geothermometry and geochemistry of aqueous and oil bearing fluid inclusions from fateh field dubai abstract the production of oil from fateh field dubai is principally from the cretaceous mishrif formation porosity in the reservoir facies is partly occluded by late coarse grained calcite cement this cement contains both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry was used to determine the temperature of that cement precipitation and calculate its timing relative to basin burial history these data were related to source rock maturation and from that the timing of oil migration was inferred to be oligocene to mid miocene which is geologically contemporaneous with early petroleum generation r 0 0 5 0 6 in the khatiyah source rock the fluid inclusions were analyzed by a thermal decrepitation gas chromatography technique benzene and low molecular weight paraffins were present and a series of normal alkenes was tentatively identified in the aqueous inclusions fresh oil inclusions consisted of c 1 n c 25 compounds whose light hydrocarbon composition was consistent with derivation from an early mature source rock altered petroleum residues detected in many mishrif samples are contained either in inclusions or along crystal cleavages these materials are the subject of an ongoing geochemical study of fateh field

the analysis of oil trapped during secondary migration abstract during secondary migration there is an opportunity for oil to be trapped as fluid inclusions fis within framework grains such as quartz and within diagenetic cements that have a crystalline structure oil saturation on migration pathways remains relatively low so typically fewer oil inclusions get trapped compared with samples from an oil column geochemical analysis of the much smaller amounts of inclusion oil present in samples from interpreted oil migration pathways has been attempted for two samples from the champagny 1 and delamere 1 wells in the vulcan sub basin northern offshore australia a combination of petrographic analysis bulk geochemical inclusion analysis and log evaluation confirmed that both samples were from oil migration pathways despite the small number of oil inclusions reliable geochemical data were acquired from both samples that were significantly above the levels detected for the system and outside rinse blanks the fi oil trapped on the interpreted oil migration pathway in champagny 1 was generated from clay rich marine source rock with little terrigenous organic matter input it was generated at peak oil window maturity and correlates best with oils derived from the late jurassic lower vulcan formation in contrast the delamere 1 fi oil contains evidence of greater input of terrigenous organic matter and was generated at early oil window maturity this fi oil also contains a signature of a biodegraded component which could have been generated either from the middle jurassic plover formation or from an older source rock these data indicate that it is feasible to geochemically map migration pathways across prospects or basins and to analyse palaeo oil compositions in oil zones where the few inclusions get trapped this also suggests that the few oil inclusions that sometimes occur in proterozoic or archaean rocks may be analysable in the future which would provide relatively pristine and robust data on the composition and diversity of earth s early biosphere

petroleum accumulation in the deeply buried reservoirs in the northern dongying depression bohai bay basin china new insights from fluid inclusions natural gas geochemistry and 1 d basin modeling abstract the deeply buried reservoirs dbrs from the lijin shengtuo and minfeng areas in the northern dongying depression of the bohai bay basin china exhibit various petroleum types black oil gas condensates and pressure systems normal pressure overpressure with high reservoir temperatures 154 185 c the pressure volume temperature composition pvtx evolution of petroleum and the processes of petroleum accumulation were reconstructed using integrated data from fluid inclusions stable carbon isotope data of natural gas and one dimensional basin modeling to trace the petroleum accumulation histories the results suggest that 1 the gas condensates in the lijin area originated from the thermal cracking of highly mature kerogen in deeper formations two episodes of gas condensate charging which were evidenced by the trapping of non fluorescent gas condensate inclusions occurred between 29 25 5 ma and 8 6 5 0 ma with strong overpressure pressure coefficient pc 1 68 1 70 resulting in the greatest contribution to the present day gas condensate accumulation 2 the early yellow fluorescent oil charge was responsible for the present day black oil accumulation in well t764 while the late blue white oil charge together with the latest kerogen cracked gas injection resulted in the present day volatile oil accumulation in well t765 and 3 the various fluorescent colors yellow blue white and blue and the degree of bubble filling fv 2 3 72 5 of the oil inclusions in the minfeng area show a wide range of thermal maturity api gravity ranges from 30 to 50 representing the charging of black oil to gas condensates the presence of abundant blue white fluorescent oil inclusions with high grain obtaining oil inclusion goi values 35 8 usually 5 in oil reservoirs indicate that a paleo oil accumulation with an approximate api gravity of 39 40 could have occurred before 25 ma and gas from oil cracking in deeper formations was injected into the paleo oil reservoir from 2 8 ma to 0 ma resulting in the present day gas condensate oil accumulation this oil and gas accumulation model results in three oil and gas distribution zones 1 normal oil reservoirs at relatively shallow depth 2 gas condensate reservoirs that originated from the mixture of oil cracking gas with a paleo oil reservoir at intermediate depth and 3 oil cracked gas reservoirs at deeper depth the retardation of organic matter maturation and oil cracking by high overpressure could have played an important role in the distribution of different origins of gas condensate accumulations in the lijin and minfeng areas the application of oil and gas accumulation models in this study is not limited to the dongying depression and can be applied to other overpressured rift basins

hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history abstract geochemical analysis of petroleum inclusions trapped in authigenic feldspar and quartz in the ula formation in the north sea ula oil field revealed a petroleum of markedly different composition than the oil presently in the reservoir using microthermometry and the burial history as a dating tools it is concluded that the petroleum in the k feldspar inclusions was present in the more porous and permeable parts of the ula formation as early as 45 75 my bp when the field was at a depth of about 1 0 1 5 km as compared with the current depth of 3 4 km this early petroleum which was trapped as inclusions in authigenic k feldspar shows a distinctly different distribution of tricyclic terpanes and pentacyclic triterpanes from that of the current petroleum charge in the ula formation which was derived from the mandal formation source rock in late neogene time molecular parameters show that the oil in the k feldspar inclusions is significantly less mature than the crude oil in the present reservoir the approximate 90 c temperature increase occurring after entrapment of the early petroleum in kfeldspar the field is currently at 143 c appears not to have reset the low maturity signature of the oil in the k feldspar inclusions this could suggest that the temperature in the inclusions is too low for isomerization selective thermal degradation to occur lack of catalysts or that there are other controls on the ratio of some of these parameters still parameters like the ratio of c21 to c28 triaromatic steroids and those based on dimethyl and trimethyl naphthalenes are comparatively similar in both the inclusions and in the reservoir crude the oil inclusions in authigenic quartz and albite formed from about 10 my bp burial depth 2 5 km until the present burial depth 3 4 km are interpreted as representing a palaeo petroleum charge having a composition intermediate between the oil found in k feldspar inclusions and the oil charge in the present reservoir our data suggest strongly that the petroleum trapped in the inclusions in quartz and plagioclase represents progressive dilution of the early reservoired oil now found only in k feldspar inclusions with oil from the mandal formation analysis of solution gas in these inclusions suggests that the first petroleum associated gas to arrive at the trap from the progressively maturing mandal formation had a much wetter composition than the current reservoir solution gas to explain the present comparatively drier and isotopically lighter reservoir solution gas composition the inference is made that there has been a recent during formation of k feldspar inclusions 45 75 my bp maturation of the upper jurassic mandal formation the main source rock in this region was limited possibly to the graben axis this suggests that the petroleum found in the k feldspar inclusions was most likely derived from a deeper post caledonian palaeozoic formation

southern african topography and erosion history plumes or plate tectonics the physiography of southern africa comprises a narrow coastal plain separated from an inland plateau by a horseshoe shaped escarpment the interior of the inland plateau is a sedimentary basin the drainage network of southern africa is characterized by three river divides broadly parallel to the coastline these features contrast strongly with the broad dome and radial drainage patterns predicted by models which ascribe the physiography of southern africa to uplift over a deep mantle plume the drainage divides are interpreted as axes of epeirogenic uplift the ages of these axes which young from the margin to the interior correlate closely with major reorganizations of spreading regimes in the oceanic ridges surrounding southern africa suggesting an origin from stresses related to plate motion successive epeirogenic uplifts of southern africa on the axes forming the major river divides initiated cyclic episodes of denudation which are coeval with erosion surfaces recognized elsewhere across africa

