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

episodic petroleum fluid migration in fault zones of the northwestern junggar basin northwest china evidence from hydrocarbon bearing zoned calcite cement hydrocarbon bearing zoned calcite cements occur widely in jurassic cretaceous fault zone cores and sandstone outcrops of the northwestern junggar basin northwest china hydrocarbon bearing bands alternate with nearly hydrocarbon free bands at a micron scale analytical results from biomarker organic geochemistry fourier transform infrared microspectroscopy and trace element geochemistry on these zoned cements suggest that at least three different types of fluids have participated in their formation the first fluid type is probably primary unmodified lacustrine formation water from which the hydrocarbon poor bands are formed and are characterized by mg rich calcite the other two types of fluids include basinal fluids e g hot hydrocarbon bearing fluids and meteoric water the hydrocarbon rich bands in which the hydrocarbons have been biodegraded and the mn content is relatively high suggest a mixture of hydrocarbon bearing basinal fluid and meteoric water the alternating growth of hydrocarbon bearing and hydrocarbon free bands of calcite cements implies that the cement formation is episodic it is related to alternating episodes of mixed petroleum bearing fluid and unmodified primary formation waters respectively the fault appears to have been a mixing zone where seismic pumping during the movement of associated regional faults occurred thus in the northwestern junggar basin the micron scale hydrocarbon bearing zoned structure of the calcite cements is likely a reflection of episodic petroleum fluid migration in fault zones

mixing zone and deep burial diagenesis relevance to reservoir porosity and oil migration middle jurassic great oolite formation wealden basin england abstract the middle jurassic great oolite limestone of the wealden basin southern england is a target of active exploration owing to recent discoveries of oil such as the conoco no 1 storrington location throughout the basin similar lithologies in the great oolite have porosities ranging from less than 5 to greater than 20 hence the principal control on porosity is a diagenetic history in the storrington no 1 production interval the porosity is mainly primary cement isotopic and trace element stratigraphies of that interval indicate that primary porosity is preserved through early mineralogical stabilization of limestones in the mixing zone between freshwater and marine phreatic environments at the nearby southwater no 1 location studies of the same types of data show a similar early diagenetic history following mixing zone diagenesis further subsidence resulted in deep burial diagenesis principally the occlusion of porosity by coarse calcite spar the deep burial origin of the spar is based on fluid inclusion data which also indicate that uplift followed the precipitation of spar the amount of uplift varies depending on basin location oil filled fluid inclusions also occur in the spar indicating oil was in a mobile phase at the time of cementation reconstruction of basinmore structure and maturation modeling show that cementation oil migration was in the cretaceous that together with the distribution of oil filled inclusions indicate the primary areas of the basin where migration and accumulation of oil occurred less

diagenetic history of tight sandstones and gas entrapment in the yulin gas field in the central area of the ordos basin china abstract the ordos basin is a large cratonic basin with an area of 250 000 km2 in central china upper paleozoic coals and shales serve as gas source rocks with peak generation and migration at the end of the early cretaceous recent exploration has verified the huge gas potential in the basin centered gas accumulation system bcgas however the mechanism for the gas accumulation is controversial with an integrated approach of thin section petrography ultra violet fluorescence microscopy fluid inclusion microthermometry raman microspectrometry scanning electron microscopy and x ray diffractometry we identified diagenetic trapping and evaluated the diagenetic history of sandstone reservoirs in the yulin gas field in the central area where structural stratigraphic and or sedimentary lithologic traps have not been found it was revealed that three phases of diagenesis and hydrocarbon charging occurred respectively in the late triassic late jurassic and at the end of the early cretaceous in the first two phases acidic water entered the reservoir and caused dissolution and cementation resulting in porosity increase however further subsidence and diagenesis including compaction and cementation markedly reduced the pore space at the end of the early cretaceous the bulk of the gas migrated into the tight reservoirs and the bcgas trap was formed in the updip portion of this system cementation continued to occur due to low gas saturation and has provided effective seals to retain gas for a longer period of time than water block in the bcgas the mechanism for the gas entrapment was changed from water block by capillary pressure in the bcgas to diagenetic sealing the diagenetic seals in the updip portion of the sand body were formed after gas charging which indicates that there is a large hydrocarbon exploration potential at the basin centered area

