experimental study of fluid transport processes in the matrix system of the european organic rich shales i scandinavian alum shale abstract this contribution presents results from a laboratory study investigating the fluid gas water transport properties in the matrix system of the scandinavian alum shale the maturity of the organic matter of the shale samples ranged between 0 5 and 2 4 vitrinite reflectance vr r gas he ar ch 4 and water flow properties were determined at effective stresses ranging between 5 and 30 mpa and a temperature of 45 c the effects of different controlling factors parameters on the fluid conductivity including permeating fluid moisture content anisotropy heterogeneity effective stress pore pressure and load cycling were analyzed and discussed pore volume measurements by helium expansion were conducted under controlled in situ effective stress conditions on a limited number of plugs drilled parallel and perpendicular to bedding for alum shale the intrinsic permeability coefficients measured parallel and perpendicular to bedding 6 10 22 8 10 18 m 2 were within the range previously reported for other shales and mudstones permeability coefficients were strongly dependent on permeating fluid moisture content anisotropy effective stress and other sample to sample variations the intrinsic absolute permeabilities measured with helium were consistently higher up to five times than those measured with argon and methane permeability coefficients he ch 4 measured on a dry sample were up to six times higher than those measured on an as received sample depending on effective stress the effect of moisture on measured permeability coefficients became more significant as effective stress increased permeability coefficients he ch 4 measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding parallel to bedding all samples showed a nonlinear reduction in permeability with increasing effective stress 5 30 mpa the stress dependence of permeability could be well described by an exponential relationship

the upper ordovician black shales of southern quebec canada and their significance for naturally occurring hydrocarbons in shallow groundwater abstract shale gas exploration in the st lawrence platform of southern quebec eastern canada focussed on the upper ordovician utica shale from 2006 to 2010 during which 28 wells were drilled 18 of which were fracked the st lawrence platform is thus considered as a pristine geological domain where potential environmental effects of fracking can be evaluated relative to the natural baseline conditions of the shallow aquifers in the saint edouard area southwest of quebec city it has been shown that groundwater carries variable and locally high levels of naturally occurring dissolved hydrocarbons in which thermogenic ethane and propane can be found fifteen shallow 30 147 m wells were drilled into bedrock and sampled cores and cuttings with the purpose of characterizing the shallow bedrock in a shale gas pre development context the shallow bedrock geology is made of three upper ordovician clastic formations the lotbiniere and les fonds formations are time and facies correlative with the utica shale present at a depth of 1 5 to 2 km in this area they are dominated by calcareous black shales with minor siltstone and micrite beds the nicolet formation is the youngest unit of the area and consists of gray to dark gray shales with locally abundant thick siltstone and fine grained sandstone beds the organic matter in the lotbiniere and les fonds formations is represented by solid bitumen with subordinate liptinite algae graptolites and chitinozoans representing normal marine type ii kerogen both formations are at the post peak hydrocarbon generation as indicated by the equivalent random vitrinite reflectance of 0 94 to 1 04 rock eval data support the type ii nature of the kerogen and the late oil window maturation level hydrocarbon extracts from the three formations have yielded high to low concentrations of c1 to c6 for all units an upward decrease in total volatiles c1 c2 c3 together with an increase in the gas dryness ratio c1 c2 c3 is recorded the transitions occurring at depths shallower than 50 m where the shales are more fractured the upward increase in the gas dryness ratio results from the more significant reduction of ethane and propane concentrations compared to that of methane consistent with the dryness ratio trend the 13 c vpdb values of methane change from thermogenic values 50 for deeper samples to more biogenic negative values 2 h vsmow trend of more negative values at shallower depths is noted the 13 c vpdb and 2 h vsmow values of rock hosted methane indicate that samples at shallow depth recorded a microbial influence it is proposed that diffusion and some microbial degradation of hydrocarbons are responsible for the decrease of rock volatiles and the in situ generation of biogenic methane in the shales at shallow depths to mix with the in situ thermogenic methane the utica shale is a very good source rock with high generation potential however thermogenic volatiles can also originate from shallower units with much shorter migration pathways the mixed thermogenic and biogenic methane in the groundwater results from fracture enhanced diffusion and biodegradation of volatiles at shallow depths

reduced atlantic storminess during last glacial maximum evidence from a coupled climate model the last glacial maximum lgm 21 000 yr before present was the time of maximum land ice extent during the last ice age a recent simulation of the lgm climate by a state of the art fully coupled global climate model is shown to exhibit strong steady atmospheric jets and weak transient eddy activity in the atlantic sector compared to today s climate in contrast previous work based on uncoupled atmospheric model simulations has shown that the lgm jets and eddy activity in the atlantic sector are similar to those observed today with the main difference being a northeastward extension of their maxima the coupled model simulation is shown to agree more with paleoclimate proxy records and thus is taken as the more reliable representation of lgm climate the existence of this altered atmospheric circulation state during lgm in the model has implications for understanding the stability of glacial climates for the possibility of multiple atmospheric circulation regimes and for the interpretation of paleoclimate proxy records

causes of reduced north atlantic storm activity in a cam3 simulation of the last glacial maximum abstract the aim of this paper is to determine how an atmosphere with enhanced mean state baroclinity can support weaker baroclinic wave activity than an atmosphere with weak mean state baroclinity as a case study a last glacial maximum lgm model simulation previously documented to have reduced baroclinic storm activity relative to the modern day climate simulated by the same model despite having an enhanced midlatitude temperature gradient is considered several candidate mechanisms are evaluated to explain this apparent paradox a linear stability analysis is first performed on the jet in the modern day and the lgm simulation the latter has relatively strong barotropic velocity shear it was found that the lgm mean state is more unstable to baroclinic disturbances than the modern day mean state although the three dimensional jet structure does stabilize the lgm jet relative to the eady growth rate next feature tracking was used to assess the storm track seeding and temporal growth of distur

wave packets and life cycles of troughs in the upper troposphere examples from the southern hemisphere summer season of 1984 85 abstract in this paper reanalysis data for the southern hemisphere summer season of 1984 85 produced by the european centre for medium range weather forecasts have been analyzed to examine wave packets and life cycles of baroclinic waves a semiobjective algorithm has been devised to track wave packets it is found that the perturbations in the upper troposphere are dominated by wave packets some of these wave packets can be tracked for several weeks during which they can make up to two trips around the latitude circle the energy life cycles of waves that make up several of these wave packets were analyzed and apart from the incipient waves that started the wave packets most of the subsequent wave development was found to be dominated by convergence and divergence of energy fluxes rather than due to baroclinic or barotropic conversions demonstrating that these wave packets are indeed coherent entities that propagate due to downstream development or dispersion the energy life cycle of the most

organic matter mineral composition pore size and gas sorption capacity of lacustrine mudstones implications for the shale oil and gas exploration in the dongying depression eastern china because clay minerals and pore size distribution are important for oil and gas accumulation in lacustrine mudstone reservoirs this study aimed to characterize the pore size distribution in lacustrine mudstone reveal the importance of clay minerals in gas sorption capacity gsc provide insights into the primary gsc controls for lacustrine mudstones and discuss the shale oil and gas resource potential and possible risks in their future production a total of 256 core samples from the lower paleogene sequence of the dongying depression in the bohai bay basin in china were analyzed to determine organic richness and hydrocarbon generation potential a series of analyses was conducted on a suite of 28 mudstone samples from the s121 well to investigate the mineral composition pore size distribution and primary controls on gsc scanning electron microscopy and x ray diffraction were used to observe the microscopic characteristics and identify various minerals nitrogen adsorption experiments at low temperatures and a methane isothermal adsorption test were conducted to study the pore sizes and gas adsorption capacities experimental results show that the majority of the samples were rich in type ii and i kerogen with moderate to high hydrocarbon generation potential and are thermally mature in the main oil window the contents of illite and mixed layer illite smectite i s are high 40 in these lacustrine mudstones the pores were mainly thin long and bottleneck shaped and dominated by type iv and h2 hysteresis loop characteristics the abundance of quartz feldspar illite and mixed layer i s all presented a positive correlation with their brunauer emmett teller surface area and total pore volume whereas the abundance of carbonate minerals dominated by calcite showed a negative correlation the volume of micropores and clay minerals were the main factors controlling gscs the results highlight the importance of clay minerals including the illite and mixed layer i s in the lacustrine mudstones because of their considerable gsc high content of illite and mixed layer i s in lacustrine mudstone is in favor of gas storage whereas at the same time it is not conducive to shale gas development because of its reducing the brittleness of shale the paleogene of dongying depression has shale oil and gas resources however several key geological factors including pore size distributions pore diameters oil density and low brittleness may pose risks in shale oil and gas development

poleward deflection of storm tracks an analysis of 11 years of european centre for medium range weather forecasts data focuses primarily on the vertically averaged high frequency transients the conclusions are discussed in the context of a the winter storm track b monthly variability and c interannual variability a winter storm track results show that the pattern of the forcing by the high frequency eddies along the storm track is highly correlated with the stationary circulation and the forcing itself is primarily responsible for the location of the trough ridge system associated with the stationary flow the results also clarify the role of wind component covariance terms u9y9 and y9 2 2 u9 2 in the column averaged vorticity forcing the simpler term u9y9 has the well known effect of intensifying the anticyclonic cyclonic tendencies on the southern northern side of the jet thereby producing an increase in the barotropic component of the zonal jet the y9 2 2 u9 2 term displays a quadrupole pattern which is also approximately in phase with the trough ridge system associated with the stationary flow b monthly variability eddy activity has been shown to possess a seasonal life cycle increasing during the early fall and reaching a maximum around the month of november then decaying for most of the winter months month to month variations in eddy activity over the pacific ocean show that energy levels increase up through november decreasing thereafter at the same time the trough ridge circulation pattern is intensifying by december baroclinicity in the western pacific has increased substantially and low level eddies are found to break by the middle of the ocean upper level eddies start to break well before reaching the west coast of north america resulting in a displacement of the maximum in y9 2 2 u9 2 westward from its november position and increasing the trough ridge forcing by the high frequency eddies c interannual variability wintertime eddy kinetic energy is seen to extend further eastward through the pacific ocean during the warm phase but displays an abrupt termination during the cold phase anomalies in the eddy transient forcing tend to be quite similar to that of the pacific north american pattern itself the extension of the storm track during the warm phase resembles that of fall conditions and is present in the winter season because the source of low level baroclinicity

a field study of the chemical weathering of ancient sedimentary organic matter weathering profiles developed on organic carbon rich black shales were studied to examine the loss and degradation of organic matter om during weathering and its role in the geochemical carbon cycle analysis of weathered shales reveals between 60 and nearly 100 total organic carbon toc loss in highly weathered samples relative to initial unweathered toc content pyrite loss coincides with or precedes organic carbon loss elemental analysis and flash pyrolysis gas chromatography py gc of kerogen concentrates indicate that there is little or no selective enrichment or depletion of norg containing sorg containing alkylaromatic branched alkyl or long chain n alkyl moieties in most profiles during weathering kerogen o c ratios consistently increase with toc and pyrite loss infrared spectroscopy ir reveals an increase in the relative abundance of c c and c o bonds relative to alkyl c h bonds in progressively weathered samples these results suggest a two component model for kerogen weathering largely non selective oxidation and hydration followed by cleavage dissolution of oxidized kerogen fragments the extent of weathering in a given outcrop is likely limited by a combination of the rate of physical erosion and exposure of the rock to oxidizing surface waters with om type composition playing a lesser role

palaeotsunami deposits a new zealand perspective abstract over the past few years geological investigations of coastal sediments in new zealand have provided evidence of past tsunami the identification of palaeotsunami deposits is helping to increase our knowledge about the sources magnitude and frequency of these events this paper briefly outlines both the key diagnostic characteristics used in new zealand to identify palaeotsunami deposits and the emerging findings related to recent research

