controlling functions of hydrothermal activity to shale gas content taking lower cambrian in xiuwu basin as an example abstract lower cambrian is the main target intervals of marine shale gas exploration and exploitation in china shale gas bearing varies greatly among different intervals and how to determine favorable targets is an important problem to be solved in this article taking jiangye 1 well in xiuwu basin as an example according to core description logging data analysis section authentication mineral and elemental composition analysis bulk and effective porosity tests total organic carbon toc and gas content tests lower cambrian wangyinpu and guanyintang formations have been studied results show that toc content is the dominating factors for effective porosity and gas bearing content redox conditions and bioproductivity control the enrichment of sedimentary organic matter the water reducibility of sq1 varies greatly of sq2 and sq3 is generally strong reducibility of all the three sequences is stronger than those of sq4 and sq5 the bioproductivity of sq3 is the highest and little difference in the bioproductivity has been found between sq1 and sq2 both of which show higher values than sq4 and sq5 except for terrigenous siliceous minerals large amounts of hydrothermal origin siliceous minerals exist in lower cambrian wangyinpu and guanyintang formations specifically siliceous origin of sq1 varies greatly part of intervals are terrigeneous origin and part of intervals are hydrothermal origin most siliceous minerals of sq2 and sq3 are hydrothermal origin whose content takes up 10 30 compared with sq2 and sq3 content of hydrothermal origin siliceous minerals drops in sq4 and terrigeneous siliceous content increases siliceous minerals of sq5 originate from normal terrigeneous clastic deposition hydrothermal activities are helpful for the increase of reducibility of seawater and enhancing bioproductivity the sedimentary organic matter abundance is thus controlled and the enrichment of shale gas is further affected hydrothermal activities are generally developed in the early cambrian in south china the intervals deposited when frequent hydrothermal activities occurred are exactly favorable targets of shale gas in lower cambrian

heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin of china this study characterizes the vertical heterogeneity of the lower silurian longmaxi marine shale in the southeast sichuan basin based on core description thin sections observation geological chemistry data interrogation and qemscan image analysis lithofacies associations mineralogy graptolite species occurrence rock fabrics as well as toc total organic carbon and gas content change noticeably and regularly in the lower silurian longmaxi marine shale within sequence stratigraphic framework lithofacies associations mainly include in situ graptolite rich and siliceous shale in the transgressive systems tract tst micro offsite graptolite rich shale and shale interbedded with siltstone laminaes in the early highstand systems tract ehst and micro offsite graptolite rich and carbonate rich shale in the late highstand systems tract lhst the tst has a greater abundance of diplogratus than ehst and lhst and has a lesser level of monograptus which is conversely higher in the ehst and lhst the tst shale is silica rich while the lhst shale is generally clay rich the ehst shale is more balanced in its silica and clay content than the tst and lhst are the sedimentary structure and fabric of shale shows that shale is homogenous in the tst with laminaes well developed in the ehst but decreasing in the lhst toc and gas content are highest in the tst and decrease upward the tst with high toc high gas content high brittle minerals silica rich and anoxic suboxic to dysoxic sedimentary environment is the most potential shale gas target interval in the study area our research also shows that the toc mainly controls shale gas accumulation and that the redox conditions mainly control the preservation of organic matter the silica also plays a significant role in shale gas content due to its contribution to hydraulic fracturing finally the study proposes a depositional and heterogeneity model for the lower silurian longmaxi marine shale in the study area

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

palynological analysis of the late ordovician early silurian black shales in south china provides new insights for the investigation of pore systems in shale gas reservoirs abstract the late ordovician wufeng and early silurian lungmachi formations are primary targets for shale gas exploration in the southeastern marginal area of the sichuan basin southwest china in this research different groups of micro fossils large numbers of taxonomically unrelated organic and inorganic walled fossil groups from the two formations were analyzed in order to investigate their pore characters under the evaluation of shale gas reservoirs a large number of biological autologous micro nano pores in radiolarians sponge spicules acritarchs conodonts chitinozoans and scolecodonts were analyzed the results show that most pores are densely and randomly distributed with honeycomb or irregular shapes although the samples are over mature and were deeply buried micro fossils remain in a large number of biological micro nano pores pore diameter varies from 20 to 4000 nm but differs among micro fossil groups the widely distributed siliceous micro fossils such as radiolarians and sponge spicules could enhance the brittleness of shales they may promote the development of natural fractures during diagenesis or artificial fractures during stimulation when fractures are connected with micro nano pores in the shale they could provide effective storage space and improve the overall connectivity in most of the analyzed shale samples micro fossils show positive correlation with high toc strata considering the importance of micro fossils and their pores in the perspective of hydrocarbon generation connectivity accumulation and production of shale gas we suggest that micro fossil pores should be included in the classification of pore systems

barnett shale gas production fort worth basin issues and discussion newark east barnett shale field fort worth basin texas is currently the most productive gas field in texas in terms of daily production and is growing at an annual rate of more than 10 however despite the fact that the barnett play has been studied intensely by very capable geologists and engineers from several companies over a period of many years there continues to be several misunderstandings concerning fundamental factors controlling the success of the barnett play of north texas barnett gas production is poorer in areas near faults and structural flexures anticlines and synclines fractures which are most abundant in these structural settings are detrimental to barnett production open natural fractures are rare in the barnett and have little or nothing to do with barnett productivity in areas where barnett shale is thermally mature with respect to gas generation it is slightly overpressured about 0 52 psi ft 11 76 kpa m limestone beds within the barnett formation are the product of debris flows that originated on a carbonate shelf to the north of the present basin center it appears that the barnett can be used as an exploration model for other basins especially analogous basins of the ouachita trend the history of the development of the barnett reservoir in north texas provides an excellent example of how persistence can lead to success in nonconventional gas plays

geologic structure controls on initial productions of lower silurian longmaxi shale in south china abstract the lower silurian longmaxi shale is the most important marine shale gas play in south china several hundred wells have been drilled to date of which more than 150 wells have obtained high initial production ip outside of the sichuan basin however wells drilled in the lower silurian longmaxi shale do not reach flow rates that are commercial developing an understanding of the key factors controlling the ips of longmaxi shale is important in screening shale resource plays in this study the toc thermal maturity porosity and gas saturation data obtained from longmaxi shale of southeastern chongqing area outside sichuan basin have been compared with that of sichuan basin the results of this study show that the shales encountered display similar properties including toc 2 thermal maturity 2 5 3 5 eqro and total porosity 3 6 a good correlation between ips and pressure coefficient suggest that the free gas content of gas shale controls on ips porosity and gas saturation of gas shale are the main factors to control its free gas volume the gas saturations in longmaxi shale from high initial production wells in sichuan basin mainly range between 50 and 90 however that of shale in the southeastern chongqing area are decreased to 10 30 this is the directly reason for low ips of wells the contrasting gas saturation of longmaxi shale between sichuan basin and the adjacent fold thrust belts are interpreted to reflect in part differences in sealed condition of fluid system intensive tectonic movements caused the exhumation faulting and fracturing that reduced or destroyed the sealed ability of shale fluid system which are the major factors for enhancing water saturation decreasing fluid pressure and ips finally the study proposes several most favorable zones for longmaxi shale gas exploration and development

pore structure of the graptolite derived om in the longmaxi shale southeastern upper yangtze region china abstract the lower silurian longmaxi shale in the southeastern upper yangtze region which has been the main target for shale gas exploration and production in china is black marine organic rich shale and rich in graptolites graptolites usually only periderms preserved in shales are important organic component of the longmaxi shale however the pore structure of graptolite periderms and its contribution to gas storage has not yet been studied before a combination of optical microscopy for identification and mark of graptolite and scanning electron microscope sem for pore observations were conducted for the longamxi shale samples results show that pores are anisotropic developed in the longmaxi graptolite periderms and greatly associated with their fine structure micrometer sized fractures and spindle shaped pores between cortical fibrils in the cortical bandage are greatly developed at section parallel to the bedding while they are rare at section perpendicular to the bedding besides numerous sapropel detritus rich in nanometer sized pores are discretely distributed in the shale though graptolite periderms are low porosity from sem image analysis microfractures and elongated pores along the graptolite periderm wall may still make the graptolite an interconnected system together with the discrete porous sapropel detritus in shale these graptolite derived organic matter om may form an interconnected organic pore system in the shale the difference of pore development observed in graptolite periderms and sapropel detritus also give us new insight for the organic pore heterogeneity study the om composition their fine structure and orientation in the rock may be important factors controlling om pore development the combination of identifying om type under optical microscopy and pores observation under sem for may be an effective method to study the om pore development especially in shale that contain more om

