the upper limit of maturity of natural gas generation and its implication for the yacheng formation in the qiongdongnan basin china abstract vitrinite reflectance vr ro measurements from residual kerogen of pyrolysis experiments were performed on immature maoming oil shale substituted the samples for the gas prone source rocks of yacheng formation of the qiongdongnan basin in the south china sea the work was focused on determination an upper limit of maturity for gas generation ulmgg or the deadline of natural gas generation ro values at given temperatures increase with increasing temperature and prolonged heating time but ro value given a definition of the difference of all values for vr related to higher temperature and adjacent lower temperature in open system non isothermal experiment at the heating rate of 20 c min is better than vr and representative examples are presented in this paper it indicates that the range of natural gas generation for ro in the main gas generation period is from 0 96 to 2 74 in which ro is in concordance with the stage for the onset and end of the main gas generation period corresponding to 0 02 up to 0 30 and from 0 30 up to 0 80 respectively after the main gas generation period of 0 96 2 74 the evolution of vr approach to the ulmgg of the whole rock for type ii kerogen it is equal to 4 38 of vr where the gas generation rates change little with the increase of maturation ro is the maximum of 0 83 corresponding to vr of 4 38 ro and the source rock does not nearly occur in the end process of hydrocarbon gas generation while ro is over 4 38 it shows that it is the same the ulmgg from the whole rock for type ii kerogen as the method with both comparison and kinetics by comparing to both the conclusions of pyrolysis experiments and the data of vr from the source rock of yacheng formation on a series of selected eight wells in the shallow water continental shelf area it indicate that the most hydrocarbon source rock is still far from reaching ulmgg from the whole rock for type ii kerogen the source rock of yacheng formation in the local areas of the deepwater continental slope basin have still preferable natural gas generative potential especially in the local along the central depression belt namely the ledong lingshui songnan and baodao sags from southwest to northeast from the depocenter to both the margin and its adjacent areas it help to evaluate the resource potential for oil and gas of the hydrocarbon source rock in the deepwater continental slope of the qiongdongnan basin or other basins with lower exploration in the northern of the south china sea and to reduce the risk in exploration

detrital modes of upper paleozoic sandstones derived from antler orogen in nevada implications for nature of antler orogeny

numerical investigation of the influence of underground water injection on the groundwater system in a shale gas reservoir in southwestern china underground injection ui is an effective and efficient means of disposing of wastewater from shale gas production however the influence of ui on groundwater systems should be examined carefully to protect drinking groundwater sources a regional hydrogeological model based on tough2 mp eos7r of part of the sichuan basin is established to simulate pressure changes and solute transport in response to wastewater injection into deep aquifers wastewater is assumed to be injected through a well at a rate of 5 45 kg s 1 for 5 years and a post injection period of 45 years the simulation results indicate that ui will cause significant pressure buildup during the injection period after which pressure will dissipate during the post injection period the mass fraction of solute increased over the entire simulation period the draft regulation under the safe drinking water act and the level iii groundwater quality standards regulated by the chinese government is referenced as the criteria for evaluating the influence of ui on groundwater systems it is found that maximum pressure levels caused by ui may exceed safe levels uncertainties with respect to permeability are analyzed from previous studies and injection test results lower levels of permeability incur higher degrees of pressure buildup when ui is implemented different injection schemes are discussed and we verify that pressure buildup from time variant injection schemes is less than that from constant injection schemes for the same total injection volume injection schemes should be carefully evaluated before implementing ui in a shale gas reservoir

calculation of petroleum masses generated and expelled from source rocks abstract an algebraic scheme for calculating the masses of petroleum formed in mature source rocks has been constructed the scheme exploits routine geochemical measurements and a basic understanding of the behaviour of sedimentary organic matter at elevated temperatures under both laboratory and subsurface conditions application of these techniques to data from a wide range of source rock types has led to the following general conclusions 1 1 major oil and gas generation from kerogen occurs between 120 and 150 c in the subsurface gas generation continues to temperatures 160 c 2 2 oil prone source rocks with average initial potential 5 kgt 1 of rock and average organic carbon contents 1 5 expel 60 90 of the total oil generated 3 3 oil expulsion from leaner source rocks is less efficient most of the oil generated remains in the source rock it is subsequently converted to lighter components at higher temperatures and expelled in the vapour state 4 4 the major loss of organic carbon from rich oil prone source rocks during generation and expulsion means that the petroleum potential and organic carbon content of mature source rocks are much less than their initial immature values hence the algebraic scheme must be used to calculate the initial values before expelled petroleum masses can be determined

the lithofacies and reservoir characteristics of the upper ordovician and lower silurian black shale in the southern sichuan basin and its periphery china abstract the black shale of the upper ordovician and lower silurian is a significant target for shale gas exploration in the southern sichuan basin in this study we introduced a lithofacies classification for shale based on rock mineral composition because the pore structure of gas shale reservoirs are complex and greatly affect the gas storage and transport in shale four different methods of low pressure nitrogen gas adsorption high pressure mercury intrusion scanning electron microscopy sem and gas expansion methods were used to investigate the reservoir pore structure and storage space combined with x ray diffraction total organic matter content toc gas content methane adsorption porosity and permeability and wireline data the key factors that affect shale gas content and storage of shale gas were analyzed according to our shale classification three main lithofacies i e calcareous mudstone cm high calcareous mixed mudstone hcmm and low calcareous mixed mudstone lcmm were identified in our study area the experiment indicates that the shale has a high toc thermal maturity and gas content the methane adsorption isotherms show that the sorbed gas content has a positive correlation with toc difference of toc between the three is small nitrogen adsorption indicates that mesopores dominate the shale pore composition and organic matter is the main source of mesopores mercury injection shows that the macropore volume accounts for approximately 14 22 of the total pore volume no obvious pore structure differences were found for different lithofacies however taking the porosity into consideration lcmm has the largest macropore volume the sem observations revealed that organic matter pores interparticle pores and intraparticle pores are the main pore types interparticle pores mainly develop in lcmm which has a relatively high quartz and low carbonate content it may be the major reason for high porosity high macropore volume and high free gas content of lcmm free gas and absorbed gas are the major storage form of shale gas given similar temperature and pressure conditions the total organic matter content is the major factor that affects the adsorbed gas content therefore with high free gas and adsorbed gas content lcmms with high total organic matter contents would be the most favorable type of lithofacies in this region

the puguang gas field new giant discovery in the mature sichuan basin southwest china the giant puguang gas field with a proven original in place gas volume of 350 109 m3 12 36 tcfg was discovered in 2003 in the eastern sichuan fold thrust belt of the mature sichuan basin southwest china the field is a combination structural stratigraphic trap closed by lateral depositional change and fault closure the trap evolved from a paleo oil reservoir originating in the triassic jurassic the entrapment of thermal gas which was derived from lower middle silurian and permian source rocks occurred during deep burial in the jurassic cretaceous tertiary quaternary compression transformed the paleotrap into the present gas reservoir gas is contained in the lower triassic feixianguan and the upper permian changxing reservoirs which consist predominantly of dolomitized oolites deposited in shelf and platform margin shoal and backreef environments reservoir quality is characterized by porosity of 1 29 and permeability of 0 01 9664 md with buried depth greater than 5000 m 16 400 ft the discovery of the puguang field exemplifies the successful application of a new play concept and new technology in a mature basin the discovery resulted from a shift in exploration strategy from structures to stratigraphic traps in reef and shoal dolomites and benefited from advanced high resolution seismic techniques the discovery will not only broaden the exploration scope in the sichuan basin but also provide an excellent analog for exploration in other fold thrust belts worldwide

sedimentology petrography and tectonic significance of the shelf flysch and molasse clastic deposits across the indus suture zone ladakh nw india abstract in the ladakh area of india a passive triassic to lower cretaceous continental margin is indicated by indian shield derived clastics on the shelf and atlantic type turbidites off the continental margin mid cretaceous initiation of ocean closing is reflected in pacific type flysch and associated island are volcanics which were initially emplaced over the northern indian continental margin in late cretaceous times resulting in the formation of a fore deep in which flysch and minor continental molasse accumulated briefly during the late cretaceous these transient uplifts were however rapidly destroyed for by the latest cretaceous to latest palaeocene uniform carbonate sediments were being laid down over the area with the early eocene the development of a second fore deep this time filled with very thick flysch and molasse sediment indicates a major uplift of the northern indian margin which we attribute to the development of an andean type magmatic arc on the northern edge of the indian plate uplift and molasse sedimentation in this fore deep continued through the oligocene and miocene when the collision of india and asia caused extensive deformation of all the sequences and the shift of molasse sedimentation southwards to the himalaya foothills and indo gangetic plain

jurassic oils in the central sichuan basin southwest china unusual biomarker distribution and possible origin abstract crude oils in the jurassic reservoirs of the shilongchang oilfield in central sichuan basin are characterized by a high abundance of methylcyclohexane relative to n heptane in the c7 light hydrocarbons high pristane phytane ratio pr ph 1 81 2 45 a c29 sterane dominance and a tendency towards lower 13c values with increasing chain length for c12 c19 n alkanes reflecting a dominantly terrigenous source deposited in a sub oxic to oxic environment the oils are extremely enriched in rearranged hopanes including 17 h diahopanes 18 h neohopanes and an unidentified rearranged hopane series with relatively short gas chromatography gc retention times the 17 h diahopanes are present in highest abundance among the hopane classes and exhibit similar carbon number distributions to those of the 17 h hopanes including a range from c27 to c35 a dominance of the c30 isomer and presence of 22s and 22r epimers for c31 c35 homologues the 18 h neohopanes are less abundant than the 17 h diahopanes with only ts c29ts and a possible c30 member detected the early eluting rearranged hopanes extend from c29 to c35 and display distributions similar to the 17 h hopanes and 17 h diahopanes as the origin of rearranged hopanes is relatively well understood their unusually high relative abundance in the studied jurassic lacustrine oils from the central sichuan basin provides strong evidence for the presence of effective highly mature and clay rich source rocks formed under a sub oxic depositional setting