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

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

preliminary hydrogeological assessment of late cretaceous tertiary ardley coals in part of the alberta basin alberta canada abstract a preliminary hydrogeological evaluation was undertaken on the gas potential of shallow coals in the pembina warburg exploration area in the alberta basin alberta canada regional data for the late cretaceous tertiary ardley coal zone acz were compiled and supplemented with site specific data collected from a key test well drilled as part of a regional exploration program limited regional pressure data suggest hydraulic communication between the uppermost ardley with the overlying paskapoo formation a comparison between hydraulic head and topography suggests that flow at least in part of the ardley paskapoo is gravity driven however a decoupling of the hydraulic regime appears evident from pressure test data in beds stratigraphically below the uppermost scollard ardley and above the base of scollard at least in the eastern part of the study area where the test well was drilled the decoupling is evident in regional pressure data but the precise stratigraphic position may vary regionally formation waters typically are na hco 3 type with salinities as tds of less than 2000 mg l anomalously high bicarbonate dissolved inorganic carbon or dic concentrations exceeding 1500 mg l with 13 c dic 22 50 and dissolved methane identified in formation waters collected directly from ardley coal in test well 103 point to the presence of secondary biogenic gas the 13 c isotopes for dic coupled with 18 o and 2 h isotopes for associated groundwater and regional hydraulic data suggest that the uppermost ardley coal zone in the eastern part of the study area is part of a regional topographically driven dynamic flow system in which methanogenic processes are modifying groundwater chemistry and gas charging parts of the area whether or not biogenic gas charging in the ardley is pervasive is uncertain the relatively small coal data set requires that further exploration in the study area should consider the presence of microbial gas and the potential for hydrogeological controls on its distribution however further detailed testing will be necessary to develop a consistent and useful database for exploration and development

paleozoic aged microbial methane in an ordovician shale and carbonate aquiclude of the michigan basin southwestern ontario abstract interest in the origin and migrational history of methane in low permeability shales reaches beyond that of resource potential to include the evaluation of such formations as geological barriers for the purposes of isolating surface environments from the impacts of deep exploitation and the deep disposal of waste here we present detailed isotope and geochemical profiles of porewaters and methane from an ordovician shale and carbonate aquiclude on the eastern flank of the michigan basin where a deep geological repository for low and intermediate level nuclear waste is proposed the solute concentrations and stable isotopes of water 18 o and d indicate that this aquiclude hosts saline brine 39 tds originating as evaporated seawater methane concentrations are 13 c and d signatures that are consistent with archaeal methanogenesis and are accompanied by a well defined positive excursion in 13 c of co 2 below the aquiclude porewaters contain lower concentrations of methane with a thermocatalytic signature consistent with regional methane elsewhere in the michigan basin no evidence for archaea was identified by microcosm experiments or through pcr rrna analysis suggesting that the microbial methane present in these sediments is not the result of recent microbial activity based on these results and considering that archaeal activity has not been observed in such hypersaline brines with low water activities

thermal maturity source rock potential and kinetics of hydrocarbon generation in permian shales from the damodar valley basin eastern india abstract this study investigates the source rock characteristics of permian shales from the jharia sub basin of damodar valley in eastern india borehole shales from the raniganj barren measure and barakar formations were subjected to bulk and quantitative pyrolysis carbon isotope measurements mineral identification and organic petrography the results obtained were used to predict the abundance source and maturity of kerogen along with kinetic parameters for its thermal breakdown into simpler hydrocarbons the shales are characterized by a high toc 3 4 mature to post mature heterogeneous type ii iii kerogen raniganj and barren measure shales are in mature late oil generation stage rr raniganj 0 99 1 22 rr barren measure 1 1 1 41 vitrinite is the dominant maceral in these shales barakar shows a post mature kerogen in gas generation stage rr barakar 1 11 2 0 and consist mainly of inertinite and vitrinite the 13corg value of kerogen concentrate from barren measure shale indicates a lacustrine marine origin 24 6 30 84 vs vpdb and that of raniganj and barakar 22 72 25 03 vs vpdb show the organic provenance to be continental the 13c ratio of thermo labile hydrocarbons c1 c3 in barren measure suggests a thermogenic source discrete bulk kinetic parameters indicate that raniganj has lower activation energies e 42 62 kcal mol compared to barren measure and barakar e 44 68 kcal mol temperature for onset 10 middle 50 and end 90 of kerogen transformation is least for raniganj followed by barren measure and barakar mineral content is dominated by quartz 42 63 siderite 9 15 and clay 14 29 permian shales in particular the barren measure as inferred from the results of our study demonstrate excellent properties of a potential shale gas system

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

coupled hydrology and biogeochemistry of paleocene eocene coal beds northern gulf of mexico thirty six formation waters gas and microbial samples were collected and analyzed from natural gas and oil wells producing from the paleocene to eocene wilcox group coal beds and adjacent sandstones in north central louisiana usa to investigate the role hydrology plays on the generation and distribution of microbial methane major ion chemistry and cl br relations of wilcox group formation waters suggest mixing of freshwater with halite derived brines high alkalinities up to 47 8 meq l no detectable so4 and elevated 13c values of dissolved inorganic carbon up to 20 5 vienna peedee belemnite vpdb and co2 up to 17 67 vpdb in the wilcox group coals and adjacent sandstones indicate the dominance of microbial methanogenesis the 13c and d values of ch4 and carbon isotope fractionation of co2 and ch4 suggest co2 reduction is the major methanogenic pathway geochemical indicators for methanogenesis drop off significantly at chloride concentrations above 1 7 mol l suggesting that high salinities inhibit microbial activity at depths greater than 1 6 km formation waters in the wilcox group contain up to 1 6 modern carbon a14c to at least 1690 m depth the covariance of d values of co produced h2o and ch4 indicate that the microbial methane was generated in situ with these late pleistocene or younger waters the most enriched carbon isotope values for dissolved inorganic carbon dic and co2 and highest alkalinities were detected in wilcox group sandstone reservoirs that were co2 flooded in the 1980s for enhanced oil recovery leading to the intriguing hypothesis that co2 sequestration may actually enhance methanogenesis in organic rich formations

logging identification and characteristic analysis of marine continental transitional organic rich shale in the carboniferous permian strata bohai bay basin abstract currently global shale gas exploration and exploitation are focused on marine shale recently major shale gas oil breakthroughs have been made within continental and marine continental transitional shale in china this study will show how transitional shale is of great importance based on geological field surveys core observations thin section analysis organic geochemistry and x ray diffraction we systematically studied the basic geological characteristics including lithology mineral composition and organic geochemistry of this transitional shale by comparative analysis of well logging data from 260 wells in the taiyuan shanxi shale we will show that these methods are effective for identifying organic rich shale from conventional well logs and determining its thickness distribution in the carboniferous permian strata of the taiyuan shanxi transitional coal bearing formation the results indicate that the taiyuan shanxi shale has a high toc most 2 4 and that the lithology is primarily carbonaceous shale with type 2 kerogens the high thermal maturation ro 1 1 favors the generation of gas the mineral components primarily include clay minerals quartz and plagioclase with a moderate brittle mineral content 47 wt and high clay mineral content 51 wt dominated by kaolinite 43 and mixed layer illite smectite 31 the transitional organic rich shale on conventional log curves is generally characterized by higher gamma ray gr neutron porosity cnl acoustic travel time ac resistivity r t potassium k and uranium u readings and a lower density den photoelectric absorption index pe and thorium uranium ratio th u after analyzing the log response characteristics of the organic rich shale the most sensitive logging curves such as cnl ac den pe and u were optimized to conduct logging overlays and to construct cross plots to qualitatively identify organic rich shale the identified organic rich shale amalgamates in the middle upper member of the taiyuan formation and the lower member of the shanxi formation consistent with the results of the toc analysis and practical gas logging based on the qualitative evaluation methods of the modified logr and a multivariate linear regression model we calculated the toc of shale wells in the taiyuan shanxi formation from this we calculated the characteristic values of organic rich shale thickness the results indicate that organic rich shale in the taiyuan formation is thicker than that in the shanxi formation additionally the thickness of organic rich shale within lagoons and deep reed swamp facies are much thicker 25 35 m and 40 80 m than other structural profile types whereas their lateral distribution is less than that of marine shale the relatively small continuous thickness of the single shale layer and high clay content may have negative effects for developing the shale gas potential

isotope techniques for tracing migration of gases in sedimentary basins the isotopic composition of methane is primarily dependent on the stage of maturation of organic matter present in the hydrocarbon source rocks and is not changed during migration the isotopic composition of in situ methane can be estimated from the maturity of the source organic matter migrated methane from deeper more mature sources is recognized by its relative 13 c enrichment compared to indigenous methane examples are presented in this paper to evaluate the migration pattern of gases in sedimentary basins

distribution of total dissolved solids in mcmurray formation water in the athabasca oil sands region alberta canada implications for regional hydrogeology and resource development total dissolved solids tds concentrations of 258 lower cretaceous mcmurray formation water samples in the athabasca oil sands region 54 to 58 n and 110 to 114 w were mapped using published data from recent government reports and environmental impact assessments mcmurray formation waters varied from nonsaline 240 mg l to brine 279 000 mg l with a regional trend of high salinity water approximately following the partial dissolution front of the devonian prairie evaporite formation the simplest hydrogeological explanation for the observed formation water salinity data is that devonian aquifers are locally connected to the mcmurray formation via conduits in the sub cretaceous karst system in the region overlying the partial dissolution front of the prairie evaporite formation the driving force for upward formation water flow is provided by the pleistocene glaciation events that reversed the regional devonian flow system over the past 2 m y in the athabasca region this study demonstrates that a detailed approach to hydrogeological assessment is required to elucidate tds concentrations in mcmurray formation waters at an individual lease area scale the observed heterogeneity in formation water tds and the potential for present day upward flow has implications for both mining and in situ oil sands resource development

natural gas formation in the western nile delta eastern mediterranean thermogenic versus microbial abstract the offshore part of the nile delta is an emerging gas and condensate province and one of the most promising areas for future petroleum exploration and supply in northern africa while the nile delta s hydrocarbon potential and its geological and stratigraphic pattern has been the focus of numerous studies the origin of its gas has been poorly studied in order to characterize the natural gas and to determine whether microbial or thermogenic processes are the dominant generation pathways of methane a regional geochemical study was performed on 38 test gases collected from 9 neogene western nile delta discoveries main constituents of the gases are methane 89 4 99 4 up to pentane with traces of carbon dioxide and nitrogen methane carbon isotopic composition ranges from 66 0 to 39 6 displaying a mixed microbial and thermogenic character for most of the gases microbial gas contributions range from 15 to 95 the mixed and the more thermogenic gases are frequently accompanied by light oils and condensates 41 59 api calculated maturities of the thermogenic gas proportions suggest source rock maturities between 0 8 and 1 4 ro which are actually present in the pre miocene section evidence for microbial alteration of petroleum accumulations in the nile delta is largely manifested in anomalously heavy isotopic compositions of both wet gas components propane and n butane and preferential removal of higher n alkanes from condensates the hydrocarbon accumulations affected by biodegradation are trapped within shallow pliocene reservoirs

