thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

reaction kinetics of gas generation in selected source rocks of the west siberian basin implications for the mass balance of early thermogenic methane abstract about one third of the actual global recoverable natural gas reserves is accumulated in the west siberian basin in several super giant and mega giant as well as numerous smaller gas fields the elucidation of the nature of this gas its mechanisms of formation and accumulation are still a matter of discussion for instance it is still not yet clear whether the enormous dry gas accumulations in cenomanian reservoirs are of microbial early thermogenic or catagenetic metagenetic origin or if they represent a mixture of these possible formation mechanisms the present contribution provides new results on the thermal gas generation properties of selected source rocks of the cretaceous pokur formation in the west siberian basin eight selected source rock core samples of the pokur formation and a recent peat sample of the same area were submitted to open system programmed temperature pyrolysis in order to quantify the formation of individual gas compounds i e methane as well as c2 and c3 hydrocarbons the rock samples were selected according to geological age and maturity i e from the aptian albian and cenomanian with the most immature samples from the latter organic carbon contents comprise the whole range from 3 to more than 60 the elevated values representing typical lignites a reaction kinetic model system was applied to the generation curves of the gases resulting in activation energy distributions and the corresponding pre exponential arrhenius factors the kinetic data were combined with the temperature history of two selected wells of the urengoy area obtained from basin modelling in order to calculate the gas generation on the geological time scale it was found that even for the low temperatures occurring in the pokur formation early gas generation could have taken place to a certain yet small degree under the assumption of a respective catchment area and the accumulation of this gas in the reservoirs however methane quantities are in the order of magnitude of the urengoy gas accumulation thus early thermogenic methane could at least partially contribute to the gas accumulated in the reservoirs

characterization of oil generation and expulsion from coals and source rocks using diamond anvil cell pyrolysis abstract a visual technique has been developed using a diamond anvil cell to characterize oil prone vs gas prone coals and source rocks and evaluate their oil expulsion efficiency the experiments conducted using 15 humic or shaly coals two boghead coals and eight source rock samples from taiwan turkey north america and australia show that the technique has potential to distinguish oil prone coals from gas prone coals the oil potential of humic coals was estimated from the amounts of total liquid generated during pyrolysis which show correlations with the hydrogen index hi from rock eval pyrolysis and the gas to oil ratio gor determined by py gc analysis the changes of visual area or volume of neoformed liquid as a function of temperature at four heating rates were used to calculate the extents of kerogen to oil transformation for determining the kinetic parameters the results confirm the kinetic controls on the measured transformations but reveal unusually high apparent activation energies and frequency factors the use of this technique as a quantitative tool to predict oil generation kinetics should be treated with caution until this discrepancy has been resolved in addition this study has demonstrated that the expulsion of oil like liquid from coals is generally more efficient than from shales possibly due to the much higher organic content in coal

understanding of hc migration in sedimentary basins present state of knowledge abstract great advances were made during the decade of 1975 1985 in the understanding of hc migration by establishing that the main mechanisms were polyphasic flow whatever its stage and that migration in solution in water and or by molecular diffusion was insignificant except for methane ethane and benzene research is now focusing on points which still have not been satisfactorily answered such as 1 1 behaviour of source rocks during hc expulsion the main driving force for fluid expulsion has been recognized to be excess fluid pressure within the source rock with respect to its surrounding environment of permeable beds the pressure build up is due mainly to accommodation by the fluids of part of the mechanical stresses which are exerted on the rock mainly sedimentary load but also stresses developed by tectonics to thermal expansion of water and to hc formation from kerogen in response to increasing temperatures however it is not clear whether or not petroleum expulsion proceeds preferentially along oil wet networks kerogen or oil wet mineral surfaces nor it is not clear whether or not microfracturing provoked by an internal fluid pressure higher than allowed by the mechanical strength of source rocks is necessary for hc expulsion 2 2 modifications of the compositions of hc phases e g oil versus gas or the distribution of biomarkers during migration and losses of hydrocarbons along the migration pathways although careful observations of natural sample series and also experimentation have been done no clear picture has emerged for the moment however compositional effects seem to be due more to changes in thermodynamic conditions along migration pathways which provoke inter alia hydrocarbon phase separation retrograde condensation than to differential retention by mineral surfaces it is likely that while careful observations on a large variety of source rock samples are needed to more clearly understand source rocks functioning progress in understanding hc migration will come increasingly from modeling and experimentation models which mathematically simulate natural processes are necessary to help the human mind in handling such complex phenomena and therefore are of precious help to focus research on the most important points they replace migration in its geological and historical dimensions with numerical or conceptual tools while observation only describes the present state models are also the tools by which knowledge on migration can be applied to exploration problems however quantitative applications of models require numerous and precise geological data that are difficult to gather at early stages of exploration in the field of experimentation it will be easier to design crucial experiments now that hc migration mechanisms are better understood thanks to experimentation it should also be possible to validate models however so as to reach such aims substantial progress has to be made in the technology of experimental systems