multiple stage migration and accumulation of permian lacustrine mixed oils in the central junggar basin nw china abstract the permian lacustrine petroleum system in the central junggar basin northwest china has recently obtained exploration success these accumulations are characterized by mixed oils and multiple stage migration and accumulation this process however has not been well constrained limiting the understanding of the general laws of hydrocarbon migration and accumulation and making it difficult to define exploration strategies here we reconstruct this process mainly based on oil bearing fluid inclusion analyses including petrography homogenization temperature and sequential extraction inclusion petrography shows that petroleum inclusions dominantly display yellow fluorescence while intergranular free oils mostly display strong blue green fluorescence this implies that the reservoirs seem to have experienced at least two stages of hydrocarbon charge from different sources and or maturities the sources maturities are determined through reservoir sequential extraction analyses the free oils are mixed and sourced from the lower permian fengcheng formation p1f and the middle permian lower wuerhe formation p2w while the inclusion oils are also mixed and derived mainly from the p1f source both oils are characterized by moderate maturity homogenization temperature measurements of oil bearing fluid inclusions combined with reconstruction of reservoir burial and thermal history not only further verify multiple hydrocarbon charging events but also characterize the timing which indicates a three stage petroleum charging model during the first stage of the late triassic carboniferous reservoirs were charged by p1f sourced oils which were dysmigrated or remigrated to jurassic reservoirs during the second stage i e the early cretaceous in contrast the third stage from the late cretaceous represents another hydrocarbon charge event that is the primary oil accumulation sourced from the p2w rocks according to this model both primary and secondary oil accumulations contribute to the current region s exploration success and provide future exploration targets

water washing of proterozoic oil in the midcontinent rift system whole oil gas chromatography shows that petroleum inclusions trapped in 1 05 ga veins in the midcontinent rift experienced variable water washing but no significant biodegradation or phase separation by comparing our results with published experimental data we estimate that water petroleum ratios varied from 200 1 to much greater than 9000 1 extreme water washing with water petroleum ratios very much greater than 9000 1 likely produced pyrobitumen solid hydrocarbon that was locally trapped as primary inclusions in vein calcite hydrothermal ore deposits with their extremely high water rock ratios are one of the best places to search for end member water washed petroleum sedimentary basins however with their variable water rock ratios also have a wide range of water petroleum ratios which significantly affect the composition of crude oils along the flow path between source rock and trap water petroleum ratios may be a useful concept to help evaluate crude oil compositions in a variety of settings

hydrocarbon generation in the permian irati organic rich shales under the influence of the early cretaceous parana large igneous province abstract the increasing global demand for natural gas and petroleum byproducts is turning organic rich shales into an important target for hydrocarbon exploration and production current understanding about hydrocarbon generation in unconventional plays such as oil shales and gas shales is still evolving especially in sedimentary basins where hydrocarbon generation is influenced by magmatism this is the case for the permian oil shales of the irati formation in the parana basin southern south america the irati shales are considered an atypical petroleum system due to thermal effects of the parana large igneous province lip emplaced during the early cretaceous in this context the focus of this study was to characterize the thermal conditions of hydrocarbon generation in the irati formation as well as the composition of related aqueous diagenetic fluids the kerogen from the irati organic rich shales has an aromaticity around 30 ar 30 as determined by carbon nuclear magnetic resonance 13c nmr and vitrinite reflectance ro of around 0 6 fluid inclusions in calcite and quartz veins present aqueous fluids with salinity of 0 5 wt of nacl equivalent and homogenization temperatures greater than 250 c hydrocarbon fluid inclusions were classified as black oil through their vapor fraction volumes fv 1 6 9 1 and homogenization temperatures th in the 60 80 c range methane ch4 or carbon dioxide co2 fluid inclusions were absent within the analyzed calcite and quartz veins the pvt model for trapped fluid inclusions suggests a shallow hydrocarbon petroleum system 2 5 km depth active during the early cretaceous synchronous with the parana lip

