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

linking the geochemistry of crude oils and petroleum inclusions in the ubarana and lorena oilfields potiguar basin brazilian equatorial margin abstract a study of petroleum inclusions based on ultraviolet fluorescence petrography microspectrophotometry and biomarker analyses was carried out on samples from two wells of the onshore lorena and the offshore ubarana oilfields potiguar basin brazil this study aimed to evaluate the contribution and compositional variability of oils associated with different source rocks through the geochemical correlation of petroleum inclusions and crude oils three groups of inclusions were identified i a group from the lorena reservoir pendencia formation ii a second from the ubarana siliciclastic reservoir acu formation and iii a third from the carbonates adjacent to the ubarana reservoir ponta do mel formation pml fluorescence microspectrophotometry shows that the three groups of inclusions have different api gravity oils variable proportion of saturate aromatic resins and asphaltenes and are not biodegraded moreover pendencia and pml inclusions suggest multiple pulses of hydrocarbon migration while acu inclusions record a homogeneous pulse biomarkers indicate that the pendencia and acu inclusion oils correlate with reservoir oil extracts the pendencia inclusion oils are similar to the lacustrine oils of the umbuzeiro graben pendencia formation whereas the acu inclusion oil displays closer biomarker signature to the areia branca trend of mixed oils alagamar formation source rock however the oil from fluid inclusions of the pml has characteristics of the alagamar formation lacustrine organic facies the absence of mixed oils in the pml suggests an earlier lacustrine oil migration through the carbonate fractures prior to the main infill of mixed oils in the ubarana oilfield

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

geochemical characteristics of the triassic chang 7 lacustrine source rocks ordos basin china implications for paleoenvironment petroleum potential and tight oil occurrence abstract the fact that high quality lacustrine source rocks generally shale and mudstone control the formation and distribution of conventional and unconventional oil and gas reservoirs in lacustrine basins has been well accepted in petroleum exploration and exploitation taking the chang 7 lacustrine source rocks in the ordos basin as an example several points having been reached are as follows 1 the chang 7 source rocks possess an excellent source rock potential and the shales hold a better potential than the mudstones 2 the paleoenvironments of the chang 7 source rocks were sub reducing to sub oxidizing conditions and fresh and brackish water depositional environments with a maximum water depth of 150 m the organic matter origins of the source rocks are mainly plankton algae bacteria and other aquatic microorganisms 3 the beginning time of the oil generation of the chang 7 source rocks is at 165 ma and the peak oil generation occurred during 115 95 ma the cumulative amounts of oil generation are up to 4711 103 t km2 and the ratios of peak generation amounts to cumulative generation amounts are 50 the beginning timing and peak generation timing of the shales are earlier than those of the mudstones respectively and the cumulative oil generation amount of the shales is higher than that of the mudstones indicating a better oil generation potential of the shales 4 due to the more remained oil possessed in the shales the hydrocarbon expulsion threshold of the chang 7 shales 2560 m is deeper than that of the chang 7 mudstones 2080 m 5 the occurrences of the chang 8 6 tight oils are predominantly controlled by the outer boundary of the chang 7 source rocks distribution while the transition areas between thickness toc and ro high value centers are the accumulation and enrichment zones the chang 7 shales controlled the occurrence of the chang 8 tight oil reservoirs and the chang 7 mudstones controlled the occurrence of the chang 7 and chang 6 tight oil reservoirs

quantitative identification of diagenetic facies and controls on reservoir quality for tight sandstones a case study of the triassic chang 9 oil layer zhenjing area ordos basin abstract the identification of diagenetic facies is essential for prospecting hydrocarbon reserves and for hydrocarbon exploration in tight oil reservoirs a comprehensive method for determining quantitative index of reservoir diagenetic facies rdi using core analysis techniques hierarchical cluster analyses hca and grey correlation analyses gca was proposed the petrological characteristics physical properties and pore structures of the chang 9 tight oil sandstones are analysed based on thin section analysis x ray diffraction xrd scanning electron microscopy sem cathode luminescence cl and mercury injection capillary pressure micp tests the properties of the chang 9 sandstones were controlled by different forms of diagenesis compaction and cementation of calcite have reduced or occluded the pore volume in the sandstones but not all cementation is deleterious to reservoir quality chlorite cementation helped preserve relict primary porosity and the direct dissolution of feldspars and unstable lithic fragments has resulted in enhanced pore connectivity following petrographic observations and quantitative analysis the sandstones were divided into four diagenetic facies calcite cementation facies intense compaction facies porosity preserved by grain coating chlorites facies and dissolution facies the intense compaction facies and calcite cementation facies are responsible for the evolution of low quality reservoirs while the reservoirs with porosity preserved by grain coating chlorites facies and dissolution facies are of better porosity and permeability the distribution of fractures improves reservoir quality by enhancing the dissolution of unstable grains and providing convenient channels and storage spaces for oil and gas migration