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

thermogenic and secondary biogenic gases san juan basin colorado and new mexico implications for coalbed gas producibility the san juan basin is the most prolific coalbed gas basin in the world with 1992 production exceeding 440 gcf footnote 12 4 billion m3 resources of approximately 50 tcf 1 4 trillion m3 and proved reserves of over 6 tcf 170 billion m3 coalbed gas wells with the highest production initial potential greater than 10 mcf day or 0 28 million m3 day occur in the overpressured north central part of the basin hydrologic analysis indicates that overpressure in the fruitland formation is artesian in origin and represents repressuring that developed during the middle pliocene highly permeable laterally continuous coal beds override abandoned shoreline pictured cliffs sandstones and extend to the elevated recharge area in he northern basin to form a dynamic regionally interconnected aquifer system coal rank and basin hydrodynamics control the composition of fruitland coalbed gases which varies significantly across the basin chemically dry gases in the north central part of the basin coincide with meteoric recharge and regional overpressure the consistency of methane dgr13c values across the basin the presence of isotopically heavy carbon dioxide in coalbed gases and bicarbonate in formation waters and biodegraded n alkane distributions of some coal extracts indicate that coalbed gases in the north central basin are a mixture of thermogenic 25 50 secondary biogenic 15 30 and migrated thermogenic 12 60 gases migrated conventionally and hydrodynamically trapped gases in situ generated secondary biogenic gases and solution gases result in gas content that plot on or above the coal sorption isotherm bacteria transported basinward in groundwater flowing from the elevated northern basin margins metabolized wet gas components n alkanes and organic compounds in the coal and generated secondary biogenic methane and carbon dioxide subsequent to coalification uplift erosion and cooling these gases may be limited to basin margins where shallow depths and structural deformation result in higher permeability or may extend more than 35 mi 56 km basinward from the recharge zone the presence of appreciable secondary biogenic gas indicates an active dynamic flow system with overall permeability sufficient for high productivity basin hydrogeology reservoir heterogeneity location of permeability barriers no flow boundaries and the timing of biogenic gas generation and trap devel pment are critical for exploration and development of unconventional gas resources in organic rich rocks

on the dynamics of a storm track abstract an idealized primitive equation model is used to determine the factors controlling the dynamics and maintenance of eddy activity in a storm track the results show that localized regions of enhanced baroclinicity do not necessarily lead to localization of eddy activity by studying the energetics of the storm track it is shown that while baroclinic conversion does indeed correlate with the region of maximum baroclinicity it is the downstream radiation of energy through the ageostrophic geopotential fluxes which acts as a trigger for the development and maintenance of eddy activity over less baroclinic regions extending the region of eddy activity much further downstream from the region of high baroclinicity examples of eddy life cycles are given that show that convergence and divergence of ageostrophic fluxes can dominate baroclinic and barotropic conversion especially in regions with weak baroclinicity factors that may limit the zonal extent of a storm track are discussed evidence of down

the utility of methane clumped isotopes to constrain the origins of methane in natural gas accumulations methane clumped isotope compositions provide a new approach to understanding the formational conditions of methane from both biogenic and thermogenic sources under some conditions these compositions can be used to reconstruct the formational temperatures of the gas and this capability can be applied to common subsets of both biogenic and thermogenic systems additionally there are examples in which clumped isotope compositions do not reflect gas formation temperatures but instead mixing effects and kinetic phenomena such kinetic effects also occur in common and recognizable subtypes of biogenic and thermogenic gases here we review the use of methane clumped isotope measurements for understanding the origin of methane in the subsurface we review methane clumped isotope measurements from numerous biogenic and thermogenic natural gas reservoirs we then place these measurements in the context of common frameworks for identifying the formational conditions of methane including the use of methane 13 c and d values and c 1 c 2 3 ratios finally we propose a framework for how methane clumped isotopes can be used to identify the origin of methane accumulations

hydrogeochemistry and gas compositions of the uinta basin a regional scale overview the geochemistry of formation fluids water and hydrocarbon gases in the uinta basin utah is evaluated at the regional scale based on fluid sampling and compilation of past records the deep formation water is dominated by na cl type where halite dissolution has the greatest effects on water chemistry its distribution and composition is controlled by both the lithology of geological formations and regional hydrodynamics the origin of the saline waters in the southeastern basin is interpreted to be a mix of ancient evaporatively concentrated seawater with meteoric water recharged in the geological past which has experienced water rock interactions at the basin scale three dimensional mapping of the dissolved solid contents further reveals that 1 in the northern uinta basin bordering the uinta mountains significant flushing of the deep basinal brines up to 6 km 3 7 mi depth by meteoric water has occurred and 2 in the central basin groundwater discharge areas along the green river valley regional upwelling of saline waters from 2 to 3 km 1 2 to 1 8 mi depth is occurring moreover gas composition and water gas stable isotope characteristics in the central to southeastern basin indicate the presence of a deep thermogenic and regionally continuous gas deposit in particular gases sampled in this region from the wasatch formation and mesaverde group indicate a similar source rock type iii kerogen of the deeply buried thermally mature mesaverde group in the central to northern basin as well as migration from the natural buttes gas field toward the southeastern basin evidence for biogenic methane formation is observed only in the upper green river formation in the central to northern uinta basin here the organic rich immature green river shales experience meteoric water invasions and formation fluid chemistry and stable isotope compositions are diagnostic of microbial methanogenesis

chemical and isotopic tracers of the contribution of microbial gas in devonian organic rich shales and reservoir sandstones northern appalachian basin in this study the geochemistry and origin of natural gas and formation waters in devonian age organic rich shales and reservoir sandstones across the northern appalachian basin margin western new york eastern ohio northwestern pennsylvania and eastern kentucky were investigated additional samples were collected from mississippian berea sandstone silurian medina sandstone and ordovician trenton black river group oil and gas wells for comparison dissolved gases in shallow groundwaters in devonian organic rich shales along lake erie contain detectable ch4 0 01 50 55 mol with low 13c ch4 values 74 68 to 57 86 and no higher chain hydrocarbons characteristics typical of microbial gas nevertheless these groundwaters have only moderate alkalinity 1 14 8 72 meq kg and relatively low 13c values of dissolved inorganic c dic 24 8 to 0 6 suggesting that microbial methanogenesis is limited the majority of natural gases in devonian organic rich shales and sandstones at depth 168 m in the northern appalachian basin have a low ch4 to ethane and propane ratios 3 35 mol c1 c2 c3 and high 13c and d values of ch4 53 35 to 40 24 and 315 0 to 174 6 respectively which increase in depth reservoir age and thermal maturity the molecular and isotopic signature of these gases show that ch4 was generated via thermogenic processes despite this the geochemistry of co produced brines shows evidence for microbial activity high 13c values of dic 10 slightly elevated alkalinity up to 12 01 meq kg and low so4 values 1 mmole l in select devonian organic rich shale and sandstone formation water samples suggest the presence of methanogenesis while low 13c dic values 22 and relatively high so4 concentrations up to 12 31 mmole l in many brine samples point to so4 reduction which likely limits microbial ch4 generation in the appalachian basin together the formation water and gas results suggest that the vast majority of ch4 in the devonian organic rich shales and sandstones across the northern appalachian basin margin is thermogenic in origin small accumulations of microbial ch4 are present at shallow depths along lake erie and in western ny

comparative optical properties of macerals and statistical evaluation of mis identification of vitrinite and solid bitumen from early mature middle devonian lower mississippian new albany shale implications for thermal maturity assessment abstract vitrinite reflectance vro in is used routinely to quantify thermal maturity in sedimentary basins reflectance and fluorescence of other macerals such as solid bitumen and amorphous organic matter aom can provide an independent means to assess thermal maturity and hydrocarbon generation potential however similarity in petrographic characteristics of these macerals solid bitumen and vitrinite in particular often causes difficulties with their identification and consequently reflectance can be measured on misidentified particles making reported vro values unreliable the purpose of this study is to compare reflectance values of various macerals in early mature shales and to evaluate the implications of misidentifying solid bitumen and vitrinite for assessing thermal maturity to address this issue 15 organic matter rich samples from the middle devonian lower mississippian new albany shale from a corehole in daviess county indiana were selected these samples were chosen because they had distinct and easily identified aom solid bitumen vitrinite and inertinite particles allowing for statistically relevant comparisons vro values 0 57 to 0 65 of the studied sample suite cover the early mature stage and expressed no trend with depth in comparison reflectance values of solid bitumen bro and aom aomro from the same samples are lower and range from 0 44 to 0 52 and 0 27 to 0 31 respectively these differences are accompanied by corresponding differences in chemistry of macerals as demonstrated by the micro ftir technique specifically compared to vitrinite and inertinite solid bitumen shows lower aromaticity and compared to aom and alginite it exhibits shorter aliphatic chains reflectance was observed to vary systematically samples having higher vro also feature elevated solid bitumen and aom reflectance values the relationship between vitrinite and solid bitumen can be expressed by the following equation vitrinite reflectance equivalent vroe in 0 83 bro 0 22 whereas for vitrinite and aom vroe 0 84 aomro 0 38 statistical evaluation of the differences in reflectance values caused by maceral misidentification indicates that in extreme cases when a petrographer cannot distinguish between vitrinite and solid bitumen the reflectance can be shifted by 0 06 0 09 for this set of samples such a difference could shift maturity assessment from early mature to immature in more common cases when the analyst can distinguish between the macerals but has difficulties with their overlapping reflectance interval the reflectance difference that results from misidentification is only within a 0 0 0 02 range therefore if the level of uncertainty in maceral identification can be determined the calculation of vroe values from measured bro can reduce inaccuracy in vro values for interpreting the thermal histories of sedimentary basins which in turn is essential for the assessment of oil and gas resources and for building a successful exploration model