hydrocarbon water interactions during brine migration evidence from hydrocarbon inclusions in calcite cements from danish north sea oil fields abstract crude oils in primary and secondary fluid inclusions in calcite from fractures in seven offshore oil fields associated with diapiric salt structures in the danish sector of the north sea were analyzed by capillary column gas chromatography and compared with crude oils produced from the same reservoirs oils from fluid inclusions in all fields show evidence of biodegradation decreased n c17 pristane and n c18 phytane ratios and loss of n c7 2 methyl hexane and 3 methyl hexane relative to methyl cyclohexane and water washing absence of benzene and depletion of toluene some oils in inclusions are extremely enriched in c6 and c7 cyclic alkanes suggesting that these samples contain hydrocarbons exsolved from ascending hotter formation waters compared to inclusion oils the produced oils are less biodegraded but are water washed indicating that both types of oil interacted with large volumes of formation water the carbon isotopic composition of the calcite host of the fluid inclusions in the dagmar and skjold fields is as light as 16 5 pdb and the sulfur isotopic composition of pyrite in and adjacent to the calcite veins in the skjold field is as light as 39 6 cdt indicating that biodegradation of the oils was a source of some of the carbon in the calcite and sulfate reduction was the source of sulfur for the pyrite the evidence for microbial degradation of petroleum is consistent with present day reservoir temperatures 65 96 c but is not consistent with previous estimates of the temperatures of calcite vein filling 95 130 c which are much higher than the temperatures of known occurrences of biodegraded oil

petroleum accumulation and leakage in a deeply buried carbonate reservoir nispero field mexico abstract the filling history of the nispero deeply buried lower cretaceous carbonate reservoir below 4000 m from the south part of gulf of mexico was studied using a combination of data from petrography stable isotopes and fluid inclusions and compared with a one dimensional burial model to derive timing a combination of techniques such as microthermometry confocal laser scanning microscopy clsm and raman microspectroscopy have been used to characterize the different fluid inclusion assemblages and discriminate between the reequilibrated and the preserved fluid inclusions the nispero reservoir is composed of a fractured finely crystalline replacement dolostone a first generation of fractures is filled by a non planar dolomite cement and a second generation by a planar e dolomite cement and a blocky sparite the reservoir is lastly stylolitised dolomite has 13c values between 0 9 and 4 0 pdb and 18o values between 4 5 and 10 8 pdb calcite has 13c values between 3 8 and 4 4 pdb and 18o values between 4 9 and 5 5 pdb these values suggest that the calcite represents a change in water composition and that dolomite and calcite cements do not precipitate from petroleum derived fluids however geological fluids are trapped as aqueous and oil inclusions in the calcite cements three petroleum aqueous inclusion assemblages were identified pseudo primary brown oil paired with brine inclusions and pseudo primary yellow oil paired with low salinity water inclusions distributed in local concentrations and secondary colourless oil paired with low salinity aqueous inclusions distributed in healed microfractures the burial model calibrated with bottom hole temperatures has been calculated using petromod 1d to generate the rock pt history under hydrostatic and lithostatic regimes reconstructed temperatures of initial trapping of fluid inclusion and calculated temperatures from 18o measured in dolomite and calcite cements are in good agreement data suggests that the reservoir was being filled at 97 c 315 bar by heavy black oils accompanied by high salinity water during the miocene period 11 6 m y the maximum estimated pressure of 700 bar at 130 c is reconstructed by petroleum inclusions trapping black oil and associated low salinity aqueous inclusions these pt conditions were reached during the pliocene 3 2m y present day reservoir conditions of 145 c and 500 bar are recorded by reequilibration of most of the fluid inclusions of the two assemblages and correspond to hydrostatic pressure the drop of pressure from 700 bar to 500 bar may be an explanation for the late stylolitisation

chemical changes of fluid inclusion oil trapped during the evolution of an oil reservoir jabiru 1a case study timor sea australia abstract this study of the jabiru oil field timor sea australia shows how the variability of visual properties of fluid inclusions in palaeo oil zones can be mapped to identify internal structures that result from fluid interactions in the reservoir variability in the attributes of oil inclusion assemblages oias is greater within an inferred palaeo gas cap zone 1 and current residual zone zone 3 and less within the current oil zone zone 2 in zone 3 where water imbibed a higher proportion of oias with visual white fluorescing oil inclusions correlates with less mono aromatic compounds and a higher abundance of polar compounds determined on a bulk extract of inclusion oil using high performance liquid chromatography hplc the ch 2 ch 3 ratios and water contents determined by fourier transform infrared spectroscopy ft ir are higher in zone 1 where gas drained there is a higher proportion of oias with visual yellow fluorescing oil inclusions and these correlate with low hplc mono aromatic and moderate polar contents and low ft ir ch 2 ch 3 ratios and water contents interpretation of the grains with oil inclusions goi and pressure volume temperature composition pvtx fluid inclusion data suggests that a gas saturated blue fluorescing palaeo oil was present in the three zones at the same pressure temperature fluid inclusion forming event pt 1 lighter gas saturated blue fluorescing oil was present in zone 2 but was rarer in zones 1 and 3 at the later fluid inclusion forming event pt 2 the yellow and white inclusion oils trapped in zones 1 and 3 respectively are gas depleted and interpreted to result from the interaction between non movable residual oil around grains with the surrounding gas and water respectively comparison between the pvtx data and the published burial curve suggests that most of the fluid inclusions were trapped during two different hot fluid flow events the full oil column is interpreted to have been present during early mid tertiary the palaeo oil column was reduced during the late miocene by imbibition of water in the present residual zone and drainage of gas at the top of the reservoir

fluorescence of organic matter and thermal maturity assessment abstract one of the aims of the organic petrologist is to study the thermal changes of the sedimentary organic matter through its consequences on a microscopical scale i e on the maceral scale different fluorescence properties of organic constituents were studied on several natural or artificial series each of them exhibiting both specific organic matter content and thermal history green river shales uinta basin u s a type i toarcian shales paris basin france type ii sancerre borehole paris basin france type ii mahakam basin indonesia type iii haltenbanken graben north sea type iii cretaceous basin sudan sbaa basin algeria in each case the results were compared to different optical and geochemical evolution parameters vitrinite reflectance rm behaves as a rank parameter and follows a monotonous evolution systematically increasing with diagenesis for its part the fluorescence of macerals is strongly influenced by their bitumen fraction when a maceral reaches a peculiar thermal evolution state maturity threshold and produces its own thermal effluents important changes in its fluorescence properties occur we show that along a thermal series each fluorescent maceral exhibits its own threshold this threshold is different from that of the whole organic content as defined by global geochemical parameters for these reasons the liptinite fluorescence parameters do not parallel the monotonous evolution of vitrinite reflectance they account for oil generation and thus behave as maturity parameters special attention must be paid to additional phenomenon affecting the organic matter oxidation oil migration etc since their resulting effect on fluorescence properties can at times hide the thermal effects or at others can be sometimes mistaken for them the experienced use of such pinpoint tools leads to an accurate knowledge of the mechanisms which govern the thermal maturation of the sedimentary organic matter considering the difference between the rank and maturity concepts and taking into account the proper maturity state of several organic constituents they allow the detailed determination of the maturity state of a source rock in relation to its microtexture