genetic types of carbonate shoal reservoirs in the middle triassic of the sichuan basin sw china abstract carbonate shoal reservoirs of the middle triassic leikoupo formation in the sichuan basin were investigated for potential gas resources the carbonate shoal reservoirs can be divided on the basis of their formation mechanism into residual intergranular pore karst further divided into syndepositional burial and epigenetic karstification types dolomitized and composite reservoirs residual intergranular pores and dissolved pores are the main reservoir spaces in the residual intergranular pore reservoirs isolated intragranular corroded pores and moldic pores are the main reservoir spaces in syndepositional karstification reservoirs the main spaces in burial karstification reservoirs are dissolved pores and holes and pores and caves on various scales are the main reservoir spaces of epigenetic karstification reservoirs intercrystal pores and intercrystal solution pores are the main reservoir spaces of dolomitized reservoirs composite reservoirs are characterized by a variety of reservoir spaces with pores holes and fissures high quality shoal reservoirs were formed by superposition of carbonate shoals and constructive diagenetic modification preservation of residual intergranular pores was crucial for development of residual intergranular pore reservoirs platform interior micro highlands relative declines in sea level and rainfall controlled the development of syndepositional karstification reservoirs dissolution by unsaturated acidic fluids pre existing pores and pore throats and the direction of corrosive fluid flow were important for burial karstification reservoirs epigenetic karstification reservoirs formed as a result of significant sea level drops or tectonic movement dolomitized reservoirs formed in shoals affected by dolomitization caused by evaporation of seawater or that occurred during burial composite shoal reservoirs were formed by two or more processes

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

geochemical characteristics and origin of natural gas from wufeng longmaxi shales of the fuling gas field sichuan basin china abstract as the first giant shale gas field in china the fuling gas field has recently been regarded as one of the most important regions for natural gas exploration and production in the sichuan basin however the origin of natural gas from upper ordovician wufeng and the bottom of lower silurian longmaxi wl shales in the fuling gas field is poorly understood to limit a comprehensive understanding of gas generation accumulation and exploration in this work based on molecular and stable carbon isotopic composition of a total of 24 gas samples from five shale gas wells in the fuling field we analyzed the geochemical characteristics and gas origin and discussed the cause for the geochemical anomalies carbon isotopic reversals molecular composition results show that gases from the fuling gas field are dry and mainly composed of methane 97 9 98 9 with a very low level of ethane c2h6 propane c3h8 and non hydrocarbon gases mainly co2 and n2 these dry gases are classified as oil associated gas and mainly derived from secondary cracking due to the lack of gas samples across a maturation gradient from immature to late mature the wl gases in the fuling field show an unclear evolution trend between the 13c2 and wetness values however all these samples are located in the isotopic reversal zone carbon isotopes of gaseous alkanes clearly display full isotopic reversals 13c1 13c2 13c3 which is indicative of a relatively high thermal maturity and consistent with the measured vitrinite reflectance and modeled values 3 0 ro the observed complete carbon isotopic reversals in the wl gases are caused by a combination of several mechanisms in which isotope exchange at high temperature is the primary controlling factor other secondary factors include rayleigh type fractionation of c2h6 and c3h8 secondary cracking and gas diffusion mixing of gases at different thermal maturity levels

heterogeneity of intergranular intraparticle and organic pores in longmaxi shale in sichuan basin south china evidence from sem digital images and fractal and multifractal geometries abstract previous studies have determined many types of pores in shale such as organic pores inorganic pores and microfractures in this study pores are classified as intergranular intraparticle and organic pores based on the location of their occurrence the heterogeneities of the three pore types and their effects on the occurrence of shale gas which is of utmost practical importance for shale gas exploration and development are discussed in this study the three types of pores are quantitatively characterized using fractal and multifractal methods the mean fractal dimension and mean width of the multifractal spectrum of these pores are found to be different i e 1 5985 and 1 665 for intraparticle pores 1 5869 and 1 475 for intergranular pores and 1 6 and 1 3725 for organic pores intraparticle pores have the highest heterogeneity intergranular pores have intermediate heterogeneity and organic pores have the lowest heterogeneity sem images show that organic pores have good connectivity homogeneous distribution and small range of aperture change but have the lowest heterogeneity even where pores are abundant thus they provide the largest shale gas occurrence space in contrast intergranular pores are less abundant have lower connectivity and have higher heterogeneity than organic pores thereby providing a relatively smaller shale gas occurrence space finally intraparticle pores are the least abundant and possess the poorest connectivity largest range of aperture change and highest heterogeneity of the three pore types thereby providing the smallest shale gas occurrence space we conclude that organic pores are crucial to the occurrence of shale gas and can provide a new index for the evaluation of shale gas exploration and development

thickness of the magnetic crust of mars 1 to estimate the thickness of the magnetic crust of mars six observational magnetic spectra are fitted with the theoretical spectrum expected from a novel bimodal distribution of magnetic sources observational spectra differ for each comes from a different map or model of variously selected and analyzed mars global surveyor magnetometer electron reflectometer measurements of the vector magnetic field around mars the new theoretical spectrum represents fields from both compact sources and extended laterally correlated sources on a spherical shell so the estimated shell depth can now be doubled to obtain layer thickness this typical magnetic crustal thickness is put at 47 8 8 4 km the extensive sources are enormous typically 650 km across and account for over half the magnetic energy at low degrees there is some indication that these sources are relatively shallow but the typical area remains about 330 000 km2 granted such extended sources represent magnetization of mars ancient crust in a core source field dominated by a reversing areocentric paleodipole each one arguably formed during a single polarity chron how did such vast regions of magnetic crust form a survey of many eligible mechanisms suggests magnetization of cooling igneous rock at minimal rates of about 1 to 0 1 km3 a during superchrons of order 15 to 150 ma long

palynology organic geochemistry and carbon isotope analysis of a latest ordovician through silurian clastic succession from borehole tt1 ghadamis basin southern tunisia north africa palaeoenvironmental interpretation abstract palynological and palynofacies analyses combined with organic carbon isotope measurements have been performed on terminal ordovician through silurian clastic sediments from the north african margin of gondwana southern tunisia a first carbon isotopic signal 13corg from gondwanan silurian sedimentary sequences is presented showing interesting correlation with existing coeval isotopic curves from other areas changes in lithology palynofacies characteristics palynomorph diversity carbon isotope developments and organic geochemistry parameters appear to be all causally linked and to reflect changes in palaeoceanographic conditions in particular the detailed chronostratigraphic correlation and the observed similarities in patterns of carbon isotopic developments and palyno and litho facies changes through the study section has permitted to identify the supposedly global earliest wenlock ireviken event and late ludlow lau event isotopic excursions for the first time in high latitude gondwana this confirms that these excursions were linked to global changes in the oceanic system the present results suggest that from rhuddanian to early wenlock times an extended period of black shale deposition occurred over the north african gondwanan margin progressively transgressing from basin palaeodepressions to basin palaeohighs palynofacies and organic geochemistry support a coastal upwelling promoted productivity increase during this interval associated to a decrease in diversity of the marine microplanktonic communities the earliest wenlock strong positive isotopic shift appears associated with this protracted period of massive black shale deposition and thus of organic carbon burial on continental platforms located in high latitude settings this could well explain the apparent paradox between excessive carbonate deposition simultaneous to a carbon isotopic shift towards lighter values observed in low palaeolatitude localities laurentia and baltica the strong distinct isotope excursion occurring in late ludlow times is possibly linked to the well know lau event evidence for extensive organic carbon burial is lacking to explain this strong excursion some significant changes in the marine palynomorph communities are recorded in connection to the increase in stable isotope values 13corg additionally a strong correlation between abundance of terrestrially derived palynomorphs miospores and 13corg development is recorded which seems to support increased clastic input from a terrestrial source