palynofacies and geochemical analysis of the triassic yanchang formation ordos basin implications for hydrocarbon generation potential and the paleoenvironment of continental source rocks abstract the petroliferous basins that have formed in china since the mesozoic are characterized by non marine organic matter input a characteristic that is significantly different from that of marine organic sources the triassic yanchang formation in the ordos basin is a suite of typical intra continental lacustrine sediments that comprise the most important source rocks for the triassic oil reservoirs the yanchang formation is divided into ten subsections from top to bottom chan 1 to chan 10 three borehole successions in the southern ordos basin located in the huachi zhidan and yichuan areas cross the chan 4 5 to chan 10 subsections and have been studied using the palynofacies method combined with organic geochemistry data palynofacies analysis indicates that the sediments are rich in amorphous organic matter aom and phytoclasts the aom content in all of the samples positively correlated with the hydrogen index hi in contrast the transparent ligno cellulosic fragments tlf opaque particles op content are negatively correlated with the hi values additionally the gelified particles gp content has no linear correlation with the geochemistry data based on the quantitative composition of the particulate organic matter three palynofacies types are identified reflecting depositional settings in a distal dysoxic anoxic deep basin a shelf to basin transition zone and a proximal suboxic shelf the palynofacies total organic carbon toc and rock eval data together indicate that type i and ii kerogen are abundant in the d48 and w22 wells in the zhidan and yichuan areas respectively these kerogen types are uncommon in the l94 well in the huachi area which suggests low hydrocarbon generation potential in detail the chan 7 and chan 9 subsections of the three wells contain abundant type i and ii kerogen indicating that these layers are likely the two primary source rocks in the southern ordos basin

geochemical constraints on the origins of calcite cements and their impacts on reservoir heterogeneities a case study on tight oil sandstones of the upper triassic yanchang formation southwestern ordos basin china calcite cementation has been identified as an active process in the upper triassic yanchang formation throughout its burial history and as a major diagenetic factor causing strong reservoir heterogeneities the origins of calcite cements and their relevance to reservoir heterogeneities were investigated using a suite of petrographic and geochemical methods including optical microscopy with fluorescence and cathodoluminescence scanning and backscattered electron microscopy with energy dispersive spectrometry x ray diffraction x ray fluorescence electron probe microanalysis quantitative evaluation of minerals by scanning electron microscopy fluid inclusion analysis and carbon and oxygen stable isotope analyses the sandstones are compositionally immature with relatively high amounts of volcanic rock fragments the two generations of calcite cements are ca i and ca ii the ca i calcites are distributed along the interface of sandstone and mudstone units and were formed during the late triassic to early jurassic at formation temperatures of approximately 90 c the ca ii calcite mainly developed in the lower part of the fining upward sandstone units and was formed in the late jurassic at higher temperatures of approximately 110 c the origins of calcite cements were constrained by geochemical and isotope measurements fluid inclusion homogenization temperature and in situ element analysis the ca i calcite cement originated from dissolution of the lacustrine depositional carbonates in the interbedded mudstones and reprecipitation in the adjacent sandstones the ca ii calcite was mainly related to organic matter decarboxylation with ca2 having been provided internally by volcanic fragment alteration and plagioclase dissolution calcite cementation had caused strong reservoir heterogeneities in the yanchang formation tight sandstones the ca i calcite cementation destroyed reservoir properties along the interface of sandstones and mudstones the lower parts of the fining upward sandstone units were tightly cemented by ca ii calcite although they originally had high porosity and permeability the middle upper parts of the fining upward sandstone units contain less calcite cements and thus have better preserved reservoir pores because of oil emplacement inhibiting the calcite cementation processes

paleomagnetic results from late paleozoic dikes from the northwestern junggar block northwestern china abstract paleomagnetic data have been obtained from late paleozoic mafic and silicic dikes in northwestern junggar a triangular fragment of early to middle paleozoic trapped oceanic crust located between the kazakhstan tarim and siberian blocks discordance between the observed declination and expected declinations from tarim and kazakhstan suggests a 30 40 counterclockwise tectonic rotation of the sampling region relative to tarim and kazahkstan this rotation is attributed to post triassic thrust and strike slip faulting at face value there is a good agreement between the observed mean inclination and those expected from kazakhstan and tarim tectonic interpretation of this mean inclination is obscured by a large difference in inclination from two sampling localities a combination of geomagnetic secular variation and local tilt of fault block may cause this dispersion

