correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

geochemical characterization of selected western canada oils by c5 c8 compound specific isotope correlation csic abstract forty two oils condensates from the western canada sedimentary basin wcsb ranging in reservoir age from devonian to cretaceous are compared using the stable carbon isotopic ratio of individual hydrocarbons in the gasoline range fraction c 5 c 8 of these oils continuous flow isotope ratio mass spectrometry cf irms using a modified solid dilution purge and trap inletting system can provide reproducible isotopic ratios for the ca 26 dominant n iso and cyclo alkanes and aromatics in the gasoline range the resulting isotopic signatures or gasoline isotopograms for oils condensates provide a diagnostic geochemical technique for oil oil and oil source correlations in many instances the non straight chained hydrocarbons are more diagnostic than n alkanes hierarchical cluster analysis provides a non subjective approach to the treatment of individual isotopic information this study confirms that oils from similar or the same sources produce isotopic signatures that are highly correlated clear carbon isotopic relationships between individual hydrocarbon compounds in the oils suggest a steady state kinetic relationship for the generation of oil and gas as opposed to a thermodynamic equilibrium relationship this mechanism explains the consistent shift in isotopic ratios between similar compounds such as the methylalkanes and dimethylalkanes

oil oil and oil source rock correlations in the carpathian foredeep and overthrust south east poland abstract the chemical composition of 35 crude oils and the extracts of potential source rock samples from south east poland were studied in detail by geochemical methods in order to understand their genetic relationships twenty six oils including three seep samples were collected from cretaceous to oligocene reservoirs within the carpathian overthrust nine oils originated from carboniferous to miocene reservoirs within the carpathian foredeep the rock samples studied were selected after rock eval pyrolysis screening of a large suite of samples and consist of one lower cretaceous sample and five oligocene menilite shale samples from three different outcrop locations all within the carpathian overthrust geochemical fingerprinting indicates at least two families of crude oils the first represented only by one oil has no specific characteristics except for a light carbon isotope composition the second family is characterized by the presence of 28 30 dinor hopane oleanane and a highly branched isoprenoid c25 alkane within this latter family four subfamilies were recognized a 19 oils having the aforementioned characteristics b seven oils similar to subfamily a but with a relatively high sulphur content c one oil with high abundance of higher plant derived triterpanes and d seven oils with abundant 28 30 dinor hopane although maturity influences the relative abundance of 28 30 dinor hopane it suggested that subfamilies a b and c had an initial low 28 30 dinor hopane content whereas subfamily d an initial high 28 30 dinor hopane content only one oil of subfamily a could potentially be a high maturity counterpart of subfamily d a palaeozoic source rock is suggested for the first family and the second family including the majority of the pils from the carpathian foredeep is most likely derived from the oligocene menilite shales an oil source rock relationship with the menilite shale is supported by the presence although not in all samples studied of 28 30 dinor hopane oleanane or its precursors and the highly branched isoprenoid alkane the strong facies variations observed within this shale gave rise to the different types of crude oils in the second family

