environmental isotopes meet 3d geological modelling conceptualising recharge and structurally controlled aquifer connectivity in the basalt plains of south western victoria australia summary to develop a conceptual model of recharge and inter aquifer connectivity for a complex aquifer system in southwestern victoria australia a three dimensional 3d geological model was constructed and used to examine the influence of the regional geology on groundwater composition and age as well as recharge mechanisms the major aquifers are three basalts differentiated on age and geomorphological features and an underlying palaeovalley deep lead system the upper fine grained sediments of the deep lead form an aquitard that separates the basalt from the permeable sands and gravels beneath recharge calculations chloride mass balance and water table fluctuation methods salinity stable isotope tritium and radiocarbon data show that volcanoes and the youngest basalts although volumetrically minor form preferential recharge areas for all the basalts up to 30 mm year and also recharge the deep lead sediments through volcanic necks that penetrate the aquitard infiltration through the thick clay rich soils on the older basalts is small typically 1 2 mm year and saline resulting in a progressive increase of groundwater salinity along the flow path in these basalts the comparison of fault location with groundwater age in the deep lead aquifer suggests that in some areas faults exert significant structural control on groundwater flow this study demonstrates the value of integrating geological hydrogeological and hydrochemical data to identify preferential recharge areas inter aquifer connectivity and the influence of faults on groundwater flow in a complex aquifer system

using environmental isotopes and dissolved methane concentrations to constrain hydrochemical processes and inter aquifer mixing in the galilee and eromanga basins great artesian basin australia summary groundwater recharge processes water rock interaction and the hydraulic connectivity between aquifers of the galilee and eromanga basins in central queensland australia were investigated using stable 2 h 18 o 13 c and 87 sr 86 sr and radiogenic 36 cl isotopes and dissolved methane concentrations complemented by major ion chemistry the central eromanga and the upper sequence of the galilee basins are both sub basins of the great artesian basin gab and the coal seams of the galilee basin are currently explored for their potential as commercial coal seam gas deposits in order to understand the potential influence of depressurisation of coal seams required to release the gas on adjacent aquifers a detailed understanding of recharge processes and groundwater hydraulics of these basins prior to any development is required each of the different isotope systems were used in this study to provide different information on specific processes for example the assessment of 13 c and 87 sr 86 sr ratios suggested that carbonate dissolution is one of the major processes controlling the water chemistry within some aquifers in addition the combined assessment of 2 h 18 o and major ion chemistry indicates that transpiration is the primary process controlling the solute concentration in the gab recharge area whereas evaporation appears to be less significant groundwaters in the galilee basin recharge area outside the limits of the gab are different to any groundwater within the gab units this difference is attributed to the dissolution of potassium bearing micas which are absent in the gab groundwater age estimates based on 36 cl cl ratios suggest that there is a steady increase along the flow paths and this lack of anomalous age estimates from the recharge areas to the deeper parts of the basin indicates that there is no evidence for regional inter aquifer mixing based in isotopes only however dissolved methane concentrations and groundwater chemistry near faults indicates the potential mix of gas and or water from the coal seams into the gab groundwaters suggesting that there may be local influence of faults as gas water conduits

reply to comments by h d holland on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

bioassay for estimating the biogenic methane generating potential of coal samples abstract generation of secondary biogenic methane in coal beds is likely controlled by a combination of factors such as the bioavailability of coal carbon the presence of a microbial community to convert coal carbon to methane and an environment supporting microbial growth and methanogenesis a set of treatments and controls was developed to bioassay the bioavailability of coal for conversion to methane under defined laboratory conditions treatments included adding a well characterized consortium of bacteria and methanogens enriched from modern wetland sediments and providing conditions to support endemic microbial activity the contribution of desorbed methane in the bioassays was determined in treatments with bromoethane sulfonic acid an inhibitor of microbial methanogenesis the bioassay compared 16 subbituminous coal samples collected from beds in texas tx wyoming wy and alaska ak and two bituminous coal samples from pennsylvania pa new biogenic methane was observed in several samples of subbituminous coal with the microbial consortium added but endemic activity was less commonly observed the highest methane generation 80 mol methane g coal 56 scf ton or 1 75 cm 3 g was from a south tx coal sample that was collected from a non gas producing well subbituminous coals from the powder river basin wy and north slope borough ak contained more sorbed original methane than the tx coal sample and generated 0 23 mol g up to 16 scf ton or 0 5 cm 3 g new biogenic methane in the bioassay standard indicators of thermal maturity such as burial depth nitrogen content and calorific value did not explain differences in biogenic methane among subbituminous coal samples no original methane was observed in two bituminous samples from pa nor was any new methane generated in bioassays of these samples the bioassay offers a new tool for assessing the potential of coal for biogenic methane generation and provides a platform for studying the mechanisms involved in this economically important activity

some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins large volumes of carbon dioxide i e up to 90 v v have been encountered in sedimentary basins from various geological settings but their origins remain enigmatic evidence from carbon and noble gas isotope analyses indicate a variety of interpretations for the origins of the co2 including mantle degassing metamorphic reactions or magmatic processes the formation of large accumulations of large volumes of co2 in sedimentary basins is discussed with specific reference to published data from the pannonian basin hungary the cooper eromanga basin australia and the south viking graben north sea these basins have occurrences of large volumes i e over 15 v v of isotopically heavy carbon dioxide thought to be of inorganic origin and although they differ somewhat in terms of sedimentary fill all have major structural features close to the gas accumulations the available geochemical data are currently neither sufficient to confirm the specific origin s of the co2 e g mantle derived carbonate metamorphism nor unscramble co2 mixed from two or more sources ongoing studies especially those involving noble gas analyses should provide fuller answers

preliminary investigation of biogenic gas production in indonesian low rank coals and implications for a renewable energy source indonesia has abundant coal resources at depths suitable to contain substantial volumes of naturally occurring methane which are currently being explored most indonesian coals are thermally immature but are composed of hydrogen rich organic components that are presumed to make them excellent substrates for biogenic methane production gas isotope results from pilot wells in south sumatra reported in this study are interpreted to indicate biogenic origins for the methane corresponding formation water samples were collected and incubated and show the presence of indigenous microbial communities capable of producing methane from indonesian and australian coal although these results are only preliminary they are promising and support the possibility of indonesia developing bio renewable energy from coal seams

recognising biodegradation in gas oil accumulations through the δ13c compositions of gas components a large suite of natural gases 93 from the north west shelf and gippsland and otway basins in australia have been characterised chemically and isotopically resulting in the elucidation of two types of gases about 26 of these gases have anomalous stable carbon isotope compositions in the c1 c4 hydrocarbons and co2 components and are interpreted to have a secondary biogenic history the characteristics include unusually large isotopic separations between successive n alkane homologues up to 29 pdb and isotopically heavy co2 up to 19 5 pdb irrespective of geographic location these anomalous gases are from the shallower accumulations 600 1700 m where temperatures are lower than 75 c the secondary biogenic gases are readily distinguishable from thermogenic gases 74 of this sample suite which should assist in the appraisal of hydrocarbons during exploration where hydrocarbon accumulations are under 2000 m while dissolution effects may have contributed to the high 13c enrichment of the co2 component in the secondary biogenic gases the primary signature of this co2 is attributed to biochemical fractionation associated with anaerobic degradation and methanogenesis correlation between biodegraded oils and biodegraded dry gas supports the concept that gas is formed from the bacterial destruction of oil resulting in secondary biogenic gas furthermore the prominence of methanogenic co2 in these types of accumulations along with some isotopically depleted methane provides evidence that the processes of methanogenesis and oil biodegradation are linked it is further proposed that biodegradation of oil proceeds via a complex anaerobic coupling that is integral to and supports methanogenesis