expulsion of petroleum hydrocarbons from shale source rocks there is compelling evidence that movement of petroleum from organic rich shales into sandstones and limestones occurs in the subsurface1 this expulsion of material must occur if crude oil accumulations are to form and it is termed primary migration2 earlier studies3 4 suggested that this movement occurs with chemical fractionation some components are more mobile than others one of the agents of expulsion at early maturity stages is compaction which is not only capable of forcing water but also organic components out of the pore network of a source rock2 5 6 because the fractionation effects associated with expulsion provide clues to the transport mechanisms involved we have made detailed quantitative comparisons of the hydrocarbons of shales of different thicknesses the centre and edges of thick shales and sandstones adjacent to shales from two cored interbedded shale and sandstone sequences from spitsbergen island svalbard norway these observations confirm considerable movement of hydrocarbons in the subsurface with lower molecular weight components being more mobile up to 90 the original amount of n pentadecane may be lost from very thin shales sandwiched between sandstone horizons and from shales close to a lithological boundary with sandstone

assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours abstract the thermal maturity of oils extracted from inclusions and the fluorescence colours of oil bearing fluid inclusions have been measured in 36 sandstone samples from australasian oil fields the inclusion oils were analysed using an off line crushing technique followed by gc ms a maturity assessment was made for each inclusion oil using 25 molecular maturity ratios including a newly defined dimethyldibenzothiophene ratio dmdr each inclusion oil was placed in one of 4 maturity brackets approximately equivalent to early mid peak and post oil generation windows the fluorescence colours of oil inclusions were visually discriminated into blue white and yellow plus orange and their proportions estimated using point counting techniques sixteen samples have 85 of oil inclusions with blue fluorescence whilst other samples have more variable fluorescence colours one sample has 100 of oil inclusions with yellow plus orange fluorescence the results show that samples containing mainly blue fluorescing oil inclusions have thermal maturities anywhere within the oil window in particular the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities calculated reflectance

relationship between the fluorescence color of oil inclusions and thermal maturity in the dongying depression bohai bay basin china part 1 fluorescence evolution of oil in the context of hydrous pyrolysis experiments with increasing maturity abstract the fluorescence evolution of oils has been measured by simulation of petroleum generation and expulsion in a half closed system using hydrous pyrolysis based on four oil prone source rocks type i and ii kerogens from the dongying depression bohai bay basin china the results suggest that the fluorescence characteristics of expelled oil are independent of oil prone kerogen types but are strongly related to oil generation and expulsion processes which are controlled by thermal maturity of source rocks the fluorescence spectral parameters max q650 500 and qf 535 of expelled oils show no obvious variation or even show gradual redshifts when the highest max occurs at peak bitumen generation depending on the expulsion process a blueshift of fluorescence color occurs only during the main oil generation and expulsion stage which immediately follows the peak bitumen generation stage however the expelled oil mainly exhibits green to yellow fluorescence colors 500 nm

hydrocarbon filling history from diagenetic evidence brent group uk north sea abstract reconstruction of the hydrocarbon filling history of a reservoir is important for prediction of field scale porosity and permeability and for the calibration of basin models published histories of the brent group show only a single phase of hydrocarbon filling which occurred after the diagenetic reactions had run their course in contrast diagenetic minerals preserve evidence of multiple episodes of hydrocarbon charging in the cormorant field uk north sea authigenic blocky kaolin shows a systematic change in oxygen isotopic composition with depth and the trend displays a conspicuous shift at the mid ness shale a regionally extensive permeability barrier the isotopic data are most readily explained if kaolin recrystallisation from earlier vermiform kaolin was synchronous with hydrocarbon charging with two hydrocarbon pools one above and one below the mid ness shale the filling history begins with a relatively early slow filling phase 45 70 c 80 50 ma that formed an oil column with the oil water contact substantially below the present day position this first hydrocarbon subsequently leaked off allowing renewed diagenetic activity including the formation of quartz overgrowths with aqueous inclusions emplacement of the present day hydrocarbon charge was the last event in the history of the reservoir 90 100 c 10 0 ma

precambrian oil inclusions in late veins and the role of hydrocarbons in copper mineralization at white pine michigan liquid oil was trapped as primary fluid inclusions in calcite crystals in late cu fe sulfide bearing veins that crosscut and offset the cupriferous shale deposit at white pine the age of the calcite 1047 35 ma is an entrapment age and thus a minimum age for the oil close temporal and spatial associations of oil and metallic sulfides in the late veins suggest that liquid and solid hydrocarbons may have been dominant controls of the main stage white pine copper mineralization

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

effects of hydrocarbon expulsion from shale source rocks of high maturity in upper carboniferous strata of the ruhr area federal republic of germany abstract based on detailed geochemical analysis of closely spaced core samples from a sequence of interbedded source rock type shales and reservoir sandstones of upper carboniferous westphalian age certain effects of primary migration were recognized qualitatively expulsion of hydrocarbons from two high mature shale source rock units 1 1 r m has occured preferentially from their edges and is indicated by the following effects an overall decrease of the concentrations of total extract saturated and aromatic hydrocarbons and decreasing values for the production index from rock eval measurements from the centre portions of the shale units towards their outer edges these depletion trends are paralleled by systematic changes in the composition of the c 15 saturated hydrocarbons also evidence was obtained to suggest that preferential depletion has occurred into a local fracture zone the effects of hydrocarbon expulsion could be quantified on a molecular level for two thin source rock type shale layers interbedded in a reservoir sandstone for the n alkanes less than c 26 the expulsion efficiencies range between 70 and 80 despite the high maturity level and despite the resulting advanced migration stage some evidence for chromatography type compositional fractionation in the shale could still be observed in the c 27 range n alkanes and between pristane and its n alkane isomer pristane is preferentially retained in the source rock

evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis a case study using a brazilian source rock with type i kerogen abstract hydrous pyrolysis hp experiments were used to investigate the petroleum composition and quality of petroleum generated from a brazilian lacustrine source rock containing type i kerogen with increasing thermal maturity the tested sample was of aptian age from the araripe basin ne brazil the temperatures 280 360 c and times 12 132 h employed in the experiments simulated petroleum generation and expulsion i e oil window prior to secondary gas generation from the cracking of oil results show that similar to other oil prone source rocks kerogen initially decomposes in part to a polar rich bitumen which decomposes in part to hydrocarbon rich oil these two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation during bitumen decomposition to oil some of the bitumen is converted to pyrobitumen which results in an increase in the apparent kerogen i e insoluble carbon content with increasing maturation the petroleum composition and its quality i e api gravity gas oil ratio c 15 fractions alkane distribution and sulfur content are affected by thermal maturation within the oil window api gravity c 15 fractions and gas oil ratios generated by hp are similar to those of natural petroleum considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous age api gravity of the hp expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes c 15 fractions i e saturates aromatics resins and asphaltenes show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition gas oil ratios gor initially decrease from 508 131 m 3 m 3 during bitumen generation and remain essentially constant 81 84 m 3 m 3 to the end of oil generation this constancy in gor is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments alkane distributions of the hp expelled oils are similar to those of natural crude oils considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous age isoprenoid and n alkane ratios i e pristane n c 17 and phytane n c 18 decrease with increasing thermal maturity as observed in natural crude oils pristane phytane ratios remain constant with increasing thermal maturity through the oil window with ratios being slightly higher in the expelled oils relative to those in the bitumen generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar brazilian lacustrine source rocks with type i kerogen of lower cretaceous with the exception of elevated ethane contents the general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of hp to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality

source rocks in mesozoic cenozoic continental rift basins east china a case from dongying depression bohai bay basin abstract lake basin evolution microscopic and organic geochemistry characteristics are investigated for the paleocene hydrocarbon source rocks of dongying depression bohai bay basin the upper e 2 3 s 4 and the lower e 2 3 s 3 are balanced filled lake basin sediments which show strong climate driven rhythmicity source rocks of these two units have relatively high organic matter content and are dominated by type i kerogen sedimentary and geochemical characteristics indicate there exist persistent lake water stratification and bottom anoxicity during the deposition process by contrast the middle e 2 3 s 3 is an over filled lake deposit dominated by uniform mudstones lacking obvious transgressive regressive cycles it indicates that the lake water lacks stratification and the bottom water is ventilated source rocks of this unit have relatively low organic abundance and are dominated by types ii and iii kerogen thermal evolution studies show that the upper e 2 3 s 4 has a relatively early and multi stage of hydrocarbon generation process and can generate immature oils while the lower e 2 3 s 3 and the middle e 2 3 s 3 have a relatively late and simple hydrocarbon generation process and mainly generate mature oils in addition the persistent increase of eom toc and total hydrocarbons toc indicates that the expelled hydrocarbons from the middle e 2 3 s 3 are in relatively small amounts compared with the other two units the middle e 2 3 s 3 acts as regional caprocks instead of significant source rocks as previously thought the viewpoint will be of great significance in future exploration

new insights on the green river petroleum system in the uinta basin from hydrous pyrolysis experiments the tertiary green river petroleum system in the uinta basin generated about 500 million bbl of recoverable high pour point paraffinic crude oil from lacustrine source rocks a prolific complex of marginal and open lacustrine source rocks dominated by carbonate oil shales containing up to 60 wt type i kerogen occur within distinct stratigraphic units in the basin petroleum generation is interpreted to originate from source pods in the basal green river formation buried to depths greater than 3000 m along the steeply dipping northern margin of the basin producing fields in the altamont bluebell trend have elevated pore fluid pressures approaching 80 of lithostatic pressure and are completed in strata where open fractures provide permeability active hydrocarbon generation is one explanation for the origin of the overpressured reservoirs in this study experiments were undertaken to examine the mechanisms of hydrocarbon generation and accumulation in the uinta basin we combined analyses of representative source rocks from the entire green river stratigraphic section with detailed laboratory simulation experiments using both open and closed system pyrolysis this information provides new insights on lacustrine source rock lithofacies gas oil source rock correlations hydrocarbon generation kinetics and basin modeling the results show that the basal green river formation contains a unique type i source facies responsible for generation of paraffinic crude oils the classic type i oil shales in the upper green river formation correlate well with low maturity aromatic asphaltic samples we determined kinetic parameters for the source rocks and used them to develop basin models for hydrocarbon generation the models show that hydrous pyrolysis kinetic parameters are more consistent with the natural data in terms of predicted timing and extent of oil generation as compared to models using rock eval kinetics begin page 1334

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

variability of petroleum inclusions in vein fossil and vug cements a geochemical study in the barrandian basin lower palaeozoic czech republic abstract although no commercial oil or gas occurrences have been found in the barrandian basin residual oils and petroleum inclusions give evidence about the petroleum history of this lower palaeozoic basin petroleum inclusions are hosted in six generations of calcite and quartz cements that can be attributed to different stages of a basinal cycle and associated diagenetic events they were analysed using an on line crushing and an off line crush and leach approach five different groups pi a to pi e and intermediate mixtures pi m could be differentiated based on the relative distribution of n alkanes all oils had a calculated aromatic maturity rc ranging between 0 9 and 1 6 pi a shows a molecular weight maximum in the range of n c8 11 with a constant attenuation towards higher carbon numbered n alkanes this distribution is interpreted as the pristine precursor oil for other petroleum inclusion groups pi b has a maximum weight abundance at n c15 20 the genetic relationship between pi b and pi a can tentatively be explained by mixing effects or by gas stripping pi c is bimodal and characterised by a molecular weight maximum at n c32 34 and also a molecular weight maximum at n c15 20 similar to that of group pi b pi d shows a normally distributed molecular weight maximum in the range n c25 28 and is interpreted as a wax precipitate from ascending gas saturated in n alkanes pi e contains predominantly gaseous compounds with only a few higher hydrocarbons thompson s aromaticity values are elevated for condensates of group pi e and also for group pi c that is dominated by long chained n alkanes this gives evidence that fault bound petroleum migration in the barrandian basin was associated with evaporative fractionation for group pi c and pi e samples of group pi e yielded gas range compounds only and all come from a last generation of vein filling whitish calcite that was formed in a late uplift phase of the basin for other petroleum inclusion groups only a vague preferential occurrence in specific mineralisation phases or stratigraphic intervals of the host rock has been found this reflects the predominance of fracture bound migration in the barrandian basin aromatic maturity values also showed no correlation between either crystal type or pi group in six of the investigated petroleum inclusion samples alk 1 enes are present these terminal olefins are interpreted to be the result of the natural pyrolysis of petroleum due to the intrusion of volcanic dykes or hydrothermal processes an artificial generation of olefins during sample work up and analysis is unlikely the preservation of alk 1 enes from palaeozoic times was possible due to the protecting environment of petroleum inclusions

laser ablation gc ms analysis of oil bearing fluid inclusions in petroleum reservoir rocks abstract the hydrocarbon composition of co occurring blue and yellow fluorescing fluid inclusions fis in ordovician reservoirs of the tarim basin nw china have been separately analyzed by laser microprobe gas chromatography mass spectrometry gc ms using a 193 nm excimer laser to drill through the host quartz a newly designed gc inlet system enabled detection of c4 c30 hydrocarbons extending the molecular weight significantly beyond the c21 limit of previous online laser based hydrocarbon analysis of oil inclusions the blue fluorescing inclusions contain notably higher proportions of aliphatic hydrocarbons e g n alkanes cycloalkanes and gaseous range products whereas the yellow fluorescing inclusions contain relatively more aromatic hydrocarbons e g alkylnaphthalenes hydrocarbon based parameters also indicate that the blue fluorescing inclusions are of higher thermal maturity than the yellow fluorescing inclusions consistent with maturity estimates based on fluorescence colors the compositional differences of the co occurring inclusions are indicative of different oil types and charge events this highlights the capacity of the new laser ablation technology to separately analyse specific inclusions amongst a mixture of inclusions of different fluorescing colors in the future integration of this new compositional detail with other inclusion and reservoir data will help reconstruct the oil charge history of the tarim basin

analysis of petroleum fractions by tlc fid applications to petroleum reservoir description abstract thin layer chromatography and flame ionization detection iatroscan tlc fid offers a rapid and accurate method for quantifying saturated and aromatic hydrocarbons and resin asphaltene fractions in solvent extracts of petroleum source rocks reservoir rocks and crude oils while the instrument is superficially simple special precautions need to be taken in calibration and parameter setting due to complexities arising from the operational characteristics of the detector system nevertheless the technique offers superior speed and precision to conventional mplc analysis of petroleum fractions this paper describes the choice of operational parameters provides comparison with the traditional group type analysis technique mplc and presents some geochemical applications