experimental heating and kinetic models of source rocks comparison of different methods abstract closed system isothermal micro pyrolysis has been carried out for nine upper jurassic source rocks from the norwegian shelf supplemented by hydrous pyrolysis experiments and open system pyromat kinetic determinations in all investigated cases open system kinetics is able to model the residual potential derived from s2 but not the respective low temperature closed system isothermal experiments the relatively detailed micro pyrolysis generation patterns obtained allow us to differentiate between primary generation and secondary cracking of different carbon number classes of hydrocarbons formation of non hydrocarbons or hydrocarbon sinks in residues can be inferred from these patterns comparison of results from low and high temperature experiments suggests that the potential of a source rock may vary according to heating history discrepancies between high and low temperature experiments may be explained in terms of competing reaction pathways these may constitute a main source of uncertainty when extrapolating bulk kinetic models into geological conditions

geothermal history and petroleum generation in the norwegian south viking graben revealed by pseudo 3d basin modelling abstract hydrocarbon exploration in the norwegian south viking graben 57 45 60 15 n began in the late 1960s and has now entered a mature phase a map based pseudo three dimensional 3d basin modelling study is performed in order to unravel regional trends in hydrocarbon generation and expulsion and to evaluate the remaining potential of this mature petroleum province generation and expulsion from all major source rock horizons in the area the draupne heather hugin and sleipner formations is simulated using a pseudo 3d model comprising 36 isochronous geological events the map based pseudo 3d model is built from 1d models combined with subsurface and source rock quality maps hydrocarbon expulsion from the middle and upper jurassic source rocks in the area occurred in two major phases the first phase lasted from palaeocene to middle miocene with peak oil and gas expulsion during the early miocene the second quaternary phase of expulsion which supplied 11 and 13 of all oil and gas respectively is related to increased subsidence rates during this period a total of 74 109 sm3 oil and 8 2 1012 sm3 gas has been expelled in the area the frigg area in the north is with 2 9 1012 sm3 gas expelled the most gas prone area and the greater balder area seems to be the most oil prone area with 17 109 sm3 oil expelled the lower syn rift section of the upper jurassic draupne formation dominated oil expulsion 54 of all expelled oil whilst the heather formation dominated gas expulsion with 37 of all gas expelled model predictions were successfully applied to explain the fill and secondary alteration history of the greater balder area norway the modelling supports the draupne formation origin of the oils in the greater balder area as well as the presence of oils deriving from multiple charge phases found in correlation studies based on the modelled cumulative volumes expelled and estimates for in place volumes in the area generation accumulation efficiencies gaes of 1 01 1 05 for oil and 9 67 12 89 for gas have been estimated for the south viking graben in light of comparisons with other petroleum systems and critical evaluation of the elements of the petroleum systems the estimated gaes should be regarded as encouraging for further exploration of the area

shale gas potential of the lower permian gufeng formation in the western area of the lower yangtze platform china abstract china is beginning to explore unconventional gas resources in the lower yangtze platform in the last two years we conducted undiscovered hydrocarbon resource assessment to investigate the geological and geochemical characteristic of the lower permian gufeng formation which is considered as one potential exploration layers in this area four outcrops and one well were used to determine the stratigraphic correlation and 40 available samples were used for an analytical investigation because of continuous changes in the sedimentary environment the shale of the gufeng formation not only includes black shale but also calcareous mudstone silicalite siliceous mudstone and carbonaceous shale the thickness of the gufeng formation is between 0 m and 200 m and it has two small depositional centers with an sw ne strike on plane the shale in the gufeng formation shows a high average toc total organic carbon content of 3 41wt based on test of 40 samples but the tocs in different tract systems have significant differences ehst early highstand systems tract average 9 85wt lhst late highstand systems tract average 0 96wt cs condensed section average 2 61wt tst transgressive systems tract average 0 76wt the shale is in the post mature stage of thermal maturity tmax temperature of maximum pyrolysis output 339 518 c and is in the dry gas window of hydrocarbon generation mean random vitrinite reflectance value ro 1 24 1 99 clay minerals dominate the mineralogy followed by quartz minerals pyrite only is found in some samples of ehst which is consistent with the presence of less anoxic conditions and lower levels of sediment dilution during sediment deposition the ehst shale of the gufeng formation which has a high content of organic carbon tentatively could be regarded as a potential shale gas exploration target in this area however because the complex multistage tectonic background could have caused gas loss the tectonic background and the hydrocarbon preservation condition must also be considered

modal composition and detrital clinopyroxene geochemistry of lithic sandstones from the new england fold belt east australia a paleozoic forearc terrane the new england fold belt of southeast australia is divided by the peel fault system into two time equivalent zones showing contrasting depositional structural and metamorphic histories these are inferred to represent a western magmatic arc frontal arc succession and an eastern subduction complex assemblage the composition of the early to middle paleozoic clastic rocks from both east and west of the peel fault system indicates derivation from an undissected volcanic arc detrital quartz is absent or present only in minor amounts and always as monocrystalline grains lithic fragments are almost exclusively volcanic and normally dominant over feldspar which is invariably plagioclase now largely albitized to the west of the fault the distribution of lathwork microlitic felsitic and vitric rock fragments as well as variation in the amount of detrital quartz indicates changes in provenance through time and two cycles of basaltic to silicic volcanic activity have been identified the composition of detrital calcic clinopyroxene grains particularly their low ti and al contents and their ti mn na ratios indicates that they crystallized mainly from subalkaline probably calc alkaline volcanic arc magmas the dominantly volcanogenic provenance of sandstone from east of the fault and the low ti content of most detrital clinopyroxene grains indicate that the volcanic chain that lay to the west of the peel fault was the most likely source for the major portion of the clastic debris in the eastern rocks however the presence of ti rich detrital clinopyroxenes identical in composition to those in the metabasalts of the subduction complex indicates that uplifted segments of the complex provided an additional sediment source

subsidence history of the tethys himalaya abstract this article reconstructs the evolution of the passive northern margin of peninsular india facing the neotethys from the earliest rifting stages in the carboniferous to final collision with the active southern margin of asia in the early eocene classical techniques of basin analysis were applied to an extensive and coherent stratigraphic data base facies analysis biostratigraphic dating and palaeoenvironmental interpretation of an over 10 km thick sedimentary succession from eight main composite sections allowed us to draw accurate sedimentation and backstripped subsidence curves and to place quantitative constraints on the palaeotectonic scenario inferred from the sedimentary record in each of the investigated composite sections three major stratigraphic gaps are consistently recognised in the rift sequence the rift unconformity mississippian the carboniferous permian hiatus largely kasimovian to asselian and the break up unconformity mid sakmarian two or even all three gaps may merge into a single hiatus spanning up to 70 ma overall gaps are associated with rift shoulder uplift which after calculation of backstripped subsidence sums up to 600 m at least in three of the investigated sections thermal subsidence and low sedimentation rates are documented by the mid permian to middle triassic drift sequence deposited while the neotethys was expanding between northern gondwana and the detached peri gondwanan blocks a marked increase in accumulation rates is recorded in the carnian norian but calculations of uniform lithospheric stretching suggest that extension was minor and associated with tectonic processes affecting distant parts of gondwana the tethys himalayan margin was uplifted around the jurassic cretaceous boundary at the onset of a major volcanic episode finally uplift exceeding in magnitude all previous events is documented by the uppermost units of the stratigraphic column deposited during the earliest stages of collision between india and asia in the latest paleocene to early eocene

predicting petroleum gravity with basin modeling new kinetic models oil api gravity predictions using published basin modeling source rock sr reaction kinetics have displayed poor matches between modeled output and field observations because these kinetic models do not predict increasing api gravities with increasing maturity ideally an sr kinetic model should use at least two liquid components of different densities which are generated and expelled from the sr such that the api gravities are a consequence of relative mixing very few available kinetic models predict apis with reasonable trends but those are either not adjustable to calibrate to field observations or do not consider sorption which is a necessary process when evaluating unconventional resources five new kinetics data sets are presented in this paper each representing a standard sr type which provide geologically reasonable api gravity trends and ranges each kinetic model uses two liquid pseudocomponents and two vapor pseudocomponents the relative ratios between the pseudocomponents at full kerogen transformation are average ratios available from public and proprietary kinetic data sets the primary generation follows published activation energies including minor shifts which allow peak generation to occur at lower activation energies for the heavier liquid pseudocomponent and at higher energies for the lighter one this systematic shift of activation energies thus results in a constant change in api gravity as primary generation progresses additional in sr sorption and secondary cracking schemes support the primary generated api gravity trends the default ranges of api gravity for the new five kinetic models represent observed averages but can be adjusted easily