origin of natural gas in sacramento basin california the remnant of a late mesozoic early cenozoic fore arch basin the sacramento valley is principally a dry gas province complex stratigraphic relations widespread deformation and faulting and the presence of igneous intrusives testify to an active tectonic history sediments are organically immature down to an average of 10 000 ft 3 000 m and are geopressured throughout much of the basin small fields with nitrogen concentrations as high as 88 are found along the shallow eastern margin gases were sampled from 94 producing wells methane dgr13c and dgrd values range from 61 to 15 pmil and 200 to 96 pmil respectively indicating a wide range of source rock maturities wet gases in the western delta area sgrc2 c5 sgrc1 c5 12 5 have ethane dgr13c values between 31 and 20 pmil and propane dgr13c values between 27 and 12 pmil dry gases elsewhere in the basin sgrc2 c5 sgrc1 c5 1 6 have ethane dgr13c values as light as 58 pmil the chemical and stable isotope data are consistent with four principal sources gases in the western delta area were generated from mature source rocks within the oil and condensate window gases in the northern and southeastern basin are mixtures of indigenous gas mostly microbial methane with small quantities of diagenetic ethane dry thermogenic gas migrated from post mature source rocks in the basin deep and nitrogen rich gases thought to originate in metasedimentary rocks deep beneath the sediment these results place logical constraints on the location of productive traps with high btu gas and suggest caution in the interpretation of stable isotope data from other tectonically active basins due to dynamic migration and mixing processes

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

geochemical and stable carbon isotopic composition of coal related gases from the sw upper silesian coal basin czech republic gas associated with carboniferous coal seams and younger miocene sediments in the sw upper silesian basin in czech republic shows wide compositional variation coal related gas extracted from cross measure degassing boreholes as well as gas released during canister desorption of coal samples from three different mines was analyzed to evaluate the genetic origin and the influence of sorption desorption processes on the gas composition analyses comprised the compositional and stable carbon and isotope composition of coal related gases the isotopic composition of gas from cross measure boreholes indicates thermogenic origin in the southern part of the basin and microbial co2 reduction and mixed type origin in the northern part gas from canister desorption shows similar origins but larger compositional and isotopic variation no consistent isotopic fractionation due to desorption could be observed differences in geochemical composition of thermogenic gases could indicate a contribution of gas migrated from deeper formations below the carpathian overthrust

an isotopic study of hydrocarbon generation processes abstract the sources of reservoired liquid hydrocarbons in australia differ substantially from their northern hemisphere counterparts not only are australian source rocks largely of terrigenous origin but the concepts accepted as defining the hydrocarbon potential of source rocks have recently been challenged although isotopic measurements on australian source rocks and liquid hydrocarbon products closely parallel those published from elsewhere new interpretations of these data have been made particularly with regard to d h ratios in coals as interesting as such results may be the most important findings relate to the origins and histories of methane the higher gaseous hydrocarbons and carbon dioxide and the interpretation of these data in terms of hydrocarbon genesis simple northern hemisphere concepts which characterize gases as being biogenic oil associated etc on the bases of their isotopic and chemical compositions are clearly not applicable to the australian scene indeed justification of such precise classifications in the northern hemisphere on the available evidence is also questioned isotopic and compositional data from gases from the cooper bowen sydney and gippsland basins and from the north west shelf australia are reviewed and assessed in terms of generation pathways

characterization of coal derived hydrocarbons and source rock potential of coal beds san juan basin new mexico and colorado u s a coal beds are considered to be a major source of nonassociated gas in the rocky mountain basins of the united states in the san juan basin of northwestern new mexico and southwestern colorado significant quantities of natural gas are being produced from coal beds of the upper cretaceous fruitland formation and from adjacent sandstone reservoirs analysis of gas samples from the various gas producing intervals provided a means of determining their origin and of evaluating coal beds as source rocks the rank of coal beds in the fruitland formation in the central part of the san juan basin where major gas production occurs increases to the northeast and ranges from high volatile b bituminous coal to medium volatile bituminous coal rm values range from 0 70 to 1 45 on the basis of chemical isotopic and coal rank data the gases are interpreted to be thermogenic gases from the coal beds show little isotopic variation 13c1 values range 43 6 to 40 5 ppt are chemically dry c1 c1 5 values are 0 99 and contain significant amounts of co2 as much as 6 these gases are interpreted to have resulted from devolatilization of the humic type bituminous coal that is composed mainly of vitrinite the primary products of this process are ch4 co2 and h2o the coal generated methane rich gas is usually contained in the coal beds of the fruitland formation and has not been expelled and has not migrated into the adjacent sandstone reservoirs in addition the coal bed reservoirs produce a distinctive bicarbonate type connate water and have higher reservoir pressures than adjacent sandstones the combination of these factors indicates that coal beds are a closed reservoir system created by the gases waters and associated pressures in the micropore coal structure in contrast gases produced from overlying sandstones in the fruitland formation and underlying pictured cliffs sandstone have a wider range of isotopic values 13c1 values range from 43 5 to 38 5 ppt are chemically wetter c1 c1 5 values range from 0 85 to 0 95 and contain less co2 2 these gases are interpreted to have been derived from type iii kerogen dispersed in marine shales of the underlying lewis shale and nonmarine shales of the fruitland formation in the underlying upper cretaceous dakota sandstone and tocito sandstone lentil of the mancos shale another gas type is produced this gas is associated with oil at intermediate stages of thermal maturity and is isotopically lighter and chemically wetter at the intermediate stage of thermal maturity as compared with gases derived from dispersed type iii kerogen and coal this gas type is interpreted to have been generated from type ii kerogen organic matter contained in coal beds and carbonaceous shales of the fruitland formation has hydrogen indexes from rock eval pyrolysis between 100 and 350 and atomic h c ratios between 0 8 and 1 2 oxygen indexes and atomic o c values are less than 24 and 0 3 respectively extractable hydrocarbon yields are as high as 7 000 ppm these values indicate that the coal beds and carbonaceous shales have good potential for the generation of liquid hydrocarbons voids in the coal filled with a fluorescent material that is probably bitumen is evidence that liquid hydrocarbon generation has taken place preliminary oil source rock correlations based on gas chromatography and stable carbon isotope ratios of c15 hydrocarbons indicate that the coals and or carbonaceous shales in the fruitland formation may be the source of minor amounts of condensate produced from the coal beds at relatively low levelsof thermal maturity rm 0 7