composition and origin of natural gases accumulated in the polish and ukrainian parts of the carpathian region gaseous hydrocarbons noble gases carbon dioxide and nitrogen abstract ten natural gas samples associated and non associated with oil in the polish and ukrainian flysch carpathians and mesozoic basement of the carpathian foredeep were analysed for molecular and stable isotope compositions as follows 12 13c in ch4 c2h6 c3h8 and co2 1 2h in ch4 14 15n in n2 and 3 4he 20 21 22ne 36 38 40ar 84kr and 132xe in noble gases the gaseous hydrocarbons both in the silesian unit of the outer flysch carpathians and mesozoic basement are generally genetically related to thermogenic processes and occasionally to microbial carbon dioxide reduction these gases were mainly generated from mixed type ii iii kerogen during middle stage of the low temperature thermogenic processes gaseous hydrocarbons from starunia in the boryslav pokuttya unit were generated from type ii kerogen during middle stage of the low temperature thermogenic processes he is generally of crustal origin with more than 99 2 of radiogenic 4he but appreciable amount of 3he is probably derived from the upper mantle the 3he might have been derived from the pieniny klippen belt deep seated fault system or neogene and pleistocene andesitic and basaltic volcanism occurred in the eastern carpathian area nucleogenic 21ne and 22ne were analysed in all the samples the nucleogenic 21ne shows good correlation with radiogenic 4he with the production ratio of 4he 21ne 1 3 107 in the crust these isotopic values indicate a common source for these gases where both the nuclear reactions of decay and n are occurring concentrations of radiogenic 4he and 40ar and excess 21ne in the samples from the mesozoic basement are generally higher and more scattered compared with those in the silesian unit the larger concentrations of radiogenic and nucleogenic isotopes in the natural gases from the mesozoic basement is probably related to older geological formations than younger formations of the silesian unit carbon dioxide was generally generated during the thermal transformation of organic matter and occasionally during microbial processes nitrogen was mainly generated during thermal transformation of organic matter and also originated from atmosphere a least part of carbon dioxide and nitrogen may have been produced in crust

molecular and isotopic compositions and origin of natural gases from cambrian and carboniferous lower permian reservoirs of the onshore polish baltic region natural gases from middle cambrian and carboniferous lower permian reservoirs of the onshore polish baltic region were studied for their molecular and stable isotope compositions the following gas species were analysed 12 13c in ch4 c2h6 c3h8 n c4h10 i c4h10 and co2 1 2h in ch4 14 15n in n2 and stable isotopes of all noble gases due to significantly different geological settings and genetic types of source rocks of eastern and western pomerania the molecular and isotopic compositions of natural gases of these two regions exhibit distinct differences hydrocarbon gases associated with oil accumulated in the middle cambrian reservoir of eastern pomerania were generated during low temperature thermogenic processes from a single source rock containing type ii kerogen at one phase of petroleum generation non associated hydrocarbon gases accumulated in the carboniferous mississippian and pennsylvanian lower permian rotliegend reservoirs of western pomerania originated during at least two phases of gas generation by thermogenic processes from mainly type iii kerogen and a small component of mixed type iii ii kerogen noble gases are in general heavily enriched in radiogenic and nucleogenic isotopes such as 4he 40ar and 21ne accumulated in the reservoirs weak contributions of mantle derived he and ne are observed radiogenic 4he 40ar ratios are higher than the average production rate ratio of about 5 for radiogenic 4he 40ar in crustal materials which might have been caused by a selective supply of 4he that is lighter than 40ar from crustal rocks or u th k ratio might be higher than the average in crustal block carbon dioxide from gases of both the western and eastern pomerania were mainly generated during thermogenic processes of transformation of organic matter although gases of western pomerania can contain an endogenic component molecular nitrogen from the eastern pomeranian natural gases was mainly generated during low temperature thermal transformation of organic matter and derived from nh3 and nh4 of crustal fluid whereas molecular nitrogen from western pomeranian natural gases contains a significant component from the destruction of organic matter at a higher maturity level which may have been caused by a high heat flux from the volcanic activity during late pennsylvanian early rotliegend ages and has a bigger component release from nh4 rich illites

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

geochemical correlation of surface and subsurface oils western greece abstract biodegraded seep oils devoid of n alkanes and most isoprenoid hydrocarbons were successfully correlated with subsurface crude oils in western greece primarily using carbon isotopes and the more microbially resistant tricyclic terpane and aromatic steroid hydrocarbon distributions all the studied oils seem to fit into three major genetic groups which are consistent with the geologic tectonic and geographic settings and are presumably related to different source rock facies group i oils are typical of the abundant oil shows in the epirus province northwest greece minor but consistent biomarker differences necessitated subgrouping of the epirus oils implying derivation from slightly different sources group ii oils are located in the katakolon area northwestern peloponnese group iii oils which are clearly distinct from the other groups are centered in zakynthos island an oil seep at trifos west central greece and a subsurface oil from paxi island because of uncertain correlations are classed intermediate between group i and ii oils an aromatic steroid hydrocarbon measurement modified after mackenzie et al 1981 appears useful in determining the relative maturity of biodegraded and conventional oils and carbonate rock extracts

