gas condensate migration and oil fractionation in deltaic systems abstract the term evaporative fractionation is proposed to describe several phenomena involved in the secondary alteration of reservoired oil firstly it is suggested that oil is frequently partially vaporized in the reservoir secondly that gas bearing substantial portions of the oil in solution is conducted along faults to form independent gas condensate accumulations thirdly that residual oils formed in this fashion bear internal evidence of fractionation in addition to the conspicuous loss of light ends there is an increase in the content of light aromatic and naphthenic hydrocarbons relative to paraffins in the residual oil evaporative fractionation effects are recognized for the first time in the distillation and physical property data of us bureau of mines routine method oil analyses fractionation effects are postulated to be the cause of sigmoid as opposed to normal curvilinear aromatic profiles the effects of evaporative fractionation are widespread in oils throughout the united states they are evident in approximately 75 of oils in the gulf coast region and in a large proportion of the gas condensate accumulations the process is a major and apparently unrecognized means of petroleum alteration and of generation of gas condensates experimental evidence shows that partial vaporization results in enhanced levels of light aromatic hydrocarbons in residual oils oil samples were partially vaporized in excess methane at elevated pressure and temperature followed by removal of the vapour the gas chromatographic features of many gulf coast oils were reproduced various levels of light end depletion and enhancement of aromaticity were brought about

controls on petroleum composition in the llanos basin colombia implications for exploration physical and geochemical characteristics of produced petroleum from the central region of the llanos basin colombia were analyzed to understand the petroleum charge history and alteration processes petroleum properties in the study area are the result of the complex charge history of the oil fields the amount of gas in fluids is controlled by the migration distance from the late or possibly the current generation kitchen located beneath the foothill deformation zone gas influx decreases toward the foreland domain as indicated by lower values of the gas oil ratio and saturation pressure the api gravity of the oil samples is mainly controlled by the intensity of biodegradation marine sourced oils accumulated in shallow reservoirs of the foreland prior to the onset of andean deformation those fluids were subjected to different levels of biodegradation depending on the time they remained at reservoir temperatures lower than 80 c 176 f and before being buried to their maximum depth geochemical data suggest multiple charge pulses from different source kitchens of two main types of source rocks as well as different biodegradation levels the proposed petroleum charge and alteration model allows prediction of the temperature history of a reservoir and the most likely physical properties of the petroleum at a specific location the model can be used as an exploration tool to assess the risk of charge prior to drilling in unexplored areas of the basin

geochemical factors controlling the phase behavior of eagle ford shale petroleum fluids petroleum types in the eagle ford resource play span the range from black oil to dry gas and are produced along regional trends that are largely maturity controlled a total of 61 shale samples covering all maturity zones were evaluated to document organic richness organic matter type and maturation characteristics using established geochemical parameters pyrolysis experiments were then performed to simulate the generation of petroleum fluids termed the phasesnapshot approach one or more target wells with known fluid properties were used as reference a match with that composition was made using next formed fluids generated from the shale in a closely located well of slightly lower thermal maturity than the target well s phase behavior predictions from the model were calibrated using a regional pressure volume temperature pvt database compiled from the public domain the conceptual model that best matched the pvt data were comprised of two reactive components 1 a mixture of kerogen and bitumen that generated petroleum within the low permeability shale matrix and 2 bitumen in zones of enhanced porosity within the matrix the combined generation of gas from both of these components as well as the strong retention of c7 fluids in the matrix during production were required to match the calibration data retention of oil was needed over a broad thermal maturity range rock eval tmax release 440 c 475 c a key result of this forward model is that phase behavior and bulk compositional properties of hydrocarbons can be quickly and effectively predicted using mature shale samples as long as calibration data from pvt reports are available