gas hydrate formation and its accumulation potential in mohe permafrost china abstract the mohe region is an area of continuous permafrost in northernmost china with strong similarities to other known gas hydrate bearing regions permafrost thickness is typically 20 80 m average surface temperature ranges from 0 5 c to 3 0 c and the geothermal gradient is roughly 1 6 c 100 m we estimate that 204 66 1012 m3 of hydrocarbon gases have been generated in the mohe basin from nearly 1000 m middle jurassic dark mudstones providing ample gas source for gas hydrate formation numerous folds in the shallow section provide opportunities to trap gas within sandstones and siltstones reservoirs bounded by competent mudstone seals gas migration to the shallow section is enabled via fault fracture zones and fracture systems based on core description and observations of gas releases from drilled wells we infer that the mohe region could hold large quantities of natural gas in the form of gas hydrate

a new method to determine the depth of the de stressed gas emitting zone in the underburden of a longwall coal mine abstract underground coal mining induces de stressing and fracturing of strata above and below the targeted seams this creates a gas emission zone which contains gas bearing coal seams and strata in the roof and floor of the mined working seam in longwall mining most of the gas released from the emission zone escapes into the coal face and the goaf caved in area behind the coal face where it presents a safety issue depending on the extent and shape of the emission zone various gas drainage strategies could be applied to maximise capture of the gas from the emitting seams we developed and trialled a new method to identify the gas emission zone in the underburden of an underground mine in the sydney basin australia in this operation all coal seams are located below the major targeted seam for mining by measuring the isotopic and molecular composition of gas desorbed from coal cores from exploration drilling and gas collected from the goaf we identified the source of gas and quantified the limit of the emission zone in the underburden of the working coal seam this has allowed drainage to be focused and limited to the required depth our study will assist others to plan the required depth of gas drainage drilling below the floor of mined seams

the influence of petrological properties and burial history on coal seam methane reservoir characterisation sydney basin australia abstract gas content of coals continuously change throughout their burial histories as a result of the changing state of equilibrium of the coal gas system caused by variations in p t conditions and coal rank to fully evaluate the prospectivity of a coalbed methane resource numerous coal properties burial history p t conditions hydrology and the likelihood of secondary biogenic gas generation need to be considered with respect to gas sorption capacity gas contents and permeability previous studies have given differing interpretations on relationships between rank and maceral composition with sorption capacity the maximum gas storing capacities for sydney basin coals is inversely related to rank up to medium volatile bituminous but a coked contact metamorphosed coal has an elevated capacity comparison of sorption capacities of coals having similar ranks and variable maceral group composition indicate that rank has a dominating effect over any effects of organic matter type for the sydney basin coals the in situ gas contents on average increase with depth up to about 600 m and with further increases in depth to 900 m the gas contents tend to plateau or even decrease such a trend probably is consistent with the combined effects of pressure and temperature on the gas sorption capacity during the geological history r mode cluster analyses of the coal and gas properties yield a positive correlation between gas contents and inertinite abundance this is related to undersaturation of the vitrinite rich coals possibly due to higher permeability and consequent leakage of more gas from vitrinite rich coals than from inertinite rich coals although a large amount of methane and other hydrocarbon gases would have been generated in the sydney basin at maximum burial during the early cretaceous a large proportion of the gas might not have been sorbed within the coal due to limited gas sorption capacities and enhanced diffusivity at high temperatures upon uplift gas that migrated from deeper in the sequence or from shallower biological activity may have been sorbed into the coals without secondary gas replenishment however many of these coals remain significantly undersaturated the areas that contain considerable amounts of secondary biogenic gas are highly prospective for coalbed methane production partly because of the higher gas contents but also because of the higher permeability which is required for access of the microbes and nutrients in meteoric waters to fully evaluate prospectivity of coalbed methane resources numerous coal properties burial history geologic setting and the likelihood of secondary biogenic gas generation need to be considered with respect to gas sorption capacity gas contents and permeability

comment on boreham et al 1998 factors controlling the origin of gas in australian bowen basin coals organic geochemistry 29 347 376

composition and origin of coalbed gases in the lower silesian basin southwest poland abstract coalbed gases in the lower silesian coal basin lscb of poland are highly variable in both their molecular and stable isotope compositions geochemical indices and stable isotope ratios vary within the following ranges hydrocarbon chc index chc ch4 c2h6 c3h8 from 1 1 to 5825 wet gas c2 index c2 c2h6 c3h8 c4h10 c5h12 ch4 c2h6 c3h8 c4h10 c5h12 100 from 0 0 to 48 3 co2 ch4 cdmi index cdmi co2 co2 ch4 100 from 0 1 to 99 9 13c ch4 from 66 1 to 24 6 d ch4 from 266 to 117 13c c2h6 from 27 8 to 22 8 and 13c co2 from 26 6 to 16 8 isotopic studies reveal the presence of 3 genetic types of natural gases thermogenic ch4 higher gaseous hydrocarbons and co2 endogenic co2 and microbial ch4 and co2 thermogenic gases resulted from coalification processes which were probably completed by late carboniferous and early permian time endogenic co2 migrated along the deep seated faults from upper mantle and or magma chambers minor volumes of microbial ch4 and co2 occur at shallow depths close to the abandoned mine workings late stage microbial processes have commenced in the upper cretaceous and are probably active at present however depth related isotopic fractionation which has resulted from physical and physicochemical e g diffusion and adsorption desorption processes during gas migration cannot be neglected the strongest rock and gas outbursts occur only in those parts of coal deposits of the lscb which are dominated by large amounts of endogenic co2

origin of natural waters and gases within the upper carboniferous coal bearing and autochthonous miocene strata in south western part of the upper silesian coal basin poland abstract the molecular and stable isotope compositions of coalbed gases from the upper carboniferous strata and natural gases accumulated within the autochthonous upper miocene skawina formation of the debowiec simoradz gas deposit were determined as well as the chemical and stable isotope compositions of waters from the skawina formation and waters at the top of the upper carboniferous strata of the kaczyce ridge the abandoned morcinek coal mine in the south western part of the upper silesian coal basin two genetic types of natural gases within the upper carboniferous coal bearing strata were identified thermogenic ch4 small amounts of higher gaseous hydrocarbons and co2 and microbial ch4 very small amounts of ethane and co2 thermogenic gases were generated during the bituminous stage of coalification and completed at the end of the variscan orogeny degassing desorption of thermogenic gases began at the end of late carboniferous until the late miocene time period and extended to the present day this process took place in the upper carboniferous strata up to a depth of about 550 m under the sealing upper miocene cover a primary accumulation zone of indigenous thermogenic gases is present below the degassing zone up to 200 m depth from the top of the upper carboniferous strata within the weathered complex an accumulation zone of secondary microbial gas occurs waters within these strata are mainly of meteoric origin of the infiltration period just before the last sea transgression in the late miocene and partly of marine origin having migrated from the upper miocene strata then both methanogenic archaebacteria and their nutrients were transported by meteoric water into the near surface carboniferous strata where the generated microbial ch4 saturated coal seams waters within the miocene strata of the debowiec simoradz and zablocie are of marine origin and natural gases accumulated within autochthonous miocene strata of the debowiec simoradz gas deposit were most probably generated by microbial processes of on organic matter dispersed within the strata though some contribution of gases migrating from the carboniferous coal bearing strata cannot be excluded