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

the sandstone memory of the evolution of a triassic volcanic arc in the southern alps italy the erosion of a southern volcanic belt provided the bulk of the fine grained and moderately sorted siliciclastic detritus in the whole deltaic to lagoonal carnian upper triassic sequence of the bergamasc alps volcanic input began in the early carnian calcare metallifero bergamasco and became prominent in early middle val sabbia sandstone and late carnian times s giovanni bianco fm after an intervening period of diminished supply gorno fm the mineralogical and chemical composition of the sandstones compares closely with that of siliciclastics derived from modern pacific type magmatic arcs and it testifies to an evolution of the source rocks from andesites and dacites during the deposition of the val sabbia sandstone towards rhyodacitic ignimbrites for the s giovanni bianco fm the marked reduction in feldspars at the top of the sequence contrasts with the classical trend from undissected to dissected magmatic arc provenance and is ascribed to the progressive deepening of erosion into middle triassic felsic volcanics an increase in undulatory and polycrystalline quartz grains in the late carnian shows that the erosion did reach deeper into the crystalline roots of the arc although non volcanic detritus never exceeded 10 after a terminal pyroclastic event in middle late carnian times suggested by the sudden appearance of pumiceous vitric clasts at the top of the val sabbia sandstone the mid triassic orogenic magmatism ended and was followed by the tensional stage which led to the birth of neotethys

pore characteristics differences between clay rich and clay poor shales of the lower cambrian niutitang formation in the northern guizhou area and insights into shale gas storage mechanisms abstract to study organic matter and pore characteristics of the lower cambrian niutitang organic rich shales 166 shale samples from the niutitang formation were collected from the studied well drilled in kaiyang county in the northern guizhou area upper yangtze region all of the 166 shale cores were analysed for total organic carbon toc total sulfur ts and the stable carbon isotope of kerogen 13 c org shale samples with varying toc values were chosen for mineral composition analysis helium porosity measurement and low pressure nitrogen adsorption measurement the lower cambrian niutitang formation features high organic matter content type i oil prone organic matter ultra thick organic rich shales and an abundance of brittle minerals exhibiting favourable characteristics for the lower cambrian shale gas exploration in the upper yangtze region helium porosity measurement and low pressure nitrogen adsorption measurements were performed on selected shale samples with varying toc content in order to analyse and characterize pore characteristics significant differences in mineral composition and pore characteristics were found between clay rich and clay poor niutitang shales quartz weakly correlated with toc content in clay rich shales which contained minor biogenically contributed quartz and performed better in terms of reservoir properties than clay poor shales and exhibited higher porosity maximum nitrogen quantity adsorbed pore volume and specific surface area in clay rich shales the maximum nitrogen quantity adsorbed total pore volume and specific surface area positively correlated with toc content r 2 0 77 0 79 and 0 75 respectively the pore volume of clay rich shales was dominated by mesopores and both micropore and mesopore volume of clay rich shales correlated significantly with toc content in clay poor shales quartz positively correlated with toc content indicating biogenic contribution to quartz micropore volume and mesopore volume of clay poor shales were weakly positively correlated with toc content pore volume especially mesopore volume may be affected by the recrystallization of biogenic silica exhibiting identical micropore volume with clay rich shales but lower mesopore volume

remigration and leakage from continuous shale reservoirs insights from the sichuan basin and its periphery china shale gas in the sichuan basin and its periphery potentially plays an important role in the world shale gas industry an understanding of remigration and leakage from continuous shale reservoirs is very important for shale gas exploration especially in the sichuan basin and its periphery the shale gas accumulation models that relate to remigration and leakage were developed within the wufeng and longmaxi black shales in the jiaoshiba and the youyang blocks first a tectono sedimentary history of the wufeng and longmaxi black shales in the sichuan basin and its periphery was developed based on the published literature the history exhibits a continuous distribution of high quality wufeng and longmaxi black shale which is the foundation of the shale gas formation second the shale gas remigration accumulation model in the anticlines was clarified by using data collected from the shale gas fields in jiaoshiba block the shale gas model for the jiaoshiba block was developed on the basis of a continuous shale reservoir distribution differentiated structural deformation and a gas self sealed system third the shale gas fault failure leakage model in the fault blocks and the erosion model in the residual areas were revealed based on the shale reservoir and shale gas content heterogeneity in the youyang block these two models were validated by available data including 13 two dimensional seismic lines and 2 shale gas exploration vertical wells in the youyang block shale gas areas with high gas resource and gas production rates in the anticlines were defined by the remigration accumulation model the fault failure leakage model was used to find shale gas with limited commercial potential whereas commercial shale gas was largely lacking according to the erosion residual model the study on remigration and leakage from continuous shale reservoirs in the sichuan basin and its periphery can be used to better understand and improve the exploration efforts based on resource preservation

oil generation kinetics for organic facies with type ii and iis kerogen in the menilite shales of the polish carpathians the menilite shales oligocene of the polish carpathians are the source of low sulfur oils in the thrust belt and some high sulfur oils in the carpathian foredeep these oil occurrences indicate that the high sulfur oils in the foredeep were generated and expelled before major thrusting and the low sulfur oils in the thrust belt were generated and expelled during or after major thrusting two distinct organic facies have been observed in the menilite shales one organic facies has a high clastic sediment input and contains type ii kerogen the other organic facies has a lower clastic sediment input and contains type iis kerogen representative samples of both organic facies were used to determine kinetic parameters for immiscible oil generation by isothermal hydrous pyrolysis and s2 generation by non isothermal open system pyrolysis the derived kinetic parameters showed that timing of s2 generation was not as different between the type iis and ii kerogen based on open system pyrolysis as compared with immiscible oil generation based on hydrous pyrolysis applying these kinetic parameters to a burial history in the skole unit showed that some expelled oil would have been generated from the organic facies with type iis kerogen before major thrusting with the hydrous pyrolysis kinetic parameters but not with the open system pyrolysis kinetic parameters the inability of open system pyrolysis to determine earlier petroleum generation from type iis kerogen is attributed to the large polar rich bitumen component in s2 generation rapid loss of sulfur free radical initiators in the open system and diminished radical selectivity and rate constant differences at higher temperatures hydrous pyrolysis kinetic parameters are determined in the presence of water at lower temperatures in a closed system which allows differentiation of bitumen and oil generation interaction of free radical initiators greater radical selectivity and more distinguishable rate constants as would occur during natural maturation kinetic parameters derived from hydrous pyrolysis show good correlations with one another compensation effect and kerogen organic sulfur contents these correlations allow for indirect determination of hydrous pyrolysis kinetic parameters on the basis of the organic sulfur mole fraction of an immature type ii or iis kerogen

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

geochemical characteristics of organic rich shale upper yangtze basin implications for the late ordovician early silurian orogeny in south china abstract the tectonic sedimentary environment of the upper yangtze basin in china underwent significant changes from the late ordovician to early silurian the widely distributed shale formed during this interval has recorded key information about paleo ocean conditions analysis of major trace and rare earth elements was conducted on 135 shale samples collected from five wells in the study area the covariation of the mo u enrichment factors indicates that the upper yangtze basin in the wufeng stage was characterized by sedimentary differentiation the southern basin was dominated by a reducing bottom water environment under euxinic conditions the northern and central basins were dominated by a suboxic anoxic environment up to the early longmaxi stage the upper yangtze basin formed a relatively uniform sedimentary environment with gradually increasing oxygen content in the bottom water the paleoproductivity index indicates that marine organisms flourished in the wufeng to early longmaxi stages making an important contribution to the siliceous content in organic rich shale subsequently terrestrial siliciclastics gradually dominated analysis of paleogeography rare earth elements and weathering indicates that chuanzhong and qianzhong uplifts in the wufeng stage were the provenance area of the upper yangtze basin with a relatively high weathering degree weathering decreased in the beginning of the longmaxi stage and then gradually increased with the xuefeng uplift becoming the main provenance areas after the early longmaxi stage controlled by stress transfer from the continuous syn caledonian kwangsian orogeny in eastern south china the upper yangtze basin and xiangzhong basin were squeezed and pushed up successively the uplift separated the open shallow sea and formed a relatively limited deep water shelf environment resulting in a relatively euxinic bottom water environment which was favorable for organic matter accumulation the tectonic sedimentary evolution of the upper yangtze basin in the late ordovician to early silurian proposed in this study indicates that the formation of organic enriched shale was not only related to glacio eustatic change but also strongly controlled by tectonic activities in south china

origin and enrichment factors of natural gas from the lower silurian songkan formation in northern guizhou province south china abstract the northern guizhou area located near the southwestern margin of the yangtze block and south of the sichuan basin is a promising area for shale gas exploration and development the discovery of a natural gas accumulation in the lower silurian songkan formation in the study area is the first discovery of natural gas in this stratum in china marking an exciting breakthrough in natural gas exploration in northern guizhou area this paper presents an investigation of this accumulation using gas geochemistry including gas composition carbon and hydrogen isotopes in context with geological information available for the study area our results indicate that the natural gas accumulation in songkan formation is probably sourced from the lower silurian wufeng longmaxi shale the 13 c ch 4 values range from 33 9 to 33 2 the 13 c c 2 h 6 values range from 37 0 to 36 2 and the 2 h ch 4 values range from 157 to 144 these results indicate that the gases are of thermogenic origin and are oil derived furthermore isotopic rollovers seen in the natural gas is similar to that seen in the natural gas from the local wufeng longmaxi shale which is identified as carbon exchange at high temperature the 13 c co 2 values range from 20 8 to 17 1 suggesting that carbon dioxide was mainly generated by thermogenic processes the fracture investigation indicates that the large development of horizontal fractures in calcareous mudstone is one of the reasons for the high yield of natural gas in songkan formation the petrophysical parameters suggest that limestone with low porosity and permeability effectively prevents natural gas escaping and seals natural gas into calcareous mudstone with horizontal fractures