molecular memory effects recording the accumulation history of petroleum reservoirs a case study of the heidrun field offshore norway abstract the immobile portion of the oil occupying the pore space of reservoir sandstones which is mostly represented by visible impregnations is shown by the present study to contain geochemical signals that record their filling history the clue to unravelling these signals is sequential extraction of such impregnations of residual oil by a high pressure solvent flow through cell in which the solvent percolates through the intact and primary pore system of the rock sample gas chromatography mass spectroscopy gc ms analysis of residual oils extracted from samples of certain reservoir sandstones within the heidrun field offshore norway reveal significant contrasts in the chemical maturity of the first and the last fractions recovered as high as 0 69 versus 0 50 for the mpi 1 ratio corresponding to 0 79 versus 0 67 rc the hypothesis is proposed that by using this extraction technique oil impregnations from different portions of the pore system i e from large versus small pores are obtained separately this interpretation is especially supported by the regular occurrence of reservoir sandstones in which the residual oil exhibits maturity contrasts between those fractions extracted from large and small pores of the same rock within the heidrun field the distribution of reservoir sandstones with such maturity contrasts is strictly controlled by their position in the oil column and the location of their fault compartment these contrasts are interpreted to reflect the maturity levels of end members of the petroleum charges which have filled this trap during an extended period of geological time reservoir sandstone samples containing such end member charges are limited to the uppermost portion of the oil column lower in the oil column the pore system of all reservoirs contains oil impregnations of a uniform maturity level regardless of their pore size origin this distribution is believed to indicate an early stage of the accumulation history of the heidrun field characterised by the formation of a palaeo oil water contact well above the present one moreover the four fault compartments studied each controlled by bordering faults with different sealing capacities were not filled during the same stages of the accumulation history in summary the present study has shown that oil impregnations depending on their location within the pore system of individual reservoir sandstones can retain molecular memory effects which in turn allow the accumulation history of petroleum fields to be reconstructed

changes in gas composition during simulated maturation of sulfur rich type ii s source rock and related petroleum asphaltenes abstract asphaltenes extracted from crude oils are proposed to possess structural features of the related source rock kerogen for the present study micro scale sealed vessel pyrolysis mssv and combustion isotope ratio mass spectrometry gc c irms were used to compare gas generation from a whole rock type ii s kerogen from southern italy with that from related sulfur rich asphaltenes isolated from a low maturity heavy crude oil the purpose of was to determine whether experimental pyrolysis of oil asphaltenes can be used to predict the timing and the chemical and isotopic composition of hydrocarbon gases generated from genetically related kerogen in the source rock during burial maturation the results show that parameters such as gas to oil ratio gor and oil and gas formation timing are very similar for these two sample types whereas gas composition product aromaticity and sulfur content are remarkably different slight differences in gor are mainly due to differences in gas formation characteristics at very high levels of thermal alteration secondary gas formation from the whole rock covers a much broader temperature range under geological conditions than that from the asphaltene products however it is remarkable that both the onset and the maximum temperature are nearly identical under geological conditions the observed differences in gas generation characteristics are supported by discrepancies in the carbon isotopic characteristics of the gas range compounds and indicate different precursors and or mechanisms for gas generated from whole rock and asphaltenes

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

unraveling secondary migration effects through the regional evaluation of pvt data a case study from quadrant 25 nocs pvt data offer a unique source of information for the characterization of hydrocarbon migration from a petroleum exploration point of view a case study is presented here in which a large fluid compositional variability encountered in the northern half of quadrant 25 norwegian north sea and especially the enigmatic occurrence of an undersaturated light oil in a shallow jurassic reservoir in well 25 6 1 are explained using pvt data recognition and numerical simulation of the effects of phase separation allowed the characterization of genetic fluid relationships and regional migration trends sequential flash calculations indicated the most likely formation mechanism for the 25 6 1 fluid which is by condensation out of a migrating saturated gas phase the volumetrics involved in this process indicate that the gas phase predominated with only 3 vol of the original fluid ending up as a liquid