reequilibration of fluid inclusions in low temperature calcium carbonate cement calcium carbonate cements precipitated in low temperature near surface vadose environments contain fluid inclusions of variable vapor to liquid ratios that yield variable homogenization temperatures cements precipitated in low temperature phreatic environments contain one phase all liquid fluid inclusions neomorphism of unstable calcium carbonate phases may cause reequilibration of fluid inclusions stable calcium carbonate cements of low temperature origin which have been deeply buried contain fluid inclusions of variable homogenization temperature and variable salt composition most inclusion fluids are not representative of the fluids present during cement growth and are more indicative of burial pore fluids therefore low temperature fluid inclusions probably reequilibrate with burial fluids during progressive burial reequilibration is likely caused by high internal pressures in inclusions which result in hydrofracturing the resulting fluid inclusions population could contain a nearly complete record of burial fluids in which a particular rock has been bathed

tectono thermal evolution of cambrian ordovician source rocks and implications for hydrocarbon generation in the eastern tarim basin nw china abstract the tectono thermal evolution is an important control on petroliferous basin development however this evolution is difficult to reconstruct in sedimentary basins subjected to multiple tectono thermal events the tarim basin is the largest petroliferous basin in northwestern china and hosts a complex oil gas system comprising several sets of source reservoir and cap rocks that have experienced multiple tectonic thermal and sedimentary events large oil and gas reserves have been discovered in the central and northern tarim basin during the last 30 years but none in the eastern part of the basin this is generally attributed to the high thermal maturity reached by source rocks during the late ordovician and subsequent hydrocarbon loss therefore reconstructing the cambrian ordovician tectono thermal evolution is critical in facilitating successful oil and gas exploration in this region we compiled equivalent vitrinite reflectance data n 178 of source rocks from seven wells in the tarim basin which for cambrian ordovician source rocks are 1 3 beyond the hydrocarbon generation threshold and in the main gas and dry gas generation stages the cambrian ordovician source rocks experienced rapid burial and heating during the caledonian period entered the hydrocarbon generation stage during the middle late ordovician and reached peak hydrocarbon generation at the end caledonian period they might have experienced secondary hydrocarbon generation after the jurassic homogenization temperatures of fluid inclusions n 616 from wells gc4 lx1 md1 and yd2 as well as the modeled thermal evolution reveal a main hydrocarbon generation event during the caledonian period and a secondary event in the yanshanian and himalayan period in other wells lx1 md1 and yd2 hercynian and indosinian uplift and exhumation in the eastern tarim basin controlled the main structures and faulting created favorable conditions for secondary hydrocarbon generation and migration at this time since the yanshanian and himalayan the tarim basin has experienced further sedimentation and heating and the tectono thermal evolution might have been related to the formation of the tibetan plateau in summary our reconstruction of the tectono thermal evolution of cambrian ordovician strata and the hydrocarbon generation history of the tarim basin suggests that the eastern tarim basin may also have hydrocarbon generation potential and can guide future oil and gas exploration

