source rocks this relationship is based on the assumption that the oil was not from a gas prone source rock and that secondary alteration processes can be excluded including migration fractionation gas deasphalting trapping fractionation and phase separation furthermore blue fluorescent oil inclusions may be a good indicator for oil prone source rocks which is significant for evaluation of source rock quality in deepwater and ultra deepwater areas in offshore basins

control of facies maturation and primary migration on biomarkers in the barnett shale sequence in the marathon 1 mesquite well texas abstract a great deal is known about the genetic relationships between biomarkers and their biogenic precursors in organic rich rocks the same is true of the way in which biomarker compound ratios change during maturation on the other hand very little is known about whether a crude oil can fully retain its inherent compositional ancestry during expulsion from a source rock thanks to shales being characterized in great detail for their unconventional resource potential new information is gradually coming to light here we report on observations in biomarker geochemistry of a thermally mature core of the barnett shale in which organofacies and maturity are essentially the same but where intraformational sources and reservoirs have already been reported our results indicate that most biomarkers are not fractionated as the primary migration of petroleum within source rocks takes place the 20s 20s 20r ratio of c27 steranes is uniform in the whole source rock sequence while the 20s 20s 20r ratio of c29 steranes shows indistinctly high values in the reservoir unit the 20s 20s 20r ratio of diasteranes and the 22s 22s 22r ratio of c31 17 hopanes do not appear to have been fractionated which may be a result of the thermal isomerization reactions predominating over and masking out the possible fractionation effects diasteranes steranes ratios do not exhibit features that suggest an association with fractionation but rather are broadly correlated with lithology however compared to the diasteranes steranes ratios the ts ts tm ratio is much more sensitive to changes in mineral compositions variations in the ts ts tm ratio show a positive correlation r2 0 73 with mixed layer illite smectite content fractionation in the ts ts tm ratio if it has so occurred may be subsequently overprinted by in situ clay catalyzed reactions

experimental investigation of the compositional variation of petroleum during primary migration anhydrous non isothermal heating experiments were conducted under controlled compressive stress on cylindrical plugs of six oil shales from permian through miocene age the objectives of this study were to investigate molecular and compound class fractionation during petroleum generation and expulsion and to highlight causes of compositional variations due to primary migration from source rocks molecular compositions of n alkanes triterpanes methylphenanthrenes and fatty acids of the original samples initial bitumen the samples after pyrolysis residual bitumen and the expelled products were compared acyclic alkanes were preferentially expelled with compositions depending on source kerogen and partial evaporative loss from the open experimental system expulsion no substantial molecular fractionation within various compound classes or preferential primary migration of n alkanes relative to acyclic isoprenoids occurred cyclic triterpanes and aromatic hydrocarbons were found only in small concentrations in the expelled bitumen indicating preferential retention relative to acyclic alkanes palmitic c16 and stearic c18 acids occurred as dominant compounds in the initial and residual bitumen in the expelled bitumen they constitute virtually the only fatty acid species indicating that expulsion efficiency is strongly dependent on concentration and generation intensity

experimental simulation of primary migration abstract around fifty expulsion experiments were performed in a high pressure vessel specifically designed for the study of primary migration on natural source rock cores the results indicate that temperature pressure source rock richness and source rock architecture are the main parameters controlling the amount of petroleum expelled during the simulation in particular the control exerted by the pressure gradient and the source rock bulk permeability is well demonstrated another relevant result is the observation of the need for the production of a sufficient quantity of petroleum in the source rock before expulsion can start all these results have been compared with migration phenomena observed in the natural system and we discuss herein the similarities observed

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

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

petroleum migration and mixing in the pearl river mouth basin south china sea abstract two oil groups have been investigated in the pearl river mouth basin using their geochemical characteristics in combination with source data the two oil groups may be extrapolated into two end member oils petroleum populations a and b the oil population a with abundant 4 methylsteranes derived from the deeper wenchang source rocks migrated and accumulated earlier the oil population b with absent 4 methylsteranes was expelled from the enping source rocks and is associated with a relatively later phase of migration and accumulation the two distinctive oil populations migrated updip through the marine blanket like sandstone carriers within the zhuhai formation to accumulate in a series of traps along the main migration pathways at different times most of the accumulations are mixtures of the two end member oils the variations of 4 methylsterane concentrations in the accumulations can be related to the contributions from the two sources the oils which migrated furthest contain greater contributions from the wenchang source rocks whereas those with shorter migration paths have greater contributions from the enping sources the later migrated oils closer to the depression areas are highly mature and the former oils in the liuhua oil fields are of relatively low maturity which may indicate the main migration direction along the hui liu structure ridge hlsr oils with abnormally high maturity in the middle of the hlsr may suggest oil filling points from which branch conduits connected the source kitchens to the main migration pathway oils with abnormally low maturities may reveal minor contributions from some small sags in the dongsha massif in a latest phase

