reservoir overprinting of crude oils abstract biomarker concentrations are generally low in high api gravity oils and condensates admixture of even small amounts of low maturity biomarker rich bitumen can drastically alter the biomarker profile of such fluids we suggest that a 41 api dst oil from the sunfish 1 well cook inlet alaska is a mixture of jurassic derived oil with approximately 5 wt tertiary input derived from coals interbedded with the reservoir sands reservoir overprinting has significantly altered the biomarker fingerprint of the sunfish 1 oil therefore biomarker patterns or parameters for biomarker lean high api gravity fluids should be scrutinized closely for internal consistency and conformity with bulk properties

geochemistry of oil inclusions in sulfide related calcites fingerprinting the source of the sulfate reducing hydrocarbons of the pb zn carbonate hosted jubilee deposit of nova scotia canada abstract sulfide precipitation in the context of carbonate hosted base metal deposits has been previously explained by numerous processes including so 4 reduction in the presence of hydrocarbons this model has been suggested for numerous deposits although clear criteria to support the model have not been systematically provided numerous oil inclusions are encompassed by fibrous calcite crystals in finely laminated carboniferous limestone at the base of the windsor group a unit that hosts numerous base metal occurrences in nova scotia particularly the hydrocarbon rich jubilee pb zn deposit in cape breton island oil from two inclusion rich samples from this deposit have been characterised by gas chromatography gas chromatography mass spectrometry gas chromatography isotope ratio mass spectrometry and bulk stable c isotopes as established in the authors former publications the jubilee deposit is a clear metallogenic case for which the ground preparation and mineralisation stages involved reduction of so 4 by hydrocarbons here the question of potential sources of these hydrocarbons is addressed it is postulated that the hydrocarbons that were trapped in the sulfide related calcites at the deposit correlate with previously characterised oil seeps and it is demonstrated that their source is not the marine host carbonates but stratigraphically deeper lacustrine formations of the horton group

constancy of silicate mineral weathering rate ratios between natural and experimental weathering implications for hydrologic control of differences in absolute rates abstract inverse models which apportion watershed effluxes geochemical mass balance over estimated mineral surface area give weathering rates for individual silicate minerals e g feldspar 1 3 orders of magnitude slower than laboratory rates comparisons of rates calculated from several recent watershed geochemical mass balance studies with experimentally determined rates reveal that the ratio of mineral weathering rates for a given silicate mineral pair determined in an internally consistent field study equals the ratio of rates for the same minerals in any internally consistent set of laboratory experimental data thus the coefficient which corrects the weathering rate for any mineral from a laboratory data set to a field setting is identical to the corresponding coefficient for any other mineral in the same data sets the correction factor linking experimental and natural rates must be independent of composition physical e g hydrologic controls rather than compositional or chemical controls cause the difference between weathering rates in nature and the laboratory because flow in natural weathering profiles is spatially heterogeneous not all of the potentially available surface in natural systems actually participates in reactions with pore fluids

upper permian lacustrine oil shales southern junggar basin northwest china upper permian organic rich lacustrine mudstones oil shales that crop out in the southern junggar basin rank among the richest and thickest petroleum source rock intervals in the world with maximum toc values reaching 34 and rock eval pyrolytic yields s 2 up to 200 kg hc t rock lacustrine sedimentary facies define an overall transgressive regressive cycle of approximately 2000 m gross thickness which includes approximately 800 m of source rocks averaging 4 1 toc and 26 2 kg hc t rock basinal facies comprise silicic organic rich laminated lacustrine mudstones and interbedded siltstones organic matter contained in the mudstones ranges in composition from type i to type iii basinal facies were deposited in a deep oxygen deficient stratified lake lake margi facies consist of nonlaminated siliciclastic mudstones rippled dolomitic siltstones and sandstones and minor limestones maximum toc values are approximately 6 desiccation cracks are common in the marginal facies but evaporite minerals are rare or absent biomarker correlation parameters measured from rock extracts exhibit significant stratigraphic variability but strongly support the hypothesis that upper permian lacustrine oil shales charge the giant karamay field in the northwestern junggar basin karamay oils are characterized by high relative abundances of beta carotane this characteristic is restricted to desiccated facies in the outcrop sections however we therefore propose that an abundance of beta carotane indicates elevated environmental salinities during deposition of the oil shales orographic precipitation induced by a paleo tian shan range may have provided fresh water to the southern areas of the basin while more evaporative conditions prevailed to the north outcrop oil seeps confirm that the outcrop sections have attained sufficient thermal maturity to generate oil t max values range from 431 to 451 degrees c vitrinite reflectances range from 0 73 to 0 88 and sterane isomerization ratios range from 0 30 to 0 48 20s 20s 20r matoil registered trademark computer modeling of burial history and thermal maturity of the outcrop sections indicates that approximately 4 5 km of triassic jurassic cover was needed to bring the oil shales to their current maturity the major phase of hydrocarbon generation in this area appears to have preceded the creation of traps by neogene thrusting which may account for the lack of discoveries in the southern junggar basin most of the oil discovered so far is trapped in structures which originated duri g the late paleozoic or mesozoic

organic maturation thermal history and hydrocarbon generation in the orcadian basin scotland the devonian orcadian basin contains thick sequences of organic rich lacustrine sediments of interest as hydrocarbon source rocks throughout the basin the range of organic maturation is large spore colours vary from yellow orange to black and vitrinite reflectance for type iii kerogens ranges from 0 7 to 10 5 maximum palaeotemperatures are estimated to range from those typical of moderate burial diagenesis 100 c to those characteristic of greenschist facies metamorphism 400 c the highest maturities are related to contact metamorphism by devonian plutons and it is postulated that a large pluton underlies much of caithness high and low maturity regions are often juxtaposed across major faults which were active during variscan inversion regionally the lowest maturity is about 0 8 r o implying uplift and erosion of 2 3 km of cover basin wide this cover was probably a sequence of late devonian and carboniferous rocks removed largely during variscan uplift geothermal gradients were high but variable during devonian extension this together with the contact metamorphic affects of the devonian plutons resulted in early maturation metamorphism of large areas of the basin most of the onshore sequence entered the oil window during devonian and carboniferous times significant generation of hydrocarbons from orcadian lacustrine facies offshore during subsequent mesozoic burial will have occurred only in those areas which escaped maturation during the palaeozoic

latest jurassic early cretaceous events and the late cimmerian unconformity in north sea area each of several regional or local unconformities may have been identified locally as the late cimmerian unconformity a supposed major break at the base of the valhall formation or roedby formation over most of the north sea the base of the valhall formation is isochronous and conformable with underlying sediments it is detected on seismic reflection profiles because it represents a widespread facies change marking the late ryazanian transgression most of the unconformities are of eustatic origin and the effects of eustatic sea level changes were never completely masked by local tectonics thus in the modeling of individual oil fields the possibility of sedimentary breaks occurring can be predicted in part by reference to regional or eustatic events modified journal abstract