fluid inclusions record thermal and fluid evolution in reservoir sandstones khatatba formation western desert egypt a case for fluid injection a fluid inclusion and petrographic study focused on quartz overgrowths was performed in reservoir sandstones from the jurassic khatatba formation salam oil field egypt s western desert the combination of detailed fluid inclusion petrography and scanning electron microscope sem cathodoluminescence imaging has allowed us to relate individual fluid inclusion assemblages that is the most finely discriminated groups of petrographically associated fluid inclusions to specific growth zones of authigenic quartz establishing the relative timing of entrapment of the inclusions after entrapment fluid inclusions in authigenic quartz have been preserved without reequilibration as indicated by the narrow ranges of homogenization temperatures 4 5 degreesc in most fluid inclusion assemblages three main growth zones are distinguished under sem cathodoluminescence in the quartz overgrowths and are termed q1 q2 and q3 from the oldest to the youngest zone q1 is further subdivided into three subzones and contains abundant primary aqueous inclusions their homogenization temperatures range from 162 to 130 degreesc with the earliest assemblages having the highest temperatures and with some large temperature fluctuations indicated between successive assemblages most q1 inclusions have salinities in the freshwater to seawater range with a trend toward increasing salinity through time zone q2 contains primary aqueous inclusions with homogenization temperatures overall range 148 125 degreesc also recording large temperature fluctuations and cooling events the q2 fluid inclusions have high salinities 5 20 wt nacl equivalent with salinity increasing through time zone q3 contains both aqueous and oil inclusions of primary origin the q3 aqueous inclusions have homogenization temperatures overall range 134 112 degreesc recording overall cooling and high salinities 21 24 wt nacl equivalent in early q3 subzones oil inclusions appear to be of medium gravity undersaturated with respect to gas in later q3 subzones oil inclusions are of gas saturated lighter oil our results indicate that fluid flow involving drastic changes in temperature and salinity was responsible for the precipitation of some of the quartz cement the earliest quartz q1 precipitated from freshwater and seawater at temperatures significantly higher than those expected from the burial history and thermal maturity of these rocks this quartz is interpreted to have precipitated during cooling of injected fluids that originated as hot connate fluids from deeper parts of the basin the q2 precipitation is interpreted to have resulted from episodes of injection of hot saline brines from below late quartz cement q3 precipitated during oil charge from progressively cooler and more saline brines interpreted to have refluxed from the surface it preserves a record of increasing oil maturity and gas saturation through time

stable isotope study of carbonate sediments from the coorong area south australia the mineralogy and isotope geochemistry of carbonate minerals in the coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water the different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral in addition the dolomite was not formed by simple solid state cation exchange the occurrence of two types of dolomite was shown by isotope analysis and sem observations the dolomite which is isotopically light 13c 1 to 2 0 18o 3 to 5 0 and of fine grain size 0 5 m probably precipitated under the influence of evaporitically modified continental water coarser grained dolomite up to 4 m is isotopically heavier 13c 3 to 4 0 18o 5 to 6 0 contains mg in excess of ca and was formed in or close to equilibrium with atmospheric co2 probably by the dolomitization of aragonite

depositional diagenetic thermal and maturation histories of cretaceous mishrif formation fateh field dubai rudist reef associated limestones comprising the cretaceous mishrif formation are the major reservoirs in fateh field a giant oil field in offshore dubai in this study mishrif cores from four wells on the western flank of the field were examined to gain insights into the depositional diagenetic thermal and maturation histories of the mishrif formation in this area the wells lowest on the west flank contain relatively deep water lower fore reef facies bounded by two erosional unconformities the upper unconformity marks the laffan mishrif contact and extends over fateh field throughout the region in fateh field the lower intra mishrif unconformity has been identified only on the western flank but is probably present in other locations low on the fateh structure the identification of the lower unconformity indicates two cycles of mishrif sedimentation the cycles are related to deep seated salt movement and epeiric sea level changes fluid inclusion data maturation calculations and burial history modeling indicate that the timing of cementation by blocky calcite spar and oil migration were approximately synchronous and occurred during the oligocene to miocene