the isotopic structures of geological organic compounds organic compounds are ubiquitous in the earth s surface sediments and many rocks and preserve records of geological geochemical and biological history they are also critical natural resources and major environmental pollutants the naturally occurring stable isotopes of volatile elements d 13 c 15 n 17 18 o 33 34 36 s provide one way of studying the origin evolution and migration of geological organic compounds the study of bulk stable isotope compositions i e averaged across all possible molecular isotopic forms is well established and widely practised but frequently results in non unique interpretations increasingly researchers are reading the organic isotopic record with greater depth and specificity by characterizing stable isotope structures the proportions of site specific and multiply substituted isotopologues that contribute to the total rare isotope inventory of each compound most of the technologies for measuring stable isotope structures of organic molecules have been only recently developed and to date have been applied only in an exploratory way nevertheless recent advances have demonstrated that molecular isotopic structures provide distinctive records of biosynthetic origins conditions and mechanisms of chemical transformation during burial and forensic fingerprints of exceptional specificity this paper provides a review of this young field which is organized to follow the evolution of molecular isotopic structure from biosynthesis through diagenesis catagenesis and metamorphism

the role of stationary eddies in shaping midlatitude storm tracks transient and stationary eddies shape the extratropical climate through their transport of heat moisture and momentum in the zonal mean the transports by transient eddies dominate over those by stationary eddies but this is not necessarily the case locally in particular in storm track entrance and exit regions during winter stationary eddies and their interactions with the mean flow dominate the atmospheric energy transport here it is shown that stationary eddies can shape storm tracks and control where they terminate by modifying local baroclinicity simulations with an idealized aquaplanet gcm show that zonally localized surface heating alone e g ocean heat flux convergence gives rise to storm tracks which have a well defined length scale that is similar to that of earth s storm tracks the storm tracks terminate downstream of the surface heating even in the absence of continents at a distance controlled by the stationary rossby wavelength scale stationary eddies play a dual role within about half a rossby wavelength downstream of the heating region stationary eddy energy fluxes increase the baroclinicity and therefore contribute to energizing the storm track farther downstream enhanced poleward and upward energy transport by stationary eddies reduces the baroclinicity by reducing the meridional temperature gradients and enhancing the static stability transports both of sensible and latent heat water vapor play important roles in determining where storm tracks terminate

biogenic methane and carbon dioxide generation in organic rich shales from southeastern brazil abstract brazilian shale formations are potential biogenic gas systems that are still poorly understood organic rich shales from ponta grossa devonian parana basin irati permian parana basin and tremembe paleogene taubate basin formations were analyzed in order to evaluate their biogenic methane ch 4 generation potential and to constrain environmental and geological conditions that may affect methanogenic metabolism additionally the generation potential of carbon dioxide co 2 was evaluated in combination with ch 4 to constrain brazilian organic rich shales as sources of greenhouse gas to the atmosphere twenty four shale samples were used for batch incubations in dry and wet conditions and after headspace refilling and acetic acid addition during one year physico chemical parameters such as total organic carbon toc specific surface area and pore volume were characterized in order to understand general geologic controls on ch 4 and co 2 production biogenic gas generation rates in dry tests reached up to 3 17 ml t d milliliter per ton of shale per day for ch 4 and 2 45 10 3 ml t d for co 2 during the first 30 days with wet samples producing about 54 more ch 4 and 151 more co 2 than dry samples headspace refilling did not demonstrate significant changes on production rates while acetic acid addition restarted or increased ch 4 and co 2 production rates in several microcosms shales from the irati formation showed the highest methane production rates for both dry and wet tests with unusual ranges of 13 c ch4 and 13 c co2 that may be linked to hydrocarbon biodegradation the studied shale formations have different pore volume and specific surface area but without significant influence over biogenic methane generation

carbon isotope fractionation during natural gas generation from kerogen abstract in petroleum exploration it is important to be able to determine the origin of any gas which is found this paper describes a new method of estimating the source type and maturity of a gas based on a rayleigh fractionation model kerogen is divided conceptually into a labile dominantly oil generating fraction and a refractory gas prone component 13 c of methane from either kerogen type and ethane propane and butane for gases from labile kerogen can be defined as a function of 13 c of the gas precursor groups in kerogen a kinetic isotope fractionation factor k and the extent of gas generation the isotopic ratio of the methane precursors relative to bulk kerogen determined from laboratory pyrolysis are 17 5 for labile kerogen and 1 4 for refractory kerogen values for ethane propane and butane from labile kerogen based on field correlations are 4 9 2 2 and 1 6 respectively the corresponding fractionation factors are 0 9892 0 9919 0 9947 and 0 9975 for methane ethane propane and butane respectively from labile kerogen and 0 9984 for methane from refractory kerogen using these parameters summary diagrams are constructed which allow differentiation of these sources from each other and from biogenic gases and cracked oil and recognition of gases of mixed origin if an independent estimate of 13 c for the source kerogen is possible then 13 c of the gas components can be used to estimate maturity in terms of the gas generation index the fraction of gas potential which has been realized

anaerobic methane oxidation on the amazon shelf anaerobic methane oxidation on the amazon shelf is strongly controlled by dynamic physical sedimentation processes rapidly accumulating physically reworked deltaic sediments characteristic of much of the shelf typically support what appear to be low rates of steady state anaerobic methane oxidation at depths of 5 8 m below the sediment water interface methane oxidation in these cases is responsible for 10 m methane charged sediment directly to seawater in this nonsteady state situation methane is a major source of recently produced co2 and an important reductant for sulfate these observations suggest that authigenic sedimentary carbonates derived from anaerobic methane oxidation may sometimes reflect physically enhanced nonsteady state exposure of methane to sulfate in otherwise biogeochemically unreactive deposits the concentration profiles of ch4 so 4 and co2 in the eroded deposit were reproduced by a coupled reaction transport model this area of the shelf was reexposed to seawater approximately 5 10 years ago based on the model results and the assumption that the erosion of the deposit occurred as a single event that has now ceased the necessary second order rate constant for anaerobic methane oxidation was 0 1 mm 1 d 1

microbial origin of australian coalbed methane bituminous coal seam gases from the permian sydney and bowen basins australia are characterized by 1 methane ethane ratios greater than or equal to 1000 2 dgr13c and dgrd values for methane of 60 10 pmil pdb and 217 17 pmil smow respectively 3 carbon dioxide contents of less than 5 and 4 dgr13c co 2 ch4 values of 55 10 pmil pdb these data suggest that microbial reduction of co2 rather than traditional thermogenic reactions is mainly responsible for gas composition invasions by co2 of deep seated external origins are readily recognized by their isotopic compositions 7 2 pmil pdb

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

identification of source carbon for microbial methane in unconventional gas reservoirs a method is proposed for identifying the carbon source for methane generated by carbonate reduction microbial methanogenesis using the isotopic and compositional mass balance of carbon in cogenerated carbon dioxide co2 and methane microbial methanogenesis from bitumen or petroleum generates more methane than co2 so the carbon isotopic compositions of methane and co2 are relatively heavy and similar to the carbon isotopic composition of thermogenic methane microbial methanogenesis that uses kerogen or recent organic matter as a carbon source generates relatively more co2 than methane therefore methane and co2 have the light carbon typical of shallow microbial methane this concept was quantified and tested against three literature examples to determine if the relative amount of co2 generation could be estimated with sufficient resolution to predict source carbon type and generation temperature in gas shales and coalbed methane antrim shale michigan gases are demonstrated to be derived mainly from immature bitumen in the shale at modern reservoir temperatures and cooler temperatures fruitland coal gases in the western san juan basin are derived mainly from bitumen in oil window maturity coals at modern temperature southwest indiana coal gases are derived mainly from thermally immature kerogen at modern and warmer temperatures identification of the methane carbon source and temperature helps delineate microbial methane resource fairways where fairways are limited by microbial gas generation temperatures may help determine if microbial methane is actively generated today or a relict from earlier microbial generation

gas geochemical evidences for biodegradation of shale gases in the upper triassic yanchang formation ordos basin china abstract fractionation of chemical components and hydrogen carbon isotopic compositions associated with biodegradation of shale gases were determined from typical shale profiles of the upper triassic yanchang formation ordos basin china the results show that the light hydrocarbons c1 c5 of the shale gases were partially degraded by microorganisms and the degradation degree decreased with depth in the profile of well yy22 however the degradation degree of wells fy2 is basically unchanging at different depths and there is no obvious evidence for biodegradation in well yy18 biodegradation of c1 and c2 can occur and the degradation of hydrocarbon gas does not occur in any obvious sequence but instead there are only small differences between the relative degradation rates the relative degradation rates in descending sequence were c3 n c4 n c5 i c5 i c4 c2 c1 with intensification of degradation 13c1 of shale gas showed no obvious change whereas a marked alteration took place in 2hc1 the 13c values of c3 and n c4 did not alter significantly during early biodegradation thus use of exceptional heavy isotopic compositions of those two components to recognize moderate levels of biodegradation is limited in contrast the 13c and 2h values of c2 became more positive even at a low degree of biodegradation hence these are effective parameters for identifying biodegraded gases with a low degree of degradation no obvious change of isotopic composition was observed for the n c5 and i c5 during degradation due to the low relative degradation rates but high content of c1 and c2 biodegradation of c1 and c2 will severely destroy and decrease the gas content of shale gas there is a positive relationship between gas content and total organic carbon toc of shale samples without biodegradation in contrast samples that have experienced biodegradation show an obvious decrease in gas content with toc

the impact of wave packets propagating across asia on pacific cyclone development abstract in this paper ecmwf 40 yr reanalysis data have been examined to study the influence of upper level wave packets propagating across asia into the pacific on surface cyclone development over the pacific previous studies have shown that in winter wave packets propagate across asia over two branches a northern branch over siberia and a southern branch along the subtropical jet across southern asia results presented here show that subsequent to the presence of wave packets on either branch the frequency of occurrence of deep cyclones defined as cyclones with central pressure below 960 hpa as well as explosively deepening cyclones those with a deepening rate of 1 bergeron or more are significantly enhanced this enhancement also clearly follows the wave packet eastward as it propagates across the pacific wave packets from the two branches are found to interfere with each other such that if wave packets of the appropriate configuration are present on both the northern and southern branch s