coalbed methane accumulation and dissipation patterns a case study of the junggar basin nw china abstract the junggar basin is a potential replacement area of coalbed methane cbm development in china to improve the efficiency of cbm exploration we investigated cbm accumulation and dissipation patterns of coal profiles located in the northwestern southern eastern and central junggar basin based on the following criteria burial depth hydrogeological zone cbm origin cbm phase and cbm migration type we identified four types of cbm accumulation patterns 1 a self sourcing cbm pattern containing adsorbed gas of biogenic origin from shallow depth coal within a weak runoff zone 2 an endogenic migration pattern containing adsorbed gas of thermogenic origin from the medium and deep coals within a stagnant zone 3 an exogenic migration pattern containing adsorbed gas of thermogenic origin from deep coal within a stagnant zone and 4 an exogenic migration pattern containing adsorbed and free gas of thermogenic origin from ultra deep coal within a stagnant zone we also identified two types of cbm dissipation patterns 1 shallow depth coal within a runoff zone with mixed origin cbm and 2 shallow and medium deep coal seams with mixed origin cbm cbm migration in low rank coals was more substantial than that adsorbed in high rank coal cbm in shallow coal could easily escape in the absence of closed structures or hydrogeological seals cbm reservoirs occurred in deep coal where oversaturated gas may accumulate future exploration should focus on gas water sealing structures in shallow coalbeds cbm that occurred in adsorbed and free phases and other unconventional natural gas dominated by free gas in the coal stratum should be co explored and co developed

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

beryllium isotopic systematics in island arc volcanic rocks from northeast japan implications for the incorporation of oceanic sediments into island arc magmas abstract we present beryllium be isotopic ratios 10 be 9 be for 55 volcanic rocks from 21 quaternary volcanoes in the northeast japan arc including the hokkaido and central japan areas the nejh although be isotopic ratios in these rocks are much lower than in other arcs reported in the literature they are much higher than in control samples ocean island basalt oib and tertiary basalts that have no recent addition of 10 be hence our results indicate the incorporation of a component derived from subducted sediments in the japan arc magmas two kinds of be isotopic variations were observed in the nejh 1 variations among lava flows of different ages in the same volcano and 2 variations among volcanoes in an along arc or cross arc direction in the first case there are no apparent differences in be isotopic ratios for lavas of the same age but relatively large variations among lavas of different ages and the degree of variation depends on the regional characteristics indicating that regional differences in near surface conditions may affect these be isotopic variations in the second case the progressive decrease in be isotopic ratios in a cross arc direction suggests the continuous incorporation of subducted sediment even in the back arc region the regional along arc be isotopic variations reflect not only the incorporation of sediments into the arc magma but also regional tectonic and or geological and geochemical processes this is the first systematic study of be isotopic systems in the ne japan arc and we provide direct evidence for the incorporation of sedimentary components from the subducting slab into the arc magma including in the back arc region at 300 km from the volcanic front where the wadati benioff zone is at a depth of 290 km

a study of hydrogeology and its effect on coalbed methane enrichment in the southern junggar basin china this paper analyzes regional hydrogeological conditions and divides the study area into three hydrogeological types and seven hydrogeological units to investigate hydrogeology and its effect on coalbed methane cbm enrichment in the southern junggar basin china from this work it is found that the groundwater flow paths in the study area are the joint effects of south to north and west to east flows this study also shows that microbial gases are widely developed although the depth limit of microbial gas occurrence is still unclear in the study area microbial co2 reduction is the leading formation path in the study area except for the houxia region where fermentation is the formation mechanism the abnormally high co2 in stagnant zones i e water flow is slow and stagnant is mainly associated with methanogenesis whereas relatively low co2 microbial or thermogenic is present where water flow is active the average cbm content within the xishanyao formation changes within various hydrogeological units moreover the average cbm content within the badaowan formation of the same hydrogeological unit e g fukang suggests that the hydrogeological and cbm enrichment conditions are different within various structural types overall the hydrogeological conditions exert control on the gas content in the study area that is the gas content is high in stagnant zones finally influenced by supplemental microbial gases changes in the cbm oxidation zone are relatively complex in the study area the depth of which has no obvious correlation with hydrogeological conditions and changes significantly from west to east

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

evaluating the gas content of coals and isolated maceral concentrates from the paleocene guasare coalfield venezuela abstract this work presents the results from evaluating the gases sorbed by coal samples extracted from the paleocene guasare coalfield marcelina formation northwestern venezuela as well as by their distinct maceral concentrates the aim of this work has been to obtain an initial experimental main value of the gas content per unit weight of high volatile bituminous a coal samples from the open pit paso diablo mine an additional goal was to study differences in the ch 4 storage ability of the distinct maceral groups forming part of the coal matrix both the coal samples and the maceral concentrates were studied by thermogravimetric analysis tga in order to determine the temperature to be used in subsequent experiments on line analyses of hydrocarbons c 1 c 2 c 3 and co 2 yielded gas concentrations plus 13 c values thermogenic gas is prevalent in the guasare coals with vitrinite reflectance r o values from 0 65 to 0 88 the amount of gas retained in the coals and maceral concentrates was measured with a special device that allows determination of the volume of gas sorbed by a solid sample subjected to controlled thermal treatment the average coalbed gas concentration obtained was 0 51 cm 3 g the following list of maceral concentrates shows the relative capacity for the volume of sorbed gas per unit weight inertinite low density vitrinite liptinite high density vitrinite it is concluded that the gas volumes retained in the distinct maceral concentrates are not controlled by porosity but rather by their microscopic morphology

stable isotopic and molecular composition of desorbed coal seam gases from the walloon subgroup eastern surat basin australia this study used compositional and stable isotopic analysis to test hypotheses on the distribution and origins of walloon subgroup coal seam gas csg in the eastern surat basin queensland australia the middle jurassic walloon subgroup play differs from many other low rank csg plays particularly in methane carbon isotopic signature i e the csg is not as microbial as could be expected the carbon isotope compositions of desorbed methane from three cored appraisal wells fall within the generally accepted range for thermogenic or mixed gas 13c 58 5 to 45 3 the 13c ch4 values from stratigraphically placed coal core samples increased became more thermogenic from the top of the upper juandah coal measures to the base of the tangalooma sandstone below the tangalooma sandstone in the lower taroom coal measures the 13c ch4 values decreased with increasing depth these positively parabolic 13c profiles tracked total measured gas content in two out of the three wells studied the third well displayed lower variance of 13c ch4 and gas content increased uniformly with depth a genetic classification based on methane stable carbon isotopes alone might interpret this pattern as a transition from microbially to thermogenically sourced methane in the central coal seams however a 13c co2 profile for one well tracks total gas content and 13c ch4 and exhibits an inverse relationship with d ch4 these results together with the mostly dry nature of the gas samples c1 c2 c3 ratios up to 10 000 and relatively uniform d ch4 values d 238 to 202 suggest that microbial co2 reduction is the primary source of walloon subgroup methane as such stratigraphic variations in gas content mainly reflect the extent of microbial methanogenesis we suggest that peak microbial utilisation of h2 co2 occurred at the tangalooma sandstone level enriching the residual co2 pool and derived methane in 13c carbon 13c co2 ch4 and deuterium isotopic differences d h2o ch4 and cross plots of d h2o and 18o h2o are also consistent with kinetic isotope fractionation during microbial mediated carbonate reduction the results are relevant for applying microbially enhanced coal bed methane mecom in the surat basin