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

fluid inclusion constraints on petroleum pvt and compositional history of the greater alwyn south brent petroleum system northern north sea abstract pressure volume temperature pvt simulation of individual petroleum inclusions that are trapped in source rocks migration pathways and reservoirs is when combined with standard inclusion analytical techniques a useful tool for the quantitative estimation of paleopressures paleotemperatures and changes in petroleum compositions over time this study presents the results from the application of these techniques to determine the evolution of the petroleum trapped through time as maturation and migration progress within the greater alwyn south brent petroleum system of the northern north sea the results for the brent reservoir from the six study fields indicate that the petroleum inclusions recorded a wide range of compositions during the filling history of the reservoir the methane concentrations and gas oil ratios of included petroleum are lower than those presently within the reservoir the fluid inclusion data suggest that changes in petroleum compositions through time can be interpreted in terms of gradual mixing of earlier reservoired oil with later migrated more mature and gas rich fluids fields nearest the kitchen area appear to have been more severely affected by the emplacement of increasingly mature petroleum phase separation during vertical migration may also occur but is thought to be a volumetrically minor process the estimated paleopressures mostly correspond to the current pressure regime which is slightly higher than hydrostatic and lower than lithostatic combining fluid inclusion results with thermal burial models suggests that petroleum migration began at approximately 55 64 ma in the area this study provides quantitative limits on and confirms the value of fluid inclusion technology in such applications as evaluating oil compositions migration timing trap fill history paleopressures and in constraining the outputs of basin modeling

novel development in fluorescence microscopy of complex organic mixtures application in petroleum geochemistry abstract new data on the spectral fluorescence properties of complex organic mixtures derived from organic rich sediments and from fossil fuels are presented both the spectral ranges of the bitumen fractions including extractable hydrocarbons and polar compounds and the factors governing the spectral characteristics of complex organic mixtures are established the data provide rapid means of determining qualitatively an abundance or low concentration of saturates of highly alkylated aromatics and of condensed aromatic systems in such entities as extractable organic matter kerogen migrated hydrocarbons and liptinite macerals the implication of the data to petroleum geochemistry is discussed

insights from fluid inclusions thermal and pvt modeling for paleo burial and thermal reconstruction of the cordoba petroleum system ne mexico abstract carbonate reservoirs in the cordoba petroleum system ne mexico passed through a multiphase deformation history complicating the petroleum geology the area evolved from passive margin and foreland setting to laramide fold and thrust belt ftb that was subsequently buried below the tertiary quaternary veracruz basin which in turn underwent transpressional deformation reconstruction of paleo burial erosion and paleo thermicity through the different zones of the ftb and adjacent foreland is a challenging task since classical calibration tools fail to discriminate between several kinematic and thermal models in this study results from detailed diagenetic and fluid inclusion fi analyses on carbonates from the western part of the cordoba platform helped constraining paleo thermicity combined microthermometry synchrotron ftir analyses and pvt modeling of cogenetic hydrocarbon aqueous fi allowed also calculation of absolute pressures thermal modeling exercises calibrated with organic maturity parameters bottom hole temperatures or temperatures from fi demonstrate that without controlling also paleo erosion the model results may be misleading

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

fluid inclusions and pvtx modelling examples from the garn formation in well 6507 2 2 haltenbanken mid norway abstract fluid inclusions study and multi techniques quantitative analyses have been coupled to reconstitute pvtx conditions of aqueous and petroleum fluid entrapment of a local haltenbanken area well 6507 2 2 from the garn formation unusual low temperature behaviour showing the liquid portion separating into two liquids has been described this behaviour is typical of a gas condensate volatile mixture with high methane content and heavy alkanes the variable liquid vapour ratio compositions and morphologies of all petroleum inclusions can be interpreted as a result of a combination of heterogeneous trapping and necking down thus all petroleum inclusions can be related to a single petroleum source three main episodes of fluid entrapment can be distinguished the first one corresponds to the water trapped within detrital quartz microfractures at around 50 c and 50 bar the second to the petroleum fluid arrival in the biphase field of a critical system around 100 120 c and 190 230 bar the third one to the main trapping of present day petroleum inclusions during the recrystallisation of quartz cements around 110 160 c and 230 280 bar within the last few million years of a short and relatively rapid burial

p t conditions in the south wales coalfield evidence from coexisting hydrocarbon and aqueous fluid inclusions siderite nodules in the carboniferous coal measures of south wales contain cavities which are often infilled with quartz carbonates sulphides and hydrocarbons the quartz contains a mixture of hydrocarbon and aqueous fluid inclusions the aqueous fluid inclusions consist of a dilute brine 3 wt nacl equivalent and have homogenization temperatures in the range 97 212 oc mean 143 oc the hydrocarbon fluid inclusions are dominated by methane with a small component of higher order hydrocarbons their homogenization temperatures are in the range 35 78 c mean 54 c it is assumed that the two fluids were trapped simultaneously during growth of the quartz and thus a p t estimate of entrapment can be obtained by graphical intersection of the hydrocarbon isochores and the aqueous fluid bubble point homogenization temperatures assuming hydrocarbon saturation this method gives temperatures between 130 and 160 oc and pressures between 40 and 55 mpa the timing of mineralization is uncertain but it is suggested that it took place during burial and low grade metamorphism of the subsiding sedimentary basin i e in the upper carboniferous the hydrothermal fluids were probably derived from evolved meteoric or connate waters expelled during subsidence and sediment compaction

relationship between reservoir diagenetic evolution and petroleum emplacement in the ula field north sea abstract the diagenetic and petroleum filling histories of the ula field have been studied by analysing aqueous and petroleum inclusions occurring in authigenic cements this study shows that diagenesis continues actively after the arrival of petroleum in the sandstones although the reaction rates and petroleum saturation remain obscure microthermometric measurements of fluid inclusions in authigenic quartz suggest an onset of extensive quartz cementation at temperatures around 110 c i e 2 5 km and that this cementation has continued to the present day synchronously with quartz cementation authigenic albite was formed as inter and intragranular cements large amounts of petroleum inclusions locally occur in the albite and quartz cements these inclusions were trapped in the cements as the main charge of petroleum arrived at the structure diffusion through thin water layers between the petroleum and the mineral surface would probably have dominated mass transfer of solutes for the precipitation of authigenic quartz and albite it is evident from analysis of the petroleum inclusions in early formed k feldspar overgrowths that some secondary migrated petroleum probably arrived in the reservoir at a shallow burial depth before the rapid subsidence in the last 25 my compared with petroleum in the free porosity of the ula formation the petroleum in the k feldspar inclusions is evidently sourced from a different source facies and most maturity parameters testify to the latter being less mature later trapped petroleum inclusions in quartz and albite have characteristics found both in k feldspar and in the ula formation dst oil and thus is likely to reflect the progressive change in the ula field petroleum charge which occurred during the time period of quartz diagenesis

fluid inclusion petrography and tectonic burial history of the al ali no 2 well evidence for the timing of diagenesis and oil migration northern oman foredeep cores cut in shallow marine lower and middle cretaceous carbonates in the al ali no 2 well umm al qaiwain united arab emirates display a five stage sequence of calcite cementation fracturing and stylolitization these stages are correlated with the tectonic history of the northern oman orogeny occurrence of fluorescent hydrocarbon fluid inclusions is restricted to stage 2 and stage 3 fracture filling calcites that are crosscut by stylolites stylolite formation during rapid burial beneath abyssal campanian foredeep sediments restricts hydrocarbon migration to post mid cenomanian and pre mid campanian time

reply to comment by oxtoby on assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours the authors welcome the opportunity to respond to some of the comments of oxtoby 2002 regarding their recent paper george et al 2001 we will respond to the two main topics that have been raised by oxtoby 2002 firstly the petrological procedures used and secondly the possible causes for the wide maturity range of blue fluorescing oil inclusions the issue of the relationship of fluorescence colour and api gravity raised by oxtoby 2002 was not discussed in the paper