detailed mapping unit design based on soil landscape relation and spatial variability of magnetic susceptibility and soil color abstract the objective was to identify landscape areas with different patterns of variability using a statistic protocol with data of magnetic susceptibility ms and soil color that are covariate attributes of soil formation factors and processes the studied area of 380 ha is located in northeast of sao paulo state brazil an amount of 86 samples was collected using 30 m intervals on the transect at the transect sides 150 samples were collected at 159 m intervals a point each 2 5 ha first the accuracy limits have been validated in the transect using the technique of split moving windows smw the limits identified in the transect were extrapolated to the sides using the contours of variability maps the ms peaks smw for both depths presented a correlation with the peaks of clay content r 0 7 p

natural gas formation in the western nile delta eastern mediterranean thermogenic versus microbial abstract the offshore part of the nile delta is an emerging gas and condensate province and one of the most promising areas for future petroleum exploration and supply in northern africa while the nile delta s hydrocarbon potential and its geological and stratigraphic pattern has been the focus of numerous studies the origin of its gas has been poorly studied in order to characterize the natural gas and to determine whether microbial or thermogenic processes are the dominant generation pathways of methane a regional geochemical study was performed on 38 test gases collected from 9 neogene western nile delta discoveries main constituents of the gases are methane 89 4 99 4 up to pentane with traces of carbon dioxide and nitrogen methane carbon isotopic composition ranges from 66 0 to 39 6 displaying a mixed microbial and thermogenic character for most of the gases microbial gas contributions range from 15 to 95 the mixed and the more thermogenic gases are frequently accompanied by light oils and condensates 41 59 api calculated maturities of the thermogenic gas proportions suggest source rock maturities between 0 8 and 1 4 ro which are actually present in the pre miocene section evidence for microbial alteration of petroleum accumulations in the nile delta is largely manifested in anomalously heavy isotopic compositions of both wet gas components propane and n butane and preferential removal of higher n alkanes from condensates the hydrocarbon accumulations affected by biodegradation are trapped within shallow pliocene reservoirs

early generation characteristics of a sulfur rich monterey kerogen this paper documents the critical role of organic sulfur in the early formation of bitumen and oil from a sulfur rich kerogen from the miocene monterey formation in california monterey kerogen commonly contains abundant chemically bound sulfur 8 14 wt which appears responsible for early low temperature generation of heavy sulfur rich petroleum due to the lower energy required to break carbon sulfur bonds compared to carbon carbon bonds hydrous pyrolysis was used to simulate the natural generation of petroleum from a sulfur rich type ii kerogen from the phosphatic member of the monterey shale the amount and distribution of sulfur in the kerogen bitumen and expelled oil generated at various temperatures indicate that 1 initial bitumen and oil generation is directly related to cleavage of weak sulfur linkages and 2 most of the expelled oil is formed by decomposition of bitumen and not directly from the kerogen finally comparison of hydrous pyrolysis results with other type ii kerogens suggests that the temperature of peak bitumen generation is inversely related to the heteroatom content primarily sulfur of the kerogen low temperature bitumen generation is an important exploration concept because kerogen rich in sulfur can generate producible oil at thermal maturities significantly below conventionally accepted values furthermore established relationships between thermal maturity sulfur content and other oil properties such as api gravity can be used to rank exploration prospects

