spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

a new family genus and species of crab crustacea decapoda brachyura from the upper cretaceous campanian of manitoba canada discovery of a single specimen of brachyuran decapod from the campanian millwood member in southern manitoba canada permits description of a new genus and species cretacocarcinus smithi comparison of sternal architecture and general carapace morphology with potentially related taxa documents that the new genus along with camarocarcinus holland and cvancara form a new family camarocarcinidae tentatively assigned to the raninoidea the camarocarcinidae are interpreted to have originated in the upper midcontinental seaway in the late cretaceous survived the k t extinction event s and dispersed into southern north dakota usa greenland and denmark in the paleocene

geochemistry of the extremely high thermal maturity longmaxi shale gas southern sichuan basin abstract the marine shale of the silurian longmaxi formation in southern sichuan basin china is characterized by its huge thickness 100 600 m high toc values 0 35 18 4 favorable types of organic matter i and ii1 high ro values 1 8 4 2 abundant brittle minerals average 56 3 and strong gas generation intensity particularly its bottom section which has toc 2 and thickness of 20 70 m has recently been a main target for shale gas exploration and development geochemical parameters of 13 gas samples from longmaxi shale from 10 wells were analyzed in this study wetness of the gas molar fraction of ethane through pentanes in total gaseous hydrocarbon is only 0 24 0 70 making the longmaxi shale gas among the driest in the world carbon isotopic compositions of the alkane gases from longmaxi shale are characterized by 13c1 13c2 13c3 with the most positive 13c1 values in the world a positive relationship was observed between its 13c1 and 13c2 values reflecting the extremely high thermal maturity of the source rock 2hch4 values range from 140 to 151 and the 2hc2h6 values range from 130 to 173 the hydrogen isotopic compositions were mainly characterized by 2hch4

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

depositional environment and organic matter accumulation of upper ordovician lower silurian marine shale in the upper yangtze platform south china abstract the main controlling factors of organic matter accumulation in the upper ordovician wufeng lower silurian longmaxi formations are complex and remain highly controversial this study investigates the vertical variation of total organic carbon toc content as well as major and trace element concentrations of four ordovician silurian transition sections from the upper yangtze platform of south china to reconstruct the paleoenvironment of these deposits and to improve our understanding of those factors that have influenced organic matter accumulation in these deposits the residual toc content of the wufeng formation averages 3 2 and ranges from 0 12 to 6 0 the overlying lower longmaxi formation displays higher toc content avg 4 4 followed upsection by consistent and lower values that average 1 6 in the upper longmaxi formation the concentration and covariation of redox sensitive trace elements mo u and v suggest that organic rich intervals of the wufeng formation accumulated under predominantly anoxic conditions organic rich horizons of the lower longmaxi formation were deposited under strongly anoxic to euxinic conditions whereas organic poor intervals of the upper longmaxi formation accumulated under suboxic conditions positive correlations between redox proxies and toc contents suggest that organic matter accumulation was predominantly controlled by preservation barium excess ba xs values indicate high paleoproductivity throughout the entire depositional sequence with an increase in the lower longmaxi formation increased productivity may have been induced by enhanced p recycling as evidenced by elevated c org p tot ratios mo u covariation and mo toc values reveal that the wufeng formation was deposited under extremely restricted conditions whereas the longmaxi formation accumulated under moderately restricted conditions during the late ordovician the extremely restricted nature of ocean circulation on the upper yangtze platform in tandem with enhanced stratification of the water column promoted anoxic conditions favorable for the preservation of organic matter during early silurian time organic matter accumulation was principally controlled by changes in sea level which affected terrigenous flux redox conditions and the degree of nutrition recycling

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

a new genus and species of polychelid lobster crustacea decapoda eryonidae from the early jurassic hettangian of british columbia a single specimen of decapod crustacean preserved in ventral view and compressed represents a new genus and species of eryonid lobster wrangelleryon perates the discovery in lower jurassic hettangian sediments of the sandilands formation in british columbia represents the first occurrence of eryonidae in north america and reinforces a global distribution of the family in the jurassic the occurrence in british columbia on the wrangellia terrane supports the lower latitude setting in which the species lived resume un specimen unique de crustace decapode preserve en vue ventrale et comprime represente un nouveau genre et une nouvelle espece de homard eryonide wrangelleryon perates la decouverte dans des sediments du jurassique inferieur hettangien de la formation de sandilands en colombie britannique represente la premiere occurrence d un eryonide en amerique du nord et consolide la these d une repartition planetaire de cette famille au jurassique la presence du specimen en colombie britannique dans le terrane de wrangellie appuie la these voulant que l espece ait vecu abasse latitude traduit par la redaction