microbial production and modification of gases in sedimentary basins a geochemical case study from a devonian shale gas play michigan basin an expanded data set for gases produced from the antrim shale a devonian black shale in the michigan basin united states has allowed for a detailed examination of the related chemical and isotopic compositional changes in the solid gas liquid systems that discriminate between microbial and thermogenic gas origin in the antrim shale economic microbial gas deposits are located near the basin margins where the shale has a relatively low thermal maturity and fresh water infiltrates the permeable fracture network the most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water along the basin margins there is also a systematic enrichment in 13c of ethane and propane with decreasing concentrations that suggests microbial oxidation of these thermogenic gas components microbial oxidation accounts not only for the shift in 13c values for ethane but also in part for the geographic trend in gas composition as ethane and higher chain hydrocarbons are preferentially removed this oxidation is likely an anaerobic process involving a syntrophic relationship between methanogens and sulfate reducing bacteria the results of this study are integrated into a predictive model for microbial gas exploration based on key geochemical indicators that are present in both gas and coproduced water one unequivocal signature of microbial methanogenesis is the extremely positive carbon isotope values for both the dissolved inorganic carbon in the water and the coproduced co2 gas in contrast the 13c value of methane is of limited use in these reservoirs as the values typically fall between the commonly accepted fields for thermogenic and microbial gas in addition the confounding isotopic and compositional overprint of microbial oxidation increasing the values to typically thermogenic values may obscure the distinction between methanogenic and thermogenic gas

carbon cycling in the pliocene velenje coal basin slovenia inferred from stable carbon isotopes abstract stable isotopes of carbon were used to trace organic and inorganic carbon cycles and biogeochemical processes especially methanogenesis within different geologic substrates of the pliocene lignite bearing velenje basin in northern slovenia lithotypes of lignite coalbed gases calcified woods xylites carbonate rich sediments and groundwaters were investigated carbon isotope 13 c values of the different lignite lithotypes ranged from 28 1 to 23 0 with the variability likely a function of the original isotopic heterogeneity of the source plant materials and subsequent biogeochemical processes i e gelification fusinitization mineralization of organic matter during the early stage of biomass accumulation and diagenesis in the lignite seam co 2 and ch 4 were the major gas components with small amounts of n 2 the carbon isotope values of co 2 13 c co2 and ch 4 13 c ch4 were highly variable ranging from 9 7 to 0 6 and 70 5 to 34 2 respectively carbon dioxide is likely sourced from a mixture of in situ microbial activity and external co 2 while ch 4 is dominantly sourced from microbial methanogenesis with possible addition of thermogenic gas from deeper formations and the influence of microbial oxidation of methane calcified xylites enriched with 13 c 13 c values up to 16 7 indicate that microbial methanogenesis was active during formation of the basin the 13 c dic values from 17 4 to 3 2 of groundwaters recharging the basin from the triassic aquifer are consistent with degradation of organic matter and dissolution of dolomite groundwaters from the pliocene sandy and lithotamnium carbonate aquifers have 13 c dic values from 9 1 to 0 2 suggestive of degradation of organic matter and enrichment via microbial reduction of co 2

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

fate of injected co2 in the wilcox group louisiana gulf coast basin chemical and isotopic tracers of microbial brine rock co2 interactions the 2800 sandstone of the olla oil field is an oil and gas producing reservoir in a coal bearing interval of the paleocene eocene wilcox group in north central louisiana usa in the 1980s this producing unit was flooded with co2 in an enhanced oil recovery eor project leaving 30 of the injected co2 in the 2800 sandstone post injection this study utilizes isotopic and geochemical tracers from co produced natural gas oil and brine to determine the fate of the injected co2 including the possibility of enhanced microbial conversion of co2 to ch4 via methanogenesis stable carbon isotopes of co2 ch4 and dic together with mol co2 show that 4 out of 17 wells sampled in the 2800 sandstone are still producing injected co2 the dominant fate of the injected co2 appears to be dissolution in formation fluids and gas phase trapping there is some isotopic and geochemical evidence for enhanced microbial methanogenesis in 2 samples however the co2 spread unevenly throughout the reservoir and thus cannot explain the elevated indicators for methanogenesis observed across the entire field vertical migration out of the target 2800 sandstone reservoir is also apparent in 3 samples located stratigraphically above the target sand reservoirs comparable to the 2800 sandstone located along a 90 km transect were also sampled to investigate regional trends in gas composition brine chemistry and microbial activity microbial methane likely sourced from biodegradation of organic substrates within the formation was found in all oil fields sampled while indicators of methanogenesis e g high alkalinity 13c co2 and 13c dic values and oxidation of propane were greatest in the olla field likely due to its more ideal environmental conditions i e suitable range of ph temperature salinity sulfate and iron concentrations

the biogenic methane potential of european gas shale analogues results from incubation experiments and thermodynamic modelling abstract core samples from the lower jurassic posidonia shale lower toarcian wealden black shales both from the lower saxony basin northern germany and from the cambrian ordovician alum shale southern sweden have been investigated for their biogenic gas potential in incubation experiments the sample set represents all stages of thermal maturity from immature to overmature methane and to a higher degree carbon dioxide are generated from all samples by added microorganisms in general overmature samples rr 1 5 show lowest gas generation rates the highest generation rates for produced methane up to 89 mol g 1 day 1 and carbon dioxide 139 mol g 1 day 1 were detected in immature alum shale samples when different hydrocarbon degrading inocula where added whereas the lowest methane production rates were detected in wealden sediments the lightest 13c values for produced methane and carbon dioxide have been detected in posidonia shale samples of oil window maturity such samples are some of the most sensitive for gas generation and exhibit the strongest decreases of hydrogen indices after incubation hydrogeochemical modelling of methane generation fate and behaviour showed that methane formed during the early diagenesis got lost from posidonia shale the mainly investigated shale in this study as the mature posidonia shale is according to the incubation experiments still sensitive for gas generation a production scenario of generically generated methane due to oil degradation is simulated the basic conditions resemble the conditions in the antrim shale in the michigan basin gas production due to dewatering and pressure decrease results in an increase of the gas volumes coupled to a progressive enrichment of carbon dioxide in the produced gas moreover calcite scaling may be the consequence during progressive production similar to the antrim shale in the michigan basin such calcite precipitation has been demonstrated to predominantly occur in natural samples at oil window maturity

simulating the seasonal cycle of the northern hemisphere storm tracks using idealized nonlinear storm track models abstract in this study an idealized nonlinear model is used to investigate whether dry dynamical factors alone are sufficient for explaining the observed seasonal modulation of the northern hemisphere storm tracks during the cool season by construction the model does an excellent job simulating the seasonal evolution of the climatological stationary waves yet even under this realistic mean flow the seasonal modulation in storm track amplitude predicted by the model is deficient over both ocean basins the model exhibits a stronger sensitivity to the mean flow baroclinicity than observed producing too large midwinter eddy amplitudes compared to fall and spring this is the case not only over the pacific where the observed midwinter minimum is barely apparent in the model simulations but also over the atlantic where the october april eddy amplitudes are also too weak when the january amplitude is tuned to be about right the nonlinear model generally produces stronger eddy amplitude with stronger b

constraints on the origins of hydrocarbon gas from compositions of gases at their site of origin it is widely accepted that natural gas is formed from thermal decomposition of both oil in reservoirs and to a lesser extent the organic matter in shales from which the oil was derived1 6 but laboratory pyrolysis experiments on shales do not reproduce the methane rich composition typical of most gas reservoirs7 leading to suggestions7 that other mechanisms such as transition metal catalysis may be important the discrepancy might however instead arise because gas and oil deposits have migrated from their source rocks so that the reservoir composition might not be representative of the composition in the source rocks where the hydrocarbons were generated to address this question we have analysed gas samples coproduced with oils directly from a source rock the bakken shales north dakota usa where the local geology has prevented significant hydrocarbon migration the methane contents of these bakken shale gases are much lower than that of conventional gas reservoirs but are consistent with that from pyrolysis experiments8 9 on these shales thus because these bakken gases form with rather than from oils we argue that compositional differences between gases from source rocks and conventional gas deposits result from fractionation processes occurring after hydrocarbon expulsion from the source rock

pleistocene recharge to midcontinent basins effects on salinity structure and microbial gas generation the hydrogeochemistry of saline meteoric water interface zones in sedimentary basins is important in constraining the fluid migration history chemical evolution of basinal brines and physical stability of saline formation waters during episodes of freshwater recharge this is especially germane for interior cratonic basins such as the michigan and illinois basins although there are large differences in formation water salinity and hydrostratigraphy in these basins both are relatively quiescent tectonically and have experienced repeated cycles of glaciation during the pleistocene exploration for unconventional microbial gas deposits which began in the upper devonian age antrim shale at the northern margin of the michigan basin has recently extended into the age equivalent new albany shale of the neighboring illinois basin providing access to heretofore unavailable fluid samples these reveal an extensive regional recharge system that has profoundly changed the salinity structure and induced significant biogeochemical modification of formation water elemental and isotope geochemistry new formation water and gas samples were obtained from devonian mississippian strata in the illinois basin these included exploration wells in the new albany shale an organic rich black shale of upper devonian age and formation waters from over and underlying regional aquifer systems siluro devonian and mississippian age the hydrostratigraphic relations of major aquifers and aquitards along the eastern margin of the illinois basin critically influenced fluid migration into the new albany shale the new albany shale formation water chemistry indicates significant invasion of meteoric water with d values as low as 46 05 into the shale the carbon stable isotope system 13c values as high as 29 4 coupled with 18o d and alkalinity of formation waters alkalinity 24 08 meq kg identifies the presence of microbial gas associated with meteoric recharge regional geochemical patterns identify the underlying siluro devonian carbonate aquifer system as the major conduit for freshwater recharge into the fractured new albany shale reservoirs recharge from overlying mississippian carbonates is only significant in the southernmost portion of the basin margin where carbonates directly overlie the new albany shale recharge of dilute waters cl 1000 mm into the siluro devonian section has suppressed formation water salinity to depths as great as 1 km across the entire eastern illinois basin margin taken together with salinity and stable isotope patterns in age equivalent michigan basin formation waters they suggest a regional impact of recharge of 18o and d depleted fluids related to pleistocene glaciation devonian black shales at both basin margins have been affected by recharge and produced significant volumes of microbial methane this recharge is also manifested in different salinity gradients in the two basins because of their large differences in original formation water salinity given the relatively quiet tectonic history and subdued current topography in the midcontinent region it is likely that repeated cycles of glacial meltwater invasion across this region have induced a strong disequilibrium pattern in fluid salinity and produced a unique class of unconventional shale hosted gas deposits