mesozoic and cenozoic volcanic rocks from central and southern tibet 39ar 40ar dating petrological characteristics and geodynamical significance field relations radiometric ages and mineralogical and chemical characteristics of the orogenic volcanic rocks from the lhasa block tibet are studied volcanic activity started before the deposition of the albian aptian sedimentary units takena formation and xigaze group volcanism is volumetrically limited in the northern part of the lhasa block basalts andesites and dacites are present while ignimbrites are scarce radiometric ages of these rocks range between 110 and 80 ma conversely in the southern part of the lhasa block volcanism is largely developed gangdese belt there paroxysmal activity occurred later than in the north between 60 and 50 ma lingzizong formation this volcanism is mainly represented by andesites and ignimbrites a younger episode at about 15 10 ma took place in this southern region the mineralogical and geochemical characteristics indicate that as a whole the volcanic rocks from the lhasa block belong to a calc alkaline continental margin series enriched in k20 and other incompatible elements subordinate potassic alkaline lavas are present in the northern margin of the gangdese belt some basalts exhibit a tholeiitic affinity daquin area southern region the geodynamic significance of these cenozoic volcanic rocks lies in the relative motion of india and the lhasa block after accretion of the latter to the northern qantang block a geodynamic model based on changes of the type of subduction of the indian oceanic crust beneath the lhasa block for the period 120 40 ma is proposed to account for the abundance age and magmatic affinity of the volcanic products

the kinetics of thermal degradation of individual oil generating macerals calibration with microscopical fluorescence spectrometry and bulk flow pyrolysis abstract kinetic models for petroleum generation describe petroleum formation as either a discrete set of reactions or a continuous distribution of reactions the kinetic models are normally calibrated with data from laboratory experiments this paper discusses theoretical analytical and numerical problems encountered when results of laboratory experiments are extrapolated to geological conditions an alternative approach based on geologically matured samples is presented where quantitative petrological micro fluorometric and hydrogen index data are used in multiple regression analysis to estimate transformation ratios and genetic potentials of compositionally different oil generating entities in source rocks the data are further used in combination with reconstructed time temperature histories to calculate consistent kinetic parameters for the thermal degradation of individual macerals the results both for the genetic potentials and transformation ratios are within the expected range the important aspect of the analysis is that the results were obtained by expressing the transformation ratio as a function of a fluorescence maturity parameter and hence allow increased confidence in the application of fluorescence in maturity studies

numerical simulation of pressure evolution and migration of hydraulic fracturing fluids in the shale gas reservoirs of sichuan basin china abstract one of the main environmental issues associated with hydraulic fracturing hf is the upward migration of the hf fluids from a shale reservoir to reach the shallow drinking water aquifers through preferential flow paths such as fractures or faults oversimplified model structures or arbitrary boundary conditions were used in the previous studies resulting in inaccurate results to better describe the flow and transport in fractures faults and matrix pores a dual medium model including fracture fault and matrix was established in this study to understand the evolution that occurs in reservoir pressure during hf and the long term migration of hf fluids in deep geological formations considering sichuan basin china as a case study both hf fractures and pre existing natural faults were characterized as highly permeable preferential flow channels simulation results show that the spatial distribution of pressure in shallow aquifers is mainly controlled by the topography while it is controlled by overpressure in the deep strata hf fluids were not found to contaminate the shallow groundwater throughout the simulation period even in the worst scenario a sensitivity analysis is carried out to quantify and understand the influence of a broad range of possibilities of parameters such as hf fracture reservoir properties and hf operation the results suggest that the reservoir properties and the duration over which the injection of hf fluid take place are the most important factors influencing the spatiotemporal distribution of hf moreover hf fluids are removed from the formation by the production of gas meaning that these fluids are unlikely to contaminate the shallow aquifers of the sichuan basin

hydrocarbon generation and shale gas accumulation in the longmaxi formation southern sichuan basin china abstract the gas bearing longmaxi formation fm records a complex tectonic history in which variations in structural and burial history directly effect the hydrocarbon maturation process through analysis of the tectonic burial history hydrocarbon maturity and easy r o numerical simulations we examine three areas representing the full spectrum of geological variability in the southern sichuan basin the changning area the luzhou area and the zigong area zishen well 1 following deposition of the longmaxi fm all three areas underwent five major tectonic events of subsidence and uplift showing an overall long term oscillation of the basin the longmaxi fm has undergone three major heating stages caledonian hercynian orogenesis time the high geothermal gradient field of hercynian and indosinian time approximately 200 300 ma and the yanshanian himalayan stage the high geothermal gradient stage is associated with extensive emeishan flood basalts or concealed basalts which could have played an important role in hydrocarbon maturation the maturation process can be divided into five stages caledonian hercyninan indosinian yanshanian and himalayan in the yanshan period the highest heating temperature of organic matter exceeded 200 c and the maturation level was more than 2 4 producing large amounts of natural gas which is the main accumulation period of shale gas in the longmaxi fm due to the large amount of hydrocarbon generated a large number of micropores were formed from organic matter evolution especially nanoscale pores during the middle diagenesis stage the longmaxi fm shale gas accumulation process is divided into four periods the source reservoir cap deposition period the initial accumulation period the main accumulation period and the adjustment period in the main accumulation period pyrolysis gas was dominant which was stored within the pores diagenetic fractures and structural fractures in adsorbed and free state ways forming the basic pattern of the longmaxi fm shale gas the current burial depth and structural stability of the longmaxi fm are critical to gas reservoir protection

geochemical and geological characteristics of the lower cambrian shales in the middle upper yangtze area of south china and their implication for the shale gas exploration abstract during the early cambrian the middle upper yangtze area of south china evolved to an open shelf with anoxic bottom waters prevailing in most places accumulated black shales in this area named niutitang formation qiongzhusi formation in some places thus become the prospective resources for shale gas exploration and development based on compiled petrological and organic geochemistry data and other information obtained by relevant laboratory tests and field investigation we documented regional distributional patterns of lower cambrian organic rich shales in the middle upper yangtze area according to their lateral extent thickness total organic carbon thermal maturity and burial depth this study also features the general reservoir properties of dark shales in this area together these results highlight several most favorable areas including youyang xiushan huayuan suiyang daozhen dejiang shiqian sinan yinjiang jiangkou tongren songtao and huangping shibing for shale gas exploration

molecular and carbon isotopic variation in 3 5 years shale gas production from longmaxi formation in sichuan basin china abstract a time series of produced shale gas samples from lower silurian longmaxi formation fm were collected from six production wells during 3 5 years production period from the weiyuan and changning shale gas pilots in sichuan basin china the molecular compositions and carbon isotopes of ch 4 c 2 h 6 c 3 h 8 and co 2 and the hydrogen isotope of methane were analyzed for these samples by an integrated method of gas chromatography combined with mass spectrometry the results showed that the produced shale gases are dominated by ch 4 90 1 99 3 with minor c 2 h 6 0 3 0 8 and non hydrocarbon gases and have low wetness 0 3 0 8 the non hydrocarbon gases are mainly co 2 and n 2 and trace amount of he the longmaxi shale gases display completed reversal pattern of carbon isotopic compositions with carbon number i e 13 c 1 13 c 2 13 c 3 except for wells w201 and w201 h1 with normal patterns between c 2 h 6 and c 3 h 8 i e 13 c 2 13 c 3 and it is a mixture of oil cracking gas and kerogen cracking gas at high over level of thermal maturity some co 2 13 c co2 ranging from 2 5 to 6 0 is mainly derived from the decomposition of carbonate minerals ch 4 concentration and the carbon isotopes of methane and ethane during 3 5 years shale gas production from year 2012 to 2016 displayed small fluctuations which possibly suggested that gas supply from shale matrix to fracture network after hydraulic fracturing is abundant the weiyuan shale gases show larger decrease of ch 4 content than the changning shale gases indicated more adequate supply in the changning area the difference in 13 c 1 values between horizontal and vertical wells on the same drilling site in the weiyuan pilot indicated that the vertical heterogeneity of lower silurian longmaxi shale plays an important role to shale gas production interestingly the shale gases in the weiyuan pilot display much lighter 13 c 1 34 46 to 36 82 and 13 c 2 37 59 to 41 89 values than those 13 c 1 27 18 27 27 13 c 2 33 70 34 14 in the changning pilot the difference in carbon isotopic compositions in weiyuan and changning pilots mainly attributes to mixing between varied proportion of oil cracking gas and kerogen cracking gas because of the regional heterogeneity of the longmaxi marine shale in particular amount of residual oil retained in organic matter rich shale the isotopic difference between weiyuan and changning shale gases doesn t disappear in the period about 3 5 years of shale gas development which further suggests the regional heterogeneity of retained residual oil exists in the longmaxi fm marine shale

neoproterozoic cambrian petroleum system evolution of the micang shan uplift northern sichuan basin china insights from pyrobitumen rhenium osmium geochronology and apatite fission track analysis the neoproterozoic strata of the sichuan basin are a key target for oil and gas to evaluate the hydrocarbon evolution and its relationship with tectonic events in the micang shan uplift northernmost sichuan basin we apply solid bitumen geochemistry bitumen reflectance and fluorescence and re os geochronology the geochemistry of the solid bitumen indicates that it is highly mature pyrobitumen that formed contemporaneously with dry gas generation during oil thermal cracking the pyrobitumen is enriched in both re 106 191 ppb and os 3030 5670 parts per trillion the re os isotope data imply an early jurassic date for pyrobitumen formation which coincides well with age estimates from fluid inclusion data and basin modeling the re os date for pyrobitumen formation coupled with previously presented apatite fission track aft analysis show that exhumation of the neoproterozoic strata occurred during the cretaceous in the micang shan uplift this extensive uplift led to the erosion of any potential gas reservoirs and surface exposure of bitumen bearing neoproterozoic strata in contrast the more southern and central portions of the sichuan basin have experienced less severe exhumation and as a result neoproterozoic sourced gas systems are present this study shows that through the combined application of re os and aft methodologies the timing of gas generation and subsequent erosion of any potential gas reservoirs in the micang shan uplift northern sichuan basin can be quantified moreover the re os and aft data illustrate the potential to constrain the timing of gas generation in petroleum systems worldwide

shale gas desorption behavior and carbon isotopic variations of gases from canister desorption of two sets of gas shales in south china abstract four shale samples from the lower silurian longmaxi formation and the lower cambrian shuijingtuo formation in the eastern part of chongqing sw china were subjected to canister desorption experiments at reservoir and elevated temperatures up to 90 c to investigate shale gas release behaviors and their variations in chemical and isotopic compositions of desorbed gases both the ratios of gas released at reservoir temperature to the total desorbed gas at reservoir and elevated temperatures and the desorption rates suggest that the longmaxi shale gas is more easily released than the shuijingtuo shale gas scanning electron microscope sem observation along with low temperature co2 and n2 adsorption results suggests that organic matter hosted pores with diameters of 2 100 nm are rich in the longmaxi shales whereas well developed micropores