investigation of methane sorption of overmature wufeng longmaxi shale in the jiaoshiba area eastern sichuan basin china abstract in china shale gas of production capacity 203 000 m3 per day has been identified in well jy1 in the upper ordovician wufeng formation shale o3w and the lower silurian longmaxi formation shale s1l jiaoshiba area sichuan basin however the adsorbed gas capacity and the relative ratio between free gas and adsorbed gas are unknown in the jiaoshiba area and this is important for further shale gas exploration and development and different adsorption models need to be calibrated very well to praise the sorption capacity the samples were obtained from the well jy1 sorption isotherm experiments were performed at a range of pressures up to 17 mpa and temperatures up to 90 c to determine the effects of toc moisture and clay minerals on methane adsorption capacity the methane maxima adsorbed capacity values have a clear positive relationship with toc clay content displays a weak correlation with methane adsorbed amounts normalized to toc indicating that clay minerals are a minor contributor to shale adsorption capacity moisture reduces methane sorption capacity by around 20 both the supercritical dubinin radushkevich sdr based and the langmuir based excess adsorption models are used to fit measured adsorption isotherms most of the methane adsorption phase density values fitted by both models are greater than the density of liquid phase methane at its boiling points 424 mg cm3 for the langmuir based model a fixed adsorption density of 424 or 373 mg cm3 was used in fitting the experimental data which will result in higher maximum adsorbed capacity values for the sdr based model maxima adsorbed capacity values remain stable and have nothing to do with sorption phase density

composition and growth history of surficial and buried manganese nodules in the penrhyn basin southwestern pacific abstract a comparative study of occurrence and composition of hydrogenetic manganese nodules and their relation to sediment lithology were carried out on material from the penrhyn basin in the southwestern pacific the regional distribution of the nodules and compositional variations within nodules are closely correlated to the sedimentary history of the basin radiochemical and fossil data indicate that the nodules started to grow after the initiation of sea floor spreading in cretaceous time or later initially co poor nodules grew on pelagic clay sediments as a result of continuous uplifting although some of them were left behind within the sediment old generation through paleogene time more abundant co rich nodules followed during or after a hiatus through to the present and formed the large manganese nodule provinces these young generation encrusted old small nodules stiff pelagic clay sediments hydrothermal manganese deposits and fossils aabw played an important role in the formation of the young generation of nodules it is inferred that the aabw flows through the aitutaki passage into the penrhyn basin and runs along the western margin of the basin scattered thick young sediments in places in the survey area have prevented the growth of nodules

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

geologic characteristics of hydrocarbon bearing marine transitional and lacustrine shales in china abstract organic rich shales spanning in age from pre cambrian to quaternary were widely deposited in china this paper elaborates the geology and unique characteristics of emerging and potential hydrocarbon bearing shales in china the pre cambrian sinian doushantuo to silurian black marine shales in the intra shelf low to slope environments were accumulated in south china and tarim platform in northwest china these marine shales with maturity ro of 1 3 5 are in dry gas window during carboniferous to permian the shales associated with coal and sandstones were mainly deposited in coastal swamp transitional setting in north china ne china nw china and yangtze platform in south china these transitional shales are generally clay rich and are potential gas bearing reservoirs since middle permian the lacustrine shales with total carbon content toc up to 30 and ro mainly in oil window are widely distributed in all the producing basins in china the lacustrine shales usually have more clay mineral content than marine shales and are characterized by rapid facies change and are interbedded with carbonates and sandstone the high quality shale reservoir with high toc hydrocarbon content and brittle minerals content is usually located at transgressive systems tract tst to early highstand systems tract ehst interval deposited in anoxic depositional setting recent commercial shale gas production from the silurian longmaxi marine shale in the southeastern sichuan basin preliminary tight oil production associated with lacustrine hydrocarbon bearing shale intervals and hydrocarbon shows from many other shales have proven the hydrocarbon bearing shales in china are emerging and potential shale gas and tight shale oil plays tectonic movements could have breached the early hydrocarbon accumulation in shales and tectonically stable areas are suggested to be favorable prospects for china shale plays exploration and production

haynesville and bossier mudrocks a facies and sequence stratigraphic investigation east texas and louisiana usa abstract upper jurassic haynesville and bossier shale gas plays of the northwestern gulf of mexico gom basin produce from organic rich marine transgressive to highstand mudrocks within mixed carbonate clastic depositional systems modern wireline log suites from 200 deep wells were used for detailed correlations and 10 cores throughout the upper kimmeridgian to lower tithonian basin were incorporated into detailed facies stratigraphic and lithologic analyses the haynesville shale lies within a 2nd order transgressive systems tract tst that encompasses back stepping ramp carbonates proximal and marine shales distal below a maximum flooding surface mfs this shale onlaps retrogradational carbonates and basement highs and is capped by the 2nd order mfs bossier shales and local sandstones prograde basinward above the haynesville shale and downlap the 2nd order mfs they grade upward and updip into the thick highstand systems tract hst fluvio deltaic sandstones of the cotton valley group distally organic rich facies developed in restricted bossier environments creating another productive gas shale opportunity several preexisting basement highs in the south and carbonate platforms in the northwest and west restrict and partition the basin thus influencing deposition of highly organic versus nonorganic and siliciclastic dominated versus carbonate dominated lithologies haynesville and bossier shales each compose three upward coarsening cycles that probably represent 3rd order sequences within the larger 2nd order tst and early hst respectively most of the three bossier 3rd order cycles are dominated by varying amounts of siliciclastics deposition of the haynesville mudrocks occurred below storm wave base under mostly dysoxic conditionsm allowing settlement of benthic bivalve communities and bioturbating organisms and oscillating periodically to more anoxic conditions on the seafloor however most of the sparse faunae found in these mudrocks are of planktonic origin bossier mudrocks exhibited more oxygenated and clastic rich lithologies related to progradation of the clastic shoreline and sea level highstand knowledge of lithologic stratigraphic geochemical and faunal variations across mudrock basins needs to be detailed so that shale gas basins might be successfully explored

understanding geophysical responses of shale gas plays unconventional resources such as shale gas are becoming increasingly important exploration and production targets to understand the geophysical responses of shale gas plays we use a rock physics relationship which is constrained with geology and formation evaluation analysis to calculate effective properties such as impedance and vp vs numerical studies suggest that in situ rock para meters such as mineral composition e g clay quartz and calcite and toc as well as the interaction among them can significantly influence the geophysical responses of the organic rich rocks thus providing the basis for the geophysical characterization of shale gas plays