experimental investigation of oil generation retention and expulsion within type ii kerogen dominated marine shales insights from gold tube nonhydrous pyrolysis of barnett and woodford shales using miniature core plugs abstract although oil retention has recently emerged as a key topic of unconventional shale resource assessment oil retention and expulsion controls in organic rich shales during thermal maturation remain poorly constrained this study presents an experimental comparison of oil generation retention and expulsion in two immature type ii kerogen dominated marine shales the mississippian barnett shale and the upper devonian lower mississippian woodford shale mainly with respect to the combined effects of the organic macerals and rock fabric involved in both cases miniature core plugs drilled from the given samples were isothermally pyrolyzed at 130 to 425 c for 72 h under a confining pressure of 68 mpa during gold tube nonhydrous pyrolysis corresponding to the thermally immature early stage of the oil window the main stage of the oil window the late stage of the oil window the main stage of oil cracking to wet gas and the late stage of oil cracking yields of generated oil retained oil and expelled oil for the two studied samples were systematically quantified on the basis of mass balance calculation of measured oil and gas yields as well as rock eval analyses on pyrolyzed subsamples through the six stages of petroleum formation investigated the principal difference in oil generation was observed in the two studied samples with approximately 38 to 68 greater yields of generated oil equivalent to 130 mg oil g toco for the woodford shale when it evolved into the main and late stages of the oil window these elevated yields of generated oil for the woodford shale were compensated for by additional oil generation resulting from conversion of abundant type i kerogen like algae such as tasmanites and leiosphaeridia which lag in onset and have a shorter period of petroleum generation upon maturation as a response to the difference in oil generation oil retention was found to be significantly enhanced for the woodford shale at equivalent stages with 0 2 to 1 7 times more free oil equivalent to 24 105 mg oil g toco and 0 7 to 3 9 times more sorbed oil equivalent to 58 76 mg oil g toco being retained than that of the barnett shale although this effect was not pronounced for oil expulsion in contrast to the barnett shale relatively low expelled oil yields and expulsion efficiencies both indicate highly limited oil expulsion in the woodford shale implying that the woodford shale whose mineral composition and lithofacies are similar to those of the barnett shale may have a relatively low permeability rock fabric to prevent oil from being expelled furthermore not only significantly higher oil saturation index osi values but also a wider range of maturity at which the oil crossover effect osi 100 mg g toc occurs is expected for the woodford shale when extrapolation to a geological setting occurs these data suggest that the presence of abundant type i kerogen like algae and relatively low permeability rock fabric in the woodford shale are critical to significant oil retention during oil generation and expulsion which jointly raise the possibility of potential commercial shale oil within type ii kerogen dominated marine shales

high temperature gc evidence for the early formation of c 40 n alkanes in coals abstract high temperature gc analyses were performed on a coal sourced waxy oil from the toka 1 well in the taranaki basin and on three bitumens extracted ultrasonically with boiling toluene from coals from the tara 1 well in the great south basin new zealand the coals represent an evolutionary trend from immature to post oil expulsion in all samples the c 40 alkanes were characterised by dominant straight chain members up to about c 65 which decreased significantly in abundance in bitumen with increasing maturity they are present at an early stage of maturity prior to the main phase of n alkane generation and may be liberated from cutan cutin sources within kerogen by thermal decarboxylation of esters or have an earlier origin in the bitumen inherited from diagenesis an odd over even predominance in the c 40 n alkanes was most marked in the c 51 c 57 range and decreased with increasing maturity suggesting that minor amounts of c 40 n alkanes with a cpi approaching 1 are also generated during catagenesis however the observed c 40 n alkane distributions may be affected to a degree by decreasing efficiency of solvent extraction with increasing n alkane molecular weight and by further long chain n alkanes generated during catagenesis being partially inaccessible to solvent extraction