composition diagenesis and weathering of the sediments and basement of the callabonna sub basin central australia implications for landscape evolution abstract the evolution of the callabonna sub basin central australia is described in terms of sediment provenance stratigraphy sedimentology and postdepositional mineral and chemical alteration six mineral exploration drillholes in the mundi mundi plain were studied using a combination of qualitative and quantitative xrd pimatm portable infrared mineral analyzer xrf normative analysis and sem the sedimentary cover consists of 160 210 m of diagenetically modified fluvio lacustrine tertiary clay silt and sand comprising sandy mottled and gray clay units overlain by quaternary soil the basement consists of weathered proterozoic schist gneiss siltstone and shale quartz kaolinite smectite and muscovite are the dominant minerals within the sediments whereas the weathered bedrock contains quartz feldspar kaolinite illite and muscovite characteristic wavelength absorption features from pimatm show that the youngest sandy clay unit exhibits the lowest reflectance intensities because of its lower diagenetic maturity weathering of primary minerals within the basement produced an illite kaolinite rich saprolite whose clays exhibit strong reflectance intensities and well developed crystallinity the micromorphology of all secondary products reflects their environment of crystallization low porosity and anoxic conditions within the sediments resulted in poorly developed clays of variable textures colors and compositions conversely the weathered bedrock developed over protracted periods of in situ weathering resulting in better developed secondary products this study distinguishes between preburial weathering of the basement detrital mineralogy postdepositional alteration of the sedimentary cover and subsequent weathering of previously formed mineral assemblages this has widespread implications for paleotopographic weathering reconstitution and landscape evolution thus 1 the extent of weathering of basement relative to diagenesis and maturity of sediments and gradational nature of their unconformity suggests that most of the alteration of basement occurred prior to and was sustained after deposition of sediments and 2 morphotectonic evolution of the region controlled the composition of transported materials by changing the style and patterns of fluvial systems further influencing the distribution and preservation of sediments and weathered bedrock and hence regional landscape morphology

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

recognition and source correlation of migrated hydrocarbons in upper jurassic hareelv formation jameson land east greenland organic geochemical analysis of an interbedded shale sandstone sequence from the upper jurassic hareelv formation jameson land east greenland has revealed oil shows in the sandstones consistent with petroleum generation and migration a comparison of the molecular characteristics of extractable material from the sandstones with those of kerogen and bitumen from the shales indicates that the most likely origin of these shows is generation within the shales with expulsion and short range migration into the sandstones this conclusion is based on comparisons of biological marker distributions stable carbon isotopic compositions of extractable material and kerogen and pyrolysate compositions of kerogen and asphaltenes oil from a seep in the savoia halvo region south of jameson land can be correlated to the jurassic sandstone oil shows based on similar isotopic compositions and asphaltene pyrolysate distributions impregnation of both sandstones and shales throughout the sequence by products generated at higher maturities is considered unlikely but cannot be ruled out by the existing data the molecular characteristics of the sandstone hydrocarbons exhibit a striking similarity to those of oils from the mid norway region the similar geologic ages of the hareelv formation and the kimmeridge clay of northwestern europe which is the acknowledged source of the mid norway oils and the geographic proximity of the two regions at the time of early north atlantic rifting indicate that hydrocarbons from these present day distant regions have been generated from very similar organic facies deposited under similar environmental conditions these results are significant in that in addition to stratigraphic correlation of depositional sequences on both margins of the early rifted north atlantic the hydrocarbons generated from source rocks contained in these sequences now can als be geochemically correlated the results also suggest that jurassic hydrocarbon source facies deposited throughout the early north atlantic are geochemically similar a trait imparted to their generation products

origin and mixing of crude oils in triassic reservoirs of mahu slope area in junggar basin nw china implication for control on oil distribution in basin having multiple source rocks abstract the origin of crude oils and their varied geochemical features along the western and northern slope of the mahu depression in the junggar basin has been controversial based on the molecular and isotopic geochemistry of hydrocarbons from 46 drill stem test crude oil samples and 36 core samples three oil groups i ii iii and five subgroups i 1 i 2 ii iii 1 and iii 2 have been recognized and oil source correlations have been established the subgroup i 1 oils originated mainly from lower permian fengcheng p 1 f carbonate source rocks subgroup i 2 from p 1 f mudstone source rock and group ii oils from middle permian wuerhe p 2 w mudstone source rock whose potential was underestimated in the past group iii consists of mixed oils i e subgroup iii 1 received contributions from p 1 f carbonates and p 2 w mudstones and subgroup iii 2 is a mixture of oils from p 1 f mudstones and p 2 w generated oils in order to determine the main source rocks the laboratory oil mixing experiments were carried out tricyclic terpane biomarker parameters tts were used to quantify the source contributions whole oil carbon isotope ratios were also used to verify the proportions of different oils in each mixture the results show that subgroup iii 1 oils have diverse mixing ratios in different reservoir subgroup iii 2 oils are mainly from p 1 f mudstones and p 2 w source rock contributes little finally the accumulation process of oil fields along the northern slope of the mahu depression was analyzed and the contributions from different sources were revealed this study provides an effective quantitative method to identify contributions from different lacustrine source rocks to mixed oils in the mahu depression which could be helpful in predicting location and composition of undiscovered oils

wishstone to watchtower amorphous alteration of plagioclase rich rocks in gusev crater mars previous observations by the spirit rover in gusev crater revealed a suite of rocks dubbed wishstone and watchtower class in which the parent lithology and daughter products of a distinctive style of aqueous alteration are evident results from spirit s miniature thermal emission spectrometer mini tes 2000 340 cm 1 were compromised by dust contamination of one of the instrument s mirrors for which a correction has since been developed now we have documented nearly 200 examples of rocks encompassing the span of alteration from wishstone class which spectrally resemble minimally altered plagioclase phyric basalt to the most altered watchtower class among them is a rock dubbed bruce that may be a previously unrecognized alteration spectral end member we employed factor analysis target transformation and linear least squares modeling to investigate the spectral characteristics and mineralogy of these rocks our results amplify those of a prior preliminary analysis showing that alteration produced a material resembling basaltic glass that masks the spectral features of plagioclase the association of this amorphous silicate component with a ferric iron nanophase oxide phase identified via spirit s mossbauer spectrometer is now clearly shown by our data further characterizing the distinctive mineralogic expression of the alteration these components and the absence of any recognizable secondary silicates or opaline silica may be an expression of alteration in the extreme aridity and cold of the martian environment similar mineralogic characteristics of soil measured with the chemin x ray diffraction instrument on the curiosity rover in gale crater may be an indication that this alteration process is widespread on mars

c30 steranes novel markers for marine petroleums and sedimentary rocks abstract a series of c30 steranes has been identified in petroleum through the application of metastable scanning gas chromatography mass spectrometry their chromatographic pattern in crude oil resembles an epimerized distribution of steranes it is proposed that the biological precursors for the c30 steranes are marine sterols which contain 30 carbon atoms hence c30 steranes are markers for input to sedimentary lipids from marine organisms

late palaeozoic hydrocarbon migration through the clair field west of shetland uk atlantic margin geochemical analysis of bitumen and hydrocarbon bearing fluid inclusions from the devonian carboniferous clair field indicates that the reservoirs contain a mixture of oils from different marine and lacustrine sources reconstruction of the clair field oil charge history using fluid inclusion petrography show that oil charging occurred at times of k feldspar quartz and calcite cementation temperature composition time data yielded from the integration of fluid inclusion microthermometry with high resolution ar ar dating date hydrocarbon bearing k feldspar overgrowths at 247 3 3 ma these data show that in order for oil to be trapped within primary fluid inclusions in k feldspar overgrowths hydrocarbon migration throughout the uk atlantic margin must have been taking place during the late palaeozoic and as such current industry oil play models based solely on oil charging from jurassic cretaceous marine sources are clearly incomplete and need revision apatite fission track analysis and vitrinite reflectance data were used to reconstruct thermal burial histories and assess potential oil generation from middle devonian lacustrine source rocks thermal history data from wells along the rona ridge adjacent to the clair field show that the palaeozoic section was heated to greater than 100 c at some time between 270 and 230 ma confirming that devonian source rocks were mature and expelling oil during the late palaeozoic at the time that authigenic k feldspar overgrowths were growing in the clair field