experimental stretching of fluid inclusions in calcite implications for diagenetic studies homogenization temperatures of fluid inclusions trapped in calcite crystals may change with increased heating beyond the homogenization temperature fluid inclusions trapped in calcite during basin subsidence will tend to yield homogenization temperatures approaching maximum burial temperatures diagenetic studies that depend on these data will be biased coarse crystalline calcite containing saline fluid inclusions was used to examine the influence of increased temperatures and pressures on measured homogenization temperatures stepped heating experiments were conducted at 1 atm over a temperature range of 90 to 245 c along with hydrothermal experiments at confining pressures of 173 and 691 bar and temperatures of 160 250 and 350 c in all cases significant increases in the homogenization temperatures of the inclusion population were recorded presumably stresses generated during heating of the fluid inclusions exceeded the combined strength of the calcite crystal and the external pore pressure and thus caused fluid inclusion stretching size is a secondary factor that controls fluid inclusion reequilibration

origin of reservoir fractures in little knife field north dakota thin vertical planar fractures observed in the mission canyon formation at the little knife field are naturally occurring and appear to be extension fractures the predominant east west trend of the fractures measured in oriented core from six wells parallels the contemporary maximum horizontal compressive stress in the williston basin the fractures occur only in carbonate units but within the carbonates their occurrence is not lithology dependent fracture density measured in cores of the reservoir carbonates averages 1 ft 3 m of fracture per 2 3 ft 7 m of core the formation and mineralization of reservoir fractures were the most recent diagenetic events in the mission canyon formation at little knife study of aqueous and hydrocarbon fluid inclusions associated with the fractures reveals 1 fractures formed after the strata were buried to at least their present depth of 9 800 ft 2 987 m which indicates their age is post mesozoic 2 the pore fluid pressure gradient was normal hydrostatic immediately after if not during fracture system development 3 formation water salinity has remained fairly constant since fracture initiation 4 migration of hydrocarbons into the reservoir probably preceded fracture genesis and 5 methane concentration may have decreased since fracture initiation

porosity preservation in the upper smackover jurassic carbonate grainstone walker creek field arkansas response of paleophreatic lenses to burial processes reply a section of the arco bodcaw no 1 core from the upper smackover jurassic of southern arkansas was studied in detail in an effort to understand the control of porosity petrographic isotopic atomic absorption and cathodoluminescence data on whole rocks and components were generated on 24 samples from a 115 foot length of core the core is composed almost entirely of accretionary and cryptocrystalline grains and cement porosity is unrelated to grain type size or sorting on a sample to sample basis the porous intervals are interpreted to have been stablized to calcite under fresh water phreatic conditions the porous intervals approach fresh water values of 5 0 per thousand delta 18 o 1 5 mol percent mg and 300 ppm sr and are further characterized by luminescent oolites and relatively slight solution compaction effects the nonporous intervals represent relict vadose and subphreatic environments which stabilized after burial the nonporous intervals approach burial values of 2 8 per thousand delta 18 o 2 5 mol percent mg and 600 ppm sr and are further characterized by nonluminescent grains and intense solution compaction data indicate that oolites were initially composed of a metastable mineralogy cryptocrystalline grains were composed of a more stable mineralogy and algal grains were composed of a mixture of mineralogies oolites in the vadose and subphreatic environments were not fully stabilized under fresh water conditions but vadose grains carried with them a light delta 13 c soil gas signal after burial these grains were fully stabilized under post fresh water burial conditions observed porosity distribution is readily explained in terms of solution compaction and cementation grains with metastable mineralogy in relict vadose and subphreatic intervals were heavily solution compacted at relatively shallow depths before being converted to stable calcite intense solution compaction destroyed pore space in these intervals dolomite cementation seems linked with the compaction process the stablized mineralogy of the phreatic lens together with associated meteoric cements resisted solution compaction and thereby preserved pore space