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

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

compositions of sandstones in circum pacific subduction complexes and fore arc basins arc trench systems of the circum pacific orogenic belt contain voluminous sandstones within fore arc terranes that include complexly deformed subduction complexes and relatively undeformed fore arc basins of several types turbidites incorporated within subduction complexes include not only axially transported trench fill but also abyssal plain sediments deposited on the sea floor beyond the trench and slope basin deposits perched on the accretionary trench slope mean framework modes of circum pacific sandstone suites can be expressed adequately by the use of qfl and qmflt plots supplementary qmpk and qplvls plots depict partial modes of mineral grains alone and polycrystalline lithic fragments respectively source rocks were mainly volcanic and plutonic terranes of he circum pacific magmatic arcs although some recycled sedimentary and metasedimentary debris is also present analysis of point counts for 2 587 rocks grouped into 104 suites from california the pacific northwest southern alaska southwest japan and new zealand indicates that the characteristic fore arc sandstones display similar compositional ranges everywhere and can be termed the circum pacific volcano plutonic graywacke suite knowledge of their petrology may aid the recognition of analogous tectonic settings in the geologic past frameworks vary across a compositional spectrum that ranges chiefly from feldspatholithic sands derived mainly from volcanic cover in undissected magmatic arcs to lithofeldspathic sands derived largely from plutonic batholiths in dissected magmatic arcs quartz contents are typically intermediate and the feldspar to quartz ratio is semiconstant plagioclas is the dominant feldspar and volcanic rock fragments are commonly the most abundant lithic fragments interpretations of compositional trends within subduction complexes and adjacent fore arc basins imply that simple transverse delivery of sediment from the arc orogene to the fore arc region is not the rule instead sand evidently is distributed along subduction zones by longitudinal turbidity currents initiated at widely spaced sediment delivery points where sediment derived from tectonic culminations along the arc trench system can bypass the sediment traps of fore arc basins moreover turbidites shed from dormant or transform segments of arc orogenes are locally spread far into the ocean basin as abyssal plains which are later rafted bodily into the subduction zone finally no sedimentologic explanations of compositional contrasts across fore arc graywacke terranes can be acce ted without considering the alternative of postdepositional tectonic transport by strike slip

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

petrologic and geochemical evidence for the formation of organic rich siliceous rocks of the late permian dalong formation lower yangtze region southern china abstract black shales are economically and scientifically important because they are commonly associated with high quality hydrocarbon source rocks and metal accumulations formed during periods of abrupt environmental change organic rich siliceous rocks of the late permian dalong formation developed extensively within middle upper yangtze region western yangtze platform however the formation mechanism of its formation in the lower yangtze region eastern yangtze platform remains a subject of debate due to a lack of outcrop exposure petrologic mineralogic and geochemical data are presented for three sections of the dalong formation within the lower yangtze region geochemical ratios including v v ni v cr ni co u th and v sc suggest that the dalong formation was deposited in an oxygen poor environment the elevated concentration of mo 100 ppm further suggests that free h2s existed in the bottom water which was favorable for the accumulation of large amounts of organic matter mo toc ratios reveal that water flow in the lower yangtze basin was moderately to strongly restricted during deposition of the dalong formation flow within the upper middle parts of the yangtze basin was also restricted suggesting that northern marginal basins on the yangtze platform formed part of a single ocean during the late permian i e changhsingian cherts of the dalong formation reflect high primary productivity similar to that of modern day upwelling zones which increased the amount of organic matter these results combined with previous work suggest that the long term oxygen poor conditions during deposition of the dalong formation were caused by restricted water circulation in a unique paleogeographic environment characterized by low latitude and submarine paleo highlands such settings of low latitude characterized by tropical climate favored the growth of siliceous zooplankton in the zones with submarine paleo highlands having created topographic barriers to water circulation restricted bottom water flow and oceanic anoxia during the late permian were likely the main controls on the accumulation of organic rich rocks elevated nutrient levels caused by frequent oceanic upwelling along the western margin of the south china craton and global volcanism at this time facilitated siliceous organism productivity

pore structure characterization for the longmaxi and niutitang shales in the upper yangtze platform south china evidence from focused ion beam he ion microscopy nano computerized tomography and gas adsorption analysis abstract pore structure is of great importance in the occurrence of shale gas in this study pores in shale samples from the lower silurian longmaxi and lower cambrian niutitang shales in chongqing in the upper yangtze platform south china were examined using focused ion beam he ion microscopy fib him nano computerized tomography nano ct and gas adsorption analysis the results show that most pores in measured samples of the niutitang shale are mineral matrix pores and have poor connectivity including both intraparticle and interparticle pores organic matter pores in measured samples of the niutitang shale are rare and have small diameters in measured samples of the longmaxi shale om pores mostly macropores and large mesopores are the most abundant the nano ct results revealed that the abundance of om pores led to good pore connectivity in the longmaxi shale samples whereas the prevalence of mineral matrix pores resulted in poor connectivity in the niutitang shale samples n2 and co2 adsorption analyses showed that the mean value of micropore mesopore volumes in the niutitang and longmaxi shales samples are 0 0332 ml g and 0 0261 ml g respectively the mean values of micropores mesopores surface area in the niutitang and longmaxi shales samples are 33 84 m2 g and 32 46 m2 g respectively thus there is little difference between measured samples of the longmaxi and niutitang shales in terms of volume and surface area of micropores mesopores the equal vitrinite reflectance equal ro values of measured samples of the longmaxi shale are lower than those of the niutitang shale samples over maturity equal ro 3 resulted in a reduction of the number of pores in organic matter small pore size and poor connectivity in measured samples of the niutitang shale relatively low maturity 2

paleo ocean redox environments of the upper ordovician wufeng and the first member in lower silurian longmaxi formations in the jiaoshiba area sichuan basin a study of paleo ocean redox environments is important for understanding the deposition of black shale and has practical implications for shale gas exploration here we selected a total of 52 shal

surface deformation and tectonic background of the 2019 ms 6 0 changning earthquake sichuan basin sw china abstract the june 17 2019 ms 6 0 changning earthquake at a depth of 3 5 km struck the changning anticline fold system no active faults have been observed in the region some studies have attributed the earthquake to the regional shale gas exploitation following the earthquake we conducted a field survey to investigate co seismic surface deformation in the area and observed many surface fractures and uplifted areas our work indicated that the deformation followed a riedel shear pattern the fractures and uplifted areas represent t fractures and s extrusions respectively the observed riedel shear pattern is indicative of left lateral strike slip motion to ascertain the relationship between the riedel shear pattern and regional tectonics we investigated the trends in layer striations and fault scratches the results indicated that there were two stages in the evolution of the anticline in the first stage the principal compressive stress that dominated the original formation of the anticline trended ne sw in the second stage the regional principal compressive stress shifted to the current e w trend generating oblique motion that included reverse and left lateral components we propose that the tectonic stress field in this region had a strong bearing on the focal mechanism of the mainshock and the co seismic surface deformation both the eastward expansion of the xianshuihe area and southeastward expansion of the longmen shan have affected the current changning anticline fold system

a rock physics model for characterizing the total porosity and velocity of shale a case study in fuling area china abstract the total porosity in a shale gas reservoir is the key parameter to evaluate its potential production capability petroleum geologists have been pursuing an accurate way of predicting total porosity in shale gas reservoirs from logging curves in the fuling area near chongqing in china we use core test data and well logging data in order to establish a logging response model for porosity through the analysis of the data we found that the porosity and the p sonic p velocity have a strong correlation by combining our results with previous research i e physical rock data we establish a new model which better predicts the total porosity of a given a shale reservoir than the models established in previous research in addition to total porosity mineral composition pore pressure pore fluid type and confining pressure affect p velocity by taking a series of artificial cores as test objects and systematic analysis of total porosity mineral composition and content pore fluid type and pressure on the p velocity we establish response templates between every individual parameter and p velocity to this end we further establish a multi parameter rock physical characterization equation for the total porosity and p velocity and analyze its applicable conditions using the rich geological and geophysical data of the lower silurian series in the fuling area we gradually improve the model for the total porosity and verify the results using well logging data finally a set of accurate methods are established to predict the total porosity in shale gas reservoirs by using well logging data