petroleum migration faults and overpressure part ii case history the haltenbanken petroleum province offshore norway abstract petroleum inclusion and geochemical data from core extracts were applied to deduce a model for oil migration overpressure development and palaeo leakage of oil from currently dry structures in the haltenbanken vest area the existence of fluorescent oil type inclusions in quartz in the smorbukk asgard 2 field suggest that oil migrated into this structure 70 50 million years before present ma bp this is also the case for the dry structures 6506 12 4 6506 11 3 and 6506 11 1 west of the main smorbukk fault zone black oil inclusions with medium gas oil ratio gor occur in these fields together with condensate type petroleum inclusions this suggests that the dry structures transformed from containing oil to condensate before leakage petroleum extracted from inclusions in these structures and in nearby fields have identical marine type ii kerogen signatures source rocks at the spekk formation level in the current drainage area of smorbukk and these dry structures were immature 70 50 ma bp and the smorbukk sor asgard 3 field did not fill at this early time thus oil must initially have entered into smorbukk from areas to the w sw through the currently pressure sealing smorbukk fault zone which today marks the westward limit of the smorbukk field diagenesis in this fault zone caused the much later overpressure development and petroleum was lost from the 6506 12 4 6506 11 3 and 6506 11 1 structures as overpressure built up regionally petroleum loss from these structures with their often thick seals must have occurred via self propagating open fracture induced mechanisms lack of petroleum in the cretaceous strata above these structures suggests that leakage occurred to even shallower strata this could imply that the cretaceous strata in halten vest were overpressured at the time of leakage in contrast the oil in the cretaceous lysing and lange formation above the jurassic reservoirs in smorbukk and smorbukk sor most likely originated based on geochemistry and gors from the jurassic reservoirs below and not from cretaceous strata this migration event would have been facilitated if it occurred before these sands became overpressured as they are today modelling suggests that the spekk formation became mature in the smorbukk sor region

effects of oil cracking on fluorescence color homogenization temperature and trapping pressure reconstruction of oil inclusions from deeply buried reservoirs in the northern dongying depression bohai bay basin china the effects of oil cracking on fluorescence color homogenization temperature tho and trapping pressure pt of oil inclusions from deeply buried reservoirs dbrs 3672 4359 m in the northern dongying depression were determined based on fluorescence spectroscopy and homogenization temperatures of oil inclusions kinetic modeling of crude oil cracking and petroleum inclusion thermodynamics modeling the modeling results demonstrate that fluorescence color tho and predicted pt have strong relationships with the transformation rate via cracking of oil to gas tr and the formation temperature tf that the inclusions experienced the fluorescence color is hardly influenced at all during the initial stages of oil cracking tr 13 tf 160 c but fluorescence color begins to shift toward shorter wavelengths blue shift during progressive oil cracking tr 24 tf 190 c with further oil cracking the fluorescence color may either experience no change or continue its blue shift eventually the fluorescence color will disappear as the aromatic compounds are completely cracked the tho increases at first tr 24 tf 190 c but then decreases or even becomes negative during major oil cracking the reconstructed pt values show a corresponding reverse trend oil inclusions from dbrs and other shallow reservoirs in the dongying depression show an obvious blue shift in fluorescence color at a depth of approximate 4000 m tf 160 c and generally contain solid bitumen below 4000 m supporting the effect of oil cracking on fluorescence variation consistent with the modeling result the tho from dbrs in the minfeng area increases with increasing burial depth tf 190 c which is also consistent with the modeling results however the tho of oil inclusions with blue white fluorescence from dbrs in the shengtuo area did not show such a trend recent trapping high trapping pressure and higher maturity oil may have led to a low degree of oil cracking and thus less modification of tho in the shengtuo area oil cracking results in consistent volume ratios of pyrobitumen to oil inclusions fvpy in the same fluid inclusion assemblage and the fvpy value increases with oil cracking level which can be used to recognize if oil cracking has occurred in oil inclusions and what level of oil cracking they have experienced as the oil cracking model used in this study did not account for the role of pressure it is more applicable for oil inclusions that were trapped under normally pressured conditions oil inclusions trapped under overpressured conditions will be less influenced by oil cracking

effects of smectite on the oil expulsion efficiency of the kreyenhagen shale san joaquin basin california based on hydrous pyrolysis experiments the amount of oil that maturing source rocks expel is expressed as their expulsion efficiency which is usually stated in milligrams of expelled oil per gram of original total organic carbon oil expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water i e hydrous pyrolysis at temperatures between 350 c and 365 c for 72 hr this pyrolysis method generates oil that is compositionally similar to natural crude oil and expels it by processes operative in the subsurface consequently hydrous pyrolysis provides a means to determine oil expulsion efficiencies and the rock properties that influence them smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous pyrolysis study involving a representative sample of smectite rich source rock from the eocene kreyenhagen shale in the san joaquin basin of california smectite is the major clay mineral 31 wt in this thermally immature sample which contains 9 4 wt total organic carbon toc comprised of type ii kerogen compared to other immature source rocks that lack smectite as their major clay mineral the expulsion efficiency of the kreyenhagen shale was significantly lower the expulsion efficiency of the kreyenhagen whole rock was reduced 88 compared to that of its isolated kerogen this significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix within the interlayers much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking as a result smectite does not promote oil generation but inhibits it bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet this change prevents potassium ion transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite as a result illitization only reaches 35 to 40 at 310 c for 72 hr and remains unchanged to 365 c for 72 hr bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite rich source rock to determine its expulsion efficiency complete illitization prior to bitumen generation is common for paleozoic source rocks e g woodford shale and retort phosphatic shale member of the phosphoria formation and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis conversely smectite is more common in cenozoic source rocks like the kreyenhagen shale and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface

microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in toarcian source rocks of different maturities abstract this study is part of a comprehensive research program on the generation and migration of petroleum from the organic rich posidonia shale lower toarcian jurassic of the hils syncline northern germany four cores of the complete posidonia shale with varying amounts of underlying pliensbachian and overlying aalenian mudstones provided the sample base depending upon their distance from a presumed subjacent heat source the vlotho massif the cores display progressive levels of increasing thermal maturation with r 0 values 0 48 0 68 0 88 and 1 45 which span the limits of the oil generation window primary stratigraphic lithologic and petrographic attributes of the four sections are all very similar each includes a lower marlstone member about 5 m thick overlain by 11 31 m of calcareous clay shale clay minerals calcite pyrite kerogen and quartz are the principal constituents thus there is no evidence that depositional conditions of the posidonia shale varied significantly over the sampled area the omnipresence of framboidal pyrite clearly formed from the activity of sulphate reducing bacteria at or near the depositional interface is strong evidence that uniform reducing anoxic conditions were persistent at all localities this conclusion supports the assumption that initially each section was identical in overall properties and that significant differences observed in geochemistry organic macerals and other properties are directly related to the variable levels of thermal maturation kerogen from the least mature section r o 0 48 is type ii and composed of alginite a alginite b liptodetrinite bituminite and some terrestrial sporinite vitrinite and inertinite macerals with increasing maturation the alginite macerals exhibit a progressive change in morphology and fluorescence properties alginite of the least mature section displays a strong green fluorescence at 0 68 r o alginite macerals exhibit yellow orange fluorescence and are structurally well preserved although geochemical data indicate generation and loss of large amounts of oil at 0 88 r o hydrocarbon generation is almost complete and few primary alginites remain they have been transformed into secondary liptinites designated as metaalginite which have similar fluorescence colours at the highest maturation level 1 45 r o metaalginites are only weakly fluorescent with a shift toward red colours calcite and or bitumen filled bedding plane micro and macrofractures occur exclusively in the organic rich posidonia shale at maturity levels of 0 68 r o and above such features are totally absent in the immature posidonia section and in the adjacent organic poor mudstones this observation indicates that the fractures developed in direct response to overpressuring i e pore pressure exceeding lithologic load related to oil and gas generation in the source rock the fractures undoubtedly provided important expulsion conduits for generated products

individual characterization of petroleum fluid inclusions composition and p t trapping conditions by microthermometry and confocal laser scanning microscopy inferences from applied thermodynamics of oils abstract this paper proposes a new method to characterize individual oil bearing fluid inclusions it uses both the homogenisation temperatures measured by microthermometry and the degree of gas bubble filling measured by confocal laser scanning microscopy in conjunction with thermodynamic modelling for describing liquid gas phase transitions and the volumetric behaviour of hydrocarbon mixtures it is associated with a two parameter compositional model that describes the wide range of compositions of petroleums we show that this method can give 1 useful estimations of the compositions and pressure temperature entrapment conditions of oils in fluid inclusions and 2 insights into the various processes that have affected these fluids either before entrapment liquid gas unmixing gas leaching mixing etc or after leakage etc