oil source rock correlations in the polish flysch carpathians and mesozoic basement and organic facies of the oligocene menilite shales insights from hydrous pyrolysis experiments the oligocene menilite shales in the study area in the polish flysch carpathians are organic rich and contain varying mixtures of type ii type iis and type iii kerogen the kerogens are thermally immature to marginally mature based on atomic h c ratios and rock eval data this study defined three organic facies i e sedimentary strata with differing hydrocarbon generation potentials due to varying types and concentrations of organic matter these facies correspond to the silesian unit and the eastern and western portions of the skole unit analysis of oils generated by hydrous pyrolysis of outcrop samples of menilite shales demonstrates that natural crude oils reservoired in the flysch sediments appear to have been generated from the menilite shales natural oils reservoired in the mesozoic basement of the carpathian foredeep appear to be predominantly derived and migrated from menilite shales with a minor contribution from at least one other source rock most probably within middle jurassic strata definition of organic facies may have been influenced by the heterogeneous distribution of suitable menilite shales outcrops and producing wells and subsequent sample selection during the analytical phases of the study

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

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

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

geochemistry and accumulation of carbon dioxide gases in china we propose the following identification indicators for co2 of different origins based on data obtained from analyzing the molecular composition of 1198 gas samples the co2 carbon isotope values of 390 samples and the helium isotope composition of 256 samples collected from wells of 16 oil and gas bearing basins and gas seepages in china and reviewing literature on organic and inorganic co2 throughout the world co2 is of organic origin if co2 content 13cco22 is of inorganic origin if dgr13cco2 8 pmil or co2 60 and co2 is of either organic or inorganic origin or a mixtur of organic and inorganic origins if 10 pmil 13cco213cco2 values of organic co2 mainly range from 10 to 22 pmil in tectonically stable oil and gas bearing basins where deep faults and magmatism are undeveloped organic co2 occurs almost exclusively in tectonically active oil and gas bearing basins where active faults and magmatism are present or in areas of modern volcanic activity the dgr13cco2 values of inorganic co2 range from 2 to 8 pmil and are distributed along faults the inorganic co2 with a dgr13cco2 value of 0 3 pmil is of metamorphic origin and that with dgr13cco2 values of 6 2 pmil is mantle derived and of magmatic origin in china the dgr13cco2 values of inorganic co2 gas pools range from 3 41 to 8 44 pmil and the helium ratio r ra is 1 which indicates that these gases are typically derived from the mantle

sources of natural gases in middle cambrian reservoirs in polish and lithuanian baltic basin as determined by stable isotopes and hydrous pyrolysis of lower palaeozoic source rocks abstract origin of natural gases associated with oil and condensate accumulations within the middle cambrian sandstone reservoir of the polish and lithuanian baltic basin was characterised by means of molecular composition stable carbon isotopes of methane ethane propane butanes pentanes and carbon dioxide stable hydrogen isotopes of methane and stable nitrogen isotopes of gaseous nitrogen generated gas from potential upper cambrian tremadocian and llandovery source rocks by hydrous pyrolysis at 330 c and 355 c for 72 h was used to characterise thermogenic gas to evaluate correlation parameters based on molecular composition and stable isotopes the pyrolysis conditions represent gas generation during oil generation which appears to be the conditions represented by the natural gas accumulations and their low gors gas oil ratios the dryness of the pyrolysis and natural hydrocarbon compositions compare well but do not provide a means of distinguishing the contributions of each source rock to the natural gas accumulations the average 13 c value of the natural methane is 6 9 depleted in 13 c compared to methane generated in the hydrous pyrolysis experiments this difference is less for ethane and essentially nonexistent for propane butanes and pentanes tentatively this diminishing difference with increasing carbon number is attributed to kinetic effects resulting from higher experimental temperatures although the 13 c values of methane and ethane from the hydrous pyrolysis experiments are not useful in direct correlations with natural gas accumulations 13 c of propane butanes and pentanes is useful and indicates that the upper cambrian and tremadocian source rocks are the main contributors and that the llandovery source rocks are not significant contributors to the polish and lithuanian baltic natural gases polish natural gases with relatively higher methane and ethane are attributed to the mixing of drier more mature gases from deeper parts of the basin to the west carbon dioxide of natural gases was generated during thermogenic processes and gaseous nitrogen was generated from nh 4 rich illites of the clayey facies and from thermal transformation of organic matter of the lower palaeozoic strata hydrous pyrolysis gases have higher concentrations of co 2 h 2 s and h 2 than the natural gases this difference is attributed to reduction or loss of these highly reactive and soluble gases during migration and entrapment of the natural gases although co 2 concentrations between pyrolysis and natural gases are different the 13 c values of the former fall within the range of the latter