different modes of the late cretaceous early tertiary inversion in the north german and polish basins several selected seismic lines are used to show and compare the modes of late cretaceous early tertiary inversion within the north german and polish basins these seismic data illustrate an important difference in the allocation of major zones of basement thick skinned deformation and maximum uplift within both basins the most important inversion related uplift of the polish basin was localised in its axial part the mid polish trough whereas the basement in the axial part of the north german basin remained virtually flat the latter was uplifted along the sw and to a smaller degree the ne margins of the north german basin presently defined by the elbe fault system and the grimmen high respectively the different location of the basement inversion and uplift within the north german and polish basins is interpreted to reflect the position of major zones of crustal weakness represented by the wnw ese trending elbe fault system and by the nw se striking teisseyre tornquist zone the latter underlying the mid polish trough therefore the inversion of the polish and north german basins demonstrates the significance of an inherited basement structure regardless of its relationship to the position of the basin axis the inversion of the mid polish trough was connected with the reactivation of normal basement fault zones responsible for its permo mesozoic subsidence these faults zones inverted as reverse faults facilitated the uplift of the mid polish trough in the order of 1 3 km in contrast inversion of the north german basin rarely re used structures active during its subsidence basement inversion and uplift in the range of 3 4 km was focused at the elbe fault system which has remained quiescent in the triassic and jurassic but reproduced the direction of an earlier variscan structural grain in contrast n s oriented mesozoic grabens and troughs in the central part of the north german basin avoided significant inversion as they were oriented parallel to the direction of the inferred late cretaceous early tertiary compression the comparison of the north german and polish basins shows that inversion structures can follow an earlier subsidence pattern only under a favourable orientation of the stress field a thick zechstein salt layer in the central parts of the north german basin and the mid polish trough caused mechanical decoupling between the sub salt basement and the supra salt sedimentary cover resultant thin skinned inversion was manifested by the formation of various structures developed entirely in the supra salt mesozoic cenozoic succession the zechstein salt provided a mechanical buffer accommodating compressional stress and responding to the inversion through salt mobilisation and redistribution only in parts of the ngb and mpt characterised by either thin or missing zechstein evaporites thick skinned inversion directly controlled inversion related deformations of the sedimentary cover inversion of the permo mesozoic fill within the mid polish trough was achieved by a regional elevation above uplifted basement blocks conversely in the north german basin horizontal stress must have been transferred into the salt cover across the basin from its sw margin towards the basins centre this must be the case since compressional deformations are concentrated mostly above the salt and no significant inversion related basement faults are seismically detected apart from the basin margins this strain decoupling in the interior of the north german basin was enhanced by the presence of the elbe fault system which allowed strain localization in the basin floor due to its orientation perpendicular to the inferred late cretaceous early tertiary far field compression

geochemical characterisation and genetic origin of oils and condensates in the south viking graben norway abstract geochemical analysis of oil and condensate samples from all major fields and discoveries in the norwegian south viking graben as well as source rock extracts of upper and middle jurassic source horizons was carried out to characterise reservoired hydrocarbons and establish genetic relationships the south viking graben is in a mature phase of exploration and this study aims at unravelling regional trends to improve predictions in exploration and will show the significance of the play models in the area seven hydrocarbon families have been identified based on interpretation of molecular and isotopic characteristics and multivariate analysis of biomarker data these families can be linked to three source horizons three families originate from different facies of the draupne formation and are characterised by pr ph ratios below 2 dominance of c 27 regular steranes over the c 29 homologues and carbon isotopic values for saturate and aromatic fraction lighter than 28 and 27 respectively the upper jurassic heather formation and the middle jurassic vestland group each source one group of hydrocarbons typical for heather sourced hydrocarbons are elevated pr ph ratios between 2 35 and 3 08 low ratios of c 27 c 29 regular steranes and average isotopic values of 28 4 13 c sat and 26 8 13 c aro hydrocarbons from a middle jurassic source are characterised by very heavy isotopic composition highest pr ph ratios of the data set and dominance of c 29 regular steranes over the c 27 homologues among other factors the two remaining families represent mixtures from upper and middle jurassic sources and are mainly encountered in the greater sleipner area the available data in this study allowed characterisation of 84 of the recoverable oil resources which proved that the main source rock in the area is the upper jurassic draupne formation the play concept including a draupne source and tertiary reservoir proves to be most prolific with 239 10 6 s m 3 of recoverable oil equalling 88 of the total characterised oil resources oils in these tertiary reservoirs are however likely to be affected by biodegradation based on the available data the zone of biodegradation in the south viking graben appears to be limited to depths above 2140 m and temperatures below 70 c