source rock characteristics and rock eval based hydrocarbon generation kinetic models of the lacustrine chang 7 shale of triassic yanchang formation ordos basin china abstract highly variable depositional environment and multiple provenances caused rapid changes in facies laterally and vertically resulting in contrasting hydrocarbon generation potential and kinetics within the chang 7 shale of the upper triassic yanchang formation of ordos basin china assessing the shale oil resource potential requires several geochemical models that provide adequate information for characterizing the variations as traditional generation kinetics is derived from a single immature sample the kinetic model will not be representative for such variations this paper discusses the source rock heterogeneity and develops hydrocarbon generation kinetic models for the chang 7 shale using kinetics inversion techniques from routine rock eval data data collected from various sources for the chang 7 shale were analyzed and subdivided into groups based on their bulk geochemical properties and linked to petrophysical facies to describe the facies variation hydrocarbon generation kinetic parameters were then estimated for each of the source rock groups this study suggests that multiple kinetic models better handle spatial variation in evaluating source rock kinetics and resource potential in a lacustrine basin with highly variable lateral organofacies

geochemical application of sterane and triterpane biomarkers to a description of oils from the taranaki basin in new zealand abstract the distributions of sterane and terpane biomarkers in a suite of 25 oils from onshore and offshore regions of the taranaki basin of new zealand have been determined by gc ms features of these distributions include the presence of relatively high concentrations of a number of c 24 tetracyclic terpanes the virtual absence of tricyclic terpanes a predominance of c 29 normal iso and dia steranes and the presence of a number of non hopanoid triterpanes in one member of the suite urenui 18 h oleanane is the most abundant component m z 191 ion chromatogram of the terpane class of biomarkers based upon the distributions of 18 h oleanane the mckee and moturoa families of oils can be delineated these terpane distributions are qualitatively similar to those encountered in crude oils from a number of far eastern basins and from the handil field of the mahakam delta indonesia the taranaki oils are of approximately the same thermal maturity maturity parameters calculated from the distributions of c 29 steranes and of 17s h 21 h and 17 h 21s h hopanes confirm recent findings of incomplete nuclear isomerisation in oils derived from tertiary sediments an attempt has been made to correlate the mckee 1 and maui 4 crude oils with potential source rocks from depths of 3708 m and 3825 m respectively the rocks studied have attained insufficient maturity to have been the sources of these oils

illitization and paleothermal regimes in the middle ordovician st peter sandstone central michigan basin k ar oxygen isotope and fluid inclusion data hydrocarbon reservoirs occur in the middle ordovician st peter sandstone in the central michigan basin at depths of 1 5 3 5 km and are diagenetically altered latest diagenetic cements include saddle dolomite pervasive microcrystalline illite and chlorite and quartz a k ar and 18o 16o study of the fine grained authigenic illite in 25 samples from 16 wells covering a large area within the basin yields k ar ages ranging from 367 to 322 ma and dgr18o values between 12 7 and 16 9 pmil smow the dgr18o values of diagenetic quartz overgrowths range from 15 2 to 18 9 pmil fluid inclusion temperatures in the quartz cement range from 70 to 170 c reflecting multiple generations of diagenetic quartz and or precipitation over m st of the diagenetic history reequilibrated fluid inclusions in the saddle dolomite cement yield temperatures ranging from 90 to 150 c a regionally significant episode of illitization occurred during the late devonian mississippian temperatures of illite formation are indirectly estimated to be in the range of 125 170 c and most paleodepths of illitization are between 2 8 and 3 2 km these results imply that 1 illite formed from 18o rich fluids and 2 elevated geothermal gradients i e greater than 34 c km existed in the michigan basin in the late paleozoic the k ar ages and the dgr18o values are not correlated to present depths of the samples or paleodepths of illitization illites with young ages and low dgr18o values tend to be geographically distributed along the north south branch of the buried precambrian rift the dgr18o values of the diagenetic quartz follow a similar trend the spread of illite k ar ages and dgr18o values and their geographic distribution are best explained as reflecting abnormally high thermal regimes in the part of the basin located above the presumably highly fractured basement along the rift