organic geochemical study of source rocks and natural gas and their genetic correlation in the central part of the polish outer carpathians abstract geochemical characteristics of organic matter quantity genetic type maturity and petroleum potential were determined in profiles of lower cretaceous miocene strata of the dukla and silesian units of the polish outer carpathians in the tarnow debica nowy s cz gorlice jaslo area this determination was based on rock eval isotopic and biomarker analyses of 159 rock samples oligocene menilite beds reveal the best hydrocarbon potential within the investigated formations depositional units of the so called flysch strata and can be considered as primary source rock in the study area marine and mixed marine terrestrial kerogen present in these rocks is immature in silesian unit and mature oil window in dukla unit respectively the lower cretaceous eocene formations ve ovice lgota godula and istebna beds variegated shales and ciezkowice beds of the silesian unit reveal variable amounts of mostly gas prone kerogen and can be considered as additional source of hydrocarbons the upper oligocene lower miocene krosno beds and miocene chaotic beds have a variable organic matter content usually over 1 wt but very low maturity and low hydrocarbon potential predispose them as a source of microbial methane ten natural gas samples from sandstone reservoirs of the upper cretaceous lower miocene strata in the silesian unit of the outer carpathians were analysed for molecular and isotopic compositions in order to establish their origin and role of thermogenic and microbial processes thermogenic gases without the admixture of microbial methane were encountered only in one well bystra 4 in the block a of szalowa heddy bystra gas deposit thermogenic gas component was generated at a maturity level of 0 7 to 1 0 of vitrinite reflectance ro scale from mixed type ii iii kerogen dispersed in the oligocene menilite beds from a few fields within the silesian unit microbial methane had been generated earlier from the same organic matter during microbial carbon dioxide reduction process a significantly high microbial component occurs mainly in the gases from kobylanka gas horizon gorlice glinik and blocks c and b of the szalowa heddy bystra fields the microbial gases were generated within the oligocene menilite beds and or miocene chaotic beds within local zones in the study area carbon dioxide originated both from thermogenic and microbial processes

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

origin and migration of oil and natural gas in the western part of the ukrainian outer carpathians geochemical and geological approach abstract we established the generation and migration processes as well as the influence of secondary processes of oil and natural gas accumulated in lower cretaceous oligocene strata of the western part of the ukrainian outer carpathians based on the results of organic geochemical analyses of oil and natural gas related to the geological setting and source organic matter the oligocene menilite beds from the boryslav pokuttya nappe are the main source rock for oil and natural gas accumulated in the fields of the boryslav pokuttya and skiba nappes co sourcing of oils and natural gas accumulated in the skiba nappe in the study area by both menilite and spas beds of this nappe cannot be excluded in some cases e g novoshidnytsya field oil and natural gas originated within the oligocene menilite beds of the boryslav pokuttya nappe migrated through thrusts and fissure zones and accumulated in the lower cretaceous reservoirs of the skiba nappe oil from small vovche field and pohar seep of the krosno nappe was generated by menilite source rocks of this tectonic unit and migrated to the traps sporadically oils underwent secondary processes mainly biodegradation and occasionally water washing hydrocarbon gases and carbon dioxide were generated mainly during low temperature thermogenic processes from type ii kerogen and partly during the microbial co2 reduction process only natural gas from the mala volosyanka oil and gas seep of the krosno nappe was documented to have undergone biodegradation