deep seismic survey images crustal structure of tornquist zone beneath southern baltic sea the tornquist zone is europe s longest tectonic lineament and bisects the continent in a nw se direction from the north sea off nw denmark to the black sea new deep seismic reflection and coinci

habitat of hydrocarbons on the norwegian continental shelf eds a m spenceret al norwegian petroleum society graham and trotman 1986 isbn 0 86010 833 3 price 65 00

detrital composition of ordovician sandstones from the rugen boreholes implications for the evolution of the tornquist ocean the lower palaeozoic sequences of the rugen boreholes are composed of pelitic clastic sediments which range in age from the cambro ordovician boundary to the late ordovician provenance studies have been carried out on cambro ordovician sandstones from the loissin borehole and on middle upper ordovician greywackes of the rugen 5 borehole

geochemical study of coral skeletons from the puerto morelos reef southeastern mexico abstract geochemical analyses in coral skeletons have been used as a proxy of marine environmental conditions and to understand the mechanisms of adsorption of chemical elements into the coral skeletons and growth forms however little attention has been given to show the possible differences in the growth rates of corals based upon major trace rare earth element and microprobe analyses to examine the physical chemical conditions influencing those differences our goal is to show how branch and fan corals incorporate elements into their skeletons comparing them with their coral growth rates we determine the development of the skeletons of two branching acropora palmata acropora cervicornis and one fan shaped gorgonia ventalina colonies in the puerto morelos reef southeastern mexico based upon geochemical data and the influence of terrigenous input into the species mg and sr concentrations were the most statistically significant elements among the species studied suggesting that mg concentration in gorgonia ventalina is probably not linked to its growth rate mn content in the sea water is adsorbed by the three corals during past growth rates during high rainfall events sr concentration may be associated with the growth rate of acropora palmata little differences in the growth rate in acropora palmata may be associated with low rates of calcitization negligible changes in the sr concentration and little influence of temperature and water depth in its growth trace elements like cr co ni and v adsorbed by the corals are influenced by natural concentration of these elements in the sea water rare earth elements in the corals studied suggests abundant inorganic ions co32 with variable ph in modern shallow well oxygenated sea water lack of terrigenous input seawards is supported by geochemical geomorphological and biological evidences this study is an example of how geochemical data are useful to observe the differences in environmental conditions related to coral skeleton growth rates and morphology

pvt and phase behaviour analysis in petroleum exploration abstract this paper describes the application of pvt data routinely determined for almost all conventional oil tests with respect to petroleum exploration in a broader context the use of pvt and phase behaviour analysis focuses on phase envelope evolution as a function of source rock maturity and secondary migration using both laboratory analyses and natural examples from the ekofisk eldfisk and snorre fields as well as data from the tampen spur area and barents sea in general pvt analysis is demonstrated to be applicable for relative maturity estimation recognition of mixing effects volumetric evaluation of complex reservoir filling histories and as a screening tool for oil population characterisation pvt analysis is used in this paper as a tool complementary to organic geochemistry allowing the integration and interpretation of data reflecting fluid response to geological conditions on a regional scale

the factors controlling the abundance and migration of heavy versus light oils as constrained by data from the gulf of suez part i the effect of expelled petroleum composition pvt properties and petroleum system geometry abstract in the gulf of suez gos petroleum systems the main factors which control the abundance and migration of heavy vs light oils are a the composition and pvt properties of the expelled fluids b the geometry of the petroleum systems and c reservoir flow processes compositional and pvt modeling of the expelled petroleum fluids from the brown limestone and the thebes formation carbonate source rocks show the following the fluids expelled below a transformation ratio of 0 5 are heavy oils stock tank api gravity 10 20 have a low gor and contain 20 25 asphaltenes these fluids are formed from source rocks which have mainly low to intermediate sulfur content and normal thermal stability the further expelled fluids up to a transformation ratio of around 0 97 are bubble point behaving fluids oils with stock tank api from 20 50 and gor 300 800 scf bbl and display a progressive decrease in asphaltene content the latest 3 expelled fluids represent dew point behaving fluids gas condensates the heavy low gor oils expelled below a transformation ratio of 0 5 have a very low saturation pressure and are not prone to asphaltene precipitation unless they are mixed with higher gor fluids the pvt properties of these early expelled oils permit their efficient migration this is consistent with an overabundance of low maturity asphaltenes in the gos discovered heavy oils the tendency for asphaltene precipitation is increased for the fluids expelled above a transformation ratio of 0 5 due to both a decrease in their asphaltene content and an increase in gor geometrically imposed mixing of fluids with large maturity induced compositional differences and reservoir flow processes have a significant effect on the pvt behavior of the migrating fluids on asphaltene precipitation and on the distribution of heavy vs light oils