effect of maturity and petroleum expulsion on pyrrolic nitrogen compound yields and distributions in duvernay formation petroleum source rocks in central alberta canada abstract a quantitative study of pyrrolic nitrogen compounds was conducted on a series of marine carbonate petroleum source rock extracts taken from the upper devonian duvernay formation in the central alberta portion of the western canada sedimentary basin with increasing thermal maturity concentrations of various pyrrolic nitrogen compounds in the rock extracts increase drastically together with significant compositional variations related to alkyl substitution position the study provides circumstantial evidence for adsorptive interactions operating between organic nitrogen compounds and solid organic mineral phases in subsurface sedimentary rocks during petroleum generation and expulsion the absolute concentrations and relative distributions of pyrrolic nitrogen compounds in the extracts of different maturity ranges provide background information for the calibration of such data in migrated petroleums as an independent measurement of secondary oil migration range of duvernaysourced oils in the basin

geo chromatographic fractionation effect of methyldibenzofuran in dolomite reservoirs and its application in tracing oil filling pathways in the sichuan basin abstract dibenzofuran and its methyl substituted homologues are the important oxygen containing polycyclic aromatic compounds in crude oils the ratio of 1 4 methyldibenzofuran has been successfully used in sandstone reservoir tracing oil migration orientation here we focus on the geo chromatographic fractionation effect of methyldibenzofuran mdbf in dolomite reservoirs we calculated the charge density differences between 1 methyldibenzofuran 1 mdbf and 4 methyldibenzofuran 4 mdbf based on density functional theory the e i n between mdbf isomers and dolomite 104 surface was also calculated according to molecular dynamics simulation the result show that comparing with the 4 mdbf there is strong interaction between 1 mdbf and dolomite 104 surface leading the ratio of 1 mdbf and 4 mdbf increase with the migration distance there is no significant correlation between bitumen reflectance and the ratio of 1 mdbf and 4 mdbf in our samples in addition molecular simulation results show that the mdbf isomers are thermodynamically stable and dissociation of ph ch3 is difficult to occur under geological condition all these demonstrate that 1 mdbf and 4 mdbf can be survived after oil cracking to gas and pyrobitumen therefore in theory the ratio of 1 4 methyldibenzofuran is also regarded as an index for oil migration orientation in dolomite reservoir gas chromatography mass spectrometry results show that mdbfs occur at relatively higher abundance in the bitumens of the ediacaran dengying formation z2dn4 and cambrian longwangmiao formation 1l in the sichuan basin the ratio of 1 4 methyldibenzofuran has been successfully used to trace the crude oil filling pathway in the z2dn4 and 1l dolomite reservoir in the sichuan basin in this study two preferential filling orientations i e from west to east and from north to south for paleo oil have been identified in the contour maps of 1 4 methyldibenzofuran in the z2dn4 and 1l which is consistent with the geological background

discovery of hotspots on io using disk resolved infrared imaging active tidally driven volcanism on jupiter s satellite io1 2 was discovered in voyager images in 1979 voyager also detected the thermal emission from the volcanoes3 4 and this emission has since been monitored from earth using a variety of techniques employing single element infrared detectors5 10 because of io s small angular size no more than 1 2 arcsec however it has normally been possible to resolve and locate only the brightest individual hotspot loki although additional hotspots can be located at five year intervals during occultations of io by the other galilean satellites11 12 here we present first results using two new techniques for ground based observation of io s hotspots first use of an infrared array camera allowed us to exploit the mauna kea observatory s excellent atmospheric stability to obtain direct infrared images of io with resolution better than 0 5 arcsec this allowed us to see more than one hotspot on io in jupiter eclipse in jupiter s shadow second we used the camera to make the first observations of the jupiter occultation disappearance behind jupiter of the hotspots these new techniques have revealed and located at least three hotspots and will now permit routine ground based monitoring of the locations temperatures and sizes of multiple hotspots on io