india asia collision implications from the geology of the eastern karakoram the shyok tectonic belt of ladakh northwest india bridges the important geologic gap between the kohistan block of pakistan and the lhasa block of tibet the geology of the shyok tectonic belt supports the model of successive collision and accretion of gondwana fragments along the southern margin of the asian plate tectonic continuity is established between gondwana fragments of afghanistan kohistan shyok and tibet on the basis of new geologic data from the shyok tectonic belt and various plate tectonic models for the india asia collision are discussed 24 references 3 figures 1 table

chemical kinetic model of hydrocarbon generation expulsion and destruction applied to the maracaibo basin venezuela this paper describes the development and application of a compositional chemical model of hydrocarbon generation expulsion and destruction for the cretaceous la luna formation source rock of the maracaibo basin venezuela applications include both laboratory and geological settings laboratory pyrolysis experiments were used to study bulk oil generation expulsion and associated changes in composition of the kerogen extractable organic matter and expelled and unexpelled hydrocarbons the laboratory experiments were also used to determine kinetic parameters to quantitatively describe organic reactions via a computer model that also includes simulation of pressure driven primary expulsion over widely varying conditions we show that the chemical model accurately sim lates the experimental results thermal history models for wells in the maracaibo basin were used to simulate hydrocarbon generation and pore pressure development in the la luna formation and expulsion into nearby cretaceous reservoirs results of the modeling indicate that both compaction disequilibrium and organic maturation play important roles in the development of excess pore pressure in the la luna formation the model simulation of the variation of indicators such as rock eval parameters and extract and oil compositions shows generally good agreement with measurements from remaining kerogen oils and extracts recovered from the la luna formation and from nearby cretaceous reservoirs

sandstone compositions from the new england orogen eastern australia implications for tectonic setting abstract sandstones from the new england orogen are mainly quartz poor lithic to feldspathic types derived from a volcanic arc terrane the variation in detritus from lower devonian to permian in the tamworth belt records a change in the nature of volcanism the detritus becomes more felsic upwards from andesitic in the devonian to dacitic and rhyolitic in the upper carboniferous and lower permian detrital quartz content is always quartz poor but increases upwards from 1 to about 15 detrital pyroxene is common low in the sequence but in younger rocks hornblende is more common documentation of vertical changes in sandstone composition within the tamworth belt allows correlation with the virtually unfossiliferous sandstones in the tablelands complex to the east of the tamworth belt t e woolomin association is correlated with the early to middle devonian portion of the tamworth belt the sandon association with the late devonian portion and the coifs harbour association with the late carboniferous to early permian portion most sandstones from the new england orogen were thus derived from an undissected volcanic arc provenance which evolved from mafic to more felsic in composition through time the volcanic source existed for a period of more than 100 million years comparison with detrital sandstone compositions from known ancient and modern tectonic settings suggests that the sandstones were possibly deposited in a backarc basin but this has not been established unequivocally and a forearc setting is not precluded

composition of carbonate overgrowths produced on iceland spar calcite crystals buried in bahamian carbonate rich sediments abstract high magnesium calcite overgrowths were precipitated on iceland spar calcite crystals buried in bahamian sediments their composition was within the range of carbonate cements in this area the precipitation rate of the overgrowths was slower and the magnesium content higher than predicted from laboratory experiments possibly due to adsorption of organic compounds

mississippian barnett shale fort worth basin north central texas gas shale play with multi trillion cubic foot potential the mississippian barnett shale serves as source seal and reservoir to a world class unconventional natural gas accumulation in the fort worth basin of north central texas the formation is a lithologically complex interval of low permeability that requires artificial stimulation to produce at present production is mainly confined to a limited portion of the northern basin where the barnett shale is relatively thick 300 ft 92 m organic rich presentday total organic carbon 3 0 thermally mature vitrinite reflectance 1 1 and enclosed by dense limestone units able to contain induced fractures the most actively drilled area is newark east field currently the largest gas field in texas newark east is 400 mi 2 1036 km 2 in extent with more than 2340 producing wells and about 2 7 tcf of booked gas reserves cumulative gas production from barnett shale wells through 2003 was about 0 8 tcf wells in newark east field typically produce from depths of 7500 ft 2285 m at rates ranging from 0 5 to more than 4 mmcf day estimated ultimate recoveries per well range from 0 75 to as high as 7 0 bcf efforts to extend the current barnett play beyond the field limits have encountered several challenges including westward and northward increases in oil saturation and the absence of lithologic barriers to induced fracture growth patterns of oil and gas occurrence in the barnett in conjunction with maturation and burial history data indicate a complex multiphased thermal evolution with episodic expulsion of hydrocarbons and secondary cracking of primary oils to gas

an improved method for evaluating the toc content of a shale formation using the dual difference δlogr method abstract the total organic carbon toc content is the most important geochemical parameter of a shale reservoir thus the methods used for its prediction require further study the logr method is currently the only available toc calculation method based on a rigorous petrophysical model derivation however because the logr method does not consider the complex mineral compositions of shales or the effects of hole enlargement the applicability of the logr method to the evaluation of an actual shale reservoir is obviously inadequate in this paper a targeted and fundamental improvement is made to the logr method and a dual difference logr dd logr method is proposed first a dynamic theoretical relation curve is derived meaning that the logr method considers the characteristics of a variable theoretical relation curve second two logr values are calculated using both the acoustic curve with toc information and the theoretical acoustic curve without toc information and the difference between the two is used to characterize the toc content finally the radioactivity of organic matter is characterized using a log curve that excludes the influence of the clay content through the processing of actual data from the sichuan basin the dd logr method effectively improves the logr calculation accuracy in consideration of rock mineral composition variations and hole enlargement effects and the prediction results are better than those obtained using machine learning algorithms the dd logr method proposed in this paper greatly expands the applicability of the logr method and can effectively aid in the exploration and development of shale reservoirs

fluid evolution of indus basin ladakh north west himalaya india constraint from fluid inclusion and oxygen isotope thermometry fluid inclusions and oxygen isotope thermometry were carried out on quartz calcite veins of the indus basin in indus suture zone isz of northwest ladakh himalaya to constrain fluid evolution history of the basin three types of veins are identified as fault fill network and sigmoidal in the study area the fault fill veins microstructures of calcite and quartz suggest the deformation temperature of veins between 250 and 400 c and oxygen isotope thermometry provide the range between 192 and 359 c the network type veins microstructures of calcite revel deformation temperature in the range of 170 250 c and oxygen isotope thermometry indicate vein temperature range between 144 and 276 c stable isotopic values of sigmoidal and network type veins suggest the magmatic source of fluid the fault fill veins display magmatic to the marine fluid signature microstructures and isotope data set advocate the formation of veins from the wall rocks by leaching processes fluid inclusion microthermometric dataset indicates that veins were formed at a maximum depth of 20 km at 700 c the co2 fluids were trapped below 6 2 kbar at 700 c ch4 fluid was trapped at a shallower depth between 4 2 kbar 650 c and 2 3 kbar 381 c the primary aqueous fluids were trapped below 3 0 kbar up to 2 3 kbar at 594 to 382 c and secondary aqueous fluids were trapped between 2 9 and 1 5 kbar at 359 to 197 c the p t path for the entrapment defines an initial isothermal decompression itd itd is also supported by decrepitated and stretched inclusions texture as well as c shaped or hook like fluid inclusions morphology which collectively points towards fast basin uplift

physical properties of petroleum formed during maturation of lower cambrian shale in the upper yangtze platform south china as inferred from phasekinetics modelling abstract lower cambrian shale in the upper yangtze platform uyp south china is an important source rock of many conventional petroleum fields and was recently recognized as a promising unconventional shale reservoir in this paper hydrocarbon generation kinetics and petroleum physical properties were investigated using the phasekinetics approach di primio and horsfield 2006 and a cambrian shale sample from the georgina basin north territory australia nta as similar paleogeological and sedimentary environments in cambrian are found for the uyp and nta the source rock comprises type ii kerogen and belongs to an organofacies generating paraffinic naphthenic aromatic low wax oil bulk petroleum generation can be described by a single frequency factor a 8 43e 14 1 s and a dominant activation energy at 56 kcal mol which is characteristic for sulphur poor organic matter deposited in an anoxic marine environment onset transformation ratio tr 10 and end tr 90 of bulk hydrocarbon generation was calculated to take place at 120 c and 165 c respectively for an assumed average geological heating rate of 1 5 c ma based on the thermal history of a local model well onset temperature was not reached until the middle triassic 241 ma when sediments were buried more than 2000 m and basalt eruptions caused enhanced heat flows the main generation stage of primary petroleum took place during the middle late triassic and ended in the early jurassic 187 ma for burial depths exceeding 4000 m tr 90 165 c temperatures increased to more than 200 c in the middle late jurassic leading to secondary cracking of primary products hydrocarbons formed at the onset tr 10 of petroleum generation can be characterized by a gas oil ratio gor of 63 sm3 sm3 a saturation pressure psat of 101 bar and a formation volume factor bo of 1 2 m3 sm3 those parameters stay low during primary petroleum generation before 203 ma at temperatures 10 000 sm3 sm3 psat 250 bar and bo 2 0 m3 sm3 during secondary cracking starting roughly at 200 ma 152 c and 3500 m burial assuming zero expulsion the shale reservoir position within the sedimentary basin indicates that bubble point pressure was always below reservoir pressure and fluids in the shale reservoir occurred only as a single undersaturated phase throughout maturation history black oil and volatile oil phases dominated during the primary cracking period whereas wet gas and dry gas phases dominated during the secondary cracking period