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

biogeochemistry of the forest city basin coalbed methane play abstract hydrogeochemical and microbial analyses of co produced formation waters and gas in the forest city basin were coupled to determine the origin of methane in shallow coal seams and make comparisons to commercial shale and coal gas plays in the adjacent illinois michigan and cherokee basins forest city basin coals contain dilute meteoric waters cl

analysis of the developmental characteristics and major regulating factors of fractures in marine continental transitional shale gas reservoirs a case study of the carboniferous permian strata in the southeastern ordos basin central china abstract fractures play an important role in the formation of shale gas reservoirs because they can enlarge the transport channels and aggregation spaces and increase the specific surface area of the gas shale for artificial hydraulic fracturing of these reservoirs the natural fracture system must be fully integrated with the artificial fracture system to form an intact fracture system in this study we first comprehensively examined the fractures in 42 shale gas wells using several approaches including a systematic examination and description of the cores and the casting of thin sections a compilation of the statistics of fracture feature parameters and observation of various analytical and test data such as the mineral composition the organic carbon contents and the rock mechanics properties for specimens from the corresponding fractured intervals the data enabled us to thoroughly explore the developmental features and major factors affecting organic rich shale fractures in the upper paleozoic carboniferous permian marine continental transitional coal bearing formation which is located in the southeastern ordos basin our results reveal that in comparison with the paleozoic marine shale in the united states and southern china as well as the paleozoic basin transitional shale in northern china the upper paleozoic black shale in the ordos basin is primarily characterized by a relatively low content of brittle minerals and a high content of clay ingredients the total content of brittle minerals e g quartz feldspar and siderite was approximately 33 which included 27 quartz and 0 3 k feldspar but did not include carbonate the total content of clay minerals reached 64 and was dominated by mixed layer illite smectite i s which accounted for more than 41 of the total clay ingredients the shale accommodated the widespread development of various types of macro and microfractures in the core specimens medium angle slip fractures and horizontal bedding cracks were the most common types of fractures whereas vertical and high angle fractures and horizontal bedding cracks were underdeveloped in the thin sections microfractures arising in organic matter laminations or at their edges as well as those of tectonic origin were the predominant type of fractures and they were mainly short narrow and open overall the surface fracture ratios of the thin sections were concentrated in a range of approximately 0 1 0 3 the developmental level of the fracture was influenced by various factors including tectonism lithology rock mechanics and organic matter and mineral content thus increased developmental level of fractures was correlated with higher paleostructural elevation and increased sand content whereas the developmental level of microfractures was correlated with high lamellation development high level of organic carbon leading to more pronounced laminations and high contents of quartz mixed layer i s and illite leading to low levels of kaolinite these findings were corroborated by other data generated in this study including the rock mechanics results for the upper paleozoic black shale and silty shale the observation results from the cores and from the thin sections sampled from more than 40 shale gas wells and the anomalies of gas logging

trapping of synoptic scale disturbances into the north pacific subtropical jet core in midwinter 1 over the northwestern nw pacific a subtropical jet stream develops at 30 n in midwinter as the east asian winter monsoon intensifies eddies with subweekly periods propagating through the midlatitude tropopause into the nw pacific storm track tend to be trapped into the jet core 1000 km away from a surface baroclinic zone at 40 n while lifted up by 3 km the trapping appears to weaken the interaction of the upper level eddies with the baroclinic zone thus acting against eddy amplification and thereby contributing to the midwinter minimum in the eddy activity as observed before the late 1980s since then under the reduced trapping effect by the weakened jet upper level eddies tended to propagate right above the surface baroclinic zone while strongly interacting it even in midwinter as in fall and spring this midwinter tendency acted to enhance the eddy amplification that led to the recent disappearance of the activity minimum

elevated ba concentrations in a sandstone aquifer summary groundwaters of the winnipeg formation have been found to have ba concentrations in excess of drinking groundwater guidelines over an area of several hundred square kilometers water samples are at or near barite saturation however so 4 concentrations are exceedingly low this inequality suggests that so 4 is being lost from the groundwater allowing for a buildup of ba in solution as barite saturation is maintained the focus of this study is to investigate the relationship between ba and so 4 and its application to anomalously high ba concentrations found in the formation these relationships are investigated through the use of transport modeling in phreeqc the model consists of the mixing two end member waters that are found within the formation reacting the mixed water with dissolved organic carbon and transporting the newly mixed and reacted water through the formation

assessing compositional variability and migration of natural gas in the antrim shale in the michigan basin using noble gas geochemistry abstract this study uses stable noble gases he ne ar kr xe volume fractions and isotopic ratios from antrim shale natural gas to assess compositional variability and vertical fluid migration within this reservoir in addition to distinguishing between the presence of thermogenic versus biogenic methane r ra values where r is the measured 3he 4he ratio and ra is the atmospheric value of 1 384 0 013 10 6 vary from 0 01 to 0 34 suggesting a largely dominant crustal 4he component with minor atmospheric and mantle contributions crustal 21ne 40ar and 136xe contributions are also present but the atmospheric component is largely dominant for these gases crustal contributions for 21ne 40ar and 136xe vary between 1 1 and 12 5 between 0 7 and 19 and between 0 1 and 2 7 respectively a few samples present higher than atmospheric 20ne 22ne ratios pointing to the presence of a small mantle ne component high horizontal and vertical variability of noble gas signatures in the antrim shale are observed these are mainly due to variable noble gas input from deep brines and to a smaller extent variable in situ production within different layers of the antrim shale in particular the lachine and norwood members estimated 4he ages considering external 4he input for antrim shale water vary between 0 9 ka and 238 2 ka and match well for most samples with the timing of the major wisconsin glaciation suggesting that antrim shale water was influenced by glaciation induced recharge consistency between measured and predicted 40ar 36ar ratios assuming ar release temperatures 250 c supports a thermogenic origin for most of the methane in these samples this thermogenic methane is likely to originate at greater depths either from the deeper portion of the antrim shale in the central portion of the michigan basin or from deeper formations given that the thermal maturity of the antrim shale in the study area is rather low

joining forces combined biological and geochemical proxies reveal a complex but refined high resolution palaeo oxygen history in devonian epeiric seas abstract two devonian black shale intervals were analysed using a carefully integrated palaeontological geochemical approach to interpret relative bottom water oxygen levels at a resolution and sensitivity possible only through the combined approach biological data presented as both trace and body fossil abundance and size suggest generally low bottom water oxygen conditions the frequently laminated sediments would be viewed traditionally as recording appreciable intervals of anoxic and or euxinic anoxic and h 2 s containing bottom waters the inclusion of parallel geochemical results however refines this perspective well established iron proxies for depositional redox tell us that anoxic and euxinic conditions were intermittent and short lived if present at all manganese and molybdenum data point to conditions with a likelihood of very low oxygen in bottom waters during intervals with high pore water concentrations of hydrogen sulphide near the sediment water interface these elevated sulphide concentrations under iron limited diagenetic conditions varied with organic content and may have further inhibited benthic colonization and an active infaunal community more specifically the combined palaeontological and geochemical data sets point to depleted bottom water oxygen contents with evidence for hydrogen sulphide limited dominantly or exclusively to the pore waters anoxia and euxinia if present occurred only intermittently and lasted only briefly perhaps on seasonal time scales tied to primary productivity cycles or climatically induced variation in water column stratification the time scales and mechanisms of rapid redox variation remain to be studied the details of such transitional and dynamic settings are best viewed from a multi proxy biogeochemical and palaeoecological perspective as an important byproduct geochemical methods refined in multi proxy studies of phanerozoic shales can then be extended with greater utility to precambrian strata without trace and body fossils

correlation of natural gas by use of carbon isotopic distribution between hydrocarbon components the natural distribution of carbon isotopes between hydrocarbon gas components is used for 1 determining a gas s maturity 2 correlating a reservoired gas to its source 3 correlating one reservoired gas with another and 4 recognizing gas mixtures calculated separations of carbon isotopes between the normal alkane components of a natural gas have been related to source rock maturity by use of a single continuous diagram independent of source type actual data from a wide variety of geologic settings and geologic ages confirm this relationship and demonstrate its applicability to the source rock levels of organic metamorphism ranging from 8 to 13 covering the entire range of oil and wet gas generation at greater maturities the wet gas components are found to undergo thermal degradation losing their usefulness for correlation three examples showing indigenous gas west texas non indigenous gas gippsland basin australia and gas mixtures from multiple sources southeastern alberta illustrate exploration applications

sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation south east atlantic off namibia abstract sulfate reduction rates srr and concentrations of so 4 2 h 2 s pyrite sulfur total sulfur ch 4 and organic carbon were measured with high depth resolution through the entire length of the so 4 2 zone and well into the ch 4 zone at two continental slope stations in the eastern south atlantic benguela upwelling area the sediments were characterized by a high organic carbon content of approx 7 5 at geob 3703 and 3 7 at geob 3714 at geob 3703 so 4 2 concentrations decreased linearly with depth to about 40 m at the sulfate methane transition zone smt at 3 5 m while at geob 3714 so 4 2 remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 m at the smt at 6 m direct rate measurements of srr 35 so 4 2 showed that the highest srr occurred within the surface 3 5 cm with peak rates of up to 20 and 7 nmol so 4 2 cm 3 day 1 at geob 3703 and geob 3714 respectively srr decreased quasi exponentially with depth at geob 3703 and the cumulative srr over the length of the so 4 2 zone resulted in an areal srr srr area of 1114 3493 mol m 2 day 1 median value 2221 mol m 2 day 1 at geob 3703 with more than 80 of the total sulfate reduction proceeding in the top 30 cm sediment at geob 3714 srr exhibited more scatter with a cumulative srr area of 398 1983 mol m 2 day 1 median value 1251 mol m 2 day 1 and with 60 of the total sulfate reduction occurring below a depth of 30 cm due partially to a deeply buried zone of sulfate reduction located between 3 and 5 m depths srr peaks were also observed in smt of both cores ostensibly associated with methane oxidation but with rates about 10 times lower than at the surface modeled srr balanced both methane oxidation rates and measured srr within the smt but severely underestimated by up to 89 the total srr area that were obtained from direct measurements modeled and measured srr were reconciled by including solute transport by irrigation described by a non local pore water exchange function which had values of up to 0 3 year 1 in the top sediment and decreased exponentially to zero i e no irrigation at 2 3 meters i e above smt these results suggested that co existing sulfate reduction processes and linear so 4 2 gradients can be maintained by a non local transport mechanism such as irrigation by which pore water in tubes or burrows is exchanged with bottom waters by activities of tube dwelling animals or some similar physical transport phenomenon i e bubble ebullition further support for an irrigation mechanism was found in the observations of open tubes of up to 8 mm id at depths down to 6 m which also contained fecal pellets indicating that these tubes were or had been inhabited

from shale oil to biogenic shale gas retracing organic inorganic interactions in the alum shale furongian lower ordovician in southern sweden methane rich gas occurs in the total organic carbon rich alum shale furongian to lower ordovician in southern sweden the lower part of the thermally immature alum shale was impregnated by bitumen locally generated by heating from magmatic intrusions from the carboniferous to the permian organic geochemical data indicate that the migrated bitumen is slightly degraded in the upper alum shale where methane is the main hydrocarbon in thermovaporization experiments centimeter size calcite crystals occur that contain fluid inclusions filled with oil gas or water the alum shale is thus considered a mixed shale oil biogenic shale gas play the presented working hypothesis to explain the biogenic methane occurrence considers that water soluble bitumen components of the alum shale were converted to methane a hydrogeochemical modeling approach allows the quantitative retracing of inorganic reactions triggered by oil degradation the modeling results reproduce the present day gas and mineralogical composition the conceptual model applied to explain the methane occurrence in the alum shale in southern sweden resembles the formation of biogenic methane in the antrim shale michigan basin united states in both models melting water after the pleistocene glaciation and modern meteoric water may have diluted the contents of total dissolved solids tds in basinal brines such pore waters with low tds contents create a subsurface aqueous environment favorable for microbes that have the potential to form biogenic methane today biogenic methane production rates with shale as the substrate using different hydrocarbon degrading microbial enrichment cultures in incubation experiments range from 10 to 620 nmol per gram and per day