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

grain assemblages and strong diagenetic overprinting in siliceous mudrocks barnett shale mississippian fort worth basin texas porosity permeability and total organic carbon toc in a heterogeneous suite of 21 high maturity samples vitrinite reflectance 1 52 2 15 from the barnett shale in the eastern fort worth basin display few correlations with parameters of rock texture fabric and composition these factors being mostly obscured by the effects of a protracted history of diagenesis diagenesis in these rocks includes mechanical and chemical modifications that occurred across a wide range of burial conditions compaction and cementation have mostly destroyed primary intergranular porosity the porosity average 5 vol by gas research institute helium porosimetry and pore size 8 nm median pore throat diameter are reduced to a degree such that pores are difficult to detect even by imaging ar ion milled surfaces with a field emission scanning electron microscope the existing porosity that can be imaged is mostly secondary and is localized dominantly within organic particulate debris and solid bitumen the grain assemblage is highly modified by replacement a weak pattern of correlation survives between bulk rock properties and the ratio of extrabasinal to intrabasinal sources of siliciclastic debris higher porosity permeability and toc are observed in samples representing the extreme end members of mixing between extrabasinal siliciclastic sediment and intrabasinal derived biosiliceous debris reservoir quality in these rocks is neither more strongly nor more simply related to variations in primary texture and composition because the interrelationships between texture and composition are complex and importantly the diagenetic overprint is too strong

small scale 5 0 m vertical heterogeneity in mudstones implications for high resolution stratigraphy in siliciclastic mudstone successions 48 mudstone samples from the peterborough member oxford clay formation have been analysed to determine the small scale vertical and lateral lithofacies variability in this succession the samples were collected every 0 15 m from saxon and king9s dyke brickpits whittlesey peterborough uk over a short vertical interval 15 m the sampled interval spans the obductum to the grossouvrei subzones of the callovian upper jurassic lithofacies present were described using combined field logging optical and backscattered electron optical techniques the succession predominantly comprises silt rich mudstones with subordinate clay rich mudstones shell beds and shell pavements the individual units are variously composed of detrital clay quartz pyrite calcite with minor apatite kaolinite and glauconite in some units millimetre scale upward fining couplets are present elsewhere the original bedding structures have been destroyed by bioturbation comparison of successive thin sections reveals that upward coarsening is present on a metre scale and that shell enriched units are located close to the tops of these upward shoaling units comparison of samples collected laterally on a 0 01 1 0 m scale from the same level 3 0 m below the top of bed 14 indicates that there is lateral lithofacies variability the small scale 0 001 m couplets are interpreted to be beds deposited by waning flow currents significant breaks between these depositional events allowed a dysaerobic infauna to colonize the sediment the metre scale upward coarsening intervals which are capped by shell enriched units are interpreted to be parasequences the observed small scale lateral lithofacies variability is interpreted to be a product of small but significant vertical miscorrelation errors rather that systematic lateral facies changes these data suggest that producing reliable bed scale lateral correlations over distances of more than 1 km in this and successions like it will be very difficult

lithofacies and sequence stratigraphy of the barnett shale in east central fort worth basin texas ten barnett shale lithofacies have been recognized in a 223 ft 68 m long core from johnson county texas eight of these lithofacies match those previously identified in the main producing area of the newark east barnett shale field in the northern part of the fort worth basin but two new lithofacies have been identified in this core resedimented spiculitic mudstone lithofacies and lag deposits both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits the recognition of cyclical stacking patterns of the lithofacies condensed sections css and transgressive surfaces of erosion were the keys to establishing the sequence stratigraphic framework in these fine grained rocks which consists of seven stratigraphic intervals in the lower barnett shale and nine stratigraphic intervals in the upper barnett shale spectral gamma ray uranium and thorium logs aided in this objective and are recommended for future sequence stratigraphic studies of these and other shales the sequence stratigraphic framework reveals that the lower barnett shale in this area was deposited mainly in a low energy relatively deep water environment somewhat far from a terrigenous source area which probably lies to the northwest by contrast the upper barnett shale was deposited in an oxygenated shallower water environment which had a source area from the west and southwest sides of the basin the higher frequency of sea level fluctuation during development of the upper barnett shale most probably indicates periodic tectonic activity perhaps associated with a structural high that was susceptible to sea level fluctuations alternatively it could have resulted from the onset of glaciations in gondwanaland during this time this higher frequency may indicate that the upper barnett is chesterian in age because cyclicity was higher than during the osagean and meramecian stages if so there may be more high frequency cycles than recognized in this core siliceous sponge spicules are more common in this core than in more northerly cores so more brittle facies might prevail in the southern part of the fort worth basin high gamma ray log responses which are caused by a high total organic carbon and or in situ phosphate minerals are commonly found in css and can be used for regional correlations however high gamma ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement correlation of the barnett stratigraphic intervals now provides a north to southeast stratigraphic framework along the fort worth basin relative hydrocarbon potential rhp is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions we recommend continued testing and use of the rhp parameter for high frequency sequence stratigraphic analysis of unconventional gas shales

organic matter hosted pore system in the wufeng longmaxi o3w s11 shale jiaoshiba area eastern sichuan basin china abstract the first commercial shale gas with the capability to produce 203 000 cubic meters per day were discovered in the wufeng longmaxi o 3 w s 1 l shale namely the upper ordovician wufeng shale o 3 w and the lower silurian longmaxi shale s 1 l of well jy1 jiaoshiba area eastern sichuan basin china in this study fe sem co 2 and n 2 sorption and micp were used to characterize the pore morphology type size and specific surface area of the wufeng longmaxi shale we focused our research on well jy1 to establish a standard well cross section to allow comparison with well studied gas shales such as barnett marcellus kimmeridge clay and others fe sem visible mineral pore sizes range from 4 nm to 3416 nm with an average of 118 nm within the wufeng longmaxi shale om hosted pore sizes vary from 5 nm to 1021 nm with an average of 68 nm within the wufeng longmaxi shale micropore volumes vary from 0 0048 cm 3 g to 0 0078 cm 3 g with an average of 0 0059 cm 3 g mesopore volumes range from 0 0108 cm 3 g to 0 0166 cm 3 g with an average of 0 0139 cm 3 g macropore volumes range from 0 00005 cm 3 g to 0 00274 cm 3 g with an average of 0 00108 cm 3 g and surface areas range from 22 05 m 2 g to 36 37 m 2 g with an average of 27 68 m 2 g the average pore diameters of wufeng longmaxi shales range from 5 31 nm to 7 40 nm toc has a significant effect on bulk shale porosity porosity measured by fe sem ranges from 0 46 to 1 54 but covers only a small fraction of the shale total porosity as the fe sem detection limit is in a m range the majority of shale pore space pores 2 and n 2 adsorption and have an obvious relationship with the toc therefore the wufeng longmaxi shale has a predominantly organic matter pore system

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

mudstone lithofacies in the kimmeridge clay formation wessex basin southern england implications for the origin and controls of the distribution of mudstones abstract lithofacies analysis has been undertaken on a suite of apparently monotonous organic rich mudstones from the upper jurassic kimmeridge clay formation kcf in the wessex basin southern england using a combination of hand specimen description whole rock geochemistry optical petrography and electron optical petrography five lithofacies have been identified these are clay rich mudstones silt rich mudstones nannoplankton rich mudstones laminated mudstones and concretionary carbonates these facies can be distinguished from one another on the basis of physical sedimentary structures and the relative proportions of allochthonous autochthonous and diagenetic components in each all five of the kcf lithofacies studied were deposited in a marine shelf environment below fair weather wave base but in relatively shallow water close to storm wave base deposition occurred in regions where sand and other coarse clastic allochthonous debris were not being supplied and the bottom waters varied from oxic to anoxic the main factors influencing the development of the five facies were distance from source area primary productivity bottom water anoxia absolute bathymetry clastic dilution and local sediment accumulation rates specifically the clay rich mudstones were deposited in regions farthest down the sediment transport paths commonly in areas by passed by the main sediment supply and beneath surface waters of relatively low primary productivity in contrast the silt rich mudstones were deposited in more proximal areas closer to the source of the sediment in regions where surface productivity and sediment accumulation rates were much higher the nannoplankton rich mudstones accumulated beneath regions where productivity in the surface water layers was fairly high dominated by coccolithophoroid production and the supply of clastic sediment was insufficient to significantly dilute the autochthonous fraction of the sediment unlike the other facies laminated mudstones were deposited in areas where the bottom waters were anoxic surface productivity was enhanced and local sediment accumulation rates were high the concretionary carbonates were precipitated by diagenetic processes in areas where sediment accumulation rates were very low these facies descriptions have enabled a detailed sedimentological study of the kimmeridge clay formation to relate depositional and diagenetic processes directly to the facies present thereby allowing classical facies analyses to be undertaken on apparently homogeneous mudstone successions