mixed marine and lacustrine input to an oil cemented sandstone breccia from brora scotland abstract a rounded cobble collected from a beach near brora scotland contains angular brecciated sandstone clasts cemented together by crude oil no oil occurs within the tight dolomite cemented clasts except along fractures provenance of the cobble is uncertain however the lithology and shape of the clasts suggests that they are fault gouge breccia composed of old red sandstone from the nearby helmsdale fault oil emplacement presumably along the fault cemented the breccia prior to transport and weathering of the cobble independent source and biodegradation parameters support mixing of two charges of oil like oil from the nearby beatrice field the oil cement contains 24 n propylcholestanes and carotane that indicate marine and lacustrine source rocks respectively the oil cement also contains pristane phytane residual n alkanes and a complete series of 25 norhopanes which indicate mild and heavy biodegradation respectively the first charge consisted of lacustrine devonian oil that was heavily biodegraded at shallow depth the origin of the second charge is unclear unlike beatrice oil the oil cement contains oleanane and shows a higher 24 24 27 nordiacholestane ratio suggesting input from a cretaceous or younger paralic marine shale source rock although cretaceous and paleocene source rocks are inferred to exist in various depocenters in the northeast atlantic margin subcrops of these rocks offshore brora are thermally immature alternately the second charge could originate from an effective middle jurassic source rock that contains oleanane this hypothesis is supported by mass spectrometric confirmation of oleanane in an extract from the marine equivalent of the middle jurassic brora coal in the nearby ukcs 11 30 2 well oleanane in crude oil is not positive proof of a cretaceous or younger source rock for the oil

use of hydrogen and carbon stable isotopes characterizing oils from the potiguar basin onshore northeastern brazil hydrogen and carbon isotopic abundances were measured in representative samples of marine evaporitic lacustrine and mixed oils from the onshore potiguar basin the isotopic data together with chemical compositions and geological information were used to investigate relationships among ddoil and d13coil and source thermal maturity biodegradation mixing and the distance of secondary migration of these oils the marine evaporitic oils are depleted in deuterium 135 to 114 and the lacustrine oils are enriched 101 to 88 values of dd for mixed oils are intermediate 113 to 104 between those of marine evaporitic and lacustrine oils showing that ddoil is a reliable tool to identify oils that differ genetically values of ddoil were not directly related to thermal maturation biodegradation or distance of the secondary migration hydrogen isotopic compositions of the oils can be related mainly to the ddwater in the paleoenvironments in which the primary producers lived therefore ddoil values can provide rough estimates of ddwater in the depositional environments of the source rocks and consequently may provide evidence about paleoclimatic conditions at the site marine evaporitic oils are enriched in 13c 26 5 to 25 7 and lacustrine oils are depleted 33 6 to 30 2 in 13c relative contributions of marine evaporitic and lacustrine sources to mixed oils thus can be calculated independently from carbon or hydrogen isotopic mixing models when these calculations are done independently the mixed oils separate into two families and a previously unrecognized component possibly associated with environments that formed during the lacustrine to marine transition is revealed the investigation thus demonstrates the superior resolving power of two element mixing systematics

organofacies and paleoenvironment of the oligocene maikop series of angeharan eastern azerbaijan the maikop formation deposited in eastern azerbaijan during oligocene and early miocene times contains prolific source rocks with primarily type ii organic matter paleontological analyses of dinoflagellate cysts revealed a lower to upper oligocene age for the investigated succession near angeharan a major contribution of aquatic organisms diatoms green algae dinoflagellates chrysophyte algae and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n alkane distribution patterns composition of steroids and 13c of hydrocarbon biomarkers microbial communities included heterotrophic bacteria cyanobacteria chemoautotrophic bacteria as well as green sulfur bacteria higher inputs of terrigenous organic matter occurred during deposition of the upper oligocene units of the maikop formation from angeharan mountains the terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the shamakhy gobustan area high primary bioproductivity resulted in a stratified water column and the accumulation of organic matter rich sediments in the lower oligocene units of the maikop formation organic carbon accumulation during this period occurred in a permanently salinity stratified mesohaline environment with free h2s in the water column this is indicated by low pristane phytane ratios of all sediments varying from 0 37 0 69 lower methylated trimethyltridecyl chromans ratio in the lower units and their higher contents of aryl isoprenoids and highly branched isoprenoid thiophenes subsequently the depositional environment changed to normal marine conditions with oxygen deficient bottom water the retreat of the chemocline towards the sediment water interface and enhanced oxic respiration of om during deposition of the upper oligocene maikop sediments is proposed parallel depth trends in 13c of total om n alkanes isoprenoids and steranes argue for changes in the regional carbon cycle associated with the changing environmental conditions increased remineralisation of om in a more oxygenated water column is suggested to result in low toc and hydrocarbon contents as well as 15n enriched total nitrogen of the upper oligocene units

palaeoenvironmental conditions during deposition of the upper cretaceous oil shale sequences in the songliao basin ne china implications from geochemical analysis abstract excellent hydrocarbon source rocks oil shales containing type i organic matter om were deposited in the continental songliao rift basin during the late cretaceous a major contribution of aquatic organisms dinoflagellates green algae botryococcus and minor input from macrophytes and land plants to om accumulation is indicated by n alkane distribution steroid composition and 13 c values of individual biomarkers microbial communities included heterotrophic bacteria cyanobacteria and chemoautotrophic bacteria as well as purple and green sulfur bacteria the presence of methanotrophic bacteria is indicated by 13 c depleted methyl hopane the sediments were deposited in a eutrophic alkaline palaeolake highly reducing saline bottom water conditions and a stratified water column existed during om accumulation of the qingshankou formation and member 1 of the nenjiang formation this is indicated by low pristane phytane gammacerane index and mttc ratios and the presence of carotane and aryl isoprenoids however an abrupt change in environmental conditions during deposition of member 2 of the nenjiang formation is indicated by significant changes in salinity and redox sensitive biomarker ratios a freshwater environment and suboxic conditions in the deep water prevailed during this period higher input of terrigenous om occurred during deposition of the upper nenjiang formation good oil to source rock correlation was obtained using biomarker fingerprints of oil stained sandstone from the quantou formation and oil shales from the qingshankou formation based on the extent of isomerisation of c 31 hopanes the oil was most probably derived from oil shales of the qingshankou formation in deeper parts of the basin

a new and working petroleum source rock on the uk continental shelf upper permian offshore yorkshire we report on the discovery of oil from the boulby mine and its likely productive source rock from yorkshire in ne england located to the west 30 km of the newly licenced petroleum exploration areas in the vicinity of the mid north sea high oil samples from the mine have likely been generated from zechstein group kirkham abbey formation kaf sapropelic carbonate rock as indicated by aliphatic and aromatic hydrocarbon biomarkers other potential source rocks of carboniferous westphalian namurian visean coals and mudrocks and jurassic the jet rock bituminous shales kimmeridge clay formation age are ruled out on the basis of organic geochemical data boulby oil was generated in the peak to late oil window and it is characterised by the high abundance of c32 and c34 homohopanes slight even over odd predominance eop of c20 25 n alkanes indicating restricted carbonate evaporite depositional conditions and c29 ethyl diacholestane 20 s likely implying a clay rich source rock the structural framework and tectonic history of the permian strata reveal the presence of several fault systems which served as conduits for migrating petroleum similar zechstein sourced oil is known from poland and germany but the occurrence at boulby is the first positive identification of oil derived from zechstein source rock in the north sea area the boulby oil is reservoired in zechstein 3 z3 brotherton formation dolomite and sealed by z3 evaporite rocks the proven oil occurrence at boulby has significant implications in terms of reducing the risk of a lack of oil mature source rock for acreage offered in the neighbouring north sea during the uk s 30th and 31st licencing rounds