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

a geochemical appraisal of oil generation in the taranaki basin new zealand from a basin wide evaluation of organic geochemical data it has been possible to characterize and differentiate various source rock units and to establish the genetic relationships of oils most of the oils are primarily terrestrially sourced and it is possible to recognize varying contributions from source rocks within the paleogene kapuni group and late cretaceous pakawau group this distinction is attributable to the rise to dominance of angiosperms over gymnosperms in coastal plain swamp communities by the eocene apart from the maui family i e maui field maui 4 and moki 1 oils the inferred relative contributions from the main source rock types generally correlate with the relative proportions of suitably thick and mature units near reservoirs given that mos cretaceous sourced oil appears to have escaped prior to trap development maui family oils do appear to be primarily sourced by rakopi formation late cretaceous coals in the northern part of the taranaki peninsula where heat flows are highest mangahewa kaimiro formation eocene coals are the chief sources of oils farther south in the kapuni and kupe south fields farewell formation paleocene coals appear to be the main oil source rocks biomarkers suggest that the onset of oil expulsion from coals occurs at a maturity level corresponding to a vitrinite reflectance of ca 0 8 ro and may be aided by the evolution of large volumes of carbon dioxide the terrestrial influence on paleogene source rocks diminishes to the north northwest of the basin and increasing marin contributions to oils are observed a late paleocene marine black shale is the source of oil in the kora volcanic structure it is possible that shales interbedded with coals reflecting periodic marine incursions of coastal flood plains also contribute to oil generation throughout much of the basin

controls on the oil and gas potential of humic coals abstract humic coals are highly heterogeneous both with respect to maceral content and chemical composition although the oldest known humic coals albeit gas prone are of devonian age the majority of humic coals capable of generating and expelling non volatile oil are of cretaceous and tertiary age from australia new zealand and southeast asia in contrast the middle jurassic humic coals of the sleipner and hugin formations in the south viking graben of the north sea are primarily gasprone but have the capability to expel aliphatic rich volatile oil these coals have toc contents up to 80 and hydrogen indices hi ranging from 200 to 400 they are vitrinite rich with some containing up to 45 inertinite liptinite concentrations are generally around 10 20 chiefly as spores pollen and abundant resinite the main control on the oil potential of humic coals is the concentration of long chain aliphatic hydrocarbons in the coal matrix although the aliphatics have a high h c ratio the inference on hydrogen content from the rock eval pyrolysis hi value can be misleading for hi values below 500 mg hc g oc there is no relation between hi and the potential of the coals to generate non volatile oil consequently the hi is a poor indicator of the non volatile oil potential of humic coals a more robust indicator is the relative amount of c8 aliphatic groups also the bulk measure of liptinite content may also prove misleading when assessing the oil potential of coals high resinite concentrations can lead to an overprediction of the non volatile oil potential as they contribute significantly to the hi value but will generate primarily volatile aromatic rich oils expulsion from the sleipner and hugin coals appears to have occurred in a gaseous phase with preferential release of short chain alkanes

predicting the quantities of oil and gas generated fromaustralian permian coals bowen basin using pyrolyticmethods abstract the aim of the study was to establish kinetic parameters for gas and oil generation and totest the applicability of the kinetic models to petroleum generation through comparisons withnatural maturity coal sequences 433 c t max ro ro ro modelled ro calculated ro calculated

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

estimation of the role of obstacles in the downslope soil flow with a simple erosion model the analytical solution and its approximation with the lattice boltzmann model abstract the description of a downslope soil particle flow is usually assumed to be uniform nevertheless the presence of obstacles like stones rock outcrops or plants hinders the uniformity of the flow culling in 1983 proposed an analytical solution for the advective dispersive flow of soil particles around circular and elliptical cross section obstacles in this paper the culling solution is extended using a more versatile numerical method based on the integration of the transport equations at the mesoscopic level the lattice boltzmann model lbm two lbms are used for the description of the flow components the first lbm simulates the advection component and the second one the diffusion component the distribution of soil or any tracer particles produced by the model is similar to the prediction of the analytical solution the lbm has a greater flexibility for the study of intricate geometries allowing more irregular boundary conditions closer to field situations the model has been applied to the analysis of the flow of soil or any tracer particles around several obstacles such as the trunks in a forest or a regular plantation