petroleum generation kinetics single versus multiple heating ramp open system pyrolysis some recent publications promote one run open system pyrolysis experiments using a single heating rate ramp and fixed frequency factor to determine the petroleum generation kinetics of source rock samples because compared to multiple ramp experiments the method is faster less expensive and presumably yields similar results some one ramp pyrolysis experiments yield kinetic results similar to those from multiple ramp experiments however our data for 52 worldwide source rocks containing types i ii iis ii iii and iii kerogen illustrate that one ramp kinetics introduce the potential for significant error that can be avoided by using high quality kinetic measurements and multiple ramp experiments in which the frequency factor is optimized by the kinetic software rather than fixed at some universal value the data show that kinetic modeling based on a discrete activation energy distribution and three different pyrolysis temperature ramps closely approximates that determined from additional runs provided the three ramps span an appropriate range of heating rates for some source rocks containing well preserved kerogen and having narrow activation energy distributions both single and multiple ramp discrete models are insufficient and nucleation growth models are necessary instrument design thermocouple size or orientation and sample weight likely influence the acceptable upper limit of pyrolysis heating rate caution is needed for ramps of 30 50 c min which can cause temperature errors due to impaired heat transfer between the oven sample and thermocouple compound volatility may inhibit pyrolyzate yield at the lowest heating rates depending on the effectiveness of the gas sweep we recommend at least three pyrolysis ramps that span at least a 20 fold variation of comparatively lower rates such as 1 5 and 25 c min the product of heating rate and sample size should not exceed 100 mg c min our results do not address the more fundamental questions of whether kinetic models based on multiple ramp open system pyrolysis are mechanistically appropriate for use in basin simulators or whether petroleum migration through the kerogen network rather than cracking of organic matter represents the rate limiting step in expulsion

the influence of partial hydrocarbon saturation on porosity and permeability in a palaeogene lacustrine shale hosted oil system of the bohai bay basin eastern china abstract palaeogene calcareous 40 carbonate mudstones ro from 0 56 to 0 88 from the bohai bay basin were studied by combined petrographical geochemical and petrophysical analysis in order to assess and quantify the pore space pore filling and its influence on gas transport capacity toc contents ranged from 1 44 to 5 12 and porosities he determined by helium pycnometry from 1 3 to 6 4 bitumen filled porosity s1 was estimated to range between 0 3 and 2 0 based on rock eval s1 values and an assumed bitumen density of 0 90 g cm3 the true total porosity total he s1 amounts to 1 9 8 5 the in situ oil saturation so was estimated to range between 25 and 52 with two samples l69 1b and l69 2 having relatively high oil saturation 71 and 91 the conductivity of the remaining open pore space was measured on three samples with different orientations and oil saturations from 17 to 24 the effective klinkenberg corrected gas permeability coefficients range between 63 and 2000 ndarcy and permeability is highest parallel to bedding upon loading from 10 to 40 mpa confining pressure the intrinsic permeability coefficients decreased by one order of magnitude revealing a relatively high exponential stress sensitivity coefficient 0 069 mpa 1 and much lower zero stress permeability 1 416 10 6 md than most gas shales this could be due to pore plugging by ductile bitumen

effect of lithofacies on pore structure and new insights into pore preserving mechanisms of the over mature qiongzhusi marine shales in lower cambrian of the southern sichuan basin china abstract research on shale pore structures has furthered the understanding of shale oil and gas accumulation however understanding of mechanisms of shale lithofacies that affect pore structures remains poor restricting evaluations of marine shale and accurate estimations of gas content this study focuses on the over mature qiongzhusi marine shales in lower cambrian of the southern sichuan basin a series of laboratory experiments were conducted on core samples including x ray diffraction xrd scanning electron microscopy sem low pressure gas adsorption n2 and co2 and high pressure mercury intrusion porosimetry mip xrd results show that four main types of shale lithofacies are found in the qiongzhusi formation according to the content of siliceous carbonate and clay minerals including silica rich argillaceous shale lithofacies sal argillaceous rich siliceous shale lithofacies asl carbonate argillaceous containing siliceous shale lithofacies c asl and argillaceous siliceous mixed shale lithofacies a sml sem images reveal that three kinds of pores within the shale samples organic matter intergranular and dissolved pores with the majority being slit like and narrow slit like pores silica rich argillaceous shale lithofacies exhibit the highest pore surface areas and volumes while other shale lithofacies and carbonate clay containing siliceous shale lithofacies exhibit relatively lower pore surface areas and volumes it can be inferred that silica rich argillaceous shale lithofacies facilitate shale gas storage and flow both toc and clay mineral content are more positively correlated with the microscopic pore structure parameters of micropores than that of mesopores and thus further interpreted as two dominant factors controlling the development and distribution of micropores a relatively high quartz content in qiongzhusi shale of lower cambrian are conductive to contribute a large macropore volume but most importantly the development of rigid frameworks established by authigenic quartz pyrite and clay minerals are favorable for the preservation of primary organic matter micropores by providing effective grain supporters clay rich siliceous shale could be deemed as one of the most typical lithofacies types displaying this unique pore preserving mechanism shale lithofacies with different toc and mineral compositions exhibit distinct differences in pore structures

principles of geochemical prospect appraisal our current understanding of the geochemical processes responsible for the creation of commercial accumulations of oil and gas can be reduced to simple rules and equations to allow the petroleum geologist to use geochemistry to estimate before drilling the likely volumes and compositions of oil and gas delivered to the trap in most sedimentary basins oil is expelled from source rocks between 120 and 150 c whereas most gas and gas condensate are released between 150 and 230 c when the initial potential of source rocks exceeds 10kg mt oil expulsion efficiencies are between 60 and 90 expelled oil and gas migrate as petroleum rich phases driven by fluid potential gradients most flow is laterally updip in beds with effective horizontal permeabilities greater than 1 md in lower permeability rocks the petroleum fluids move vertically up or down along the path of least resistance i e the most permeable or thinnest beds separating them from a high permeability lateral carrier bed the residual saturations of petroleum left behind along the migration pathway are of the order of a few percent of the porosity geochemical analysis of source rocks helps determine the yields and compositions of petroleum fluids expelled in the catchment area of a prospect these fluid masses are converted to volumes from knowledge of the phase relations and densities of petroleum fluids evaluation of the total volume of rock through which the petroleum potentially can migrate and the mean porosity of the rocks that constitute the migration pathway allow migration losses to be assessed these losses constrain both the range of migration of petroleum fluids away from the mature source rock and the volumes of petroleum remaining for entrapment in the prospect

metagenetic methane generation in gas shales i screening protocols using immature samples abstract the gas generative potential of organic matter is one key parameter for the calculation of total gas in place gip when evaluating thermogenic shale gas plays having first demonstrated that late gas forming structures are present in coals of anthracite rank 2 r0 we go on to examine other rocks at the immature stage of maturity and report on how to recognise which might generate significant amounts of late dry gas at geologic temperatures well in excess of 200 c in the zone of metagenesis r0 2 0 i e subsequent to primary and secondary gas generation by thermal cracking of kerogen or retained oil such a distinction could clearly be of major value when assessing risks and pinning down sweet spots a large selection 51 samples of source rocks i e shales and coals stemming from different depositional environments and containing various types of organic matter which contribute to the formation of petroleum in putative gas shales were investigated using open and closed system pyrolysis methods for the characterisation of kerogen type molecular structure and late gas generative behaviour a novel rapid closed system pyrolysis method which consists of heating crushed whole rock samples in mssv tubes from 200 c to 2 different end temperatures 560 c 700 c at 2 c min provides the basis for a newly proposed approach to discriminate between source rocks with low high or intermediate late gas potential it is noteworthy that late gas potential goes largely unnoticed when only open system pyrolysis screening methods are used high late gas potentials seem to be mainly associated with heterogeneous admixtures or structures in terrestrially influenced in some cases marine type iii and type ii iii coals and shales aromatic and or phenolic signatures are therefore indicative of the possible presence of elevated late gas potential at high maturities high temperature methane was calculated to potentially contribute an additional 10 40 mg g toc which would equal up to 30 of the total initial primary petroleum potential in many cases low late gas potentials are associated with homogeneous paraffinic organic matter of aquatic lacustrine and marine origin source rocks exhibiting intermediate late gas potentials might generate up to 20 mg g toc late dry gas and seem to be associated with heterogeneous marine source rocks containing algal or bacterial derived precursor structures of high aromaticity or with aquatic organic matter containing only minor amounts of aromatic phenolic higher land plant material

pmod a flexible model of oil and gas generation cracking and expulsion a new computer program pmod is used to develop and test a wide variety of global models of varied complexity for the generation and destruction of hydrocarbons from petroleum source rocks chemical reaction models are constructed interactively by supplying the empirical formula of the reactants and products desired reactions and reaction constraints pmod calculates stoichiometric coefficients that conserve elemental balance the chemical reactions are integrated into two compaction and bulk flow expulsion models in order to predict the amounts and compositions of products expelled from the source rock under geological conditions a variety of published and unpublished experiments are used to show when various model types are required and to derive the parameters for the various models this exercise provides a good means to compare the strengths and weaknesses of the various models and provides guidance on the types of information needed to calibrate them chemical properties calculated by pmod for all models include apparent rock eval parameters and other common geochemical measurements