applications of mineral surface chemistry to environmental problems environmental surface chemistry involves processes that occur at the interface between the regolith hydrosphere and atmosphere the more limited scope of the present review addresses natural and anthropogenically induced inorganic geochemical reactions between solutes in surface and ground waters and soil and aquifer substrates important surficial reactions include sorption ion exchange dissolution precipitation and heterogeneous oxidation reduction processes occurring at the solid aqueous interface recent research advances in this field have addressed both directly and indirectly societal issues related to water quality pollution biogeochemical cycling nutrient budgets and chemical weathering related to long term global climate change this review will include recent advances in the fundamental and theoretical understanding of these surficial processes breakthroughs in experimental and instrumental surface characterization and development of methodologies for field applications

oil source rock correlations limitations and recommendations a rigorous defensible and causal oil source rock correlation definitively ties an individual source rock sample to an individual crude oil using genetically based internally consistent parameter matches such a correlation is a relationship established between the two components which is consistent with all known chemical geochemical and geological information and meets three criteria a the relationship must be causal the oil must arise at least in part from the specified source rock s b chemical data used in the correlation must be comparable the elemental molecular and isotopic data derived from the source rock must be of the same type as that derived from the oil and c all available geological data must be supportive clear geological evidence must exist which allows the proposed source rock to have sourced the oil the three points of this definition are satisfied and the correlation is successful if we solve one analytical and three geological problems natural extraction of crude oil from its source rock i e expulsion differs mechanically and temporally from laboratory extraction leading to a correlation problem referred to as extraction differences and representing the single greatest analytical uncertainty in correlation efforts geologically three aspects confound oil source correlations occurrence of multiple source units and or source units at differing maturity levels lateral and vertical depositional variations in source unit s organic matter and lateral and vertical variation in reservoir unit s organic matter these concerns are overcome by taking five actions for each oil source correlation effort 1 select representative samples using statistically defensible methods 2 establish the inherent compositional variability laterally and temporally due to depositional and maturation processes in each prospective source unit 3 assess the extent of migration induced changes in oil composition including post migration changes such as in reservoir alteration 4 support each correlation with migration histories derived from 4d models 5 iterate correlation results with new data gathered from ongoing exploration efforts these five actions will a allow correlation success to be measured more objectively b establish risking parameters for direct use in basin assessment and c provide baseline criteria for use in assessing the reliability of oil source rock correlations although these approaches will improve conventional oil source rock correlation efforts ultimately they may not be needed if inversion methods become more reliable the ability to invert compositional data for crude oil i e predict the age lithology maturity and other characteristics of a source rock solely through chemical analysis of its expelled oil could eventually result in successful oil source rock correlations in which source rock analysis for oil source rock correlation purposes is less critical

preferential flow in a sandy vadose zone 1 field observation abstract field experiments of water movement in the lower portion of an unsaturated zone i e vadose zone are far more difficult to conduct than those in the root zone thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone recent results from field experiments conducted at the hancock agricultural research station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone by using dye tracing and profile excavation field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the central sand area of wisconsin csaw the results confirmed that preferential flow paths constitute the dominant flow pattern at this location water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport the observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper the mechanism and implications of preferential flow are presented in a companion paper

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

lacustrine organic facies a biomarker study using multivariate statistical analysis abstract four distinct depositional settings in the devonian orcadian basin of scotland have been characterised by their minerology and organic geochemistry with the help of multivariate statistical analysis the data visualise the organic matter source input the depositional environment and the level of thermal maturity principal component analysis proved invaluable for extracting information from a data set composed of a large number of parameters the thermal maturity of the majority of the samples lies within a restricted range in the oil window and biomarker composition reflects predominantly organic input and depositional environment basin margin deposits are clearly differentiated from deeper water central lake deposits salinity and anoxicity variations are seen within the latter type of deposits

statistical approaches for the definition of landslide rainfall thresholds and their uncertainty using rain gauge and satellite data abstract models for forecasting rainfall induced landslides are mostly based on the identification of empirical rainfall thresholds obtained exploiting rain gauge data despite their increased availability satellite rainfall estimates are scarcely used for this purpose satellite data should be useful in ungauged and remote areas or should provide a significant spatial and temporal reference in gauged areas in this paper the analysis of the reliability of rainfall thresholds based on rainfall remote sensed and rain gauge data for the prediction of landslide occurrence is carried out to date the estimation of the uncertainty associated with the empirical rainfall thresholds is mostly based on a bootstrap resampling of the rainfall duration and the cumulated event rainfall pairs d e characterizing rainfall events responsible for past failures this estimation does not consider the measurement uncertainty associated with d and e in the paper we propose i a new automated procedure to reconstruct ed conditions responsible for the landslide triggering and their uncertainties and ii three new methods to identify rainfall threshold for the possible landslide occurrence exploiting rain gauge and satellite data in particular the proposed methods are based on least square ls quantile regression qr and nonlinear least square nls statistical approaches we applied the new procedure and methods to define empirical rainfall thresholds and their associated uncertainties in the umbria region central italy using both rain gauge measurements and satellite estimates we finally validated the thresholds and tested the effectiveness of the different threshold definition methods with independent landslide information the nls method among the others performed better in calculating thresholds in the full range of rainfall durations we found that the thresholds obtained from satellite data are lower than those obtained from rain gauge measurements this is in agreement with the literature where satellite rainfall data underestimate the ground rainfall registered by rain gauges

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

an aem tem study of weathering and diagenesis abert lake oregon i weathering reactions in the volcanics abstract abert lake in south central oregon provides a site suitable for the study of sequential weathering and diagenetic events in this first of two papers transmission electron microscopy was used to characterize the igneous mineralogy subsolidus alteration assemblage and the structural and chemical aspects of silicate weathering reactions that occur in the volcanic rocks basalts basaltic andesites and dacitic rhyolitic extrusive and pyroclastics that outcrop around the lake olivine and pyroxene replacement occurred topotactically whereas feldspar and glass alteration produced randomly oriented smectite in channels and cavities the tetrahedral octahedral and interlayer compositions of the weathering products largely dioctahedral smectites varied with primary mineral composition rock type and as the result of addition of elements released from adjacent reaction sites weathering of the highly evolved fe rich jug mountain complex at the north end of the lake produced a homogeneous smectite assemblage that contrasts with the heterogeneous smectite assemblage replacing the volcanics along the eastern margin of the lake the variability within and between the smectite assemblages highlights the microenvironmental diversity fluctuating redox conditions and variable solution chemistry associated with mineral weathering reactions in the surficial environment late stage exhalative and aqueous alteration of the volcanics redistributed many components and formed a variety of alkali and alkali earth carbonate chloride sulfate and fluoride minerals in vugs and cracks overall substantial mg si na ca and k are released by weathering reactions that include the almost complete destruction of the mg smectite that initially replaced olivine the leaching of these elements from the volcanics provides an important source of these constituents in the lake water the nature of subsequent diagenetic reactions resulting from the interaction between the materials transported to the lake and the solution will be described in part ii banfield et al 1991