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

quantitative microscopic spectral fluorescence measurement of crude oil bitumen kerogen and coal ten samples each of black shale kerogen and bitumen fractions from lias epsilon coal from western canada and nine crude oil and condensate samples from alaska and northern germany have been studied using quantitative microscopic spectral fluorescence the parameters used are lambda sub max red green quotient q and alteration of fluorescence emission intensity under uv excitation using the same parameters the data show that kerogen and crude oil have opposite maturation trends autochthonous bitumens include both kerogen and crude oil characters immature biodegraded or normal crude oil of different maturity can be characterized using these parameters quantitative spectral fluorescence microscopy yields more accurate maturation parameters for the type i and ii kerogens than vitrinite reflectance because the fluorescence of liptinites are used i e the main oil generating macerals this method may become the most suitable inexpensive scanning technique for the characterization of crude oil condensate and autochthonous allochthonous source rock bitumens

mineral chemistry of high mg diorites and skarn in the han xing iron deposits of south taihang mountains china constraints on mineralization process abstract the han xing region is located in the south taihang mountains tm in the central part of the north china craton and is an important iron producing area the iron deposits in this region are of skarn type related to an early cretaceous high mg diorite complex including gabbro diorite hornblende diorite diorite diorite porphyrite and monzonite in this study we report the detailed mineral chemistry of the high mg diorites and skarn rocks the olivine in the gabbro diorite shows chemical composition similar to that in mantle peridotite xenoliths clinopyroxene in the gabbro diorite is dominantly augite with only minor diopside whereas the clinopyroxenes in the diorite and monzonite are diopside amphiboles in the high mg diorites show compositional range from magnesiohornblende to magnesiohastingsite with minor pargasite and tschermakite most plagioclase in the high mg diorite is andesine and oligoclase the magnesio biotite in gabbro diorites shows chemical characteristics of re equilibrated primary biotites and those in calc alkaline rocks in the diorite and diorite porphyrite plagioclase shows complex chemical zoning clinopyroxene and garnet in skarn rocks show varying feo contents the former containing low feo 25 wt content we computed the pressure temperature oxygen fugacity and water contents based on the mineral chemistry of amphibole and biotite based on the results the magma crystallization can be divided into two stages one within the deep magma chamber forming clinopyroxene amphibole and plagioclase phenocrysts the other after emplacement forming the rim of phenocrysts and matrix minerals the magma during the early stage shows high temperature 900 c 950 c pressure 300 mpa 500 mpa relatively high logfo 2 nno nno 2 and h 2 o content in melt 4 8 during the late stage the magma temperature dropped to about 750 c and pressure came down to less than 100 mpa with the logfo 2 rising to nno 1 nno 2 the zoning of amphibole and plagioclase records the process of magma mixing and crystallization with injection of mafic magma into the felsic magma chamber the relatively high logfo 2 and h 2 o content inhibited partitioning of iron into mafic minerals and favored concentration of fe in the melt iron ore precipitation occurred when the magma was emplaced at shallow level and was principally controlled by the chemical composition of carbonate wall rocks the high logfo 2 fe 3 rich ore forming fluid generated andradite and clinopyroxene when it reacted with limestone and dolomitic limestone respectively

fluorescence properties of palaeozoic oil prone alginite in relation to hydrocarbon generation williston basin saskatchewan canada abstract alginite macerals the oil prone microscopic components of hydrocarbon source rocks fluoresce in the visible region when irradiated with ultraviolet light the fluorescence properties max and red green quotient of coccoidal unicellular and filamentous alginite macerals were investigated in palaeozoic potential hydrocarbon source rocks northern williston basin saskatchewan canada this study documents the variation in fluorescence properties of alginite during thermal maturation and the onset of petroleum generation values of max nm of disseminated coccoidal gloeocapsomorpha alginite from upper cambrian siliciclastics and upper ordovician carbonates show different magnitudes of red shift with increasing thermal maturity gloeocapsomorpha prisca disseminated alginite and g prisca stromatolitic alginite from upper ordovician kukersites exhibit unique fluorescence properties with increasing thermal maturity the former undergoes a greater red shift in fluorescence than the latter over an 1800 m change in depth of burial devonian and mississippian unicellular prasinophyte leiosphaeridia and tasmanites alginite show a minimal change in fluorescence properties max 450 500 nm between vitrinite reflectance values of 0 35 and 0 65 ro beyond 0 65 ro vitrinite reflectance prasinophyte alginites show a marked red shift to a max of 560 600 nm this phenomenon is coincident with peak hydrocarbon generation from a type ii filamentous alginite bituminite kerogen within middle devonian carbonate source rocks a comparison of the fluorescence properties of palaeozoic prasinophytes with the fluorescence properties of mesozoic prasinophytes reveals that the latter undergo a substantially greater red shift in max with increasing thermal maturity relative to the former this conspicuous difference is interpreted as a reflection of the well documented distinct difference in species and abundance of leiosphaeridia and tasmanites alginite between the geological eras

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

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

constraining the oil charge history of the south pepper oilfield from the analysis of oil bearing fluid inclusions abstract the south pepper oilfield located in the barrow sub basin on the nw margin of the australian continent has experienced a multi phase charge history abundant oil bearing fluid inclusions are present in samples from within the current gas cap suggesting that an oil column existed prior to gas this palaeo oil gas leg fi oil has ts tm and c29 c30 hopane ratios of 1 and the c35 homohopanes are a significant proportion of the extended homohopanes it has lower pr ph and diasterane sterane ratios than the currently reservoired live oil and contains gammacerane a series of peaks tentatively identified as c30 to c34 17 h 30 norhopanes and a large amount of 2 methylhopanes collectively geochemical analysis of the gas leg fi oil suggests that it was generated from a less mature more calcareous source rock deposited under more reducing conditions than the upper jurassic dingo claystone the main source of the live oil in addition the presence of c30 dinosteranes in the gas leg fi oil provides a triassic or younger age constraint this makes palaeozoic carbonates an unlikely source possible source intervals for the gas leg fi oil are thin lower jurassic limestones and marls which occur at the base of the lower dingo claystone or a thin limestone unit the cunaloo member at the base of the triassic locker shale samples from within the present oil leg also contain abundant oil inclusions consistent with high oil saturations at the present day however these oil inclusions exhibit different fluorescence colours suggesting they represent a second oil charge geochemically the oil leg fi oil has an intermediate composition between the live oil and the gas leg fi oil suggesting that gas charge displaced the first oil charge samples of which were preserved as fluid inclusions in the oil leg sample biodegradation of the first oil charge indicated by the presence of 17 h 25 norhopanes in the currently reservoired live oils can be attributed to the ingress of meteoric waters probably during sub aerial exposure of the basin margin during miocene wrenching changing environmental conditions curtailed bacterial activity and allowed unaltered oil sourced from the dingo claystone to accumulate below the gas cap and mix with the biodegraded residues of the first oil charge to achieve the live oil composition the biodegradation event must have preceded the second charge as the live oil contains compounds such as n alkanes which would have been removed had alteration occurred after the second charge complex charge histories are common and the analysis of palaeo oils trapped within fluid inclusions provides the opportunity to achieve a more comprehensive assessment of hydrocarbon charge