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

investigation of fluid inclusion and oil geochemistry to delineate the charging history of upper triassic chang 6 chang 8 and chang 9 tight oil reservoirs southeastern ordos basin china abstract the chang 6 chang 8 and chang 9 reservoirs of the upper triassic yanchang formation in the zhenjing area of the ordos basin are characterized by low porosity low permeability high oil saturation and large oil reserves which indicate huge tight oil potential to comprehensively investigate the hydrocarbon contributors and charging history fluid inclusions were systemically studied coupled with basin modeling and oil geochemical analysis according to the petrographic characteristics two episodes of fluid inclusions occurred in each of the three reservoirs microthermometry analysis suggests that the hydrocarbon inclusions of the first episode in each reservoir are distributed mainly along overgrowth quartz or secondary microcracks and exhibit light yellow or light brown fluorescence the coeval aqueous inclusions display low homogenization temperature th peaks with 80 100 c the hydrocarbon inclusions of the second episode in each reservoir are mainly distributed in microcracks that cut across or within quartz grains and exhibit light green or bluish green fluorescence the coeval aqueous inclusions are characterized by high th peaks with 110 120 c the different characteristics of the two episodes of the fluid inclusions imply the existence of two episodes of hydrocarbon charging events the burial and geothermal histories of the various reservoirs were reconstructed using one dimensional basin modeling and pressure volume temperature composition pvtx simulation coupled with the authigenic illite k ar dating the reconstruction implied the time of the two hydrocarbon charging episodes to be early cretaceous and late cretaceous oil source correlation studies illustrate that the chang 6 chang 8 and chang 9 crude oils all originate from the chang 7 source rock the migration characteristics and directions were comprehensively analyzed by using maturity parameters this explanation of the charging history and oil migration pathway of the upper triassic yanchang formation in the zhenjing area provides a theoretical basis for further exploration

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

charging of carboniferous volcanic reservoirs in the eastern chepaizi uplift junggar basin northwestern china constrained by oil geochemistry and fluid inclusion substantial amounts of petroleum were recently discovered in the carboniferous andesite tuff breccia and basalt reservoirs of the chepaizi uplift in the western junggar basin however the charging history of the carboniferous petroleum reservoir is poorly understood oil oil correlation studies indicate that all of the oils were mainly derived from the middle permian wuerhe formation source rocks possibly mixed with a small contribution from carboniferous baogutu formation source rocks in the neighboring changji sag based on the petrographic and microthermometry of fluid inclusions two hydrocarbon charging episodes are defined these episodes were characterized by a low peak range homogenization temperature th distribution 80 c 90 c and high salinity 13 22 13 42 wt nacl and a high peak range th distribution 120 c 130 c and low salinity 4 89 11 72 wt nacl respectively through one dimensional basin modeling and pressure volume temperature composition simulation the burial thermal histories for wells p61 p66 p668 and p663 were reconstructed and their trapping temperatures of the hydrocarbon inclusions were calculated to be higher than their corresponding highest paleotemperature i e 56 8 c 53 7 c 60 9 c and 58 1 c respectively implying fast hydrocarbon charging processes promoted by deep hydrothermal fluids associated with the hydrocarbon generation history sealing process of the hongche fault and regional tectonic evolution these two hydrocarbon charging events were deduced as the adjustments of oils previously accumulated along the hongche fault zone because of the tectonic extension in the paleogene and regional tilting in the neogene respectively the general direction of oil charging was traced from south to north and from east to west as indicated by the molecular parameters of nitrogen bearing compounds and c20 c21 triaromatic steroids c20 c21 c26 c28 triaromatic steroids ta i ta i ii which roughly coincided with the active fracturing

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

quantitative impact of diagenesis on reservoir quality of the triassic chang 6 tight oil sandstones zhenjing area ordos basin china abstract the upper triassic chang 6 sandstone an important exploration target in the ordos basin is a typical tight oil reservoir reservoir quality is a critical factor for tight oil exploration based on thin sections scanning electron microscopy sem x ray diffraction xrd stable isotopes and fluid inclusions the diagenetic processes and their impact on the reservoir quality of the chang 6 sandstones in the zhenjing area were quantitatively analysed the initial porosity of the chang 6 sandstones is 39 2 as calculated from point counting and grain size analysis mechanical and chemical compaction are the dominant processes for the destruction of pore spaces leading to a porosity reduction of 14 2 20 2 during progressive burial the porosity continually decreased from 4 3 to 12 4 due to carbonate cementation quartz overgrowth and clay mineral precipitation diagenetic processes were influenced by grain size sorting and mineral compositions evaluation of petrographic observations indicates that different extents of compaction and calcite cementation are responsible for the formation of high porosity and low porosity reservoirs secondary porosity formed due to the burial dissolution of feldspar rock fragments and laumontite in the chang 6 sandstones however in a relatively closed geochemical system products of dissolution cannot be transported away over a long distance as a result they precipitated in nearby pores and pore throats in addition quantitative calculations showed that the dissolution and associated precipitation of products of dissolution were nearly balanced consequently the total porosity of the chang 6 sandstones increased slightly due to burial dissolution but the permeability decreased significantly because of the occlusion of pore throats by the dissolution associated precipitation of authigenic minerals therefore the limited increase in net porosity from dissolution combined with intense compaction and cementation account for the low permeability and strong heterogeneity in the chang 6 sandstones in the zhenjing area