geochemistry of petroleum systems in the eastern pearl river mouth basin evidence for mixed oils abstract detailed analyses of crude oils and source rock extracts indicate the presence of two effective petroleum source rocks in the eastern pearl river mouth basin of the south china sea region oils derived from the lacustrine source rocks in the eocene wenchang formation are characterized by abundant c 30 4 methyl steranes with relatively few c 19 tricyclic terpane and bicadinanes in contrast oils from the eocene oligocene enping formation source typically contain significant amounts of c 19 tricyclic terpane and bicadinanes with relatively few 4 methyl steranes and high pristane phytane ratios however the chemical compositions of a large number of oils do not conform to those of the unknown source rocks consistent with mixing of the two sources mixed oils occur mainly in the huizhou sag and along its south margin and the highest proportion of the enping formation source in the reservoired mixed oils is estimated to be around 80 laboratory mixing experiments using selected end member oils indicate that even with 50 80 contribution from the enping formation source the mixtures still display sterane biomarker ratio signatures diagnostic of the wenchang formation source therefore the presence of abundant 4 methyl steranes is a necessary but not sufficient indicator for the wenchang formation source in the eastern pearl river mouth basin although our results support the wenchang formation as a major source to the known oil discoveries in the study area the contribution of the enping formation source to traps in the huizhou sag and surrounding area cannot be ignored there is clear evidence for the recharge of enping formation derived oils into early biodegraded oil accumulations to form light oil accumulations

direct observation of reactant product interfaces formed in natural weathering of exsolved defective amphibole to smectite evidence for episodic isovolumetric reactions involving structural inheritance abstract high resolution transmission electron microscopy hrtem and energy dispersive x ray microanalysis eds were employed to characterize grain boundary structures in naturally weathered amphibole our observations provide insights into the submicroscopic mineralogic controls on transport of solutions to and from reaction sites finely exsolved amphibole anthophyllite gedrite in outcropping slightly weathered gedrite gneiss transforms isovolumetrically to smectite stacking faults and exsolution lamellar boundaries focus weathering reactions whereas chain width defects decrease the susceptibility of the surrounding amphibole to alteration relatively al poor anthophyllite lamellae alter slightly more readily than those of al rich gedrite large quantites of mg fe si and al are removed from reaction sites however smectite compositions directly reflect

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

the recognition of multiple hydrocarbon generation episodes an example from devonian lacustrine sedimentary rocks in the inner moray firth scotland burmah well 12 27 1 drilled on a structural high in the inner moray firth penetrated over 3000 ft 914 m of lower devonian organic rich sedimentary rocks these have been analysed for source rock potential and contain a substantial proportion of oil prone thermally mature kerogen a decompacted vitrinite reflectivity profile shows that the lower part of the devonian section has a steeper thermal maturity gradient which is interpreted as indicating a high devonian geothermal gradient associated with basin extension solid bitumen reflectivities and organic petrography show that the most recent hydrocarbon generation occurred in the upper part of the devonian interval during maximum tertiary burial vitrinite reflectivity data from the jurassic rocks in the beatrice field and onshore east sutherland enable the position of the oil generation window to be predicted in relation to the depth of the top of the devonian sequence the main controls on devonian source rock potential in the inner moray firth are not the depth of mesozoic and tertiary burial but the distribution of source rocks their degree of permian truncation and the pre permian thermal maturity level

high resolution geochemical analysis of organic matter accumulation in the qingshankou formation upper cretaceous songliao basin ne china abstract in the well known continental songliao basin the oil shale successions of the cretaceous qingshankou formation are excellent source rocks for oil the oil shale layers with high toc total organic carbon contents developed at the bottom of the formation they are divided into the lower oil shale toc up to 18 3 and the upper oil shale layer toc up to 14 4 the oil shale layers and accompanying mudstones are investigated by high resolution analyses of drill cores by pyrolysis organic petrology organic and inorganic geochemistry the results demonstrate the predominance of type i kerogen derived from algal microbial mats i e lamalginite however increased proportions of plant derived organic matter are indicated by rock eval parameters and the presence of vitrinite in the upper oil shale as evidenced from lower concentrations of hopanes higher sinking rates of organic matter om are suggested to have been responsible for a lower extent of microbial degradation during accumulation of the lower oil shale unit the environmental conditions are characterized by anoxic saline bottom water overlain by an extended zone of freshwater favorable for om production and preservation under these preconditions oil shale thickness and quality are governed by primary productivity related to accommodation space and nutrient supply redox conditions within the water column are the key factor controlling organic matter preservation

source rock analysis and petroleum geochemistry of the trym discovery norwegian north sea a middle jurassic coal sourced petroleum system abstract the 3 7 4 well trym in the norwegian part of the sogne basin north sea discovered condensates in middle jurassic reservoir sandstones and in addition penetrated four middle jurassic coal seams 0 14 0 56 m thick the precursor peats of the coals which have a complex vitrinite and inertinite rich composition accumulated in coastal plain mires and the depositional conditions of the peats influenced the source rock potential of the resulting coals vitrinite reflectance values from 0 86 0 87 r o and an average t max of 438 c indicate that the coals are thermally mature but they may be interpreted only to be in the early phase of petroleum generation the hydrogen indices of the coals are generally below 200 and crude oil saturation of the coals may have been hindered by an uneven in seam distribution of favourable hydrogen indices 200 coupled with the comparatively thick seams condensate source rock correlations indicate a similarity between the trym condensates and extracts from the coals in the 3 7 4 well and stable carbon isotope data infer a common source for the trym condensates and the condensates and oils from the harald and lulita fields in the danish part of the sogne basin the harald and lulita fields have recently been proven to represent a middle jurassic coal sourced petroleum system the lulu bryne lulu petroleum system and the trym condensate discovery is thus another example of this petroleum system which may be more widespread in the central graben

the influence of thermochemical sulphate reduction on hydrocarbon composition in nisku reservoirs brazeau river area alberta canada abstract the upper devonian nisku formation reservoirs of the brazeau river area of west central alberta canada produce oil and sweet and sour gas condensate generally oil pools are located updip in the study area and sour 6 31 h2s gas condensate downdip h2s in the study area is formed by thermochemical sulphate reduction tsr all liquid hydrocarbons probably have one source with the duvernay formation being the most likely candidate assessing the relative maturity of the oils and condensates is difficult because of the wide variation in thermal maturity and the effects of tsr but the ratio of pristane n heptadecane does appear to decrease with increasing maturity for this sample set with increasing tsr the following changes were noted decrease in the saturate aromatic hydrocarbon ratio increase in the relative abundance of organo sulphur compounds e g benzothiophenes 34s values of liquid hydrocarbon samples approached the values for anhydrite of the nisku formation in the study area and an increase in 13c of the saturate fraction h2s concentrations in hydrodynamically isolated pools provide a good estimate of the extent of tsr in these reservoirs however other pools have anomalously high h2s concentrations for their depth suggesting that the h2s was generated at greater depths and migrated updip into these pools

geochemistry of selected oils and rocks from the central portion of the west siberian basin russia six analyzed oils produced from middle jurassic to upper cretaceous strata in the middle ob region of the west siberian basin show biomarker and stable carbon isotope compositions indicating an origin from the upper jurassic bazhenov formation the chemical compositions of these oils are representative of more than 85 of the reserves in west siberia kontorovich et al 1975 bazhenov sourced oil in cenomanian strata in the van egan field underwent biodegradation in the reservoir resulting in a low api gravity an altered homohopane distribution and the appearance of 25 norhopanes without alteration of the steranes high api gravity oil from the salym field has surpassed the peak of the oil window consistent with abnormally high temperatures and pressures in the bazhenov source rock from which it is produced the remaining oils are very similar including samples from valanginian and bathonian callovian intervals in a sequence of stacked reservoirs in the fedorov field bazhenov rock samples from the study area contain abundant oil prone marine organic matter preserved under anoxic conditions organic matter in a bazhenov core from the pokachev 58 well was compared with the oils because it is thermally mature and shows total organic carbon toc 13 8 wt and hydrogen index values hi 489 mg hc g toc representative of the average for the formation 10 7 wt for 840 samples 420 mg hc g toc for 75 samples other rocks in the middle ob region are far less likely to have generated these oils than the bazhenov formation no prospective source rocks older than middle jurassic were available geochemical analyses indicate a lack of thermally mature hauterivian or younger source rocks in the study area core samples from the lower cretaceous frolov formation either are thermally immature hauterivian or show little oil generative potential berriasian valanginian the upper jurassic vasyugan formation shows lower oil generative potential than the bazhenov formation the average toc for vasyugan rocks is 3 20 wt 240 samples average atomic h c ratios for vasyugan and bazhenov kerogens are 0 90 10 samples and 1 13 25 samples respectively the vasyugan formation cannot be excluded as a source rock because insufficient sample was available for biomarker analysis core from the lower to middle jurassic tyumen formation in the yemyegov 15 well was compared with the oils because it is thermally mature and shows toc and hi values 2 78 wt and 137 mg hc g toc respectively indicating slightly more favorable oil generative characteristics than the average for the formation 2 75 wt for 720 samples 95 mg hc g toc for 25 samples the core contains terrigenous gas prone organic matter that shows no relationship with the analyzed oils

new evidence for evaporitic middle devonian lacustrine sediments with hydrocarbon source potential on the east shetland platform north sea the ukcs united kingdom continental shelf well 9 16 3 drilled on the western flank of the beryl embayment encountered a middle devonian sequence interpreted as part of the lacustrine orcadian basin an anhydrite layer found within the sequence provides confirmation of the local development of hypersaline environments within the orcadian basin detailed geochemical analysis of a representative source interval equivalent to the achanarras sandwick fish bed has revealed a close affinity with contemporaneous middle devonian source rocks found in the inner moray firth and crude oil from the beatrice oil field

circum arctic petroleum systems identified using decision tree chemometrics source and age related biomarker and isotopic data were measured for more than 1000 crude oil samples from wells and seeps collected above approximately 55n latitude a unique multitiered chemometric multivariate statistical decision tree was created that allowed automated classification of 31 genetically distinct circum arctic oil families based on a training set of 622 oil samples the method which we call decision tree chemometrics uses principal components analysis and multiple tiers of k nearest neighbor and simca soft independent modeling of class analogy models to classify and assign confidence limits for newly acquired oil samples and source rock extracts geochemical data for each oil sample were also used to infer the age lithology organic matter input depositional environment and identity of its source rock these results demonstrate the value of large petroleum databases where all samples were analyzed using the same procedures and instrumentation

lateritic weathering of pyroxenites at niquelandia goias brazil the supergene behavior of nickel two typical lateritic weathering profiles jacuba ahd angiquinho from the niquelandia ni deposits brazil were studied in order to establish the petrological relationship between the supergene ni products and the parental pyroxenes frbm the base to the top of the profiles pyroxenes are replaced by goethite and kaolinite through a series of transitional ni bearing phyllosilicates the mineralogy and the chemical composition especially the ni content of these clay minerals depends on the degree of fracturing and serpentinization of the pyroxenite and the location of the pyroxenite with respect to neighboring dunite within the jacuba profile smectite and pimelite pseudomorphs after pyroxene are especially ni rich and in fact are the most ni enriched clay minerals now known in lateritic weathering profiles

novel cyclised and aromatised diagenetic products of β carotene in the green river shale abstract a suite of novel diagenetic products of carotene has been identified in an extract of a sample from the green river shale identification is mainly based on comparison of mass spectra with those of diagenetic products of another carotenoid isorenieratene these compounds were formed by i cyclisation and aromatisation of the polyene isoprenoid chain ii explusion of toluene and m xylene from the polyene isoprenoid chain and iii aromatisation of the 1 1 5 trimethylcyclohex 5 enyl moieties resulting in 1 2 dimethylbenzene end groups reduction of the double bonds of carotene is the most important diagenetic process however as judged from the high relative amount of carotane 63 of quantified diagenetic products of carotene these results indicate that the fossilisation potential of carotenoids is greater than previously thought

geochemistry and origin of organic rich sediment veins in fractured granitic basement helmsdale sutherlandshire uk abstract black sediment veins up to 2 cm width penetrate the caledonian helmsdale granite in the vicinity of the helmsdale fault onshore moray firth the black colour and geochemistry of the veins reflect a high content of organic carbon both devonian and jurassic shales are conceivable available sources but sterane compositions relate the organic matter to the jurassic shales a content of extractable organic matter higher than in the shales suggests that the carbon in the veins represents oil rather than mechanically mobilized shale the oil was present during sediment vein emplacement the veins were emplaced forcefully which may reflect high fluid pressure associated with post jurassic movement on the helmsdale fault

faulting and graben formation in western and central europe rifts and rift related basins play a pre eminent role among the sedimentary basins of western and central europe through time grabens developed in a number of different megatectonic settings whereby the principal mechanisms governing their subsidence was crustal stretching and subcrustal erosion the level of volcanic activity associated with rifting is highly variable and can change significantly during the development history of a rift some rifts are totally non volcanic the development of rift domes is generally associated with volcanic activity uplifting of a rift dome can induce a reversal in the subsidence pattern of a rift intracontinental rifts with their thinned crust are prone to inversion when the respective craton is subjected to tangential stresses in the process of inversion the crust of rifts is mechanically thickened again

reactant product textures volume relations and implications for major element mobility during natural weathering of hornblende tallulah falls formation georgia blue ridge u s a natural weathering of hornblende from the tallulah falls formation georgia u s a takes place under thoroughly leached oxidizing conditions at the earliest stage of weathering corrosion of hornblende forms denticulated terminations with only minimal porosity apparent within the partially pseudomorphic kaolin group weathering product or between it and the reactant mineral isovolumetric replacement of hornblende by kaolin group clay or precursor products implies inheritance of parent mineral silica tetrahedra by the weathering products and largely immobile behavior of si during early weathering aluminum normally considered immobile or minimally mobile during weathering must be imported into early stage weathering products more advanced weathering of hornblende forms denticulated terminations separated from the earlier formed products by a large continuous peripheral void porosity is much more conspicuous at this stage late stage ferruginous products precipitate from fe mobilized in solution dissolved fe to form the late stage goethite can be entirely derived from the parent hornblende requiring only short transport distances for aqueous fe between the source parent mineral and the location of product precipitation textural and volumetric relationships between naturally weathered hornblende and its partially pseudomorphic weathering products suggest structurally controlled immobility of much parent mineral si and considerable mobilization of al at early stages of weathering but at more advanced stages of weathering the textural and volumetric relationships are consistent with immobility of al and fe and leaching of substantial si and all base cations

statistical analysis as a tool for assisting geochemical interpretation of the upper triassic yanchang formation ordos basin central china abstract the yanchang formation in the ordos basin is the most important petroleum play not only for conventional oil and gas accumulations but also for newly emerging shale oil and tight gas resources the molecular characterization of the basinwide source rocks predicts three groups of generative petroleum types paraffinic high wax oil mixed base paraffinic naphthenic aromatic low wax oil and gas and condensate supplementary to previous work 68 samples including the crude oils source bitumens and reservoir extracts from the yanchang petroleum play are analyzed the distribution of two terpane classes eight tricyclic terpanes and eight pentacyclic terpanes are determined with subsequent simultaneous rq mode factor analysis for a composite data set of these samples alongside 216 published crude oils worldwide with known facies descriptions thermal maturity has been evaluated as a consistent distribution at first using a combined method of a maturity related biomarker ts ts tm and aromatic parameters methyldibenzothiophene ratios to alleviate the maturity differences effect when discussing geochemical characterization the r mode factor analysis consists of the first two factors that are describing 45 present of the cumulative total variance in the data set and presents a sample grouping pattern in q mode factor analysis which is determined by different contributions of terpane associations i e the tricyclic c21 coupled with pentacyclic c26 c27 c28 and c30 in the same factor space three terpane associations the c26 and c28 terpanes the c21 and c30 terpanes and the c27 pentacyclic terpenes are respectively responsible for discriminating crude oil reservoir extracts and source bitumens in rq mode factor analysis molecular compositions further address more detailed interrelationships among three sample groups that crude oils and reservoir extracts are sharing close genetic relationships both in depositional environment typing and c27 c28 c29 sterane distribution samples from source rocks vary much significantly a mixing process which occurs after oils has been expelled from host source rocks into carrier units during accumulation in addition the migration contamination of c29 sterols when oils are cross through the chang 7 2 unit along migration pathways might also explain this lack of correlation between source rocks and oil reservoir system