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

integrated study of the judy field block 30 7a an overpressured central north sea oil gas field the triassic reservoirs of the judy field an overpressured petroleum accumulation in the central north sea have been studied to determine their pressure and petroleum filling history the magnitude of overpressure in the pre cretaceous aquifer is similar across the field at about 24 mpa 3500 psi but with some higher pressure laterally in areas closest to the major depocentres pressure modelling shows that the magnitude of the overpressure can be attributed almost entirely to disequilibrium compaction and largely due to late rapid tertiary burial although modelling does require nanodarcy i e shale like permeability in the cretaceous chalk section the contributions from other mechanisms which may be relevant in this setting i e gas generation and lateral transfer appear to be small the existence of both aqueous and petroleum phases in secondary fluid inclusions in microfractures in quartz and feldspar grains allows estimation of palaeopressure the data show fracture healing from 115 to 136 c during a time when reservoir palaeopressures were above hydrostatic reconstruction of the temperature history of the reservoir places the timing of the fluid inclusion formation during fracture healing at between 3 and 1 my ago coincident with a period of rapid burial the palaeopressure estimation using fluid inclusions validates the pressure modelling studies which are derived independently from commercial basin modelling software the fluid inclusions also revealed a low gor oil over the whole field prior to late stage flooding by gas leading to the variable low to high gor fluids plus gas condensates within the field today

evolution of petrophysical properties of oil shales during high temperature compaction tests implications for petroleum expulsion abstract the transport properties of permian to miocene oil shales torbanite posidonia messel himmetoglu and condor were studied using petrophysical and geochemical techniques the aims of this study were to assess permeability of oil shales evaluate the evolution of porosity specific surface area and intergranular permeability during high temperature compaction tests and to verify the suitability of intergranular permeability for petroleum expulsion measured permeability coefficients for two samples were 0 72 10 21 m for the eocene messel shale and 2 63 10 21 m for the lower jurassic posidonia shale from s germany respectively bet specific surface areas of the original samples ranged from 0 7 to 10 6 m g and decreased after compaction to values from 0 3 to 3 7 m g initial porosity values ranged from 7 6 to 20 1 for pre deformation and from 9 99 to 20 7 for post deformation samples porosity increased during the high temperature compaction experiments due to petroleum generation and expulsion permeability coefficients estimated using the kozeny carman equation varied from 6 97 10 24 m to 5 22 10 21 m for pre deformation and from 0 2 10 21 m to 4 8 10 21 m for post deformation samples reflecting the evolution of their porosity and bet specific surface areas measured and calculated permeability were similar for the messel shale whereas calculated permeability was two orders of magnitude lower for the posidonia shale from s germany petroleum expulsion efficiencies under the experimental conditions ranged from 38 6 for the torbanite to 96 2 for the posidonia shale from s germany they showed strong positive correlation with the petroleum generation index r 0 91 and poor correlations with porosity r 0 46 average pore throat diameters r 0 22 and compaction r 0 02 estimated minimum pore system saturations for petroleum expulsion during the experiments were 12 for the torbanite and 30 for the posidonia shale from n germany pore system saturation determines whether expulsion occurs mainly through matrix or fracture permeability for samples with saturation levels above 20 fracture permeability dominated during the experiments evidence based on the measured permeability coefficients expulsion flow rates consideration of capillary displacement during generation related pore invasion and the existence of transport porosity suggests that fracture permeability is the principal avenue of petroleum expulsion from source rocks this conclusion is supported by microscopic observations

microspectrofluorimetric and microthermometric evidence for variability in hydrocarbon fluid inclusions in quartz overgrowths implications for inclusion trapping in the alwyn north field north sea abstract hydrocarbon inclusions trapped in quartz cement from alwyn north field sandstones of well 3 9a 6 north sea have been analyzed using microthermometric and microspectrofluorimetric methods they are two phased with consistent gas oil ratios and mainly occur along the detrital grain overgrowth boundary their homogenization temperatures vary from 60 to 129 c with a great variability within a single fluid inclusion assemblage up to 40 c the fluorescence colour of the hydrocarbon inclusions has been characterized using a microspectrofluorimeter which allows the analysis of very small inclusions 1 7 m with good reproducibility hydrocarbon inclusions display large variations in their fluorescence colour converted in chromaticity coordinates even within a single fluid inclusion assemblage moreover they are concentrically distributed within the detrital grain overgrowth interface according to the relationship between api gravity and fluorescence colour established with reference to crude oils from alwyn north field this observation is interpreted as representing compositional variations such compositional variability in a single fluid inclusion assemblage could result from either the progressive entrapment of oils in which api gravity evolves through time and or the fractionation of hydrocarbons at the time of trapping

combined use of confocal laser scanning microscopyand pvt simulation for estimating the composition andphysical properties of petroleum in fluid inclusions we present a method to determine the composition and pvt properties of petroleum inindividual petroleum fluid inclusions confocal laser scanning microscopy is used to generatethree dimensional images of single petroleum inclusions because liquid petroleum fluorescesunder the laser the images readily distinguish the liquid and vapour within the inclusion and canbe used to determine the inclusions volumetric liquid vapour ratio using pvt modellingsoftware the liquid vapour ratio is used along with the homogenisation temperature to determinethe bulk composition phase envelope isochore and a range of physical properties of the includedpetroleum this is done using an iterative series of pvt calculations which match twoparameters 1 the molar volume of the petroleum at room and homogenisation temperatures 2 the liquid vapour ratio of the inclusion at room temperature key uncertainties in the methodare explored including the accuracy with which the liquid vapour ratio can be determined thecomposition of the titrant gas used in the iterative procedure and the composition of thepetroleum chosen to model the physical properties of the included petroleum data from coevalinclusions suggest that the saturation pressure gas oil ratio viscosity molar volume densityand surface tension of included petroleum are determined with a precision of a few percent confirmation of the accuracy of the method awaits tests using inclusions grown in the laboratoryunder carefully controlled pvtx conditions however it is likely that the physical properties ofincluded petroleums are more accurately modelled by fluids which are genetically related tothem if proven to be accurate the method will provide a routine method for determiningpalaeopressure in petroleum systems finally we present data from a central north sea examplewhich are geologically realistic and which for the first time record the evolution of fluid pressureand petroleum composition in a petroleum reservoir

geochemical comparison of oil bearing fluid inclusions and produced oil from the toro sandstone papua new guinea abstract a detailed study was carried out to compare the geochemistry of the crude oil in the lower cretaceous toro sandstone reservoir in the iagifu 7x well with oil trapped in fluid inclusions in this sandstone in the iagifu 7x and p nyang 2x wells in the papuan fold belt the drill stem test dst oils and the oils trapped in fluid inclusions show different source and maturity dependent geochemical parameters biomarkers suggest that the dst oils at iagifu 7x were derived from clay rich mixed marine terrestrial source rocks deposited under oxic conditions probably middle to late jurassic mudstones the fluid inclusion oils were derived from a less terrestrially influenced marine source rock deposited under less oxic conditions the fluid inclusion oils contain 1 2 7 trimethylnaphthalene and oleanane biomarkers indicative of angiosperm input and a cretaceous or younger source rock these oils are more mature calculated reflectance rc 1 02 than the reservoired oil at iagifu 7x rc 0 84 and condensate at p nyang 2x rc 0 84 source and thermal maturity parameters for all three fluid inclusion samples are similar suggesting that they were derived from similar source rock facies furthermore samples with predominantly blue vs white fluorescing oil inclusions have no discernible geochemical maturity difference suggesting that the use of fluorescence colours as a qualitative guide to the maturity of the trapped oil is not valid in this case fluid inclusion oils were trapped prior to charge of the reservoir with oil at the iagifu 7x and gas condensate at the p nyang 2x wells the fluid inclusion oils therefore represent an early oil charge from a deeply buried probably cretaceous source rock which started migrating into the toro sandstone during the miocene at iagifu this early oil was probably diluted by a larger volume of jurassic oil generated at the end of the miocene the absence of fluid inclusions with compositions like the currently reservoired oil is interpreted to be due to oil charging an already oil saturated zone when diagenesis is likely to have been inhibited at the p nyang well the transition from oil as represented by the oil inclusions to gas condensate was most likely caused by gas displacement