the kosice meteorite fall atmospheric trajectory fragmentation and orbit the kosice meteorite fall occurred in eastern slovakia on february 28 2010 22 25 ut the very bright bolide was imaged by three security video cameras from hungary detailed bolide light curves were obtained through clouds by radiometers on seven cameras of the european fireball network records of sonic waves were found on six seismic and four infrasonic stations an atmospheric dust cloud was observed the next morning before sunrise after careful calibration the video records were used to compute the bolide trajectory and velocity the meteoroid of estimated mass of 3500 kg entered the atmosphere with a velocity of 15 km s 1 on a trajectory with a slope of 60 to the horizontal the largest fragment ceased to be visible at a height of 17 km where it was decelerated to 4 5 km s 1 a maximum brightness of absolute stellar magnitude about 18 was reached at a height of 36 km we developed a detailed model of meteoroid atmospheric fragmentation to fit the observed light curve and deceleration we found that kosice was a weak meteoroid which started to fragment under the dynamic pressure of only 0 1 mpa and fragmented heavily under 1 mpa in total 78 meteorites were recovered in the predicted fall area during official searches other meteorites were found by private collectors known meteorite masses ranged from 0 56 g to 2 37 kg the meteorites were classified as ordinary chondrites of type h5 and shock stage s3 the heliocentric orbit had a relatively large semimajor axis of 2 7 au and aphelion distance of 4 5 0 5 au backward numerical integration of the preimpact orbit indicates possible large variations of the orbital elements in the past due to resonances with jupiter

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

major marine cycles in the mesozoic the cycles postulated by fischer 1979 are considered in the light of the mesozoic stratigraphical and palaeontological record it is suggested that the most important events were i the late permian regression ii the late mid triassic transgression iii the late late transgression iv the late early jurassic transgression v the late mid jurassic transgression vi the end jurassicre gression vii the late early cretaceous transgression viii the end cretaceous regression these are related to episodicity in ocean floor spreading climatic changes and major happenings in the history of the shallow marine benthos

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

applications of fluid inclusion studies to reservoir diagenesis and petroleum migration smackover formation u s gulf coast and fateh field dubai abstract the smackover trend of the united states gulf coast is a prolific producer of oil and gas the distribution of porosity is partly controlled by precipitation of late void filling calcite the timing of the formation of these cements is interpreted from fluid inclusion geothermometry in general the fluid inclusion filling temperatures closely approximate those of the formation of the calcite and indicate that cementation occurred near the maximum depth of burial the trapped fluid is a dense calcium rich brine consistent with modern formation fluids the geochemistry of the fluid inclusions reflects the environment of diagenesis for example h2s rich inclusions occur in cements from deep dolomitic reservoirs the fateh field offshore dubai has estimated petroleum reserves of 2 3 billion bbl of oil production is principally from the mishrif formation an upper cretaceous rudist reef complex late coarse grained calcite cements partly occlude porosity these cements contain both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry indicates temperatures consistent with the geothermal gradient indicating a miocene age for cement deposition since oil was trapped during growth of the calcite cement petroleum generation and migration are also miocene in age preliminary analyses of the oil trapped in inclusions show it to be different than the oil in the reservoir the oil trapped in the inclusions may be an early generated less mature oil end of article last page 957

origin of fracture porosity example from altamont field utah the occurrence of natural fracture systems in subsurface rock can be predicted if careful evaluation is made of the geologic processes that affect sedimentary strata during their cycle of burial diagenesis uplift and erosional unloading variations in the state of stress within rock arise for example from changes in temperature pore pressure weight of overburden or tectonic loading hence geologic processes acting on a sedimentary unit should be analyzed for their several contributions to the state of stress and this information used to compute a stress history from this stress history predictions may be made as to when in the burial cycle to expect fracture joint formation what type of fractures extension or shear may occur and which geologic factors are most favorable to development of fractures a stress history is computed for strata of the naturally fractured altamont oil field in utah s uinta basin calculations suggest that fractures formed in extension that the well cemented rocks are those most likely to be fractured that fractures began to develop only after strata were buried to great depth and that the fracture system continued to develop as strata were uplifted and denuded of overburden geologic evidence on fracture genesis and development is in accord with the stress history prediction stress history can be useful in evaluating a sedimentary basin for naturally fractured reservoir exploration plays