atmospheric methane from organic carbon mobilization in sedimentary basins the sleeping giant abstract the mass of organic carbon in sedimentary basins amounts to a staggering 1016 t dwarfing the mass contained in coal oil gas and all living systems by ten thousand fold the evolution of this giant mass during subsidence and uplift via chemical physical and biological processes not only controls fossil energy resource occurrence worldwide but also has the capacity for driving global climate only a tiny change in the degree of leakage particularly if focused through the hydrate cycle can result in globally significant greenhouse gas emissions to date neither climate models nor atmospheric co2 budget estimates have quantitatively included methane from thermal or microbial cracking of sedimentary organic matter deep in sedimentary basins recent estimates of average low latitude eocene surface temperatures beyond 30 c require extreme levels of atmospheric co2 methane degassing from sedimentary basins may be a mechanism to explain increases of atmospheric co2 to values as much as 20 times higher than pre industrial values increased natural gas emission could have been set in motion either by global tectonic processes such as pulses of activity in the global alpine fold belt leading to increased basin subsidence and maturation rates in the prolific jurassic and cretaceous organic rich sediments or by increased magmatic activity such as observed in the northern atlantic around the paleocene eocene boundary increased natural gas emission would have led to global warming that was accentuated by long lasting positive feedback effects through temperature transfer from the surface into sedimentary basins massive gas hydrate dissociation may have been an additional positive feedback factor during hyperthermals superimposed on long term warming such as the paleocene eocene thermal maximum petm as geologic sources may have contributed over one third of global atmospheric methane in pre industrial time variability in methane flux from sedimentary basins may have driven global climate not only at time scales of millions of years but also over geologically short periods of time earth system models linking atmospheric ocean and earth surface processes at different timescales with the sedimentary organic carbon cycle are the tools that need to be developed in order to investigate the role of methane from sedimentary basins in earth s climate

on the filling and leakage of petroleum from traps in the laminaria high region of the northern bonaparte basin australia abstract a 3d petroleum systems model of the northern bonaparte basin indicates that the potential nancar trough source kitchen could be currently expelling hydrocarbons from numerous jurassic source rocks into traps on the laminaria high based on a range of kinetic models defined for such source rocks within the plover laminaria and frigate formations two phases of hydrocarbon generation are predicted source rocks within the lower cretaceous echuca shoals formation are immature for hydrocarbon generation in this region hydrocarbon generation in the laminaria high commenced during the mid to late cenozoic and in the nancar trough during the early cretaceous in response to elevated heat flow during the syn rift phase the second and main phase of hydrocarbon generation and expulsion started in the mid eocene and is ongoing this phase was controlled by deposition of the thick cenozoic carbonate shelf which resulted in deep burial and continued heating of the mesozoic source rocks this second phase of expulsion coincided with the reactivation of fault bounded traps the consequence of which is that either some or all of the initially trapped hydrocarbons have escaped out of the charged structures thus the most plausible explanation for the occurrence of under filled and dry structures within the study area is that the faults bounding these traps remained permeable from the late miocene to the present day secondary alteration processes including water washing and phase fractionation are necessary to explain the bulk composition of laminaria high and neighbouring under saturated light oil accumulations