primary migration behaviour of hydrocarbons from laboratory experiments to geological situations through fluid flow models abstract primary migration is a complex process involving coupled fluid generation and mass transfer in low permeable rocks joint experimental and modelling work have been performed in order to better understand this problem eventually experimental results have been modelled and extrapolated to geological conditions maturation and expulsion experiments have been carried out with water saturated immature type ii source rocks from the paris basin with sample weights up to 3 kg temperatures were stepwise increased from 20 c to 285 330 or 380 c at constant hydrostatic pressures of respectively 17 or 55 mpa during up to 5000 h during the experiments generated fluids expelled out of the heating cell and were sampled prior to a complete analysis mass balances were checked on hydrocarbon gases liquid hydrocarbons co 2 and water meanwhile closed system pyrolysis experiments were performed on isolated kerogen extracted from the same source rocks they allowed us to derive a compositional kinetic cracking reaction network it was then possible to tackle the expulsion of fluids out of the source rock the kinetic scheme provides a guideline to understand the generation of fluids from kerogen the expulsion experiments provide an insight into the expulsion mechanisms no axial stress has been applied to the samples in the experiments therefore the influence of rock compaction due to effective stress was not studied in these experiments a numerical model of expulsion has been set up based on volume and mass balance conservation equations in the source rock the volume is assumed to vary as solid kerogen transforms to liquid products and solid residue the mass of each compound is kept in balance as it is created or destroyed through primary and secondary cracking and expelled through multiphase fluid flow therefore depending on pressure temperature and composition fluids in the source rock are split into several phases following a thermodynamical equation of state all mobile phases flow according to darcy s law experiments were modelled the best fit being achieved with the following conditions all fluids including water co 2 and hydrocarbons are allowed to form a multiphase mixture the heavy compounds resins and asphaltenes are in a single very viscous phase and are less easily expelled as most of them are cracked inside the source rock extrapolations to geological pressure and temperature conditions were performed afterwards in order to check the phase behaviour and the expulsion efficiency

light hydrocarbon diffusion in a caprock abstract concentration profiles for light hydrocarbons c 2 c 7 were obtained by geochemical analysis of closely spaced samples from a caprock shale overlying a commercial size gas condensate accumulation interpretation of these data suggests that considerable diffusive transport of light hydrocarbons has occurred from the reservoir accumulation into the caprock a simple one dimensional diffusion model was used in order to quantify these transport processes evaluation of the analytical data with this model yields estimates for the duration of the diffusive transport and thus the maximum age of formation of the hydrocarbon accumulation in the reservoir alternatively if this age can be estimated from geological evidence the order of magnitude of effective light hydrocarbon diffusion coefficients in shale caprocks can be obtained

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

ground based observations of time variability in multiple active volcanoes on io abstract since before the beginning of the galileo spacecraft s jupiter orbital tour we have observed io from the ground using nasa s infrared telescope facility irtf we obtained images of io in reflected sunlight and in eclipse at 2 3 3 5 and 4 8 m in addition we have measured the 3 5 m brightness of an eclipsed io as it is occulted by jupiter these lightcurves enable us to measure the brightness and one dimensional location of active volcanoes on the surface during the galileo era two volcanoes were observed to be regularly active loki and either kanehekili and or janus at least 12 other active volcanoes were observed for shorter periods of time including one distinguishable in images that include reflected sunlight these data can be used to compare volcano types and test volcano eruption models such as the lava lake model for loki

controls of oil family distribution and composition in nonmarine petroleum systems a case study from inner mongolia erlian basin northern china abstract the erlian basin is a continental rift basin located in inner mongolia northern china it is a typical representative of cretaceous northeast asian rift system which includes many small petroliferous basins in mongolia republic and northern china although lower cretaceous source rocks are understood to be most important in the erlian petroleum systems the precise identification of these source rock intervals and their determination on oil families distribution and composition are poorly understood in this tectonically complicated nonmarine basin new bulk data have been gathered from source rock intervals oil sands and crude oil samples in eight main oil producing subbasins geochemical analyses indicate that lower cretaceous aershan formation k1ba and tengger 1 formation k1bt1 are two main source intervals in the erlian basin and their source rock facies vary from profundal lacustrine to marginal lacustrine according to biomarker and trace elements calibration the profundal lacustrine facies is characterised by brackish water and anoxic environment which is similar to their correlative oils family 1 oils the marginal lacustrine facies is characterised by freshwater and suboxic environment which sourced the most common family 2 oils meanwhile different maturation processes exercise the second control on oil groups and their compositions the profundal lacustrine source rocks characterised by their sulphur rich kerogens lead to two oil groups group 1 and group 2 oils whose maturity range from low to normal while the marginal lacustrine source rock only lead to normal maturity oils at last biodegradation affected the composition of a certain oils and formed group 4 heavy oils in addition short migration distance in small subbasins made the contamination or fractionation less notable in the erlian basin