hydrologic mechanisms governing fluid flow in a partially saturated fractured porous medium in contrast to the saturated zone within which fluid moves rapidly along fractures the fractures with apertures large relative to the size of matrix pores will desaturate first during the drainage process and the bulk of fluid flow would be through interconnected pores in the matrix within a partially drained fracture the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture the residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small normal to the fracture surfaces the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block a general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions results are obtained from an aperture distribution model for fracture saturation hydraulic conductivity and effective matrix fracture flow areas as functions of pressure the effects of distortion of flow paths by the air pockets are taken into account by a phase separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition the reduction of matrix fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture which is inversely proportional to the suction head drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the topopah spring member at yucca mountain southern nevada the column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores the fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area the characteristic curves for the matrix are based on laboratory measurements of tuff samples from the cases simulated for the fractured porous columns with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties however the quasi steady changes of the fluid flow of a partially saturated fractured porous system could be approximately simulated without taking the fractures into account

oil source rock correlation using biological markers norwegian continental shelf abstract oil source rock correlation is an integral part of exploration geochemistry and biomarkers have been used successfully for this purpose this paper reports three case studies which illustrate some of the inherent problems in oil source rock correlations on samples from the norwegian continental shelf in the first study an oil is compared directly with mature source rocks on the structure showing that the oil must have been expelled very early in the second oils are compared with immature source rock units on the structure showing the potential of multivariate analysis for correlation problems finally an unusual barents sea oil is compared with triassic source rocks from spitsbergen it is shown that correlations based on individual characteristics can only be supported in rare cases multivariate analysis is a safer method of correlation of oils to a typical potential source rock of mixed kerogen facies and low maturity

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

origin and migration pathway of biodegraded oils pooled in multiple reservoirs of the chepaizi uplift junggar basin nw china insights from geochemical characterization and chemometrics methods abstract the chepaizi uplift possesses three sets of oil bearing reservoirs six sets of source intervals multiple episodes of hydrocarbon charging and variable physical properties of crude oils in this study based on geochemical characterization source intervals and the biodegradation rank of the crude oils four oil populations named as group a b c and d d1 d2 were defined the combined results of q cluster analysis qca and discriminant analysis da indicate that group a occurred mainly in lower neogene shawan formation n1s in the western chepaizi uplift and were primarily derived from the middle lower jurassic xishanyao badaowan sangonghe formations j2x j1b j1s and a little of paleogene anjihaihe formation e2 3a of the sikeshu sag group b occurred essentially in upper carboniferous xibeikulasi formation c2x of the western chepaizi and originated mainly from the j1b mudstone of the shawan sag in addition the crude oils of group c occurred mainly in the lower cretaceous tugulu group k1tg of the eastern chepaizi and were primarily derived from carboniferous sourced oil from the chepaizi uplift the crude oils of groups d d1 and d2 are mixed with permian p1f and p2w of shawan sag and carboniferous sourced oil from the chepaizi uplift based on the reconstruction of the migration history the oils of group a in the n1s formation of western chepaizi migrated predominantly from the south sikeshu sag to the north and northeast with wells su1 2 and c27 as the initial filling points the oils of group b in the n1s formation of the western chepaizi travelled predominantly from the southeast shawan sag to the north and northwest the oils of group d1 in the c2x formation of eastern chepaizi migrated mainly from the northeast and southeast shawan sag to the west with well p661 as the initial filling point wells sm011 and c64 are the initial filling points of the k1tg group in the hongche fault belt crude oils of group c in the k1tg group travelled predominantly from the southeast shawan sag and northeast to the west into the eastern chepaizi and from well p68 to the southwest according to the paleo oil preferential filling orientations and paleogeomorphology some favourable targets for petroleum exploration of the chepaizi uplift are forecast in this study

the preservation of fossil biomarkers during meteorite impact events experimental evidence from biomarker rich projectiles and target rocks a devonian siltstone from orkney scotland shows survival of biomarkers in high velocity impact experiments the biomarkers were detected in ejecta fragments from experiments involving normal incidence of steel projectiles at 5 6 km s 1 and in projectile fragments from impact experiments into sand and water at 2 5 km s 1 the associated peak shock pressures were calculated to be in the range of 110 147 gpa for impacts of the steel projectiles into the siltstone target and hydrocode simulations are used to show the variation of peak pressure with depth in the target and throughout the finite volume projectiles thermally sensitive biomarker ratios including ratios of hopanoids and steranes and the methylphenanthrene ratio showed an increase in thermal maturity in the ejecta and especially the projectile fragments measurement of absolute concentrations of selected biomarkers indicates that changes in biomarker ratios reflect synthesis of new material rather than selective destruction their presence in ejecta and projectile fragments suggests that fossil biomarkers may survive hypervelocity impacts and that experiments using biomarker rich rock have high potential for testing survival of organic matter in a range of impact scenarios

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

petroleum migration and mixing in the potiguar basin brazil regional studies of petroleum samples from both offshore and onshore reservoirs of the potiguar basin brazil reveal compositional differences with discernible landward trends attributable to oil mixing these chemical discrepancies can be related to a combination of source rocks maturity and migration history the source rocks are classified in two groups based on their geochemical and molecular characteristics 1 neocomian and aptian lacustrine freshwater shales and 2 aptian marine evaporitic shales and marls both lie in an offshore structural low the geochemically contrasting oils derived from these source beds migrated updip constrained by a monoclinal structure through aptian carrier beds to thermally immature strata evaluation of compositional heterog neities in the oils and an investigation of migration effects on their compositions reveal trends related to the amount of mixing which in turn reflects the timing of both oil generation and migration and the direction of migration the more migrated oils contain greater contributions from freshwater sources whereas the less migrated oils display more pronounced contributions from the younger and shallower hypersaline source beds biomarker maturity parameters indicate that the most migrated oils are less mature consistent with their early generation from the deeper lacustrine freshwater source beds and migration to fill the shallower reservoirs first the results suggest that drainage of the basin evolved from lateral to vertical and enable prediction of the distribution of petrol um types within the basin

organic geochemistry petrology and palynofacies of middle devonian lacustrine flagstones in the orcadian basin scotland depositional environment thermal history and petroleum generation potential during middle devonian time a thick succession of organic rich mainly lacustrine flagstones developed within the orcadian basin these petroleum source rocks crop out in northern scotland nineteen samples were studied using organic petrology palynology and organic geochemistry in order to characterize kerogen type depositional environment thermal maturity and petroleum generation potential c org carbonate and sulphur content as well as hydrogen index hi values are quite variable e g hi from 79 to 744 mg hc g c org based on biomarker data organic material mainly originates from aquatic organic matter deposited under lacustrine conditions with oxygen depleted but not permanently anoxic bottom waters petrography reveals small quantities of vitrinite particles indicating minor input of terrestrial material this is supported by biomarker data and the palynofacies which is characterized by a high amount of oil prone amorphous organic matter aom and generally few miospores maturity of the succession studied in caithness and orkney is between immature and oil mature one dimensional basin modelling shows that a significant remaining hydrocarbon generation potential exists within the middle devonian succession in contrast to the low hydrocarbon generation in the onshore area offshore oil generation was significant especially after deposition of thick upper jurassic upper cretaceous sediments at the end of cretaceous time hydrocarbon generation ceased due to uplift the contribution to known oil fields from the devonian flagstones is a realistic scenario including a contribution to the beatrice oil field in the south of the modelled area