coalbed methane in the ruhr basin germany a renewable energy resource abstract around the globe underground hard coal mining leads to a release of methane into the atmosphere about 7 of the global annual methane emissions originate from coal mining in the year 2002 16 countries used coal gas to generate heat and electricity in many cases the exact size of coalbed methane reservoirs is not identified the possibility of a long term gas production and its profitability at single sites are unknown to clarify these points the processes of gas generation as well as the gas in place volume have to be determined both issues are tackled here for the ruhr basin within this basin coal gas samples were taken at 13 gas production sites spread over three samplings within 14 months there were virtually no changes in the concentrations of gas components at single sites within this period the isotope composition of methane 13c methane 40 0 to 57 3 vs pdb revealed that the produced methane is a mixture of gases of thermogenic and microbial origin the microbial contribution of methane seems to be more pronounced at sites of active and especially abandoned coal mining than at unmined places ethane and propane are of thermogenic origin with ethane s isotopic composition tending to heavier values richer in 13c with time this time dependent phenomenon is interpreted as being caused by desorption in addition living methanogenic archaea were detected in mine water samples from depths down to 1200 m

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

spatial temporal variation of seismicity and spectrum of the 1980 earthquake swarm near the izu peninsula japan abstract the spatial temporal variation of seismicity of the 1980 earthquake swarm off the east coast of the izu peninsula japan was investigated hypocentral distribution focal mechanism wave forms and spectra of seismic waves were studied the hypocenters were relocated by using the master event method the forerunning earthquakes which started about one week before the largest shock main shock the 1980 izu hanto toho oki earthquake m 6 7 occurred within the quiescent area of the earthquake activity for the preceding one year the swarm area migrated toward the south with time and triggered the main shock in june 1980 the fault dimension and geometry were estimated from the aftershock area the fault length and width are 14 km and 8 km the strike and dip angles of the fault are n15 w and 65 to n75 e locations of the events in an earlier earthquake swarm 1978 were also examined by using difference in the s p time at five selected stations distributed around the epicentral area the 1978 swarm events were found to have clustered within a very small area of 8 1 km 2 located about 2 km to the west of the 1980 swarm area the earthquakes which occurred after the main shock of the 1980 swarm were classified into two groups aftershocks and swarm events according to the location of epicenters wave forms and spectra of s waves the peak frequencies of spectra were distributed around 5 to 8 hz for the aftershocks and around 10 to 15 hz for the swarm events most of the aftershocks characterized by low frequency content occurred to the south of the main shock within 2 weeks after the main shock the number of aftershocks decayed following the modified omori9s formula with p 1 5 0 3 the swarm activity on the other hand continued intermittently for about 1 month after the main shock the 1980 seismic activity is interpreted as a complex of a foreshock main shock aftershock sequence and swarm activity the direction of the longer axis of the swarm area coincided with the direction of the maximum pressure axis of the main shock the trend of the aftershock zone coincided with the strike of the fault planes of the main shock and aftershocks this feature strongly suggests that tension cracks trending in the maximum stress direction opened prior to the occurrence of the main shock the opening of cracks may be accounted for by increasing of interstitial pore pressure associated with increase in regional stress

geochemical characteristics and isotopic reversal of natural gases in eastern kopeh dagh ne iran abstract natural gas samples from two gas fields located in eastern kopeh dagh area were analyzed for molecular and stable isotope compositions the gaseous hydrocarbons in both lower cretaceous clastic reservoir and upper jurassic carbonate reservoir are coal type gases mainly derived from type iii kerogen however enriched d values of methane implies presence of type ii kerogen related material in the source rock in comparison upper jurassic carbonate reservoir gases show higher dryness coefficient resulted through tsr while presence of c 1 c 5 gases in lower cretaceous clastic reservoir exhibit no tsr phenomenon carbon isotopic values indicate gas to gas cracking and tsr occurrence in the upper jurassic carbonate reservoir as the result of elevated temperature experienced prior to the following uplifts in last 33 37 million years the 13 c of carbon dioxide and 34 s of hydrogen sulfide in upper jurassic carbonate reservoir do not primarily reflect tsr as uplift related carbonate rock dissolution by acidic gases and reaction precipitation of light h 2 s have changed these values severely gaseous hydrocarbons in both reservoirs exhibit enrichment in c 2 gas member with the carbonate reservoir having higher values resulted through mixing with highly mature completely reversed shale gases it is likely that the uplifts have lifted off the pressure on shale gases therefore facilitated the migration of the gases into overlying horizons however it appears that the released gases during the first major uplift 33 37 million years ago have migrated to both reservoirs while the second migrated gases have only mixed with upper jurassic carbonate reservoir gases the studied data suggesting that economic accumulations of natural gas shale gases deeper than upper jurassic carbonate reservoir would be unlikely

composition and origin of coalbed gases in the upper silesian and lublin basins poland abstract coalbed gases in the upper silesian coal basin uscb are highly variable in molecular and stable isotope composition geochemical indices and stable isotope ratios for coalbed gases from uscb vary within the following ranges ch4 c2h6 c3h8 hydrocarbon index from 122 to more than 10 000 cdmi carbon dioxide methane index cdmi co2 co2 ch4 100 from 0 0 to 21 0 13c ch4 from 79 9 to 44 5 d ch4 from 202 to 153 13c c2h6 from 24 6 to 22 3 13c c3h8 24 7 one sample and 13c co2 from 27 2 to 2 8 only two coalbed gases were collected from the lublin coal basin lcb geochemical indices and stable isotope ratios for these samples show the following values hydrocarbon index more than 10 000 cdmi 4 3 and 34 6 13c ch4 67 3 and 52 5 d ch4 201 one sample and 13c co2 13 7 and 11 9 methane higher gaseous hydrocarbons c2 to c5 and carbon dioxide occurring in the coalbed gases in both the uscb and the lcb were generated during the bituminous stage of the coalification process and probably during microbial reduction of carbon dioxide however depth related isotopic fractionation which has resulted from physical e g diffusion and adsorption desorption processes during gas migration cannot be neglected in both basins the coalification process lasted no longer than several ma and was completed at the end of the variscan orogeny at the turn of carboniferous and permian

effects of deep co 2 on petroleum and thermal alteration the case of the huangqiao oil and gas field abstract the co2 rich natural gas from the huangqiao oil and gas field of the subei basin is produced along with crude oil the co2 content ranging from 80 56 to 99 30 and the 3he 4he ratio of 0 94 10 6 to 4 67 10 6 indicates that this includes a substantial fraction of mantle derived co2 in the huangqiao region although the positive carbon isotopic series of alkane gases i e 13c1 the crude oil of the huangqiao region is light or condensate oil with low densities of 0 7933 0 8255 g cm3 saturated hydrocarbons comprise 90 06 97 37 the crude oil while the aromatic non hydrocarbon and asphaltene fractions are very small the n alkanes range from c13 to c34 with highest abundances at c16 and c17 the gas chromatogram of the crude oil shows an unresolved hump or unresolved complex mixture ucm distribution of a complete n alkane series non odd even predominance and major n alkane peaks on the highest positions of the ucm distribution this may indicate that deep mantle derived co2 fluid extracted and accumulated the oil now found in the reservoirs or source rocks

geology spatial distribution of methane content and origin of coalbed gases in upper carboniferous upper mississippian and pennsylvanian strata in the south eastern part of the upper silesian coal basin poland abstract the subject of the investigation was both vertical and horizontal distribution of methane content in coal series within the south eastern part of the upper silesian coal basin in the study area coal deposits are characterized by various methane structures and varied spatial distribution of methane brzeszcze coal deposit located in the upthrow of jawiszowice fault zone represents the so called open methane pattern in which the upper parts of coal bearing series to the depth of 300 500 m seam 327 are naturally degassed beneath methane content rapidly increases with depth and often achieves high values between ten and twenty m 3 ch 4 mg coal daf the area located to the south of jawiszowice fault zone represents the so called closed methane pattern which means that the primary methane zone was reworked due to the forming of carpathian foredeep in the miocene period a thick cover of miocene claystones overlying the carboniferous formations favors gas accumulation in the uppermost parts of the carboniferous coal bearing complex especially in the roof elevations free methane occurs within the elevated part of porous and permeable aziska sandstones covered by miocene claystones the highest methane content characterizes the coal seams which lie within mudstone or upper silesian sandstone series smaller methane content is typical of the seams lying within aziska sandstones the fault tectonics is another factor influencing the distribution of methane content therefore the large size dislocations i e jawiszowice and bzie czechowice fault zones move the high methane coal seams according to throw direction southwards the carboniferous lithology fault tectonics and also miocene claystones covering the carboniferous formations are the crucial factors influencing the various methane contents in the area discussed methane the main component of gases accumulated in coal deposits and the minor components such as ethane propane butanes and carbon dioxide are of thermogenic origin that resulted from variscan coalification whereas the methane of the secondary accumulation in the uppermost part of carboniferous formations beneath the impermeable miocene cover contains a large microbial component which is a result of paleocene infiltration of meteoric waters with nutrients for methane bacteria into the coal series

characterization of the origin of coalbed gases in southeastern illinois basin by compound specific carbon and hydrogen stable isotope ratios abstract coalbed gases and waters from exploratory and production gas wells in the southeastern illinois basin were sampled to assess geochemically the origin of coalbed gases with an emphasis on the springfield and seelyville coal members that are commercially targeted for coalbed methane production in indiana on line analyses of hydrocarbon gases methane to butanes c 1 c 2 c 3 n c 4 i c 4 and co 2 yielded gas concentrations plus d and 13 c values the low thermal maturity of indiana coals with vitrinite reflectance r 0 0 6 is in agreement with an overwhelmingly biogenic isotopic signature of coalbed gases containing 96 methane generated via bacterial co 2 reduction in contrast thermogenic gas was generated in the stratigraphically equivalent coal beds in western kentucky s rough creek graben zone where higher maturities of up to r 0 0 8 were reached owing to tectonic and hydrothermal activity no secondary biogenic methane was observed in more mature western kentucky coal beds where greater burial depth limits the recharge of meteoric water biogenic and thermogenic coalbed gases represent two end members that are compositionally and isotopically distinct microbial biodegradation of thermogenic c 2 hydrocarbon gases in indiana coal beds preferentially targets c 3 and introduces isotope fractionation whereby remaining c 3 is enriched in deuterium and 13 c

the influence of macroscopic texture on biogenically derived coalbed methane huntly coalfield new zealand abstract secondary biogenic gas content can be related to textural characteristics in eocene age subbituminous coals from the huntly coalfield new zealand however the relationships between the two major coal seams in the basin are considerably different despite their close stratigraphic proximity less than 25 m in this study 163 coal samples were collected and desorbed from eight drill holes gas adsorption capacity and proximate analyses were conducted as well as macroscopic logging for coal type and vitrain banding characteristics vitrain bands were quantitatively point counted and the longest dimension of the shortest axis measured three coal types were recognized bright luster non banded bright moderately banded and bright highly banded vitrain band thickness converted to the phi log 2 scale was found to increase across the coal types with the thickest bands being associated with the most banded coal type overall when normalized by seam and location the dataset reveals a relationship between coal type and gas content with the non banded coal type having the highest gas contents and conversely the coal types with the most vitrain bands having the lowest gas contents however when the seams are considered separately it can be seen that in the stratigraphically higher renown coal seam gas has an indirect association with increasing band thickness in agreement with the overall trend while the stratigraphically lower kupakupa coal seam appears to have a direct relationship interestingly the renown seam which has a greater percentage of non banded material generally has a greater methane adsorption capacity as well as a greater gas content compared to the kupakupa seam it is believed these differences are related to macroscopic texture and that the differing proportions of the coal types between the two seams has a fundamental effect on microporosity ultimately controlling the available surface area for gas adsorption

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

the stable isotope geochemistry of australian coals abstract d h 13 c 12 c 18 o 16 o and 34 s 32 s ratios in the organic matrix and organic solvent extracts of australian coals and in the fluids and minerals associated with these coals are reported and reviewed against similar isotopic data for coals from other regions where coals are immature original isotopic differences between macrolithotypes and between solvent extracts lipid concentrates and insoluble residues are largely preserved however with increasing maturity these characteristic differences particularly those between macrolithotypes are rapidly erased conversely where as indicated by low total sulfur contents coals of cretaceous to permian age were deposited under essentially freshwater conditions 34 s values for the organically bound sulfur remain remarkably constant at 4 3 relative to meteoritic sulfur in similar younger tertiary coals the organic sulfur is markedly enriched in 34 s five distinctive isotopic patterns which may be interpreted in terms of the environment of sulfate reduction can be recognized from 34 s 32 s ratio measurements on the various forms of sulfur in australian coals isotopic studies of seam gas hydrocarbons collected in situ show these to be unexpectedly strongly depleted in the heavier isotopes of hydrogen and carbon relative to natural gases from proposed humic sources furthermore no pronounced increase in the 13 c content in methane with increase in rank of the parent coal was observed in addition several sources of associated carbon dioxide have been delineated including normal maturation processes invasion of the seams by magnetic carbon dioxide and interaction of the coal with intrusive magma isotopic exchange between free seam gases is not accepted as an explanation for some unusual isotopic fractionations seen rather the data suggest that these gases may be formed in a state approaching isotopic equilibrium this argument also satisfactorily explains the isotopic compositions of primary siderite and secondary calcite associated with bituminous coal seams however where seams are invaded and permeated with externally derived carbon dioxide usually of magnetic origin carbonates are frequently absent presumably as a result of the action of carbonic acid

coalbed methane from hazard to resource abstract coalbed gas which mainly consists of methane has remained a major hazard affecting safety and productivity in underground coal mines for more than 100 years coalbed gas emissions have resulted in outbursts and explosions where ignited by open lights smoking or improper use of black blasting powder and machinery operations investigations of coal gas outbursts and explosions during the past century were aimed at predicting and preventing this mine hazard during this time gas emissions were diluted with ventilation by airways e g tunnels vertical and horizontal drillholes shafts and by drainage boreholes the 1970 s energy crisis led to studies of the feasibility of producing the gas for commercial use subsequent research on the origin accumulation distribution availability and recoverability has been pursued vigorously during the past two decades since the 1970 s research investigations on the causes and effects of coal mine outbursts and gas emissions have led to major advances towards the recovery and development of coalbed methane for commercial use thus coalbed methane as a mining hazard was harnessed as a conventional gas resource

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

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

co2 storage and gas diffusivity properties of coals from sydney basin australia abstract measurements of co 2 adsorption and diffusion properties of coals are reported for various coalfields within sydney basin new south wales nsw australia adsorption measurements were undertaken using a gravimetric method measurements carried out on 27 coals show that sydney basin coals at co 2 sub critical conditions namely gas pressures below 6 mpa and temperatures below 39 c can adsorb a maximum volume langmuir volume of 40 to 80 m 3 of co 2 per tonne of coal on a dry ash free basis daf the coals used in this study are of sub bituminous to bituminous rank ranging from 0 66 to 1 45 mean maximum vitrinite reflectance and are from depths ranging from about 27 m to 723 m the highest adsorption capacity applies to the highest rank coal which is also the deepest coal the standard deviation between langmuir modeled and measured values is less than 1 5 m 3 t corresponding to a relative error of less than 2 7 for all except one coal based on adsorption isotherms the co 2 storage capacity for in situ seam pressure conditions range from about 6 to 51 m 3 t co 2 diffusion properties of 15 of these coals determined using a newly developed system capable of accurately measuring diffusivity of gases in solid coal indicate that co 2 diffusivity diffusion coefficient in the sydney basin coals varies from 1 2 10 6 to 10 2 10 6 cm 2 s the diffusivity does not show any discernable trend with the variation in depth and rank porosity measured by a mercury injection method varies from 4 to 10 and decreases with increase in coal depth and rank for some of the coal samples adsorption measurements for pure ch 4 co 2 and n 2 indicate that the sydney basin coals can store twice as much co 2 as ch 4 and six times more co 2 than n 2 volume basis also measurement of diffusivity in solid coal samples shows that co 2 diffuses twice as quickly as ch 4 the data obtained from this study and the estimated coal resources in the state of new south wales allow co 2 sequestration potentials to be calculated

biogenic origin of coalbed gas in the northern gulf of mexico coastal plain u s a new coal gas exploration and production in northern louisiana and south central mississippi gulf of mexico basin is focused on the wilcox group paleocene eocene where the depth to targeted subbituminous c to high volatile c bituminous coal beds ranges from 300 to 1680 m and individual coal beds have a maximum thickness of about 6 m total gas content generally excluding residual gas of the coal beds ranges from less than 0 37 cm3 g as analyzed or raw basis 1 2 cm3 g dry ash free basis daf at depths less than 400 m to greater than 7 3 cm3 g as analyzed basis 8 76 cm3 g daf in deeper 1 500 m parts of the basin about 20 wilcox coal gas wells in northern louisiana produce from 200 to 6485 m3 of gas day and cumulative gas production from these wells is approximately 25 million m3 as of december 2006 u s geological survey assessment of undiscovered technically recoverable gas resources in the gulf of mexico coastal plain including northern and south central mississippi indicates that coal beds of the wilcox group contain an estimated mean total 109 3 million m3 3 86 trillion ft3 of producible natural gas to determine the origin of the wilcox group coal gases in northern louisiana samples of gas water and oil were collected from wilcox coal and sandstone reservoirs and from under and overlying late cretaceous and eocene carbonate and sandstone reservoirs isotopic data from wilcox coal gas samples have an average 13cch4 value of 62 6 vpdb relative to vienna peedee belemnite and an average dch4 value of 199 9 vsmow relative to vienna standard mean ocean water values of 13cco2 range from 25 4 to 3 42 vpdb produced wilcox saline water collected from oil conventional gas and coalbed gas wells have dh2o values that range from 27 3 to 18 0 vsmow these data suggest that the coal gases primarily are generated in saline formation water by bacterial reduction of co2 shallow 150 m wilcox coal beds containing freshwater have little or no biogenic gas molecular and isotopic analyses of gas samples collected from conventional gas and oil wells suggests that both biogenic and thermogenic gases are present in and adjacent to the wilcox intervals that contain biogenic coal gases oil probably sourced from thermally mature down structural dip parts of the wilcox group is produced from sandstones within the coal bearing interval gas chromatograms of c10 saturated hydrocarbons from wilcox oils show a depletion of n alkanes probably resulting from biodegradation of the oil isotopic composition of the gases associated with the oils is of mixed themogenic and biogenic origin average 13cch4 44 4 vpdb and average dch4 182 4 vsmow

timing of biogenic gas formation in the eastern qaidam basin nw china abstract quaternary biogenic gas from the qaidam basin nw china is regarded as one of the representative examples of early generation biogenic gas gases formed by microbial activity during sedimentation of source rocks however new age determinations of natural gas and formation waters make this generally accepted assumption questionable gas in the qaidam basin is dominantly methane 99 0 and has 13 c ch 4 values in the range of 68 to 65 reflecting the microbial origin carbon and hydrogen isotope values of methane coupled with carbon isotope values of carbon dioxide and dissolved inorganic carbon dic reflect water derived hydrogen in the methane and a dominant co 2 reduction metabolic pathway for the formation of biogenic methane coproduced formation waters have hydrogen and oxygen isotope values similar to surface water from the golmud and ortmuren rivers t test 0 75 but different from the original formation water t test 1 sequence around 1 35 ma bp this corresponds to a regional uplift erosion and water influx event economic accumulations of biogenic gas were thus most likely generated late in the qaidam basin rather than at the same time as sediment deposition fresh water recharge may be critical to enhancing biogenic methane generation by introducing nutrients and or microbes into the reservoir

late cretaceous stratigraphy and paleoceanographic evolution in the great australian bight basin based on results from iodp site u1512 abstract the upper cretaceous sedimentary sequence at international ocean discovery program site u1512 in the ceduna sub basin of the great australian bight represents a continuous 690 m thick interval of black silty clay and claystone spanning the lower turonian through lower campanian 10 million years sediments were deposited in an elongate e w oriented 2500 km long rift system that developed between australia and antarctica with an open ocean connection to the west and a continental bridge to the east site u1512 cores provide a unique continuous record of late cretaceous deposition in the ceduna sub basin on the hanging wall of the wallaroo fault zone study of u1512 samples could provide both an important high latitude southern hemisphere perspective on climatic evolution during the peak and demise of the cretaceous hothouse and an offshore record of the sedimentation history in the basin during the late cretaceous portion of the gondwanan breakup the upper cretaceous sequence at site u1512 is notable for its lithologic uniformity burrow mottled to massive claystone and silty claystone make up the majority of the almost 700 m section while rare n 28 isolated 2 to 21 cm thick medium to fine sandstone beds are a minor lithology macrofossils present include common inoceramids and rare occurrences of other bivalves and ammonites microfossils include common occurrences of calcareous nannofossils agglutinated and calcareous benthic foraminifera radiolaria and organic walled dinoflagellate cysts as well as rare small surface dwelling planktonic foraminifera carbonate