the significance of iron stained foraminifera off se trinidad west indies western central atlantic ocean eleven samples of seafloor sediment were taken from water depths of 78 90 m within the savonette field off se trinidad western atlantic ocean this surface sediment is relict having been deposited during an early holocene transgression the samples yielded much iron stained quartz and a rich assemblage of dead foraminifera of which 75 of planktonic foraminifera were stained with iron as was 66 5 of the calcareous benthonic foraminiferal assemblage the fauna both iron stained and unstained was dominated by cibicidoides ex gr pseudoungerianus and is concluded despite the proximity of the orinoco delta to be equivalent to a relict cibicidoides biofacies in carbonate rich areas of the gulf of mexico staining was by limonite and hematite differing percentages of calcareous benthonic species had been stained with iron anova revealing three groups of species within which the mean percentage of iron stained specimens per sample did not differ a globocassidulina subglobosa and hanzawaia concentrica b amphistegina gibbosa cassidulina norcrossi australis cibicioides ex gr pseudoungerianus c io elphidium translucens and quinqueloculina lamarckiana and c eponides antillarum and e repandus it is concluded that species differ in their susceptibility to iron staining and that planktonic foraminifera are more susceptible than most benthonic species although waters off northern south america are turbid and the photic zone only 25 m deep the relict assemblage contained 8 4 algal symbiont bearing foraminifera especially a gibbosa and e translucens that would be limited to the photic zone these are thought to have lived at a time early in the holocene transgression when sequestration of sediment within the orinoco delta rendered the water sufficiently clear for viable populations of symbiont bearing foraminifera should iron stained foraminifera prove to be restricted to transgressive systems tracts this would make them a useful sequence stratigraphic tool

expulsion of oil from petroleum source rocks inferences from pyrolysis of samples of unconventional grain size oil expulsion efficiencies from different lithologies have been investigated and compared employing pyrolyses of samples of unconventional grain size from 300 mg hc g corg show that liquid range hydrocarbons are expelled from coal when the generated oil exceeds the coal sorption capacity this suggests that expulsion of oil from liptinite poor or in general h poor humic coals is primarily limited by the release of generated liquid hydrocarbons from kerogen because such coals generally do not generate sufficient amounts of liquid hydrocarbons to overcome the coal sorption capacity

primary migration by diffusion through kerogen iii calculation of geologic fluxes abstract geologic flux calculations were performed to assess diffusion through kerogen as a mechanism of liquid hydrocarbon transport through fine grained rocks such transport can be important in primary migration within source rocks and in leakage through seals from previous experimental measurements of hydrocarbon diffusivities through kerogen a geologic hydrocarbon flux was estimated for rocks similar to the experimental sample diffusion driven by the hydrostatic pressure gradient through its influence on chemical potential gave an estimated bitumen flux of 2 5 bbl acre ma 98 m 3 km 2 ma this was compared to fluxes required to source oil accumulations in four basins and it indicated that diffusion through kerogen could account for small to moderate accumulations

comparison of three series of organic matter of continental origin abstract three series of sediments containing land plant derived organic matter were studied they include wells from mahakam delta indonesia miocene douala basin cameroon upper cretaceous and eastern paris basin france paleozoic all of the kerogens and coals isolated from these series can be related to type iii in a van krevelen diagram however they obviously differ in terms of chemical structure as reflected by their pyrolysis gc patterns and by their bitumen composition these observations indicate the variations in the nature of land plant derived sedimentary organic matter and thus differences in quantity and composition of the hydrocarbons which are are released upon maturation based on hydrocarbons potential of the insoluble organic matter and on pyrolysis gc there is no reason to disregard coals and to favor shales as potential source rocks in these two deltaic sequences moreover we assume that the bitumen depletion in coal samples is a reflection of loss by migration which is favored in coals when compared to shales the gc patterns of the residual saturates compared to the pyrolysis gc patterns of the related insoluble coals suggest that migration of hydrocarbons proceeds in these coals without any significant alteration of their distribution at least in the c15 range

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