pomeranian caledonides nw poland a collisional suture or thin skinned fold and thrust belt abstract a main goal of this study was to understand the character of the caledonian deformation front in pomerania nw poland and its relationship to the adjoining teisseyre tornquist zone ttz in the context of the avalonia baltica early palaeozoic collision since the pomeranian caledonides are concealed beneath 1 4 km thick platform cover of upper palaeozoic and mesozoic sediments we used a combination of potential field seismic and well data to investigate the basement architecture and structure of the lower palaeozoic rocks starting from a qualitative review of gravity and magnetic data we built a 2d gravity and magnetic model upon the polandspan pl1 5600 seismic reflection line and applied 3d gravity inversion for a depth to basement study using well tops a top lower palaeozoic horizon and lower palaeozoic isopach map were created we found out that the pomeranian caledonides represent a thin skinned fold and thrust belt involving ordovician and silurian sediments of the caledonian foreland basin the deformation front was developed due to the buttressing effect of a basement ramp occurring directly above the ttz the latter corresponds to a precambrian suture zone overprinted by successive extensional tectonics and buried beneath the foreland basin in northern poland the suture is defined by a remnant crustal keel still preserved underneath the ttz probably resulting from precambrian collision during formation of the rodinia paleocontinent we propose that the extension of the thor suture separating baltica and avalonia must exist west from the ttz probably in the rugen area in our interpretation the ttz represents an intra cratonic crustal discontinuity comparable to its nw prolongation the sorgenfrei tornquist zone that runs across the baltic sea sweden and denmark consequently the basement underlying the palaeozoic platform in nw poland may be considered to have been part of baltica in early palaeozoic times

late vendian early palaeozoic tectonic evolution of the baltic basin regional tectonic implications from subsidence analysis abstract subsidence analysis was performed on 43 boreholes penetrating the upper vendian lower palaeozoic sedimentary succession of the baltic basin the results were related to lithofacial and structural data to elucidate subsidence mechanisms and the regional tectonic setting of basin development tectonic subsidence patterns are consistent throughout the basin for the time period studied an extensional tectonic subsidence event possibly of two phases is indicated from the late vendian to the beginning of the middle cambrian this event is seen in the southwestern part of the baltic basin peri tornquist zone until the earliest cambrian after which it is also observed in the sw ne trending baltic depression part of the basin basin development during this time is interpreted as recording the latest stages of break up of the precambrian super continent rodinia and ultimately the formation of the tornquist sea the late middle cambrian to middle ordovician tectonic subsidence pattern of the baltic basin is characteristic of post rift thermal subsidence of the newly formed passive continental margin of baltica developed along its southwestern edge a gradual increase in subsidence rate is observed from the middle late ordovician and throughout the silurian particularly for ludlow and pridoli times creating subsidence curves with convex shapes typical of foreland basin development the rate of late silurian tectonic subsidence increases significantly towards the southwest margin of the baltic basin adjacent to the present location of the north german polish caledonides the baltic basin therefore appears to have developed primarily as a flexural foreland basin during silurian oblique collision of baltica and eastern avalonia a foreland setting is supported by the influx of distal turbidites into the basin from southwest sources in the late silurian compressional deformation structures of early devonian lochkovian age are seen in seismic sections in the central part of the baltic basin lithuania these together with a change in subsidence pattern mark the end of the caledonian stage of basin development of the baltic basin

the micro scale simulation of maturation outline of a new technique and its potential applications a micro analytical technique has been developed for artifically maturing sedimentary organic matter and then quantifying the major components generated during this process in a single analytical step such a capability is well suited for examining the compositional relationships between kerogens and petroleums determining reaction kinetics and making precursor product mass balances according to this technique simulations are made using sealed glass capillary tubes heated here for three days at 300 c 330 c and 350 c pyrolysis products are then released directly into a combined thermovaporisation pyrolysis gc instrument and the major components of the entire c1 yto c35 range can be quantified in a single step using gas chromatography alkene yields are very low and pyrolysates are oil like this is exemplified by the fact that then c9 c19 alkane distribution range of simulated whole petroleum chromatograms from originally immaturegloeocapsamorpha typz alginite a resembles that seen in crude oils generated from this same kerogen type in nature sealed tube experiments usingbotryococcus type alginite a generated a high wax pyrolysate the relative abundance ofn alkanes in the c2 c32 range of many kerogen pyrolysates does not appear to change significantly despite an approximately fifteen fold difference inn alkane yield between the 300 c and 350 c experiments kerogens which are paraffinic oil prone and whose pyrolysates are very rich inn alkanes might therefore generate petroleums in nature with a fixed wet gas c2 c4 to oil c5 ratio alginite b in a greenland shale is much more thermally labile than eitherbotryococcus type alginite a orgloeocapsamorpha type alginite a the mass balance capabilities of the technique have been tested using alum shale kerogen two gas chromatograms were obtained one for the free compounds generated during simulation and one for the high temperature pyrolysate of the kerogen residue for each heating experiment precursor product relationships were qualitatively assessed and dead carbon formation was quantified in this exercise

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

geochemical characterisation and predicted bulk chemical properties of petroleum generated from jurassic and cretaceous source rocks in the vulcan sub basin bonaparte basin north west shelf of australia abstract a geochemical investigation was carried out on 61 core and cuttings samples from selected mesozoic source rocks in the offshore vulcan sub basin of the bonaparte basin australia rock eval pyrolysis data reveal that these source rock samples contain type ii type ii iii and type iii kerogen with variable potential for gas and liquid hydrocarbon generation in the vulcan sub basin samples from the marine lower cretaceous echuca shoals formation and upper jurassic lower cretaceous upper vulcan formation have fair to moderate quality organic matter the samples from these two formations are marginally mature but where burial is sufficient to attain higher maturity as in the nancar trough to the north of the vulcan sub basin these formations have potential to be additional sources for marine oil samples from the marine middle upper jurassic lower vulcan and fluvio deltaic lower middle jurassic plover formations contain good to very good quality organic matter mixed oil and gas prone type ii iii kerogens in the lower vulcan and plover formations are mature for hydrocarbon generation and can be depending on their location and depositional environment source rocks for oil with terrigenous and or marine geochemical signatures assuming a constant geological heating rate of 3 3 c ma the onset of hydrocarbon generation 10 transformation ratio tr from the echuca shoals and upper vulcan formations occurs at 120 c compared to 120 160 c for the lower vulcan and plover formations generally low gas oil ratios gors comparable to those measured in the natural accumulations were reproduced at 400 mg hc g toc suggest the potential for high wax pna oil generation in addition to wet gas

from petroleum type organofacies to hydrocarbon phase prediction the organic facies concept states that kerogen abundance and composition are relatable to depositional settings this link has been extended using open system pyrolysis methods to include major petroleum types whose gross compositions are inherently defined by source rock kerogens and hence to petroleum composition which directly controls the physical response of fluids to changing pressure and temperature conditions during secondary migration the possibility to model petroleum composition during hydrocarbon generation as well as the phase behavior of the fluids during migration is now available in modern basin modeling software however whereas pyrolysis methods can accurately reconstruct hydrocarbon gas oil ratios and liquid compositions they are inherently incapable of correctly reproducing the gas composition of natural fluids and because the gas composition dominantly controls the phase behavior of petroleums multicompound compositional kinetic predictions based on pyrolysis results alone are inappropriate for the prediction of phase behavior the new phasekinetics approach described here combines open and closed system pyrolysis techniques to characterize the compositional evolution of the fluids generated as a function of increasing thermal stress as well as correcting experimentally determined gas compositions and therefore overcomes these deficiencies it has been used to develop compositional kinetic schemes capable of predicting natural petroleum phase behavior for different organofacies types the methodology uses a compositional description of the generated fluids similar to that used in pressure volume temperature pvt simulation selected studies in the norwegian north sea brazil and mexico demonstrate the quality of the tuned compositional predictions for different organic facies types

thermal maturation of gas shale systems shale gas systems serve as sources reservoirs and seals for unconventional natural gas accumulations these reservoirs bring numerous challenges to geologists and petroleum engineers in reservoir characterization most notably because of their heterogeneous character due to depositional and diagenetic processes but also because of their constituent rocks fine grained nature and small pore size much smaller than in conventional sandstone and carbonate reservoirs significant advances have recently been achieved in unraveling the gaseous hydrocarbon generation and retention processes that occur within these complex systems in addition cutting edge characterization technologies have allowed precise documentation of the spatial variability in chemistry and structure of thermally mature organic rich shales at the submicrometer scale revealing the presence of geochemical heterogeneities within overmature gas shale samples and notably the presence of nanoporous pyrobitumen such research advances will un