organic geochemical study and genetic correlation of natural gas oil and menilite source rocks in the area between san and stryi rivers polish and ukrainian carpathians abstract we studied the source rocks and petroleum accumulations in the carpathian mountains of the polish ukrainian border area between the san and stryi rivers a total of 108 oligocene menilite formation rock samples 12 oil and 15 gas samples accumulated in the oligocene reservoirs and one oil and gas sample from an upper cretaceous reservoir were analysed the aim of this study was to evaluate the petroleum potential of the menilite formation in this area and to evaluate potential genetic correlations between source rock and petroleum the menilite formation represents a prolific source rock with toc content ranging from 2 to 7 wt locally exceeding 20 wt algal type ii and mixed type ii iii kerogens dominate but sometimes type iii kerogen and rarely type i kerogen occur thermal maturity of the oligocene menilite formation increases from outer to inner tectonic units from the immature in the boryslav pokuttya and skole units to the overmature in the southern parts of silesian and dukla units as a consequence petroleum potential decreases in the same order geochemical analyses reveal that oil and gas generation and migration processes within the carpathian flysch succession are complicated all analysed oils were generated from the menilite formation during early and peak stages of the oil window associated gas is of low temperature thermogenic origin sometimes containing an admixture of microbial gas high temperature thermogenic gas occurs only in the polish part of the silesian unit

abundance and carbon isotopic composition of neo pentane in australian natural gases abstract here we report the abundance and carbon isotopic composition of neo pentane or 2 2 dimethylpropane in australian natural gases derived from source rocks of late proterozoic to early tertiary age in australian natural gases neo pentane abundance is low ranging from 6 to 295 ppm the 13cneo pentane shows a strong source control and together with the other gaseous hydrocarbons a maturity effect albeit less pronounced than the source effect in severely biodegraded natural gases neo pentane abundance is similar to that in non biodegraded gases as a result of a counter balance between preservation of neo pentane relative to other wet gases and the addition of biogenic methane nevertheless neo pentane can become the most abundant pentane isomer with neo pentane iso n pentane ratios up to 9 9 here the 13cneo pentane is identical between biodegraded and non biodegraded natural gas from the same source providing strong evidence that neo pentane is resistant to biodegradation even within severely biodegraded gases where the carbon isotopic composition of all the other gaseous hydrocarbons has been altered the carbon isotopic composition of neo pentane ranges from 13c 50 8 to 24 4 vpdb and is typically isotopically more depleted in 13c up to 9 7 than iso pentane and n pentane this wide carbon isotopic variability between the pentane isomers most likely results from the interplay between decomposition isomerisation and methylation mechanisms for neo pentane formation in biodegraded gases the iso pentane and n pentane become progressively enriched in 13c resulting in much larger isotopic differences 13cneo pentane iso pentane values of up to 16 6 in this paper we show how the carbon isotopic composition of neo pentane is related to source rock type and age and demonstrate the usefulness of neo pentane in gas gas correlation particularly in biodegraded accumulations

the kiaman reversed polarity superchron at kiama toward a field strength estimate based on single silicate crystals abstract we present the first geomagnetic paleointensity measurements on single plagioclase crystals from lavas formed during the 262 318 ma permo carboniferous reverse polarity superchron commonly known as the kiaman rock magnetic experiments suggest that feldspar crystals separated from two lavas of the kiaman superchron type area near kiama australia carry pseudo single domain low ti magnetic inclusions capable of faithfully retaining a primary paleointensity signal thellier paleointensity experiments yield virtual dipole moments of 8 5 0 2 1022 am2 and 9 3 0 3 1022 am2 for these crystals furthermore these results lack the alteration problems that prohibit paleointensity and sometimes paleodirection determination using whole rock lava samples from the type area the derived field strengths are 5 6 times higher than some other virtual dipole moment vdm values of kiaman age derived from whole rock igneous samples this suggests either high paleointensity variability during the kiaman superchron or that unrecognized non ideal magnetic behavior has compromised some prior paleointensity results reported from whole rocks elsewhere