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

methanogenic pathways of coal bed gas in the powder river basin united states the geologic factor abstract coal bed gas of the tertiary fort union and wasatch formations in the powder river basin in wyoming and montana u s was interpreted as microbial in origin by previous studies based on limited data on the gas and water composition and isotopes associated with the coal beds to fully evaluate the microbial origin of the gas and mechanisms of methane generation additional data for 165 gas and water samples from 7 different coal bed methane bearing coal bed reservoirs were collected basinwide and correlated to the coal geology and stratigraphy the c1 c2 c3 ratio and vitrinite reflectance of coal and organic shale permitted differentiation between microbial gas and transitional thermogenic gas in the central part of the basin analyses of methane 13c and d carbon dioxide 13c and water d values indicate gas was generated primarily from microbial co2 reduction but with significant gas generated by microbial methyl type fermentation aceticlastic in some areas of the basin microbial co2 reduction occurs basinwide but is generally dominant in paleocene fort union formation coals in the central part of the basin whereas microbial methyl type fermentation is common along the northwest and east margins isotopically light methane 13c is distributed along the basin margins where d is also depleted indicating that both co2 reduction and methyl type fermentation pathways played major roles in gas generation but gas from the latter pathway overprinted gas from the former pathway more specifically along the northwest basin margin gas generation by methyl type fermentation may have been stimulated by late stage infiltration of groundwater recharge from clinker areas which flowed through highly fractured and faulted coal aquifers also groundwater recharge controlled a change in gas composition in the shallow eocene wasatch formation with the increase of nitrogen and decrease of methane composition of the coal bed gas other geologic factors such as burial thermal and maturation history lateral and vertical continuity and coalification of the coal beds also played a significant role in controlling methanogenic pathways and provided new perspectives on gas evolution and emplacement the early stage gas produced by co2 reduction has mixed with transitional thermogenic gas in the deeper central parts of the powder river basin to form old gas whereas along the basin margins the overprint of gas from methyl type fermentation represents new gas thus a clear understanding of these geologic factors is necessary to relate the microbiological biogeochemical and hydrological processes involved in the generation of coal bed gas

discussion of the article by a c lasaga and h ohmoto on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

geochemical characteristics and microbial populations of neogene brown coal from zhaotong basin china for the first time in china a preliminary survey of geochemical characteristics and microbial populations of neogene brown coal from zhaotong basin in yunnan province china was conducted to provide a basis for an understanding of the generation of biogenic coal bed methane in this basin coals in this region consist of soft brown coal with lower maturity and good bioactivity as determined by coal petrologic measurements soluble organic matter in coal exhibits the characteristics of unsaturated humic hydrocarbon source rock organics in coal were generally associated with higher plants and lower grade aquatic organisms the bacterial community was dominated by fermentation bacteria and sulfate reducing bacteria were relatively rare

the origin and formation of co2 gas pools in the coal seam of the yaojie coalfield in china abstract high concentrations of co 2 have been observed in the no 2 coal seam in the yaojie coalfield a number of instantaneous co 2 outbursts occurred during coal mining the co 2 concentration range in the eastern coalfield is 18 79 to 96 6 the 13 c co 2 values are mainly in the range of 5 0 to 1 0 pdb suggesting an inorganic origin of co 2 the 3 he 4 he ratios are 0 6 25 9 10 8 and the r ra is 0 0042 0 185 which is a characteristic of crust derived co 2 gas the dynamic thermal metamorphism of the f19 ductile brittle shear zone is believed to result in the release of co 2 from basement marble formations which show an inorganic source of co 2 in the yaojie coalfield the regional geological evolution and multi periodical f19 fault movement control the formation migration and accumulation of the co 2 in addition to the development of co 2 gas pools in the yaojie coalfield the f19 fault played multiple roles in the generation transport and sequestration of gas during the co 2 formation the displacement of ch 4 carbonate generation and pore structure transformation of coal due to a series of physical and chemical effects occurred after co 2 flux into the coal seams

organic geochemical and stable carbon isotopic investigation of coals formed in low lying and raised mires within the eastern alps austria abstract up to 16 m thick coal seams formed in miocene pull apart basins within the eastern alps in low lying and raised mires despite similar rank sub bituminous stage coal quality differs significantly coals from low lying mires e g fohnsdorf are characterized by significantly higher ash yields and sulfur contents than coals from raised mires e g leoben organic geochemical and carbon isotope investigations were performed to assess the differences in facies the fohnsdorf coals are characterized by higher yields of soluble organic matter som slightly higher proportions of hydrocarbons in the som generally lower pristane phytane ratios and the occurrence of high corg normalized n alkane concentrations only n alkane patterns in the leoben samples show a marked odd over even predominance these differences are indicative of a more intensive dys to anaerobic biochemical degradation of plant material within the fohnsdorf mire terpenoid biomarkers characteristic of conifers and angiosperms were detected in the leoben coals whereas the latter are missing in the fohnsdorf samples in the leoben coals higher saturated to aromatic diterpenoid ratios were detected than in the fohnsdorf coals because of similar rank enhanced aromatisation in the fohnsdorf basin is probably related to microbial activity despite this the fohnsdorf coals are characterized by lower hopane concentrations the results imply that the aromatisation of terpenoid biomarkers is governed by the activity of anaerobic rather than aerobic bacteria an overall negative correlation between 13c of organic matter and the degree of aromatisation of diterpenoid biomarkers is observed it is suggested that the carbon isotopic composition results from different extents of microbial degradation of the biomass the fohnsdorf coals are rich in sulfur high contents of coalbed methane were encountered during mining suggesting high activities of anaerobic bacteria in a nearly neutral sulfate bearing brackish environment of the low lying mire and methanogenesis during or after coalification sulfate reduction and methanogenesis are known to increase 13c values of residual organic matter

origin of methane in the elk valley coalfield southeastern british columbia canada coalbead methane is part of the non conventional gas reservoirs and makes a significant contribution to gas production in some parts of the world initially it was assumed that coalbed methane was of thermogenic origin but most recent studies based on isotope and chemical data and taking into account the hydrogeology of the basin have demonstrated that secondary biogenic gases are formed in many coal bearing basins this study using a similar approach evaluated the origin of the gas in the elk valley coalfield located in british columbia canada isotope data in methane samples collected from testhole wells and piezometers show a range that varies from 51 8 to 65 4 and 303 to 415 for 13c and 2h respectively the 2h data which are among the most depleted data reported for coalbed methane have to be related to the very depleted 2h values of the groundwater 148 to 163 isotope and chemical data collected from dic show a trend of increasing 13c values 11 9 to 34 9 associated with an increase in dic concentration 216 to 1650 mg l the most 13c depleted dic and low dic waters are found in the shallow groundwater flow system representing conditions close to recharge areas while the most 13c enriched dic and high concentration dic waters are found in the discharge areas associated with a deep groundwater flow system the dic pattern which is typical for methanogenic aquifers and the isotope data obtained in methane samples clearly indicate that the gas found in the elk valley coalfield is mainly biogenic in origin this study reaffirms that an approach that combines an evaluation of the groundwater flow system the isotopic characterization and concentration pattern of the main carbon pools ch4 and dic and the isotopic characterization of the groundwater is needed to fully evaluate the origin of gases in coal basins