noble gas isotopic variations and geological implication of longmaxi shale gas in sichuan basin china the large difference in carbon isotopic compositions of shale gases from the lower silurian longmaxi formation marine organic rich shales between changning and weiyuan areas in sichuan basin china is a still debate issue in this study 30 produced shale gas samples were collected during 3 years production period and analyzed for noble gas he ne and ar abundances and isotopic compositions to reveal the origin and variation causes of shale gases the results show that the longmaxi shale gases show low 3he 4he and 20ne 22ne and varied but high 21ne 22ne and 40ar 36ar ratios the weiyuan shale gases are characterized by low 3he 4he high 40ar 36ar ratios and varied 4he and 40ar abundances and a large increase in 40ar contents and a slight decrease in 40ar 36ar ratios display during 3 years shale gas production period from jan 2014 to jun 2016 whereas the changning shale gases are characterized by low and varied 3he 4he ratios and high 4he and 40ar abundances and small fluctuations in 40ar contents and 40ar 36ar ratios exhibit during 3 years production period in addition the shale gases produced from horizontal wells in the weiyuan area possessed higher 40ar and 40ar 36ar ratio than that those from vertical wells at same well site the noble gas isotopic compositions and variation of longmaxi shale gases suggested that they are originated mainly from crust air saturated fluid asf and radiogenic accumulation the variation of 40ar and 4he contents during shale gas production mainly reflects the degree of shale gas source supply from mineral matrix to fracture network and the greater increases in 40ar and 4he contents with production time show less abundant shale gas supply therefore the increase trend of 40ar contents with shale gas production time in the weiyuan area during 3 years production period possibly suggests less adequate shale gas supply in contrast the uniform or nearly constant of 40ar content through production time in the changing area indicates abundant supply of shale gas sources from mineral matrix resulting in less production decline variation in 4he and 40ar contents through shale gas production time could be sensitive indicators of abundant or depleted shale gas source supply

a sequence stratigraphic framework for the upper devonian woodford shale permian basin west texas criteria for recognizing stratigraphic sequences are well established on continental margins but more challenging to apply in basinal settings we report an investigation of the upper devonian woodford shale permian basin west texas based on a set of four long cores identifying sea level cycles and stratigraphic sequences in an organic rich shale the woodford shale is dominated by organic rich mudstone sharply overlain by a bioturbated organic poor mudstone that is consistent with a second order eustatic sea level fall interbedded with the organic rich mudstone are carbonate beds chert beds and radiolarian laminae all interpreted as sediment gravity flow deposits bundles of interbedded mudstone and carbonate beds alternate with intervals of organic rich mudstone and thin radiolaria rich laminae defining a 5 10 m 16 33 ft thick third order cyclicity the former are interpreted to represent highstand systems tracts whereas the latter are interpreted as representing falling stage lowstand and transgressive systems tracts carbonate beds predominate in the lower woodford section associated with highstand shedding at a second order scale chert beds predominate in the upper woodford section responding to the second order lowstand additional variability is introduced by geographic position wells nearest the western margin of the basin have the greatest concentration of carbonate beds caused by proximity to a carbonate platform a well near the southern margin has the greatest concentration of chert beds resulting from shedding of biogenic silica from a southern source a well in the basin center has little chert and carbonate here third order sea level cycles were primarily reflected in the stratigraphic distribution of radiolarian rich laminae

non connected pores of the longmaxi shale in southern sichuan basin of china abstract the characteristics of non connected pores of four longmaxi shale samples from the southern sichuan basin of china were investigated from the studies of pore size distribution psd pore volumes pore types using helium pycnometry gas injection porosimetry gip and gri gas research institute method nuclear magnetic resonance nmr nuclear magnetic resonance cryoporometry nmrc and spontaneous water and oil imbibition experiments gri porosity on particle sizes less than 5 mm sample and a 2 mpa helium injection pressure provides information on the total porosity including both non connected and connected pores gip porosity using core plugs only measures connected pores which extend to the surface of the sample accessible by helium so the difference between gri and gip porosities is used to estimate the volumes of non connected pores and the volumes of non connected pores accounts for 17 5 40 3 of the total pore volume for nmrc test results total pore volume increases with sample size decrease and the great difference of pore volume with a pore diameter range from 5 nm to 31 nm between small cylinder sample and 0 15 0 075 mm crushed sample is caused by non connected pores opened with a decrease of length for cubic samples the increase in volume and rate of oil imbibition is greater than that of water imbibition indicating that the non connected pores are considered to be mainly oil wet in addition the percentage of non connected pores has a good correlation with toc total organic carbon content therefore this evidence implies that non connected pores are mainly within the organic matter nmr tests at different drying temperatures and a nmrc experiment provide a quantitative classification of the shale pore system which indicates that the exploitable pore diameters are larger than 4 25 nm so non connected pores with a diameter of 5 31 nm could be effectively exploited if connected by fracturing the more the non connected pores are opened the better the pore connectivity of shale reservoir will be with a less possibility of water blocking in the process of shale gas development attention should be paid to the interaction between fracturing fluid and rock components in order to release more non connected pores therefore to increase shale gas extraction efficiency more effort should be directed towards identifying natural and creating induced porosity

wettability and connectivity of overmature shales in the fuling gas field sichuan basin china the fuling gas field in sichuan basin china has produced greater than 1 5 1010 m3 0 53 tcf of natural gas from overmature upper ordovician wufeng and lower silurian longmaxi shales to systemically investigate the characteristics of wettability and connectivity and to understand the underlying causes of production behavior we study five samples of wufeng and longmaxi shales with different total organic carbon contents and mineral compositions complementary approaches include mercury intrusion capillary pressure micp contact angle measurement spontaneous imbibition and saturated diffusion and tracer both nonsorbing and sorbing migration mapped via laser ablation inductively coupled plasma mass spectrometry according to measured contact angles and imbibition tests conducted on aqueous deionized water and brine and oleic n decane phases wufeng and longmaxi shales are strongly oil wet and moderately strong water wet the lower boundary of estimated permeability obtained from n decane imbibition can reach 137 nd which is higher than the geometric mean permeability derived from the micp method 5 5 68 8 nd effective diffusion coefficients of the wufeng and longmaxi shales are in the range of 10 13 m2 s 1 1 10 12 ft2 s tests of imbibition and saturated diffusion using tracer containing brine show that concentrations of nanometer sized tracers decrease rapidly a factor of 10 over a migration distance of a few millimeters from the sample edge suggesting the presence of poorly edge connected water wet pores sparsely connected hydrophilic pores mixed wettability and highly restricted pathways collectively contribute to the limited migration of nano sized tracers which probably results in the production behavior of initial steep decline and low overall recovery in the fuling gas field

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

depositional controls on mineral assemblage and organic matter accumulation of upper ordovician lower silurian mudstones in northwestern guizhou area china abstract the control of depositional conditions on sedimentary records spanning the ordovician wufeng silurian longmaxi successions on the yangtze platform is not fully understood due to a lack of high resolution faices analysis this study aims to build a regional depositional model of this stratigraphic interval to reveal the fundamental controls on the mineral assemblage and organic matter om accumulation vertical lithofacies variability of two continuous cores in northwestern guizhou area south china was analyzed at high resolution by roqscan an automated mineralogy tool and field emission scanning electron microscope fe sem imaging based on multiscale sedimentary structure mineral composition total organic carbon toc content and geochemical characteristics seven lithofacies were identified and interpreted as four facies associations fa a d to characterize the spatio temporal variation in these sedimentary environments the deep siliceous shelf fa a is the richest in toc content and biogenetic quartz attributed to the strong anaerobic watermass minimal terrestrial flux and enhanced organic productivity during two global transgressions the middle mixed shelf fa b has moderate toc and mixed minerals resulting from reworking processes during a fall of sea level caused by regional uplifts although the primary organic productivity was promoted by increased volcanic ash fall dilution due to increased terrestrial inputs made om difficult to accumulate the shallow muddy shelf fa c and the shallow silty shelf fa d were not favorable for om accumulations because of the low organic productivity strong oxygenated watermass and high detrital dilution through long term sea level drops the facies attributes of the target mudstones were remarkably influenced by regional tectonic eustasy in addition to global glacio eustasy