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

kinetics of oil group type generation and expulsion an integrated application to dongying depression bohai bay basin china pyrolysis of two kerogens isolated from the e2 3s 3 3 and e2 3s 1 4 source rocks in the niuzhuang sag dongying depression bohai bay basin china was performed in a confined system the products were extracted with solvent and separated using micro column chromatography into group type fractions saturates aromatics resins and asphaltenes with the kerogen residue in each case undergoing swelling with a variety of solvents the kinetics for generation and retention of crude oil and its group type fractions from the kerogens were studied and the kinetic parameters applied to modeling generation and retention of crude oil and its fractions from the e2 3s 3 3 and e2 3s 1 4 source rocks on the basis of burial and thermal history of the niuzhuang sag the results show that the normal oil was generated at about 4 26 ma and 24 85 ma ago but expelled at about 3 96 ma and 17 46 ma ago respectively from e2 3s 3 3 and e2 3s 1 4 source rocks the current proportions of the expelled saturates aromatics and nsos are about 60 15 and 25 respectively

factors controlling organic matter accumulation in the upper ordovician lower silurian organic rich shale on the northeast margin of the upper yangtze platform evidence from petrographic and geochemical proxies abstract organic rich shales are widespread in the upper ordovician lower silurian wufeng longmaxi formations on the northeastern margin of the upper yangtze platform and these shales have been recognized to be the hydrocarbon source rocks and shale gas reservoirs with the greatest development potential in china however organic matter accumulation in these shales needs further research especially in the areas which experienced an extensive upwelling and volcanism here this work integrates detailed petrographic and geochemical proxies namely redox sensitive trace elements rstes and ratios of si al ti al from two ordovician silurian sections on the northeast margin of upper yangtze platform in order to understand the depositional environment and identify the major factors controlling the organic matter accumulation during the ordovician silurian transition data of si al and ti al ratios indicate that the deposition of black gray siliceous mudstones in the lower wufeng formation commenced with a transgression triggered by the boda warming event which led to a reduced detrital input based on rstes the black carbonaceous shales of the upper wufeng formation are organic rich owing to an elevated primary productivity caused by seasonal upwelling driven by the vigorous thermohaline circulation abundant nutrients supplied by the post glacial transgression and a mass biotic recovery of marine microorganisms stimulated productivity and further strengthened the depletion of oxygen in the water column which lead to high concentrations of organic matter in lower longmaxi formation although the water column conditions were not conducive to the accumulation of organic matter it was possible that the increased productivity from upwelling resulted in relatively high organic matter contents in the middle longmaxi formation the rstes especially cd mo co mn reveal that the organic matter accumulation of the wufeng longmaxi formation during ordovician silurian transition may have been primarily controlled by the preservation conditions and also influenced by the marine primary productivity and the detrital input

characteristics of microorganisms and origin of organic matter in wufeng formation and longmaxi formation in sichuan basin south china abstract to evaluate the characteristics of microorganisms and the origin of organic matter of the wufeng formation and longmaxi formation wf lmx in sichuan basin south china the type and number of microorganisms were determined in this study using scanning electron microscope sem microphotographs and microbial extraction the contribution of various microorganisms to organic matter was analyzed in combination with the data of biomarkers and total organic carbon toc it can be deduced from the paleogeography and pristine phytane pr ph ratio that the microorganisms of wf lmx resided in 60 m 200 m deep shelf with anoxic bottom water from sem microphotographs and microbial microscopy analysis it was demonstrated that the microorganisms in the wf lmx can be divided into 3 types planktonic algae mainly including acritarchs and green algae fungi and benthic algae acritarchs were the most common microorganisms in the wf lmx with the average relative content of 60 5 the average relative contents of benthic algae fungi and green algae were 17 6 18 0 and 3 9 respectively since the acritarchs and green algae in the wufeng formation and the longmaxi formation basically belong to planktonic algae the relative content of planktonic algae in them is about 64 4 the strata of wf lmx can be divided into 3 sections based on the distribution characteristics of various microorganisms the relative content of acritarchs gradually decreased upwards while that of benthic algae gradually increased the multiple proxies of biomarkers proved that the planktonic algae was the main source of organic matter in the wf lmx combining the statistical data of microorganisms it was considered that the organic matter in wf lmx was mainly derived from acritarchs which might be the components of planktonic algae the fungi had a significant contribution to the organic matter in organic rich layers toc 2 0 rather than in organic poor layers while green algae and benthic algae made little contribution to the organic matters in wf lmx

practical kinetic modeling of petroleum generation and expulsion abstract models for petroleum generation used by the industry are often limited by a sub optimal laboratory pyrolysis methods for studying hydrocarbon generation b over simple models of petroleum generation c inappropriate mathematical methods to derive kinetic parameters by fitting laboratory data d primitive models of primary migration expulsion and its coupling with petroleum generation and e insufficient use of subsurface data to constrain the models problems a b and c lead to forced compensation effects between the activation energies and frequency factors of reaction kinetics that are wholly artificial and which yield poor extrapolations to geological conditions simple switch or adsorption models of expulsion are insufficient to describe the residence time of species in source rocks yet the residence time controls the thermal stresses to which the species are subjected for cracking to lighter species the shellgenex model for petroleum generation and expulsion has been developed since 1988 in this multi species model the rate limiting step of primary migration is treated as the slow diffusion of the petroleum through the kerogen itself other key aspects of the model are the reaction and transport behaviour of the heavy compounds the role of free radicals in the cracking kinetics of hydrocarbon species in the model and the evolving free volume of the kerogen the last of these has a particularly strong effect on the primary migration of the generated petroleum molecules some implications of this model are that a compositions of expelled petroleum vary more strongly than the standard parallel reaction model suggests and b expulsion is not immediately extinguished by waning temperatures and pressures but continues with decreasing gor of the expelled petroleum and increasing density of the expelled oil

reservoir evaluation of the lower silurian longmaxi formation shale gas in the southern sichuan basin of china abstract the lower silurian longmaxi formation the palaeozoic is organic rich black shale in the southern sichuan basin the yangtze plate of china this study analyses the lateral extent and thickness burial depth total organic carbon content and thermal maturity of the longmaxi formation black shale as the key features of the shale gas reservoir the thickness of the black shale ranges from 10 to 170 m the thickest reservoir is located in changning naxi yongchuan region the toc of the shale at the bottom of the formation 50 m thickness is above 2 0 the lateral distribution of toc varies with the lateral distribution of thickness with the maximum toc in the gongxian luzhou yongchuan region the burial depth ranges from 2000 to 4500 m the shale is thermally over mature the evaluation of reservoir characteristics indicates that the longmaxi formation has conditions appropriate for shale gas accumulation and thus resource potential in the southern sichuan basin of china the objective of this preliminary evaluation of the reservoir characteristics is to locate potential areas favourable for exploration the most favourable areas are defined here as those where the thickness of black shale is more than 100 m and the burial depth is less than 3000 m these cover approximately 12 600 km 2 the most favourable areas which cover an area of approximately 5100 km 2 are located in the northeast luzhou region

nano scale pore structure and fractal dimension of organic rich wufeng longmaxi shale from jiaoshiba area sichuan basin investigations using fe sem gas adsorption and helium pycnometry abstract much attention have been recently paid to the upper ordovician wufeng shale o3w and lower silurian longmaxi shale s1l in the jiaoshiba area of sichuan basin which is now the largest producing shale gas field in china field emission scanning electron microscopy fe sem low pressure gas n2 and co2 adsorption helium pycnometry x ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in o3w s1l shale formation in the jiaoshiba area fe sem images show that organic matter om pores are dominant in the organic rich samples and these pores are often irregular bubble like elliptical and faveolate in shape while in organic poor samples limited and isolated interparticle interp intraparticle intrap and om pores are observed reversed s shaped isotherms obtained from nitrogen adsorption are type and hysteresis loops indicate that the shape of micropore in the samples is slit or plate like bet surface areas and total pore volume vary from 12 2 to 27 1 m2 g and from 1 8 10 2 to 2 9 10 2 cm3 g with an average of 19 5 m2 g and 2 3 10 2 cm3 g respectively adsorption volume from both n2 and co2 adsorption increases with respect to toc contents porosities obtained from helium porosimetry are comparable with these from gas co2 and n2 adsorption in o3w s1l shale however porosity determined by quantitative fe sem analysis is much smaller which is mainly related to limited resolution and the small areas of investigation based on the frenkel halsey hill fhh model of low pressure n2 adsorption fractal dimensions of the pores varied from 2 737 to 2 823 relationships between pore structure parameters and toc content mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores samples with higher toc content higher quartz content and lower clay content tend to contain more heterogeneous micropores resulting in higher fractal dimensions and more complicated pore structure in shales therefore fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in o3w s1l shale

applying isotopic geochemical proxy for gas content prediction of longmaxi shale in the sichuan basin china abstract numerous studies have been conducted on the isotopic geochemical characteristics of shale gas however a systematic study of the relationship between the isotopic geochemical characteristics and gas content has not been addressed to date in this study we investigated the geochemical and isotopic compositions of shale gas samples and the gas content of the lower silurian longmaxi marine shale in the huangjinba area southern sichuan basin china in addition we analyzed the quantitative relationship between the geochemical parameters and the gas content the longmaxi shale gas is a dry gas with a low wetness 0 12 0 67 dominated by methane 89 49 99 00 with a small amount of ethane 0 11 0 61 the average values of 13cmethane 13cethane and 13cpropane are 29 8 35 0 and 33 2 characterized by a partial isotopic reversal 13cmethane 13cpropane 13cethane with a maturity level ro 2 30 2 51 the total gas content of the longmaxi shale varies widely from 0 42 m3 t to 3 88 m3 t correlation analyses revealed that the ethane isotope 13cethane and the magnitude of isotopic reversal 13cmethane 13cethane exhibit strong correlations with the total gas content and the free gas content this study demonstrates that carbon isotopic reversal of shale gas largely depends on the secondary cracking and thermal maturity and residual liquid hydrocarbons content are important factors affecting the magnitude of carbon isotopic reversal based on the quantitative study conducted in this paper we provide a new proxy for predicting the gas content of high maturity shale using an isotopic method