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

quartz types authigenic and detrital in the upper cretaceous eagle ford formation south texas usa abstract lithologic heterogeneity of the eagle ford formation in south texas arises from mixing of extrabasinal grains of siliciclastic composition with intrabasinal grain assemblages composed dominantly of marine carbonate with a lesser component of biosiliceous debris detrital quartz in particular is derived from both extrabasinal and intrabasinal sources posing a challenge for the use of bulk compositional data for mudrock classification extrabasinal detrital quartz supplied along a major axis of siliciclastic influx the woodbine depositional system of east texas is reduced to a minor part of the grain assemblage in south texas petrographic evidence and point count results indicate that around 85 percent of total quartz in these rocks equal to about 12 6 volume percent is authigenic thus significant quantities of authigenic silica are not restricted to siliceous mudrocks but can be found in carbonate rich mudrocks as well formerly opaline skeletons of radiolaria the dominant source of silica for authigenic quartz precipitation are only poorly preserved by replacements including calcite dolomite pyrite and quartz dissolved silica released by dissolution of radiolarians and perhaps also by volcanic glass dissolution is re precipitated in a variety of forms including matrix dispersed microquartz cement fillings within primary intragranular pores and grain replacement of both calcareous and siliceous allochems the mass balance of dissolved silica mobilized from radiolarians and other reactive silicates and the precipitation of authigenic quartz is uncertain because the initial volumes of now dissolved detrital material versus the final volume of authigenic material quartz and other authigenic silicates cannot be determined with accuracy

depositional environment of the lower silurian akkas hot shales in the western desert of iraq results from an organic geochemical study abstract the lower silurian hot shales in the lower part of akkas formation in akkas field western iraq were studied to determine their depositional environments for this purpose organic and inorganic proxies were used these include total organic carbon content toc sulfur pyrite and carbonate content measurements as well as the saturated and aromatic biomarkers organic carbon content toc pyrite and carbonate contents were high and pristane phytane ratio pr ph was low in these hot shales indicating deposition under anoxic marine conditions the presence of gammacerane suggests water column stratification the presence of aryl isoprenoids originating from aromatic carotenoids of green photosynthetic sulfur bacteria indicates deposition under euxinic conditions extending from the photic zone to the sediment water interface the conditions became more oxygenated upward which led to the deposition of organic poor gray green shales in the upper part of akkas formation with low pyrite and carbonate contents and high pr ph ratios

abrupt change in atmospheric co2 during the last ice age 1 during the last glacial period atmospheric carbon dioxide and temperature in antarctica varied in a similar fashion on millennial time scales but previous work indicates that these changes were gradual in a detailed analysis of one event we now find that approximately half of the co2increase that occurred during the 1500 year cold period between dansgaard oeschger do events 8 and 9 happened rapidly over less than two centuries this rise in co2 was synchronous with or slightly later than a rapid increase of antarctic temperature inferred from stable isotopes

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

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

cause of shale gas geochemical anomalies and mechanisms for gas enrichment and depletion in high maturity shales abstract this article reviews the abnormal characteristics of shale gases natural gases produced from organic rich shales and discusses the cause of the anomalies and mechanisms for gas enrichment and depletion in high maturity organic rich shales the reported shale gas geochemical anomalies include rollover of iso alkane normal alkane ratios rollover of ethane and propane isotopic compositions abnormally light ethane and propane 13 c values as well as isotope reversals among methane ethane and propane these anomalies reflect the complex histories of gas generation and associated isotopic fractionation as well as in situ mixing and accumulation of gases generated from different precursors at different thermal maturities a model was proposed to explain the observed geochemical anomalies gas generation from kerogen cracking at relatively low thermal maturity accounted for the increase of iso alkane normal alkane ratios and ethane and propane 13 c values normal trend simultaneous cracking of kerogen retained oil and wet gas and associated isotopic fractionation at higher maturity caused decreasing iso alkane normal alkane ratios lighter ethane and propane 13 c and corresponding conversion of carbon isotopic distribution patterns from normal through partial reversal to complete reversal relatively low oil expulsion efficiency at peak oil generation low expulsion efficiency at peak gas generation and little gas loss during post generation evolution are necessary for organic rich shales to display the observed geochemical anomalies high organic matter richness high thermal maturity high degrees of kerogen gas and oil gas conversions and late stage the stage of peak gas generation and post generation evolution closed system accounted for gas enrichment in shales loss of free gases during post generation evolution may result in gas depletion or even undersaturation total gas content lower than the gas sorption capacity in high maturity organic rich shales