the behaviour of aromatic hydrocarbons in artificial mixtures of permian and jurassic end member oils application to in reservoir mixing in the eromanga basin australia abstract artificial mixing of two non marine oils one permian and the other jurassic from the cooper and eromanga basins australia was employed to assess the degree of co mingling in reservoirs of the latter basin and to verify estimates of mixing ratios based on a simple mass balance approach using absolute concentrations of individual aromatic hydrocarbons a cross plot of the methylphenanthrene ratios 1 mp 9 mp and 2 mp 1 mp already shown to be useful for recognising dual sourced oil pools has been re calibrated against the model mixing curves both artificial and theoretical obtained for experimental blends of the two end member oils both curves reveal that previous attempts to identify the sources of mixed oils in this petroleum province using di and tri aromatic hydrocarbons seriously overestimate the eromanga jurassic cretaceous contribution samples plotting away from the model curves are likely to be mixtures of oils with maturities different to those of the end members used in this experiment jurassic 0 52 rc permian 1 00 rc the observed increase in thermal maturity rc of the mixed oil as its permian contribution increases casts doubt on the validity of distinguishing oil origins using only the maturity contrast between the cooper and eromanga petroleum systems

source rock evaluation of middle jurassic coals northeast greenland by artificial maturation aspects of petroleum generation from coal paralic liptinite enriched coals and carbonaceous mudstones in northeast greenland constitute potential highly oil prone source rocks whereas the humic coals may be marginal source rocks the liptinite rich coals are dominated by resinite or fluorescing amorphous organic matter and alginite resulting in hydrogen index hi values generally above 300 and reaching up to 728 during artificial maturation up to 330 degreesc 72 hr the coals follow the maturation paths of kerogen types i and ii on an hi vs tmax diagram and calculations show that upon passage through the oil window roughly 85 of their generation potential is realized activation energy ea distributions with prominent principal ea values centered around 60 62 kcal mole and frequency factors from 5 855 x 1015 s 1 to 3 249 x 1016 s 1 strongly influence the generation characteristics from 300 to 330 degreesc 72 hr artificial maturation important changes include marked loss of liptinite fluorescence and increase in resinite reflectance small change in tmax significant decrease in hi pronounced increase in extract yields increased generation of saturates and generation of labile bitumen with low ea values these observations indicate significant bitumen petroleum formation from the coals during a relatively narrow temperature range which together with the petrographic composition may facilitate expulsion of a waxy crude oil the coals demonstrate that under certain depositional conditions highly prolific coal source rocks can form with the capacity not only to generate but also to expel liquid petroleum begin page 234

an aem tem study of weathering and diagenesis abert lake oregon ii diagenetic modification of the sedimentary assemblage abstract this paper compares the mineralogy and chemistry of clay minerals in sediments from various depths and positions in abert lake and surrounding playa with those of the weathered materials entering the lake in order to reveal the nature and extent of post depositional mineralogical modification analytical electron microscope aem data from individual clay particles reveal that each sample is comprised of a highly inhomogeneous smectite assemblage the thin clay flakes commonly less than 10 nm wide display a complete range in octahedral sheet compositions from nearly dioctahedral to nearly trioctahedral the very abundant mg rich lake smectites with an estimated composition k 0 29 al 0 23 mg 2 16 fe 0 30 si 3 80 al 0 20 o 10 oh 2 are not formed by weathering this confirms the importance of diagenetic mg uptake lattice fringe imaging failed to reveal distinct brucite like or vermiculite like layers suggesting that interstratifications of this type are rare or absent siliceous coatings on clay particles identified by silica excess in smectite analyses seem to favor topotactic overgrowth of stevensite rather than addition of brucite like layers to the dioctahedral nuclei the growth of k stevensite dilutes the al content of the crystal and thus the increasing diagenetic modification reduces rather than supplements its illite component smectite compositions within individual samples were highly variable yet source related characteristics such as the abundance of fe rich smectite were apparent little evidence for systematic k or mg enrichment with depth was identified in samples from depths of down to 16 feet below the sediment water interface the most magnesian assemblages are associated both with weathering sources of mg rich smectite and playa environments subjected to repeated wetting and drying cycles thus the observations suggest that clay compositions primarily reflect changes in lake levels brine composition and source characteristics rather than time and depth compaction effects other diagenetic reactions in the sediment include recrystallization of na rich silica gel and diatom fragments abundant submicron sized untwinned euhedral crystals of k feldspar are interpreted to be authigenic in origin

vanadium nickel and sulfur in crude oils and source rocks and their relationship with biomarkers implications for the origin of crude oils in venezuelan basins abstract this work presents a study of vanadium nickel and sulfur concentrations and biomarkers in a suite of crude oils and source rocks from three venezuelan basins maracaibo and eastern basins and barinas sub basin crude oils range from unaltered to altered by biodegradation and source rocks are characterized by having different kerogen types type ii iii or iv and maturity levels early mature to post mature vanadium nickel and sulfur concentrations v ni or v v ni and saturate biomarkers were used to classify the oils and source rocks based on inferred paleo redox environment lithology and maturity of the source rock oils are classified into five groups based on v ni ratios they appear to be related to variations in the paleo redox environment from suboxic dysoxic to anoxic suboxic of source rocks with variable lithological composition and organic matter input regardless of their maturity or biodegradation level these five groups are also classified based on biomarkers related to maturity organic matter type paleo redox environment and source rock lithology in source rocks vanadium nickel and sulfur concentrations together with v ni or v v ni ratios provide information about the paleo redox environment and are related to lithology regardless of their maturity these results also indicate variable paleo redox conditions during the sedimentation of venezuelan source rocks all this suggests that while the main source rocks in venezuelan basins are well established there are still uncertainties regarding their lateral and vertical variations in organic and inorganic facies and paleo redox conditions the presence of other source rocks contributing to the accumulation of hydrocarbons in the venezuela basins is also a possibility

the origin and accumulation of multi phase reservoirs in the east tabei uplift tarim basin china abstract a giant deep strata oil gas field with complex fluid characteristics was recently discovered in the hade yuke area of the east tabei uplift tarim basin nw china the deep fluids show a lateral co existence of several gas condensate and oil phase reservoirs characterized through the integration of complimentary geochemical e g bulk composition biomarker and stable carbon isotope and geological data typical features of the gas and condensate reservoirs which were mainly distributed in the eastern parts of the study site included high gor gas to oil ratio hydrocarbon gases with relatively heavy 13c values and crude oils with high wax content in contrast oil reservoirs which mostly occurred in more westerly locations had lower gor values lighter 13c values and lower wax content indicating gradual change of fluid characters the petroleum accumulations derive from two hydrocarbon charge events an early oil charge in the late hercynian and a later gas charge in the late himalayan which migrated from east to west leading to a gradual variation in fluid phase and characteristics alteration of paleo oil reservoirs by this secondary gas charge was therefore primarily responsible for the complex fluid character and multi phase reservoirs presently in place secondary condensates were formed from the retrograde condensation of paleo reservoirs our re construction of the hydrocarbon accumulation process encourages future exploration endeavours to target commercially viable gas accumulations in the deep east strata and oil reservoirs in the west