climate and tectonic driven deposition of sandwiched continental shale units new insights from petrology geochemistry and integrated provenance analyses the western sichuan subsiding basin southwest china abstract how the depositional setting efficiently governs the characteristic sandwiched continental shale units remains uncertain which restricts an integrated assessment of organic rich fluvio lacustrine shale reservoirs and accurate estimation of potential natural gas resources here we present new results from petrological observations element geochemical fingerprinting and integrated analyses of heavy mineral basinal subsidence history and sandstone stratum ratio on typical and terrigenous sandwiched like depositional systems of the targeted upper triassic xujiahe formation in the western sichuan subsiding bain southwest china in view of the representative and environment sensitive indices we suggest that passive continental margin and continental island arc dominated by granite to granodiorite source are the major tectonic settings of the provenance and both a more warm humid climate characterized by intensified chemical weathering conditions and a calm tectonically quiescent setting are identified as two major drivers forcing the accumulation and preservation of organic matter in organic rich continental shale units finally a comprehensive depositional model is established for providing new insights into the linkage between palaeoclimatic conditions tectonic pulses and terrigenous clastic sedimentation both the cyclic palaeoclimate fluctuations and episodic tectonic activities are believed to have exerted a very considerable force on development of the unique sandwiched like stratigraphic framework and the coupling interactions between the tectono climatic evolution and fine grained sedimentation are thus also stressed

organic carbon deposition and coastal upwelling at mid latitude during the upper ordovician late katian a case study from the welsh basin uk a lack of stratigraphical sedimentological and geochemical data for sediment accumulation rates and indicators of productivity and anoxia means that causative models for ancient black shales are largely inferred from modern settings coastal upwelling has been suggested as a general hypothesis for ordovician black shale deposition within the iapetus ocean but has not been directly tested despite anchizone metamorphism we utilize a suite of geological and geochemical environmental proxy data toc wt 13corg ba al p to elucidate the mechanism for the origin of a single grey black shale cycle within the upper katian succession of the welsh basin here we interpret organic carbon oc rich deposition to be suggestive of a period of high photic productivity higher toc wt with 12c and ba enrichment comparable to high productivity events in modern coastal upwelling systems productivity proxy values are consistent with those from margins where sedimentation rates are high e g gulf of california inter bedded grey shales have low toc wt more positive 13corg and marginally lower ba and are interpreted as low productivity events thalassinoides planolites and chondrites ichnofacies indicate changing seafloor oxygen levels these show predominantly dysoxic conditions even during the deposition of oc poor grey shales during an oc rich laminated hemipelagite event oxygen levels declined at the sea floor before the deposition of the oc rich layers full anoxia was established early on in the deposition of oc rich layers and the return to more oxic conditions was rapid though fluctuating and coincident with the return of grey shale deposition this pattern suggests oc accumulation at the seafloor resulted from a complex interaction of productivity and preservation none of the widely used trace element redox proxies are reliable in anchizone metamorphic rocks climate sensitive detrital proxies k al and ti al indicate arid temperate conditions in the basin hinterland during the deposition of the oc rich layers the welsh basin was situated on the southern margin of the iapetus ocean in 30 s beneath the prevailing se trade winds we interpret the occurrence of oc rich laminated hemipelagite events to represent the intensification of upwelling prior to the hirnantian glaciation possibly having resulted from a strengthening of the trade winds associated with stepped changes in ice volume and a more arid local climate

paleo environmental cyclicity in the early silurian yangtze sea south china tectonic or glacio eustatic control abstract the yangtze sea of the south china craton experienced strong environmental perturbations during the first 5 6 myr of the silurian the lower silurian lungmachi formation in the jiaoye 1 drillcore chongqing china records three sea level cycles stratigraphic sequences characterized by rapid deepening at the base of each cycle followed by slow shallowing each deepening event was associated with shifts toward higher marine productivity more intensely reducing bottomwater conditions reduced watermass restriction lower detrital input and enhanced siliciclastic weathering intensity we infer control by glacio eustasy in which deglacial sea level rises and concurrent climatic warming triggered the observed environmental changes shallowing was associated with renewed glaciation and characterized by the opposite set of conditions the results of this study thus provide evidence in support of continued continental glaciation during the early silurian i e following the termination of the major end ordovician hirnantian glaciation the study core also exhibits a long term shallowing trend through the entire lower silurian the origin of which may have been tectono epeirogenic uplift of the south china craton during the kwangsian orogeny

effect of lithofacies on the pore system of over mature longmaxi shale in the jiaoshiba area sichuan basin china abstract ten longmaxi shale samples were collected from the jiaoshiba area china where 5 billion cm 3 year of shale gas is produced the samples were evaluated to characterize the pores of various shale lithofacies three shale lithofacies were determined in the jiaoshiba area sichuan basin china based on the shale mineral components namely siliceous lithofacies sl argillaceous lithofacies al and mixed lithofacies ml field emission scanning electron microscopy fe sem which was performed under high and low voltages gri porosity and carbon dioxide and nitrogen adsorptions were used to investigate the bulk shale porosity pore type pore size pore morphology and pore volume among the lithofacies lithofacies affects the shale total organic carbon toc bulk shale porosity pore size shape and volume sl and ml contain high porosity high toc abundant organic matter om hosted pores and high om porosity whereas al contains few om pores and has low toc and low porosity in the same lithofacies samples with various toc values exhibit different pore morphologies for sl the low toc sample has a round and elliptical om pore forms whereas the high toc samples show linear and narrow pore shapes that are probably associated with gas expulsion in ml the higher toc is related to spherical or near spherical om pores whereas the om pore shape collapses in the low toc shale therefore lithofacies affect the shale reservoir and the characteristic and evolution of om pores should be considered as constraints in shale lithofacies in sl sections with a higher toc value are prime targets despite the high expulsion efficiency which does not affect the enrichment and high yield of the shale gas sections of ml and low toc sl should be considered as potential targets because of higher om porosity and low expulsion efficiency whereas sections of al engender risk in exploration and development of shale gas

main factors controlling marine shale gas enrichment and high yield wells in south china a case study of the fuling shale gas field abstract the marine shale in south china is characterized by multiple layers a wide distribution and a large amount of resources however the characterization of the enrichment degree of marine shale gas and the main factors affecting the enrichment and high yield wells are still unclear which seriously affects the process of shale gas exploration and development in south china we integrated a large amount of drilling data core analysis data seismic data as well as gas testing results from fuling shale gas field to study the shale gas bearing properties the results suggest that any single parameter is insufficient to accurately characterize the gas bearing properties consequently we propose to integrate multiple parameters including total hydrocarbon values gas content gas saturation porosity pore diameters formation pressure coefficient and resistivity to comprehensively evaluate shale gas content and determine the origins of shale gas enrichment for the lower section of wufeng longmaxi formation in the fuling shale gas field we infer that the depositional environment and shale reservoir characteristic are the major factors affecting the stratigraphic variation of shale gas enrichment the differences of structural deformation and uplift and erosion in the later period are the main factors leading to differential enrichment in the lateral direction in factors affecting high yield well the completion parameters such as the lateral placement and lateral length of horizontal wells are the major factors affecting the test production