pore and pore network evolution of upper cretaceous boquillas eagle ford equivalent mudrocks results from gold tube pyrolysis experiments low maturity boquillas formation eagle ford formation equivalent organic lean calcareous mudrock samples collected from outcrop were heated in gold tubes under confining pressure to investigate the evolution of organic matter om pores and mineral pores the majority of om in the boquillas samples was migrated petroleum bitumen based on evidence from geochemical analyses solvent extraction and scanning electron microscopy sem petrography the sem images showed several diagenetic events including framboidal pyrite precipitation and euhedral calcite quartz kaolinite and chlorite cementation that were all interpreted to have occurred prior to petroleum expulsion and pore scale to bed scale petroleum bitumen migration two major pore types were present prior to heating primary mineral pores and modified mineral pores with migrated relic om from heating experiments pores were found to be associated with stages of om maturation during the bitumen generation stage modified mineral pores were dominant and primary interparticle and intraparticle pores were present during the oil generation stage modified mineral pores with isopachous om rim were observed to be the most abundant pore type during the gas generation stage both modified mineral pores and nanometer sized spongy om pores were predominant we interpreted the occurrence of modified mineral pores to be the result of 1 oil and gas filled or partially filled voids that developed during petroleum migration and water expulsion 2 voids after removing of oil gas and water during sample preparation and 3 trapping of water molecules the formation of these nanopores was interpreted to be related to gas generation and structural rearrangement of om

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

organic rich marcellus shale lithofacies modeling and distribution pattern analysis in the appalachian basin the marcellus shale is considered to be the largest unconventional shale gas resource in the united states two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content the fracture attributes reflect the geomechanical properties of the rocks which are partly related to rock mineralogy the natural gas content of a shale reservoir rock is strongly linked to organic matter content measured by total organic carbon toc a mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition rock geomechanical properties and toc content core log and seismic data were used to build a three dimensional 3 d mudrock lithofacies model from core to wells and finally to regional scale an artificial neural network was used for lithofacies prediction eight petrophysical parameters derived from conventional logs were determined as critical inputs advanced logs such as pulsed neutron spectroscopy with log determined mineral composition and toc data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies sequential indicator simulation performed well for 3 d modeling of marcellus shale lithofacies the interplay of dilution by terrigenous detritus organic matter productivity and organic matter preservation and decomposition affected the distribution of marcellus shale lithofacies distribution which may be attributed to water depth and the distance to shoreline the trend of normalized average gas production rate from horizontal wells supported our approach to modeling marcellus shale lithofacies the proposed 3 d modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies

offset of an upper pliensbachian geographic zonation in the north american cordillera by transcurrent movement the north to south climatic zonation of upper pliensbachian ammonites known in europe has been recognized in the north american cordillera this simple geographic arrangement has been disrupted by northwest trending dextral transcurrent faults with further documentation the amount of offset of these zones should provide a measure of the amount of movement on these faults since pliensbachian time and further document the allochthoneity of the western part of the cordillera

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

source and seal coupling mechanism for shale gas enrichment in upper ordovician wufeng formation lower silurian longmaxi formation in sichuan basin and its periphery abstract in recent years theoretical geologic research has made important progress in shale gas exploration and development and new discoveries such as the jiaoshiba weiyuan and changning shale gas fields provide geological cases to define key controls on shale gas accumulation in wufeng formation longmaxi formation marine shale strata a mechanism coupling source and seal development for shale gas enrichment is proposed in this study based on detailed research results of isochronous stratigraphic distribution of source rock and seals and source seal dynamic evolution great thickness wide distribution and high total organic carbon content toc of sources are key controls on the shale gas content and storage capacity in organic matter hosted pores micro cracks and bedding fissures is intensively developed the wufeng formation and the lower part of the first member of the longmaxi formation wf2 lm4 graptolitic zone are favorable sources that feature a slow deposition rate well graptolitic zone favorable organic organism type and high toc the organic matter type is benefit to the development of organic matter pores because the planktonic algae tends to generate and expulse large amounts of hydrocarbon and form many organic matter pores both high biogenic quartz and high toc ensure development of abundant organic matter hosted pores and result in a three dimensional network of interconnected organic matter pores that allows shale gas storage and flow the seal can be divided into direct and indirect seals the direct seal refers to the middle and upper parts of the first member of the longmaxi formation lm5 and higher graptolitic zone that are characterized by low toc and low porosity the indirect seal refers to the regionally distributed lower middle triassic gypsum layer s and mudstone that maintain regional geopressure systems the shale gas fields of jiaoshiba fushun yongchuan and changning have high geopressure coefficient factors 1 5 2 0 and 1 5 respectively in the absence of the lower middle triassic gypsum layer s and mudstone regional seals the high pressure system was destroyed and resulted in low normal geopressure shale gas reservoirs for instance the pengshui and zhaotong wells the static match and dynamic match of source and seal constrain the location of shale gas reservoirs and the degree of shale gas enrichment the model of a mechanism coupling source and seal for shale gas enrichment provides new ideas and methods for the assessment of shale gas this model promotes the evaluation of shale gas from the static parameters approach to the source and seal dynamic approach in the sichuan basin and its peripheral areas the promising areas for shale gas accumulation are those with favorable sources in the wf2 lm4 graptolitic zone and the presence of the lower middle triassic gypsum layer s and mudstone regional seal