geochemistry and occurrence of inorganic gas accumulations in chinese sedimentary basins abstract inorganic gases are commonly seen in eastern china and occasionally in southern china from the shallow water columns above hot and cold springs the gases contain 68 to nearly 100 co2 with 13 c co 2 and 13c1 values in the range of 1 18 to 6 00 and 19 48 to 24 94 respectively all of the 34 large inorganic co2 and one inorganic methane accumulations discovered in china are distributed in eastern parts of the country from both onshore and continental shelf basins no commercial inorganic gas accumulation has been found in central and western china this is a review of the occurrence and geochemical characteristics of inorganic gas accumulations in chinese sedimentary basins a detailed study of gas samples collected from four representative inorganic co2 pools and one possible inorganic methane pool indicates that inorganic alkane gases typically show 13c1 values greater than 10 versus pdb mostly 30 with a positive stable carbon isotope sequence of 13c1 13c2 13c3 13c4 inorganic gases also tend to show less negative 13 c co 2 values 10 than biogenic gases

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

aspects of petroleum basin evolution due to gas advection and evaporative fractionation abstract criteria are proposed for the recognition of depletion by evaporative fractionation in reservoir fluid analyses pvt data the characteristics of original as generated molar concentration profiles of marine oils are postulated oils derived from clastic or carbonate sediments bearing respectively type ii or iis kerogens in unaltered marine oils two decreasing exponential concentration series occur separated by a discontinuity between p5 the 5 carbon pseudo component and p6 such that p6 exceeds p5 rendering the profile abruptly bimodal a suite of 195 detailed pvt analyses c1 to p30 of reservoir fluid oils shows that concentrations in the p6 fraction are frequently perturbed the maximum migrating to p7 p8 or a higher carbon number alteration attributable to additive gas advection followed by evaporative fractionation in the subject oils four variables are adduced which track these changes c1 c2 p4 p8 e3 a light gas liquid heavy end ratio and e7 a gasoline range heavy end ratio increase in c1 c2 is accompanied by decreasing values of p4 p8 for which there is no a priori rationale other than the precepts of evaporative fractionation involving the advection of highly mature dry gas dividing a suite of 535 pvt analyses detailed analyses plus 340 analyzed to p7 of world wide provenance into seven subsets on the basis of c1 c2 ratios a well defined separate regression of gas oil ratio on saturation pressure is revealed in each subset such correlations depend primarily upon the processes involved in evaporative fractionation the curves embrace the full commonly encountered range of combinations of gas oil ratio and saturation pressure both of which correlate poorly with level of maturity expressed in a liquid fraction slope factor these observations lead to the hypothesis that progressive evaporative fractionation is a widespread if not universal evolutionary process in petroleum basins

reservoir geochemistry of south pass 61 field gulf of mexico compositional heterogeneities reflecting filling history and biodegradation abstract cluster analysis of gc data for gasoline and mid range hydrocarbon ratios from fifty one south pass 61 field oils reveals geochemically similar oil clusters corresponding to geographically coherent groups insight into the groupings is obtained from examination of indicators of geochemical processes e g anaerobic biodegradation aerobic biodegradation and extensive remigration of light ends six duplicate samples collected in 1986 and 1992 as well as replicate runs on a single sample showed excellent analytical reproducibility subtle but consistent differences in both gasoline and oil range hydrocarbon maturity indicators are observed between the east west and far west flanks of the field suggesting filling of different segments of the reservoir from different kitchens at slightly different stages of thermal maturity or with slightly different chemical character the west flank of the salt dome was charged with slightly more thermally mature petroleum than the east flank the stratigraphically oldest and deepest sand on the far west flank has received the most mature petroleum different fluid contacts and gors are observed in different sands and different fault blocks the stacked pay geometry of the field and widespread faulting have led to considerable remigration of gas and condensate as observed in other fields in the gulf of mexico thompson 1987 biodegradation varies in severity with depth and reservoir zone but is frequently overprinted by remigration of light end hydrocarbons anaerobic biodegradation by sulfate reducing bacteria is probably the cause of light to moderate alteration in intermediate depth pliocene sands which are hydraulically connected to the salt dome with dissolution of anhydrite from the salt dome providing the sulfate widespread late pyrite formation in reservoir sandstones is inferred to represent the ultimate sink for reduced sulfur from sulfate reduction during oil biodegradation co produced water compositions suggest no oxygenated freshwater infusion