petroleum composition in the cuu long basin mekong basin offshore southern vietnam abstract the cuu long basin mekong basin is a rift basin off southern vietnam and the most important petroleum producing basin in the country however information on petroleum type and characteristics has hitherto been largely unavailable to the public this paper presents petroleum geochemical data on nine oil samples from four different producing fields in the cuu long basin the dragon rong black lion sutu den sunrise rang ong and white tiger bach ho fields the oils are highly paraffinic with bimodal normal alkane distributions and show moderate pristane to phytane ratios and a conspicuous hyperbolic decrease in abundance with increasing carbon number of hopane homologues from c30 to c35 the tpp index of holba et al holba a g dzou l i wood g d ellis l adam p schaeffer p albrecht p greene t hughes w b 2003 application of tetracyclic polyprenoids as indicators of input from fresh brackish water environments organic geochemistry 34 441 469 is equal to 1 in all samples which in combination with tricyclic triperpane t26 t25 ratios 1 and the n alkane and hopane distributions mentioned above provide a strong indication of an origin from lacustrine source rocks this is supported by the absence of marine c30 desmethyl steranes i e 24 n propylcholestanes and marine diatom derived norcholestanes based on the overall biological marker distributions the lakes probably belonged to the overfilled or balanced fill types defined by bohacs et al bohacs k m carroll a r neal j e mankiewicz p j 2000 lake basin type source potential and hydrocarbon character an integrated sequence stratigraphic geochemical framework aapg studies in geology 46 3 34 the oils were generated from source rocks at early to mid oil window maturity presumably oligocene lacustrine shales that are present in the syn rift succession oils from individual fields may however be distinguished by a combination of biological marker parameters such as the oleanane index the gammacerane index the relative abundance of tricyclic terpanes the proportions of diasteranes and 28 norspergulane complemented by other parameters the oils of the cuu long basin show an overall similarity to the b 10 oil from the song hong basin off northern vietnam but are markedly different from the seepage oils known from dam thi nai on the coast of central vietnam

observations and temperatures of io s pele patera from cassini and galileo spacecraft images abstract pele has been the most intense high temperature hotspot on io to be continuously active during the galileo monitoring from 1996 2001 a suite of characteristics suggests that pele is an active lava lake inside a volcanic depression in 2000 2001 pele was observed by two spacecraft cassini and galileo the cassini observations revealed that pele is variable in activity over timescales of minutes typical of active lava lakes in hawaii and ethiopia these observations also revealed that the short wavelength thermal emission from pele decreases with rotation of io by a factor significantly greater than the cosine of the emission angle and that the color temperature becomes more variable and hotter at high emission angles this behavior suggests that a significant portion of the visible thermal emission from pele comes from lava fountains within a topographically confined lava body high spatial resolution nightside images from a galileo flyby in october 2001 revealed a large relatively cool

efficiency of petroleum expulsion from shale source rocks the limited data available on the mechanism and the efficiency of the processes by which petroleum is expelled in the subsurface from source rocks into adjacent reservoir rocks are mostly qualitative1 2 we present here material balance type comparisons of sample series extending from the centre portions of two adjacent hydrocarbon source rock units towards their outer edges3 which enable expulsion efficiencies to be determined in certain parts of the shale the expulsion efficiencies for total extract and its saturated and aromatic hydrocarbon fractions have much higher values than previously thought reaching up to 80 for the total extract which increase towards possible secondary migration avenues the expulsion is associated with fractionation effects such as those based on polarity differences also expulsion efficiencies were found to be related to the degree of hydrocarbon saturation of the pore system they are higher for a rich oil prone source rock unit compared with a poorer quality one which had generated less hydrocarbons

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

generation of nitrogen and methane from sedimentary organic matter implications on the dynamics of natural gas accumulations nitrogen n2 contents of natural gases in rotliegend and buntsandstein reservoirs of the north german basin regionally approach 100 a review is given of the various hypotheses primordial origin volcanic or magmatic origin radiogenic origin atmospheric origin organic origin inorganic nitrogen in sedimentary rocks presented to account for nitrogen anomalies in this area and other parts of the world the objective of the present study was to investigate sedimentary organic matter in particular coals as a potential source of molecular nitrogen in the subsurface comparison of reservoir sizes and gas generation potentials indicates that carboniferous coal measures which are considered as the source of the natural gas in the north german basin can readily account for the nitrogen quantities found in present day reservoirs laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a fractional generation of methane and nitrogen in natural systems based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates gas containing more than 50 nitrogen is generated under these conditions at temperatures in excess of 300 c nitrogen rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased it is concluded that the amounts of gas encountered in nitrogen rich gas accumulations represent only a small fraction possibly 1 of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere the present day composition of the reservoir gases reflects the composition of only the most recently generated gas on a geologic time scale

geochemical assessment of petroleum migration phenomena on a regional scale case studies from brazilian marginal basins geochemical effects of secondary migration on marine oils derived from a single source of enhanced salinity have been investigated in the sergipe alagoas basin but no molecular migration characteristics that are independent of source constraints were identified mixed oils from the potiguar basin derived from both lacustrine freshwater and marine source beds of enhanced salinity reveal compositional trends which are related to source rock features and maturity conditions heterogeneities in their oil compositions can be related to the history of migration and reservoir filling also short term stratigraphic variations seen for biomarker compositions observed in core samples of source rocks from the potiguar basin help explain anomalies in the trends defined by the migrated mixed oils in the basin