a new species of lobster astacidea erymidae from the smithers formation middle jurassic of british columbia canada a single carapace and its counterpart of an erymoid lobster collected from the middle jurassic smithers formation in british columbia permits description of a new species eryma walkerae the specimen represents only the fourth species of eryma described from north america and documents a north polar route of dispersal for erymids into north america

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

modeling of gas generation from the barnett shale fort worth basin texas the generative gas potential of the mississippian barnett shale in the fort worth basin texas was quantitatively evaluated by sealed gold tube pyrolysis kinetic parameters for gas generation and vitrinite reflectance ro changes were calculated from pyrolysis data and the results used to estimate the amount of gas generated from the barnett shale at geologic heating rates using derived kinetics for ro evolution and gas generation quantities of hydrocarbon gas generated at ro 1 1 are about 230 l t 7 4 scf t and increase to more that 5800 l t 186 scf t at ro 2 0 for a sample with an initial total organic carbon content of 5 5 and ro 0 44 the volume of shale gas generated will depend on the organic richness thickness and thermal maturity of the shale and also the amount of petroleum that is retained in the shale during migration gas that is reservoired in shales appears to be generated from the cracking of kerogen and petroleum that is retained in shales and that cracking of the retained petroleum starts by ro 1 1 this result suggests that the cracking of petroleum retained in source rocks occurs at rates that are faster than what is predicted for conventional siliciclastic and carbonate reservoirs and that contact of retained petroleum with kerogen and shale mineralogy may be a critical factor in shale gas generation shale gas systems together with overburden can be considered complete petroleum systems although the processes of petroleum migration accumulation and trap formation are different from what is defined for conventional petroleum systems

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

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

empirical relationship between gas composition and thermal maturity in eagle ford shale south texas organic rich and carbonate rich eagle ford shale is a self sourced oil and gas reservoir with little alteration of gas chemistry as might be affected by petroleum expulsion and migration as such it provides an ideal natural laboratory to quantify the compositional variation of gases generated from oil prone type ii kerogen during thermal maturation the chemical composition of the gas released from rock crushing was conducted and integrated with rock eval pyrolysis to define the empirical relationship between gas compositional parameters and thermal maturity in this study from 10 wells in the eagle ford shale in south texas we collected 74 core samples having a range of thermal maturity the measured maximum temperature tmax values of hydrocarbons generated in rock eval pyrolysis range from 427 c to 494 c 800 f to 921 f and the calculated equivalent vitrinite reflectance roe values range from 0 51 to 1 73 based on tmax values total organic carbon content ranges from 0 3 to 8 53 with an average of 3 12 standard deviation of 1 77 burial depth is from 2989 6 to 13 827 3 ft 911 2 to 4214 6 m our results showed that gas composition in the eagle ford shale is mainly controlled by thermal maturity and three stages of gas generation are identified based on the c1 and c2 concentrations of the gases released by rock crushing from eagle ford shale core samples the three stages of gas generation correspond to the following processes of organic matter conversion 1 kerogen and bitumen thermal cracking to crude oil 2 bitumen and heavy crude oil thermal cracking to light oil and 3 light oil cracking to gas methane rich gas and an abundance of branched butane and pentane are generated in light oil cracking to gas resulting in high c1 c2 c1 c2 c3 i c4 n c4 and i c5 n c5 ratios increased cracking of normal alkanes such as n butane and n pentane occurs in the light oil cracking to gas empirical equations between gas compositional parameters and thermal maturity tmax or roe are obtained for oil prone type ii the c1 c2 c1 c2 c1 c2 c3 and i c4 n c4 ratios are the five best parameters for determining thermal maturity with an exponentially derived r2 value of 0 74 the composition of gas produced from the eagle ford shale following hydraulic fracturing is used to validate the empirical equations calculated thermal regime for the oil production based on the produced gas is located at the peak of oil generation and the beginning of light oil cracking to gas corresponding to tmax from 454 c to 464 c 849 f to 867 f or at an roe ranging from 1 01 to 1 19 empirical equations provide a basis for interpretation of mud gas logging data and produced gas composition

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