organic geochemical study of source rocks and natural gas and their genetic correlation in the eastern part of the polish outer carpathians and palaeozoic mesozoic basement abstract geochemical characteristics of organic matter in the profiles of dukla silesian sub silesian and skole units of the polish outer carpathians and of the palaeozoic mesozoic basement in the debica rzeszow lezajsk sanok area were established based on rock eval vitrinite reflectance isotopic and biomarker analyses of 485 rock samples the oligocene menilite beds have the best hydrocarbon potential of all investigated formations within the dukla silesian and skole units the ordovician silurian lower devonian and locally middle jurassic strata of the palaeozoic mesozoic basement are potential source rocks for oil and gas accumulated in palaeozoic and mesozoic reservoirs thirty one natural gas samples from sandstone reservoirs of the lower cretaceous lower miocene strata within the outer carpathian sequence and eight from sandstone and carbonate reservoirs of the palaeozoic mesozoic basement were analysed for molecular and isotopic compositions to determine their origin natural gases accumulated both in the outer carpathian and the palaeozoic mesozoic basement reservoirs are genetically related to thermogenic and microbial processes thermogenic gaseous hydrocarbons that accumulated in the dukla and silesian units were generated from the menilite beds thermogenic gaseous hydrocarbons that accumulated in the sub silesian unit most probably migrated from the silesian unit initial and probably also secondary microbial methane component has been generated during microbial carbon dioxide reduction within the oligocene menilite beds in the dukla unit and oligocene lower miocene krosno beds in the silesian unit natural gases that accumulated in traps within the middle devonian mississippian upper jurassic and upper cretaceous reservoirs of the palaeozoic mesozoic basement were mainly generated during thermogenic processes and only sporadically from initial microbial processes the thermogenic gases were generated from kerogen of the ordovician silurian and middle jurassic strata the microbial methane component occurs in a few fields of the dukla and silesian units and in the two accumulations in the middle devonian reservoirs of the palaeozoic mesozoic basement

effect of water washing on c15 hydrocarbon fraction of crude oils from northwest palawan philippines recognition and subsequent correlation of biodegraded and or water washed oils with their unaltered counterparts has been a long recognized problem in petroleum geochemistry because water washing and biodegradation can occur concurrently it is difficult to delineate the individual effects of these two oil altering processes especially on the c15 hydrocarbon fraction both processes can cause an oil to become enriched in sulfur and to have a lower api gravity owing to loss of the more volatile components thus the altered oil may appear to be a high sulfur crude of low maturity altered and unaltered oil fractions extracted from cores of a water washed carbonate reservoir offshore northwest palawan were studied to observe the effect of alteration on correla ion parameters water washing resulted in the following changes 1 depletion of 13c in the c15 branched cyclic alkane fraction whereas virtually no change occurred in isotope composition of the aromatic fraction 2 selective loss of dibenzothiophenes followed by loss of aromatic hydrocarbons and 3 virtually no change in steranes or tricyclic and pentacyclic terpanes with the exception of enhancement of 17 agr h norhopane and decrease of 18 agr h trisnorhopane in situations of severe water washing mild biodegradation also occurred as indicated by the loss of n alkanes and possible selective loss of n alkanes having less than 25 carbon atoms relative to branched alkanes cycloalkanes and aromatic components because cycloalkanes and aromatic hydrocarbons are not generally preferentially utilized by bacteria as long as n alkanes are present the changes observed in these two fractions most likely result from water washing because of the potential for extreme compositional changes in the n alkane and aromatic fractions the most useful correlation parameters between the altered and unaltered oils are sterane and terpane distributions stable carbon isotope ratios are also useful however more studies of oils in which water washing is known to have occurred need to be made to explain the general response or various responses of the isotopic composition of oils to water washing