geochemical and petrographic characteristics of wufeng longmaxi shales jiaoshiba area southwest china implications for organic matter differential accumulation abstract the organic matter rich shales in wufeng longmaxi formation have been considered to be a high quality source rock and a main shale gas producer in southern china as the material basis of shale gas the organic matter content in shales exhibits a notable vertical difference in the jiaoshiba area of fulin shale gas field this study integrated detailed geochemical analysis and sedimentary observations to investigate organic matter enrichment and depletion mechanism three intervals are identified by organic matter contents and their according variations six major lithofacies are identified based on mineral composition x ray diffraction xrd analyses microscopic observations and focused ion beam scanning electron microscopy fib sem data geochemical redox proxies mo ef u ef v cr and corg p indicate that organic matter rich shales of wufeng and bottom longmaxi formation are deposited in anoxic conditions whereas organic matter lean shales of the middle to top longmaxi formation are deposited in oxic environment this pattern is influenced by both worldwide marine transgression and regional tectonic movement the productivity proxies p al cu al ni al sio2 bio indicate that the organic matter rich wufeng longmaxi shales were deposited under moderate to high surficial primary productivity increasing terrigenous influxes dominated organic matter dilution and may have been promoted by regional tectonic uplift the organic matter enrichment or depletion mechanisms in each unit are controlled by different geological events enrichment was controlled by multiple reasons including both global and regional factors whereas depletion was mainly dominated by regional tectonic uplift additionally the sequence stratigraphic boundaries coincide with organic matter shifting interfaces indicating that high resolution sequence stratigraphy of fine grained sediments may have a certain effect on optimal reservoir predication conversely boundaries of toc and geochemical proxies may also help to subdivide sequence boundaries

non uniform subsidence and its control on the temporal spatial evolution of the black shale of the early silurian longmaxi formation in the western yangtze block south china abstract the ordovician silurian transition was a significant period when an obvious variation occurred worldwide in terms of tectonics climate oceans paleontology and sedimentology here we use stratigraphic forward modeling constrained by paleobiota paleobathymetry sedimentology and geochemistry to study the tectonic subsidence history of the early silurian in the western yangtze block south china numerical modeling suggests that the tectonic subsidence was not uniform during the deposition of the early silurian black shale of the longmaxi formation with acceleration of tectonic subsidence during the later regression period furthermore the subsidence rate at this time was at least three times that during the early transgression period this acceleration resulted from the collision between the yangtze block and the southeastern cathaysia block which affected the tectonic subsidence and the heterogeneity of the black shale the results may provide quantitative implications for the reconstruction of the paleoenvironment the evolution of paleobiota the temporal spatial distribution of the black shale and the mechanism of block assemblage in south china

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

complex rotation of maximum horizontal stress in the wufeng longmaxi shale on the eastern margin of the sichuan basin china implications for predicting natural fractures abstract the in situ stress state of the eastern margin of the sichuan basin where there is a complicated fault zone is poorly understood this study offers vital insights into the in situ stress state based on information from 17 wellbores in the wufeng longmaxi shale near the eastern boundary fault i e the qiyueshan fault of the sichuan basin china drilling induced tensile fractures and borehole breakouts revealed a decrease in the angle between the shmax maximum horizontal stress orientation and fault strike when the wellbores are close to the damage zone of the qiyueshan fault this stress rotation may be caused by the lateral contrast in the poisson s ratio between the country rock and damage zone of the qiyueshan fault a high angle between the shmax orientation and fault strike also appeared in the individual fault blocks of the qiyueshan fault as a result of local stress concentration the higher magnitudes of horizontal stresses indicate stronger lateral compression in the qiyueshan fault zone owing to the lateral compression of a sandwich consisting of a high e young s modulus roof and low e shale intervals natural fractures mainly appeared in the low e shale intervals when the wellbore was close to the fault damage zone the low fracture intensity in the low e shale intervals of the wellbores located at the boundaries of the stress concentration blocks may be associated with an extensional stepover process

identification of microbial and thermogenic gas components from upper devonian black shale cores illinois and michigan basins differentiation of microbial versus thermogenic methane in coalbed and black shale accumulations can affect strategies for exploration and may influence the total gas content in a given area early identification of these processes from crushed core materials even before formation fluids and produced gas samples are available could permit a more efficient and cost effective exploration total gas contents and compositional and isotopic data from new albany shale core materials are presented which delineate regional occurrence of microbial thermogenic and mixed gas generation in the illinois basin these trends are consistent with those identified from detailed prior studies of produced gas and water chemistry from the same locations the most useful markers for microbial gas in crushed core gases are elevated co2 contents characterized by high values 5 core gas analyses from wells in which microbial gas is identified commonly have significantly more total gas absorbed than do core samples from wells producing gases solely of thermogenic origin these observations are independent of variations in sample depth and organic carbon content in a given core thus this integrated case study of core and produced gases in the illinois basin illustrates that the areas containing microbial gas in addition to early thermogenic gas may be more productive than pure thermogenic zones for these early to immature unconventional gas deposits

merging sequence stratigraphy and geomechanics for unconventional gas shales the recent revelation of vast global quantities of potentially gas and oil productive shales has paved the way for rapid advancements in understanding their geological properties many of which affect their geomechanical properties and ultimately reservoir operations and performance because of shale s unique and very intricate geological physical and mechanical properties at all scales from nano to macro scale abousleiman et al 2010 compared with sandstones and carbonates the ad jective unconventional has often been applied to their characterization although many shale characteristics are different than those of sandstones and carbonates and require new technologies to measure them other characteristics mentioned below are similar as such customized conventional methodologies and concepts can be applied to exploration and production of shale gas and oil

sequence stratigraphy and depositional environments of the shamokin union springs member marcellus formation and associated strata in the middle appalachian basin organic carbon rich shales of the lower marcellus formation were deposited at the toe and basinward of a prograding clinothem associated with a mahantango formation delta complex centered near harrisburg pennsylvania distribution of these organic carbon rich shales was influenced by shifts in the delta complex driven by changes in rates of accommodation creation and by a topographically high carbonate bank that formed along the findlay algonquin arch during deposition of the onondaga formation specifically we interpret the union springs member shamokin member of the marcellus formation and the onondaga formation as comprising a single third order depositional sequence the onondaga formation was deposited in the lowstand to transgressive systems tract and the union springs member was deposited in the transgressive highstand and falling stage systems tract the regional extent of parasequences systems tracts and the interpreted depositional sequence suggest that base level fluctuations were primarily caused by allogenic forcing eustasy climate or regional thermal uplift or subsidence instead of basement fault reactivation as argued by previous workers paleowater depths in the region of marcellus formation black mudrock accumulation were at least 330 ft 100 m as estimated by differences in strata thickness between the northwestern carbonate bank and basinal facies to the southeast geochemical analysis indicates anoxic to euxinic bottom water conditions these conditions were supported by a deep stratified basin with a lack of circulation

organic geochemical characteristics mineralogy petrophysical properties and shale gas prospects of the wufeng longmaxi shales in sanquan town of the nanchuan district chongqing thick marine shales occur in the wufeng formation and longmaxi formation of sanquan town of the nanchuan district chongqing municipality which is located on the southeast margin of the sichuan basin however few details of the characteristics of the wufeng longmaxi shales in this area have been reported in this study a well approximately 100 m 328 ft deep was drilled a high quality shale total organic carbon toc 2 0 wt clay 40 interval that was approximately 24 m 79 ft thick with an average toc value of 3 0 wt mainly occurs in the ordovician wufeng formation katian and hirnantian and base of the silurian longmaxi formation rhuddanian shales with higher toc values commonly have a higher porosity and specific surface area tectonic movements may also have been very important factors that influenced the petrophysical properties of the shales for example a detachment layer that resulted from complex tectonic movements is extensive in the wufeng formation the cracks and microcracks in the detachment layer can result in good pore connectivity consequently the detachment layer can be an effective migration pathway the longmaxi wufeng shales of sanquan town are also compared with those of the famous jiaoye 1 well in the jiaoshiba shale gas field in the eastern sichuan basin although the shales in sanquan town have considerable shale gas generation potential the shale gas resource potential in sanquan town is probably poor because the escape of shale gas may be accelerated by the detachment layer in destroyed anticlines and synclines