the impact of zonal propagation and seeding on the eddy mean flow equilibrium of a zonally varying two layer model this paper investigates the role of zonal propagation for the equilibration of zonally varying flow it is hypothesized that there exist two ideal limits for very small or very large group speed in the first limit the eddies equilibrate locally with the forcing while in the second limit the equilibration can only be understood in a global sense to understand these two limits and to assess which is more relevant for the extratropical troposphere a series of idealized experiments that involves changing the magnitude of the uniform zonal wind is performed the results of the idealized model experiments suggest that the actual troposphere is likely to be in a transition regime between the two limits but perhaps closer to the global than the local limit near the global limit both the eddy amplitude and local baroclinicity over the baroclinic zone are strongly affected by the amount of upstream seeding when the propagation speed is reduced relative to the control run the zonal mean eddy activity decreases because the residence time increases more over the stable part of the channel than along the baroclinic zone with the decrease in upstream seeding the local supercriticality along the baroclinic zone increases although the increase is moderate the decrease in seeding and increase in baroclinicity partially offset the effects of each other leading to only small changes in the maximum eddy amplitude downstream of the baroclinic zone changes in upstream seeding can also be achieved by enhanced damping when the eddies are locally damped the baroclinicity is also enhanced downstream of the damping region due to reduced eddy fluxes for typical parameters the recovery of the eddy amplitude occurs over very long distances based on these idealized results it is argued that the coexistence of enhanced baroclinicity and weaker eddy amplitude over the pacific storm track as compared to the atlantic storm track is consistent with the effects of strong eddy damping over asia

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

extensive microbial modification of formation water geochemistry case study from a midcontinent sedimentary basin united states the upper devonian antrim shale in the michigan basin is an economically significant source of microbially produced methane along the basin margins where meteoric recharge has been focused oxygen and hydrogen stable isotope compositions of antrim formation waters show that fresh waters recharged from pleistocene glaciation and modern precipitation suppressed basinal brine salinity to great depths and enhanced methanogenesis this paper presents results of integrated elemental and isotope analyses of antrim shale formation waters from the margins and center of the michigan basin focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis cl br na systematics reveal that salinity is controlled not only by mixing between variable amounts of basinal brine and meteoric water but also by halite dissolution where fluids recharged through underlying devonian carbonate aquifers with localized evaporite deposits divalent cations carbonate system parameters and carbon isotope compositions of dissolved inorganic carbon have been systematically and profoundly altered by microbial methanogenesis large decreases in formation water ca mg and ca sr ratios accompany increasing carbonate alkalinity values in areas with high rates of microbial gas production thermodynamic and reaction path modeling show that these changes are consistent with calcite precipitation during progressive microbial methanogenesis similar variations in fluid chemistry are evident in databases from other sedimentary basins containing black shales and coal beds associated with microbial gas microbial methanogenesis may play an important role in the geochemical evolution of divalent cation relationships in crustal fluids and should be considered in models of formation water origin and evolution

differential fluid migration behaviour and tectonic movement in lower silurian and lower cambrian shale gas systems in china using isotope geochemistry abstract isotope geochemistry has been introduced as a means to trace origin of the hydrocarbon and characterize highly productive shale gas systems recently to assess the impact of tectonic movement and the sealing of shale gas systems isotope geochemistry pressure coefficients and the distribution of bitumens are analysed many samples yield isotope geochemical data with typical carbon isotopic reversals 13 c 1 13 c 2 and hydrogen isotopic reversals 13 d c2h6 13 d ch4 in the lower silurian shale gas isotopically reversed gases are considered to originate in sealed self contained petroleum systems besides isotope reversals order degree of shale gas has positive correlation with gas production isotopically normal gases from the lower cambrian indicate that this formation was a continued relatively open petroleum system when oil and gas generated the pressure coefficients of the lower silurian shale gas reservoir range from 1 45 to 2 03 indicating that the reservoir is overpressurized whereas the lower cambrian shale gas reservoir possesses a normal pressure system overpressurization of the lower silurian shale gas reservoir also indicates that it is a well sealed system the distribution and isotope geochemistry of bitumens in the sinian dolomite and cambrian shale suggests that the source rock of the sinian hydrocarbon is the cambrian shale an unconformity induced from tectonic movement during the tongwan period is interpreted to be the fluid migration tunnel and the cause of the differential shale gas content and production finally the isotopic reversals associated with maturity pressure coefficients and tectonic evolution can both assess the preservation conditions of the reservoir and explain the differential fluid migration behaviour

are the northern hemisphere winter storm tracks significantly correlated abstract in this study the correlation between the northern hemisphere winter pacific and atlantic storm tracks is examined using the ncep ncar reanalysis and the 40 yr ecmwf re analysis era 40 as well as unassimilated aircraft observations by examining month to month variability in the 250 hpa meridional velocity variance the correlation between the two storm track peaks is found to be as high as 0 5 during the winters between 1975 76 and 1998 99 here it is shown that the correlation between the two storm tracks can be clearly detected from the aircraft data further analyses of the reanalysis data show that the correlation can also be seen in other eddy variance and covariance statistics including the poleward heat flux at the 700 hpa level the correlation between the two storm tracks as seen in both reanalysis datasets is shown to be much weaker during the period 1957 58 1971 72 suggesting a possible regime transition from largely uncorrelated storm tracks to highly correlated storm tracks

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

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

stable isotope geochemistry of coal bed and shale gas and related production waters a review coal bed and shale gas can be of thermogenic microbial or of mixed origin with the distinction made primarily on the basis of the molecular and stable isotope compositions of the gases and production waters methane ethane carbon dioxide and nitrogen are the main constituents of coal bed and shale gases with a general lack of c2 hydrocarbon species in gases produced from shallow levels and more mature coals and shales evidence for the presence of microbial gas include 13c ch4 values less than 50 covariation of the isotope compositions of gases and production water carbon and hydrogen isotope fractionations consistent with microbial processes and positive 13c values of dissolved inorganic carbon in production waters the co2 reduction pathway is distinguished from acetate methyl type fermentation by somewhat lower 13c ch4 and higher d ch4 but can also have overlapping values depending on the openness of the microbial system and the extent of substrate depletion crossplots of 13c ch4 versus 13c co2 and d ch4 versus 13c h2o may provide a better indication of the origin of the gases and the dominant metabolic pathway than the absolute carbon and hydrogen isotope compositions of methane in the majority of cases microbial coal bed and shale gases have carbon and hydrogen isotope fractionations close to those expected for co2 reduction primary thermogenic gases have 13c ch4 values greater than 50 and 13c values that systematically increase from c1 to c4 and define a relatively straight line when plotted against reciprocal carbon number although coals and disseminated organic matter in shales represent a continuum as hydrocarbon source rocks current data suggest a divergence between these two rock types at the high maturity end in deep basin shale gas reversals or rollovers in molecular and isotopic compositions are increasingly reported in what is effectively a closed shale system as opposed to the relative openness in coal measure environments detailed geochemical studies of coal bed and shale gas and related production waters are essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gases

diabatic and orographic forcing of northern winter stationary waves and storm tracks abstract in this study a dry global circulation model is used to examine the contributions made by orographic and diabatic forcings in shaping the zonal asymmetries in the earth s northern hemisphere nh winter climate by design the model mean flow is forced to bear a close resemblance to the observed zonal mean and stationary waves the model also provides a decent simulation of the storm tracks in particular the maxima over the pacific and atlantic and minima over asia and north america are fairly well simulated the model also successfully simulates the observation that the atlantic storm track is stronger than the pacific storm track despite stronger baroclinicity over the pacific sensitivity experiments are performed by imposing and removing various parts of the total forcings in terms of the nh winter stationary waves in the upper troposphere results of this study are largely consistent with previous studies diabatic forcings explain most of the modeled stationary waves with orographic

microbial generation of economic accumulations of methane within a shallow organic rich shale although methane of bacterial origin is ubiquitous in marine and freshwater sediments economic accumulations of bacterial gases occur mainly at depths of several kilometres in tertiary basins that had high sedimentation rates1 2 here we present an integration of geochemical and isotopic data from gas and water extracted from the upper devonian antrim shale along the northern margin of the michigan basin which demonstrates that significant volumes of bacterial gas have been generated in organic rich shales at depths of less than 600 metres the antrim shale is mainly a self sourced reservoir in contrast to conventional gas deposits that have migrated from a source to a reservoir and has become one of the most actively exploited gas reservoirs3 in the united states the gas forming processes operating at shallow depths in the antrim shale are not unique4 and an understanding of these processes should lead to the identification and development of other economic non conventional gas deposits around the world

distribution composition and origin of coalbed gases in excavation fields from the preloge and pesje mining areas velenje basin slovenia abstract coal gas outbursts especially co 2 present a high risk in mining of lignite in the velenje coal mine located in the velenje basin in northern slovenia a programme of monitoring geochemical parameters was set up to help understand the behaviour of the coalbed gas distribution in advance of the working face using mass spectrometric methods to study its molecular and isotopic compositions and origin coalbed gas samples from four different excavation fields g2 c and k 130 a from the north and south preloge mining area and k 5 a and k 50 c from the pesje mining area which were operational between the years 2010 and 2011 were investigated the major gas components are co 2 and methane temporal changes in the chemical and isotopic composition of free seam gases were observed within boreholes as a function of the advancement of the working face the study also revealed that at a distance of around 120 m from the working face the influence of coal exploitation by the velenje longwall mining method causes coalbed gas to migrate at a distance of 70 m the lignite structure is crushed causing desorption of fixed co 2 from the coal differences in coalbed gas composition at the longwall panels which underlie the unmined area or under previously mined areas were found a high cdmi co 2 co 2 ch 4 100 index with values up to 95 6 was typical for areas of pre mined excavation fields south preloge k 130 a and pesje area k 5 a while in excavation fields with no previous mining activity north preloge g2 c and pesje area k 50 c up to 61 9 vol of ch 4 was detected the concentration measurements and isotopic studies revealed endogenic co 2 including co 2 originating from dissolution of carbonates with 13 c co2 values ranging from 7 0 to 5 5 microbial methane and co 2 with values ranging from 70 4 to 50 and from 11 0 to 7 0 respectively higher 13 c ch4 values ranging from 50 to 19 8 could be attributed to so called secondary processes influencing the 13 c ch4 value such as migration due to lignite excavation escape of isotopically lighter methane in excavation fields g2 c and k 50 c with no premining activity higher 13 c ch4 values could also be explained by migration of methane from deeper strata the 13 c ch4 value also depended on the depth of the excavation field at shallower levels of the excavation field k 5 a a lower 13 c ch4 value was traced indicating microbial gas while at deeper levels higher 13 c ch4 values were found