fluid inclusion constraints on temperatures of petroleum migration from authigenic quartz in bitumen veins abstract solid bitumens in fracture systems commonly contain microscopic crystals of authigenic quartz which were precipitated coevally with the bitumen early in the paragenesis of the fracture fillings the quartz contains primary fluid inclusions both aqueous and hydrocarbon yielding homogenization temperatures particularly in the range 95 130 c indicating minimum temperatures of entrapment during petroleum migration volumes of up to 50 entrained quartz and a predominance of aqueous inclusions indicate that the petroleum fluid had a substantial aqueous component

evidence against natural deformation of fluid inclusions in diagenetic quartz abstract this paper describes evidence for and against burial induced deformation of fluid inclusions in diagenetic quartz fluid inclusions in diagenetic minerals are prone to non elastic deformation stretching or leakage if subjected to progressive burial in a sedimentary basin if they deform they cannot record mineral growth conditions correctly a correlation between homogenization temperature and depth may be interpreted as indicating wholesale leakage or stretching experimental work and theoretical studies suggest that heating 200 c higher than the homogenization temperature is required to produce significant deformation but it may not be possible to extend the results to natural conditions the experiments further predict a correlation between homogenization temperature and inclusion size in a sample of inclusions that have undergone natural deformation this is not observed in natural examples but the absence of a correlation is not proof that leakage has not occurred several features of inclusion data in quartz cements do however argue against stretching or leakage homogenization temperatures commonly show narrow distributions and are compatible with independent data such as illite potassium argon ages and petrography different generations of inclusions in a single sample set also retain homogenization temperature distributions compatible with their sequential origin taken as a whole the body of evidence argues against widespread stretching or leakage of fluid inclusions in diagenetic quartz

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

tracing of deeply buried source rock a case study of the wc9 2 petroleum pool in the pearl river mouth basin south china sea abstract the identification of a deeply buried petroleum source rock owing to the difficulty in sample collection has become a difficult task for establishing its relationship with discovered petroleum pools and evaluating its exploration potential in a petroleum bearing basin this paper proposes an approach to trace a deeply buried source rock the essential points include determination of the petroleum charging time of a reservoir reconstruction of the petroleum generation history of its possible source rocks establishment of the spatial connection between the source rocks and the reservoir over its geological history identification of its effective source rock and the petroleum system from source to trap and evaluation of petroleum potential from the deeply buried source rock a case study of the w9 2 petroleum pool in the wenchang a sag of the pearl river mouth basin south china sea was conducted using this approach the w9 2 reservoir produces condensate oil and gas sourced from deeply buried source rocks the reservoir consists of a few sets of sandstone in the zhuhai formation and the possible source rocks include an early oligocene enping formation mudstone and a late eocene wenchang formation mudstone with a current burial depth from 5000 to 9000 m the fluid inclusion data from the reservoir rock indicate the oil and the gas charged the reservoir about 18 3 5 ma and after 4 5 ma respectively the kinetic modeling results show that the main stages of oil generation of the wenchang mudstone and the enping mudstone occurred during 28 20 ma and 20 12 ma respectively and that the 13 c 1 value of the gas generated from the enping mudstone has a better match with that of the reservoir gas than the gas from the wenchang mudstone results from a 2d basin modeling further indicate that the petroleum from the enping mudstone migrated upward along the well developed syn sedimentary faults in the central area of the sag into the reservoir but that the petroleum from the wenchang mudstone migrated laterally first toward the marginal faults of the sag and then migrated upward along the faults into shallow strata the present results suggest that the trap structure in the central area of the sag is a favorable place for the accumulation of the enping mudstone derived petroleum and that the wenchang mudstone derived petroleum would have a contribution to the structures along the deep faults as well as in the uplifted area around the sag