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

ediacaran cambrian ordovician silurian and permian shales of the upper yangtze platform south china deposition thermal maturity and shale gas potential abstract for many years the yangtze platform has been successfully explored and exploited for petroleum the lower silurian longmaxi shale proved to contain commercial quantities of gas but several other formations might also have a high potential for shale hosted gas exploration this paper comprises of geochemical petrographical petrophysical and mineralogical information on the major proterozoic and paleozoic gas shales in the upper yangtze area which provides insights on the depositional environment the thermal maturity of organic matter shale gas storage capacity and the fracability of these rocks the total organic carbon toc content varies from 0 1 to 22 5 with an average value of 2 7 and most of these shales were deposited in an oxygen depleted marine environment equivalent vitrinite reflectance vrr values range from 2 20 to 4 25 indicating that all samples are in the gas generation window and lost a large amount of primary organic carbon porosity varies between 1 5 and 13 6 with an average value of 5 8 while the excess sorption capacity ranges from 0 10 to 0 22 mmol g rock minerology data show that quartz is the predominant mineral except for the upper permian longtan formation in which clay minerals account for 29 to 84 new data were combined with those from other publications and compared to information on other well studied shale hosted gas systems

heterogeneity characterization of the lower silurian longmaxi marine shale in the pengshui area south china abstract the heterogeneity of shale is significant for the evaluation and sweet spot prediction of a shale gas reservoir core observations thin sections field emission scanning electron microscopy fe sem nitrogen gas adsorption n2ga and geochemical analyses were performed on shale samples from the lower longmaxi formation in the pengshui area of south china in this study the macroscopic and microscopic heterogeneities of the longmaxi shale are revealed and their origins and inner link are also discussed the results show that three systems tracts were developed in the lower longmaxi formation a transgressive systems tract tst early highstand systems tract ehst and late highstand systems tract lhst from tst to lhst toc total organic carbon siliceous minerals quartz feldspar and pyrite show an upward decreasing trend in weight content while the clay minerals and carbonate contents increase upward hence the tst ehst and lhst shales are generally characterized by organic rich shale lithofacies organic moderate shale lithofacies and organic lean shale lithofacies respectively the in situ gas content decreases from tst to lhst and primarily depends on toc content the sedimentary environment of the tst shale is an anoxic environment with high paleoproductivity which then evolves to a dysoxic oxic environment in the ehst shale and an oxic environment in the lhst shale with relatively low paleoproductivity organic matter pores are the primary contributors to the total pore volume in the tst shale and then the pore content and role in porosity decrease upward from ehst to lhst however the proportions of clay related pores and brittle mineral related pores gradually elevate from the tst shale to the lhst shale the sedimentary environment including water depth redox conditions paleoproductivity terrigenous input and hydrodynamics etc control the development of organic matter mineral composition lithofacies association color bedding and palaeobios in the lower longmaxi shales which constitute the macroscopic heterogeneity nevertheless the microscopic heterogeneity of shale originates from diagenesis catagenesis specifically shales are primarily composed of interparticle pores and clay related pores during deposition and the porosity is reduced primarily under mechanical compaction and chemical cementation as the burial depth and diagenetic degree increase a large number of organic matter pores and dissolution pores begin to appear which are associated with the hydrocarbon generation process moreover macroscopic shale composition plays a crucial role in development levels of microscopic shale pores

high resolution geochemistry and sequence stratigraphy of the hushpuckney shale swope formation eastern kansas implications for climato environmental dynamics of the late pennsylvanian midcontinent seaway abstract the hushpuckney shale member of the swope formation missourian stage eastern kansas is the core shale of a kansas type cyclothem formed during the late transgressive to early regressive phases of a late pennsylvanian glacio eustatic cycle coeval high frequency climato environmental dynamics of the midcontinent seaway are preserved in the kgs orville edmonds no 1a study core as centimeter scale variation in major components organic carbon authigenic sulfides and phosphate detrital siliciclastics organic macerals trace element redox proxies mo u v zn and ichnofabric features benthic o 2 levels declined sharply from the base of the black shale 0 cm went sulfidic at 4 cm and reached a redox minimum at 21 cm above this level redox potential gradually rose fluctuating between sulfidic and nonsulfidic conditions from 35 cm to the black shale gray shale contact at 52 cm onset of dysoxic conditions at that contact allowed establishment of a benthic community of soft bodied organisms comprised of deep tiered tracemakers tolerant of low o 2 conditions trichichnus and shallow tiered tracemakers favoring soupground helminthopsis or firmground substrates the zoophycos phycosiphon schaubcylindrichnus planolites association most geochemical records exhibit a low order cycle spanning the full 52 cm thickness of the black shale submember reflecting a dominant glacio eustatic control the base and top of the black shale submember record lateral migration of the pycnocline across the midcontinent shelf during the transgressive and regressive phases respectively the maximum flooding surface mfs is at 17 23 cm an interval containing the euxinic peak and characterized by high concentrations of illite representing a cratonic siliciclastic flux and terrestrial organic macerals the product of transient increases in humidity weathering rates and the export of coal swamp vegetation associated with the interglacial highstand of the swope cyclothem although a transgressive surface of maximum starvation sms cannot be confidently identified a phosphate rich regressive condensation surface at 28 34 cm records pycnoclinal weakening due to increased aridity associated with renewed southern hemisphere icesheet growth a correlative shift in dominance from terrestrial to marine derived organic macerals reflects increased upwelling of nutrient rich deepwaters and enhanced primary productivity penecontemporaneous paleogeographic and climatic factors e g semirestricted circulation monsoonal precipitation predisposed the midcontinent seaway toward sensitivity to high frequency climato environmental fluctuations which are preserved as 2 to 7 cm thick cycles in the study core the 52 cm thick black shale submember contains 12 such high order cycles which have an estimated average duration of 2 to 9 kyr implying a sub milankovitch band i e millennial scale climatic control the results of this study are relevant to the sequence stratigraphic interpretation of kansas type cyclothems the dynamics of gondwanan ice age glacio eustatic cycles and the development of boundary conditions for late pennsylvanian paleoclimate models

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

pore characterization and methane sorption capacity of over mature organic rich wufeng and longmaxi shales in the southeast sichuan basin china abstract currently the upper ordovician wufeng o3w and lower silurian longmaxi s1l formations in southeast sichuan basin have been regarded as one of the most important target plays of shale gas in china in this work using a combination of low pressure gas adsorption n2 and co2 mercury injection porosimetry mip and high pressure ch4 adsorption we investigate the pore characteristics and methane sorption capacity of the over mature shales and discuss the main controlling factors for methane sorption capacity and distribution of methane gas in pore spaces low pressure co2 gas adsorption shows that micropore volumes are characterized by three volumetric maxima at about 0 35 0 5 and 0 85 nm the reversed s shaped n2 adsorption isotherms are type with hysteresis being noticeable in all the samples the shapes of hysteresis loop are similar to the h3 type indicating the pores are slit or plate like mesopore size distributions are unimodal and pores with diameters of 2 16 nm account for the majority of mesopore volume which is generally consistent with mip results the methane sorption capacities of o3w s1l shales are in a range of 1 63 3 66 m3 t at 30 c and 10 mpa methane sorption capacity increase with the toc content surface area and micropore volume suggesting organic matter might provide abundant adsorption site and enhance the strong methane sorption capacity samples with higher quartz content and lower clay content have larger sorption capacity our data confirmed that the effects of temperature and pressure on methane sorption capacity of shale formation are opposite to some extent suggesting that during the burial or uplift stage the gas sorption capacity of hydrocarbon reservoirs can be expressed as a function of burial depth based on the adsorption energy theory when the pore diameter is larger than 2 nm much methane molecular will be adsorbed in pores space with distance to pore wall less than 2 nm while free gas is mainly stored in the pore space with distance to pore wall larger than 2 nm distributions of adsorption space decrease with the increasing pore size while free gas volume increase gradually assuming the pore are cylindrical or sphere particularly when the pore size is larger than 30 nm the content of adsorbed gas space volume is very low and its contribution to the all gas content is negligible