bacterial methane oxidation in sea floor gas hydrate significance to life in extreme environments samples of thermogenic hydrocarbon gases from vents and gas hydrate mounds within a sea floor chemosynthetic community on the gulf of mexico continental slope at about 540 m depth were collected by research submersible the study area is characterized by low water temperature mean 7 c high pressure about 5 400 kpa and abundant structure ii gas hydrate bacterial oxidation of hydrate bound methane ch sub 4 is indicated by three isotopic properties of gas hydrate samples relative to the vent gas from which the gas hydrate formed 1 methane bound methane is enriched in sup 13 c by as much as 3 8 pdb peedee belemnite 2 hydrate bound methane is enriched in deuterium d by as much as 37 smow standard mean ocean water and 3 hydrate bound carbon dioxide co sub 2 is depleted in sup 13 c by as much as 22 4 pdb hydrate associated authigenic carbonate rock is also depleted in sup 13 c bacterial oxidation of methane is a driving force in chemosynthetic communities and in the concomitant precipitation of authigenic carbonate rock that modifies sea floor geology bacterial oxidation of hydrate bound methane expands the potential boundaries of life in extreme environments

experimental study on the gas generation processes of lacustrine and marine shales in north china source implications for shale gas abstract using a high pressure semi closed thermal simulation system two organic rich lacustrine and marine immature shales from north china were investigated to probe the dynamic processes and potential for the gas generation throughout the oil gas window the results identified at least two processes during gas generation as revealed by changes of the gas dry coefficient c1 c1 5 and carbon isotopic composition of methane 13cmethane the first process is associated with kerogen thermal degradation and occurs during the main phase of oil generation showing an increasing trend of the dry coefficient and 13cmethane the second process begins during the late phase of oil generation accompanied by increasing yields of wet gas components and 13c depleted methane due to the lack of aliphatic carbon in kerogen in the highly to over mature stage as demonstrated by ftir analyses the second process is mainly related to the cracking of kerogen generated bitumen which is retained in the shale the hydrogen content a key parameter for petroleum generation is then used to quantitatively evaluate the gas generation potential from kerogen thermal degradation and retained bitumen cracking mass balance calculations show that kerogen generated bitumen that is retained in lacustrine and marine shales is estimated to contribute 30 of the total gas yields at the stage of 1 5 2 0 ro this result is consistent with the theoretical calculations from xia et al 2013 and has important implications for the shale gas sources and further the shale gas resource assessments before exploration in shale gas petroleum systems

early history of the michigan basin subsidence and appalachian tectonics geometries of cambrian to silurian stratigraphc sequences in the michigan basin record discrete episodes of basin centered subsidence separated by periods of regional tilting backstripping reveals irregular subsidence rates that argue against a simple thermal contraction model depositional facies architecture also reflects episodic subsidence patterns basin centered facies tracts dominating during subsidence reactivations these three lines of evidence indicate that subsidence cessations and reactivations characterize the early history of the michigan basin periods of episodic subsidence correlate temporally with orogenic events in the appalachians suggesting that reactivation of basin subsidence is related to tectonic activity we propose that appalachian orogenic activity caused the episodic subsidence of the michigan basin possibly through weakening of the lower crust and reactivation of a preexisting upper crustal isostatic imbalance

methanogenic microbial community of the eastern paris basin potential for energy production from organic rich shales abstract shallow thermally immature organic rich shales represent considerable resources in the paris basin france we investigated the presence of methanogenic consortia i e syntrophic bacteria and methanogens in the lower toarcian paper shales formation to link geochemical and lithological properties of the rocks to the spatial distribution of microbial communities the presence of methanogenic microbial populations demonstrated via their growth in enrichment cultures occurs throughout most of the rock layers and may be explained by the transport of organics and microorganisms within the formation the enriched consortia were able to utilize the organic matter of the rock as sole carbon source in microcosm indicating a strong potential of these microbial communities for methanogenesis in situ

the role of the central asian mountains on the midwinter suppression of north pacific storminess abstractthe role of the central asian mountains on north pacific storminess is examined using an atmospheric general circulation model by varying the height and the areas of the mountains a series of model integrations show that the presence of the central asian mountains suppresses the north pacific storminess by 20 30 during boreal winter their impact on storminess is found to be small during other seasons the mountains amplify stationary waves and effectively weaken the high frequency transient eddy kinetic energy in boreal winter two main causes of the reduced storminess are diagnosed first the decrease in storminess appears to be associated with a weakening of downstream eddy development the mountains disorganize the zonal coherency of wave packets and refract them more equatorward as the zonal traveling distance of wave packets gets substantially shorter downstream eddy development gets weaker second the central asian mountains suppress the global baroclinic energy conversion the decre

organization of storm tracks in zonally varying flows abstract a simple two layer quasigeostrophic model is employed to investigate the sensitivity of storm tracks to changes in an externally imposed zonally varying large scale flow zonally asymmetric temperature and horizontal deformation fields are varied systematically in order to compare the effects of baroclinicity and horizontal deformation on storm track dynamics the sensitivity of the storm tracks to uniform barotropic zonal flows is also examined the results show two competing processes for storm track organization one associated with a local maximum in baroclinicity and the other with a local minimum in horizontal deformation when the equilibrium state consists of a zonally symmetric temperature field and a barotropic stationary wave the maximum in synoptic scale transient eddy energy storm track is located in the entrance region of the upper jet just downstream of the point of minimum horizontal deformation as zonal variations in baroclinicity become large keeping the upper layer horizo

volumetrically significant recharge of pleistocene glacial meltwaters into epicratonic basins constraints imposed by solute mass balances melting of kilometer thick continental ice sheets during pleistocene glaciation profoundly altered regional scale groundwater flow in the low lying stable interior of the north american craton in this paper we show that large volumes of glacial meltwater penetrated to great depths in underlying sedimentary basins through regionally extensive silurian devonian carbonate aquifers disrupting relatively stagnant saline fluids and creating a strong disequilibrium pattern in fluid salinity these dilute isotopically light meteoric waters migrated into overlying fractured organic rich upper devonian shales and significantly enhanced microbial methanogenesis generating a unique class of natural gas deposits along the shallow basin margins new data on formation water chemistry of upper devonian antrim shale gas wells along the northern and western margins of the michigan basin were integrated with previously published shale data and brines in subjacent silurian devonian carbonates this comprehensive database provides important constraints on fluid and solute transport and makes a compelling case for the reorganization of drinking water resources and salinity structures along the shallow basin margins by pleistocene glaciation na ca cl br relations and mass balance calculations were used to determine the relative volume of meteoric waters and sources of salinity in antrim shale fluids the majority of shale formation waters contain greater than 50 meteoric water with most containing over 80 meteoric water up to 300 m beneath the shale subcrop despite the presence of a strong salinity gradient meteoric water recharge dissolved variable amounts of halite from evaporite bearing silurian devonian carbonates along the flow path into the shale and displaced highly saline nacacl remnant marine brines the majority of antrim shale fluids owe greater than 60 of their salinity to halite dissolution while less than 40 of cl is from mixing with brines in silurian devonian strata oxygen and hydrogen isotope chemistry and carbon 14 age dating indicate these nacl brines were likely generated since the late pleistocene our conceptual model of fluid flow along the michigan basin margins and its role in generation of microbial gas were extrapolated to the larger glaciated midcontinent region where the silurian devonian carbonate subcrop is continuous along the illinois michigan and appalachian basin margins and is overlain by upper devonian black shales major differences in the hydrostratigraphy and fluid salinity of the epicratonic basins controlled the extent of meteoric water invasion and generation of microbial methane increased hydraulic gradients from melting of the continental ice sheets greatly enhanced recharge of dilute waters into deep silurian devonian aquifers and overlying fractured shales reversing regional scale groundwater flow and altering the major ion composition these fluid migration events occurred over relatively short time scales thousands of years compared to well documented basinal scale fluid migration events driven by tectonics and sediment compaction over millions of years understanding the hydrogeochemistry of the saline meteoric water mixing zones and the sources of salinity in sedimentary basins are both important for constraining fluid and solute transport chemical evolution of basinal fluids and physical stability of brines during meteoric water invasion

methanogenic biodegradation of petroleum in the west siberian basin russia significance for formation of giant cenomanian gas pools approximately 1700 tcf 48 trillion m3 of dry gas 99 methane reserves and resources occur in western siberia mostly in shallow 1500 m 4921 ft cenomanian pools in the northern part of the basin this dry gas constitutes about 11 of the world s conventional gas endowment and about 17 of the annual gas production the origin of the dry gas has been debated extensively over the last 45 yr but remains controversial widely discussed hypotheses on the origin include early mature thermogenic gas from coal primary microbial gas from dispersed organic matter or coal and thermogenic gas from deep source rocks however all these hypotheses are in some ways inconsistent with the molecular or isotopic composition of the gases or the results of basin and petroleum systems modeling here i present geochemical and geological evidence that a significant although yet not quantified part of the shallow dry gas in the northern west siberian basin originated from methanogenic biodegradation of petroleum circumstantial evidence includes the occurrence of heavily biodegraded oil legs and residual oil in many cenomanian gas pools as well as geochemical evidence of heavy to slight biodegradation in jurassic albian reservoirs commonly underlying the cenomanian pools direct evidence includes most importantly 13c enriched co2 in pools with biodegraded oil although data are limited which indicates 40 70 wt conversion of oil derived co2 to secondary microbial methane distinctive hydrocarbon molecular and isotopic compositions of most gases in cenomanian pools average dryness c1 sum c1 c5 is 0 9976 average 13c of methane is 51 8 suggest that they represent mixtures of biodegraded thermogenic gases from deep mainly jurassic source rocks and secondary microbial methane with an occasional small addition of primary microbial methane contribution of early mature coal derived gas is possible in areas with the most significant thermal stress of hauterivian aptian sediments but remains speculative review of petroleum habitats of five representative oil gas condensate fields in western siberia including the world s second largest gas field urengoyskoe suggests that methanogenic biodegradation may best explain the observed distribution and properties of fluids in the shallow reservoirs of those fields recognition of secondary microbial gas in western siberia helps explain the observed dominance of gas in the shallow cool northern part of the basin where conditions were more favorable for prolonged petroleum biodegradation than in the central and southern parts of the basin secondary microbial gas has been recognized worldwide and may 1 represent a volumetrically significant exploration target in shallow reservoirs perhaps more significant than primary microbial gas and 2 indicate effective thermogenic petroleum systems in the deeper sections large volumes up to 66 500 tcf 1884 trillion m3 of secondary microbial methane could have been generated from biodegraded petroleum accumulations worldwide although a part of that gas accumulated as oil dissolved free and hydrate bound gas most gas apparently escaped into the overburden atmosphere and ocean and could have affected global climate in the geologic past