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

impact of diagenesis on reservoir quality and heterogeneity of the upper triassic chang 8 tight oil sandstones in the zhenjing area ordos basin china abstract reservoir quality and heterogeneity are critical risk factors in tight oil exploration the integrated analysis of the petrographic characteristics and the types and distribution of diagenetic alterations in the chang 8 sandstones from the zhenjing area using core log thin section sem petrophysical and stable isotopic data provides insight into the factors responsible for variations in porosity and permeability in tight sandstones the results indicate that the chang 8 sandstones mainly from subaqueous distributary channel facies are mostly moderately well to well sorted fine grained feldspathic litharenites and lithic arkose the sandstones have ultra low permeabilities that are commonly less than 1 md a wide range of porosities from 0 3 to 18 1 and two distinct porosity permeability trends with a boundary of approximately 10 porosity these petrophysical features are closely related to the types and distribution of the diagenetic alterations compaction is a regional porosity reducing process that was responsible for a loss of more than half of the original porosity in nearly all of the samples the wide range of porosity is attributed to variations in calcite cementation and chlorite coatings the relatively high porosity reservoirs formed due to preservation of the primary intergranular pores by chlorite coatings rather than burial dissolution however the chlorites also obstruct pore throats which lead to the development of reservoirs with high porosity but low permeability in contrast calcite cementation is the dominant factor in the formation of low porosity ultra low permeability reservoirs by filling both the primary pores and the pore throats in the sandstones the eogenetic calcites are commonly concentrated in tightly cemented concretions or layers adjacent to sandstone mudstone contacts while the mesogenetic calcites were deposited in all of the intervals and led to further heterogeneity this study can be used as an analogue to understand the variations in the pathways of diagenetic evolution and their impacts on the reservoir quality and heterogeneity of sandstones and is useful for predicting the distribution of potential high quality reservoirs in similar geological settings

paleotemperatures and paleofluids recorded in fluid inclusions from calcite veins from the northern flank of the ponta grossa dyke swarm implications for hydrocarbon generation and migration in the parana basin abstract the parana basin southern brazil has an atypical thermal and fluid history due to the occurrence of an episodic continental flood volcanism during the early cretaceous so far there are few data about the influence of this volcanic event on the paleotemperatures and paleofluids of the parana basin sedimentary rocks the teresina formation in the northern flank of the ponta grossa dyke swarm hosts high concentration of subsurface igneous rock bodies sills and dykes besides its covering by a hundreds meter thick volcanic rock cap in this study we used fluid inclusion analysis performed in horizontal and vertical calcite veins from the teresina formation and from a late cretaceous basic dyke to estimate paleotemperatures and to characterize the composition of diagenetic paleofluids homogenization temperatures of requilibrated fluid inclusions show that the teresina formation reached temperatures above 200 c horizontal parallel bedding calcite veins from the teresina formation record low to high salinity 2 26 wt nacl eq aqueous paleofluids the prevalence of high salinity fluid inclusions associated with light hydrocarbon fluid inclusions indicates deep buried fluids fluid inclusions in vertical calcite vein from basic dyke comprise only low salinity aqueous fluids 0 3 wt eq nacl interpreted as dominated by meteoric water the recorded paleotemperatures are attributed to the heating by the parana volcanic event during the early cretaceous with the thermal effect of the volcanic rock cap surpassing the effect of nearby sills and dykes estimated paleotemperatures higher than 200 c would allow the generation of light liquid and gaseous hydrocarbons overpressured compartments in the teresina formation allowed the expulsion of buried pore fluids high salinity aqueous fluids and hydrocarbons to fracture systems where they mixed with meteoric water the input of meteoric water through fracture systems connected with the surface favored hydrocarbons degradation in the early stages of source rock maturation during the early cretaceous

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

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge