active methanogenesis and acetate utilization in powder river basin coals united states coal deposits of the powder river basin prb in wyoming united states contain significant reserves of natural gas proven to be of biogenic origin the timing of gas generation in this basin and many others is either unknown or questionable luca technologies evaluated the prospect that methanogenesis is ongoing in prb coals using a combined laboratory and field approach the anaerobic bioconversion of coal to methane in laboratory experiments was observed in multiple samples indicating that indigenous microorganisms can generate methane from prb coal acetate was found to be a quantitatively important intermediate in methane formation the detection of microbial metabolites including acetate in coalbed methane formation waters and the ability of prb methanogenic consortia to convert the detected metabolites to methane is also consistent with in situ methanogenesis field tests revealed in situ microbial acetate utilization and significant dilution dispersion and migration of injected water and solutes in the coal seam this is believed to be important for contacting significant coal surface area and important for the measurement of in situ microbial activities collectively this information indicates that methanogenesis is active in the coal seams evaluated in the prb and that all of the methane present in the coals need not be a remnant of past methanogenesis

preliminary research on cbm enrichment models of low rank coal and its geological controls a case study in the middle of the southern junggar basin nw china abstract to date prospecting work on low rank coalbed methane cbm resources in the middle of the southern junggar basin is still in the primary stage and only a few cbm exploration wells or pilot wells have been deployed in local regions systemic understanding of cbm reservoir forming conditions and geological controlling factors is lacking in the study area resulting in the mismatch between cbm well deployment and actual geological conditions as well as poor exploration efficiency in this paper the geological controlling effects of the structure sedimentation and hydrogeology on cbm enrichment are systematically discussed for the first time based on the early cbm exploration achievements the results show that the xishanyao coal and the badaowan coal are developed in the upper and lower part of the neutral surface of a fold respectively the reservoir forming conditions of the badaowan coal are not discussed in this paper due to its poor development the xishanyao coal that developed in the axial part of the syncline is most beneficial to cbm enrichment with concentrated extrusion stress and great methane adsorption capacity while the axial part of the anticline is not favorable for cbm preservation with large tensional stress the gas content of the xishanyao thick seams developed in the syncline is higher average of 4 63 6 34 m3 t than that in the monocline average of 2 84 4 56 m3 t reverse faulting is more beneficial to cbm enrichment than normal faulting due to the better sealing capability the gas content of the xishanyao coal is obviously influenced by the coal thickness and its roof lithology the hydrodynamic conditions and total dissolved solids tds values of coalbed water range greatly on regional scale which leads to a deeper methane weathering zone in the middle west areas 1119 62 m than the eastern liu huanggou areas

geological interpretation of gas content trends walloon subgroup eastern surat basin queensland australia abstract the middle jurassic walloon subgroup is a prolific low rank coal seam gas csg resource in the surat basin australia this study applied a regionally consistent stratigraphic framework model to open file gas desorption and coal property data from 69 cored csg wells to assess spatial trends in gas content and test the influence of large scale geological heterogeneity on present day gas distribution continued successful exploration and production and possible future microbial regeneration of the walloon csg resource require an improved understanding of the controls on gas content distribution across the core region of production in the eastern surat basin the walloon subgroup can be subdivided into upper juandah and lower taroom coal measures separated by a relatively coal barren and sandstone dominated unit tangalooma sandstone within these units lateral variation in coal character is high precluding a regionally agreed coal group or seam correlation while the total dataset shows a general increase in gas content dry ash free d a f with increasing depth as a function of hydrostatic pressure there is considerable scatter in the distribution within individual wells gas content follows one of three trends gas content either 1 increases 2 increases then decreases or 3 decreases with depth trend 2 parabolic wells predominate with the gas content maxima coinciding with the tangalooma sandstone regardless of depth as such gas content layering follows rather than cross cuts the stratigraphy in the majority of wells the change in gas content with depth between the different units and the wells was used to identify domains of different gas gradients which could relate to differing gas saturations and geological setting the well profiles and gas gradients were analysed against available open file coal quality data without strong correlation to rank or type parameters the majority of very high gas gradient values occur in coals within or above the tangalooma sandstone suggesting that it forms a regional scale barrier both to possible gas migration from underlying and higher rank coals and to meteoric and biogenic recharge from above increased ethane values in the upper taroom and tangalooma csg support this interpretation alternatively this distribution may be the result of alternating adsorption desorption cycles linked to burial and uplift the wells containing the highest mean gas gradients span a range of subtle rank and structural domains but generally occur in structural highs under topographic lows with hydrostatic head wells from smaller scale anticlines not associated with topographic surface lows mainly exhibit lower mean gas gradients the study significantly expands the number of published gas content trends and proposes several factors influencing their formation and geographical distribution the results form the basis for future targeted sampling to test for gas origins migration retention and biogenic recharge processes within the surat basin

molecular sequences derived from paleocene fort union formation coals vs associated produced waters implications for cbm regeneration coalbed methane regeneration is of increasing interest and is gaining global attention with respect to enhancement of gas recovery the objective of this study is to determine if there are differences in methanogen nucleic acid sequences associated with low rank coals from the powder river basin wyoming in comparison with sequences that can be recovered from coal bed associated produced waters based on results obtained to date the sequences from the coals appear to be associated with putatively deep rooted thermophilic autotrophic methanogens whereas the sequences from the waters are associated with thermophilic autotrophic and heterotrophic methanogens the recovered sequences associated with coal thus appear to be both phylogenetically and functionally distinct from those that are more closely associated with the produced water to be able to relate such recovered sequences to organisms that might be present and possibly active in these environments it is suggested that direct observation followed by isolation and single cell based physiological molecular analyses be used to characterize methanogenic consortia possibly associated with coals and or produced waters it is also important to characterize the microenvironment where these microbes might be found in both ecological and geological contexts to be able to develop effective ecologically relevant coalbed methane regeneration processes

a survey of the microbial populations in some australian coalbed methane reservoirs isotopic data indicate that coalbed methane cbm in many australian reservoirs comprise secondary biogenic gas however little is known of the microbes active in these reservoirs therefore for the first time in australia a preliminary culture independent survey of the prokaryotic microbial composition of some of these reservoirs was undertaken to provide a basis for an understanding of the origin of the observed biogenic gas four water and three coal samples from the east coast of australia were examined for their prokaryotic diversity by 16s rdna analysis dna was extracted from the samples and amplified using bacterial and archaeal selective primers and the resulting amplicons were cloned and sequenced dna amplicons derived from gram negative bacteria predominated relatively few archaeal and gram positive bacterial sequences were amplified from the original samples by and large coal samples yielded almost exclusively archaeal and proteobacterial amplicons whereas the water samples contained amplicons derived from the remaining proteobacteria e and bacteroidetes amplicons from three genera of archaea were observed none of which were genuine methanogens although the dominant genus archaeoglobus is reported to have some weak methanogenic activity further integrated studies of microbiology hydrochemistry gas geochemistry and geology of cbm reservoirs are continuing in order to better understand the parameters for methane production in eastern australian basins

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

microbial controls on the origin and evolution of coal seam gases and production waters of the walloon subgroup surat basin australia abstract the walloon subgroup coal seam gas csg play in the surat basin queensland is australia s pre eminent onshore gas field concerted multi disciplinary research is underway investigating the distribution origin and composition of waters and gases in this dominantly microbial csg reservoir to guide both continued production and potential microbially enhanced coal bed methane mecom applications however prior to the present research a detailed study of co produced waters and gases from across the surat basin was not available in the public domain this study tested whether co produced water compositional and stable isotopic data show relationships with production gas stable isotope compositions to elucidate further evidence for microbial co2 reduction and explore the down dip geochemical evolution of walloon coal bed waters and gases a total of 41 wells were sampled with 50 water and 25 gas samples spanning the 3 major production areas of the surat basin detailed isotopic and hydrochemical analysis of these samples revealed distinct spatial trends between the different production locales water compositions were distinct for each of the production regions reflecting the different lithologies of adjacent recharge zones differing fluid rock interactions likely different microbial consortia and the extent of methanogenesis on the western side of the basin near roma waters were the freshest with the lowest median values for alkalinity 861 mg l and cl 588 mg l and a 13cdic of 14 2 on the eastern side of the basin the kogan nose waters were the most saline with the highest median values for na 1955 mg l cl 2280 mg l and 13cdic 20 0 also in the east in the present gas fairway the undulla nose waters had the highest median alkalinity 1841 mg l and were found to have a na excess median 1050 mg l and a lower than expected median 13cdic 14 0 co mingled produced methane carbon isotope values 13c 57 0 to 44 5 from both the upper juandah and lower taroom coal measures plot within the mixed thermogenic microbial genetic field by contrast deuterium isotopic difference 2h h2o ch4 values and cross plots of 2h h2o and 18o h2o suggest that microbially mediated co2 reduction is the dominant methane generation process in situ at a given depth the undulla nose waters in the east are more depleted in 2h and 18o than elsewhere in the surat basin which may suggest these samples have been more heavily impacted by water rock microbial reactions 14c values from the 3 production regions 0 115 to 1 769 pmc age 32 400 to 50 000 years before present b p suggest that walloon coals likely recharged in the last 50 000 years limit of radiocarbon dating consistent with these dates 2h h2o and 18o h2o values for the surat basin 2h 32 to 56 18o 5 9 to 9 0 echo the stable isotopic composition of meteoric waters during the initial part of the last glacial period in southeast queensland based on a strong correlation between 2h ch4 and 2h h2o we suggest that methane was generated since the late pleistocene pca analysis showed a degree of positive correlation between total alkalinity and both the 13cdic median 14 2 and 13c ch4 median 52 1 vectors that is consistent with finite reservoir effects the results inform ongoing studies of gas distribution and origins and mecom potential in the surat basin and underpin a broader study examining aquifer interactions

controls on coal cleat spacing this study was undertaken to determine the relationship between cleat spacing cleat height and coal banding texture for queensland permian age coals of different rank four of which are presented here whereas relationships between cleat frequency and rank and with coal type or grade have been reported in the past relationships between the spacing and height among the different kinds of cleats are not quantitatively established for other layered sedimentary rocks joint or fracture spacing relates directly to both bed thickness and rock strength coal is similar to other layered rocks four major classes of cleats were distinguished which were separate data populations when cleat spacing was plotted against cleat height master cleats single vitrain layer cleats multiple vitrain layer package cleats and durain dull coal cleats understanding the relationship between cleat height and spacing for specific coals and the specific kinds of cleats within those coals will lead to more accurate predictions of cleat density and hence coal permeability this can improve modelling and prediction of methane gas deliverability in coal seams in the australian permian coals studied narrowly spaced cleats exist at all ranks but the distribution of cleat spacing with cleat height is what varies for specific cleat classes cleat spacing was found to be directly proportional to cleat height in most cases

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

benthic foraminiferal response to variations in surface water productivity and oxygenation in the northern arabian sea abstract a benthic foraminiferal record of 120 000 year obtained from the base of the oxygen minimum zone omz at a site in the northern arabian sea was studied quantitative benthic foraminiferal data were compared with palaeoproductivity indices corg and globigerina bulloides and indices for bottom water oxygen concentration pteropod preservation index mo al v al and mn al the benthic foraminiferal record revealed two distinct assemblages that show variations in the precession frequency band a high diversity low equitability assemblage proliferates in isotopic stages 1 4 and 5 and has been interpreted to reflect relatively oxygenated bottom water conditions this assemblage shows a strong covariance with minima in summer monsoon productivity a low diversity low equitability fauna typically with a few species showing high dominances is considered to reflect low bottom water oxygen conditions related to eutrophic surface water conditions dominating species in this assemblage are bolivinids buliminids and globobuliminids this assemblage dominates during precession driven maxima in summer surface water productivity and also during isotopic stages 2 and 3 we suggest that an intensified and colder glacial winter ne monsoon led to increased winter production which superimposed on the precession driven changes in surface water productivity resulted in overall poorly oxygenated bottom water during glacial stages 2 and 3 a promising proxy for tracing winter productivity in the northern arabian sea is the planktonic foraminifer globigerina falconensis the benthic foraminiferal species rotaliatinopsis seminvoluta in particular is prolific under glacial conditions

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

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

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

assessing aquitard hydraulic performance from hydrocarbon migration indicators surat and bowen basins australia abstract basin hydrodynamic assessment methods are being applied to australia s developing coal seam gas csg to liquefied natural gas lng export developments in the queensland s bowen and surat basins technical challenges include the need to predict the cumulative impacts of csg production on formation pressure in adjacent great artesian basin aquifers and assess to what degree if any there may be fugitive methane liberated from the reservoir but not captured by production wells both these challenges require an understanding of the distribution of aquitard hydraulic sealing performance we use hydrocarbon systems analysis to illuminate basin scale geological seal performance of the low permeability strata and provide baseline data on hydrocarbons in groundwater we collected indicators of hydrocarbons including 1 drill stem wireline and production test sample analysis 2 staining fluorescence and streaming hydrocarbon occurrences from drill cuttings and core and 3 mud log gas detector data this data was allocated to stratigraphic horizons mapped and compared to the geographic stratigraphic location of source rocks conventional and unconventional reservoired hydrocarbons and aquitard sealing strata and faults we found asymmetric trapping of conventional hydrocarbon reservoirs with eastern basin leakage and western basin preservation indications of some thermogenic gas in the walloon coal measures exist yet maturity indicators are sub thermogenic suggesting that although much of the walloon coal measures gas is biogenic thermogenic gas may have previously migrated into the walloon coal measures from elsewhere stratigraphically below the walloon coal measures hydrocarbon migration indicators are often clustered along lineations such as the moonie goondiwindi and burunga leichhardt fault systems at the top of the walloon coal measures hydrocarbon migration indicators are clustered along the northeastern subcrop edge of the basin where the muddy strata at the top are either thin or eroded suggesting vertical leakage occurred to the overlying springbok sandstone aquifer whilst we can see where seals are either more or less effective at this stage we cannot make a quantitative assessment of background methane flux to surface or potential future proportional allocation of methane flux to natural vs anthropogenic causes

microbial degradation of sedimentary organic matter associated with shale gas and coalbed methane in eastern illinois basin indiana usa molecular biodegradation indices for extracts from five pennsylvanian coals and six new albany shale devonian mississippian samples from the eastern part of the illinois basin help constrain relationships between the degradation of biomarkers and the generation of coalbed methane and shale gas investigation of these gas source rocks of varying thermal maturity from different depths facilitates evaluation of the association of microbial degradation with biogenic gas formation distinct from thermogenic processes extensive biodegradation of both aliphatic and aromatic hydrocarbons is observed in the coal extracts whereas in shale extracts only short chain c15 c19 n alkanes from the shallowest depth appear to be microbially altered with minimal evidence for losses of acyclic isoprenoid alkanes and aromatic hydrocarbons by contrast biodegradation of aromatic hydrocarbons specifically alkylated naphthalenes and phenanthrenes occurs in coal extracts in concert with losses of n alkanes attributable to microbial activity thus the progress of hydrocarbon biodegradation in coals differs from the sequence recognized in petroleum where the effects of microbial alteration of aromatic constituents only appear after extensive losses of aliphatic compounds the extent of hydrocarbon biodegradation in these coals also decreases with depth as recorded by the nc25 nc30 index i e abundance relative to 17 h 21 h hopane among the aliphatic constituents and several aromatic compounds methyl dimethyl and trimethylnaphthalenes phenanthrene and trimethyl and tetramethylphananthrenes however the depth variations in the distributions of aliphatic and aromatic hydrocarbons in the shale extracts primarily reflect the effects of thermal maturity rather than biodegradation overall variations in the extent and patterns of biomarker biodegradation among coals and shales likely reflect their distinct microbial consortia that can be attributed to differences in i surviving microorganisms and inoculations from meteoric water ii the characteristics of the sedimentary organic matter especially the preponderance of aromatic constituents in coals and iii the accessibility to that substrate through pores and cleats these results help constrain the processes involved in biodegradation and controls on its extent which in turn assist in recognizing sites favorable for methanogenesis and improved estimates of biogenic gas resources in the illinois basin

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

sangay volcano ecuador structural development present activity and petrology abstract sangay 5230 m the southernmost active volcano of the andean northern volcanic zone nvz sits 130 km above a 32 ma old slab close to a major tear that separates two distinct subducting oceanic crusts southwards quaternary volcanism is absent along a 1600 km long segment of the andes three successive edifices of decreasing volume have formed the sangay volcanic complex during the last 500 ka two former cones sangay i and ii have been largely destroyed by sector collapses that resulted in large debris avalanches that flowed out upon the amazon plain sangay iii being constructed within the last avalanche amphitheater has been active at least since 14 ka bp only the largest eruptions with unusually high plinian columns are likely to represent a major hazard for the inhabited areas located 30 to 100 km west of the volcano however given the volcano s relief and unbuttressed eastern side a future collapse must be considered that would seriously affect an area of present day colonization in the amazon plain 30 km east of the summit andesites greatly predominate at sangay there being few dacites and basalts in order to explain the unusual characteristics of the sangay suite highest content of incompatible elements except y and hree of any nvz suite low y and hree values in the andesites and dacites and high nb la of the only basalt found a preliminary five step model is proposed 1 an enriched mantle in comparison with an morb source or maybe a variably enriched mantle at the site of the sangay prior to quaternary volcanism 2 metasomatism of this mantle by important volumes of slab derived fluids enriched in soluble incompatible elements due to the subduction of major oceanic fracture zones 3 partial melting of this metasomatized mantle and generation of primitive basaltic melts with nb la values typical of the nvz which are parental to the entire sangay suite but apparently never reach the surface and subordinate production of high nb la basaltic melts maybe by lower degrees of melting at the periphery of the main site of magma formation that only infrequently reach the surface 4 afc processes at the base of a 50 km thick crust where parental melts pond and fractionate while assimilating remelts of similar basaltic material previously underplated producing andesites with low y and hree contents due to garnet stability at this depth 5 low pressure fractionation and mixing processes higher in the crust both an enriched mantle under sangay prior to volcanism and an important slab derived input of fluids enriched in soluble incompatible elements two parameters certainly related to the unique setting of the volcano at the southern termination of the nvz apparently account for the exceptionally high contents of incompatible elements of the sangay suite in addition the low cr ni values of the entire suite another unique characteristic of the nvz also requires unusual fractionation processes involving cr spinel and or clinopyroxene either in the upper mantle or at the base of the crust

differential transport of co2 and ch4 in coalbed aquifers implications for coalbed gas distribution and composition coalbed gas content and composition are critical for the successful exploration and production of coalbed methane we investigated the differential transport of a preadsorbed co2 ch4 gas mixture along a coalbed aquifer by groundwater flow or across a coal bed by upward diffusion through pore water consistent analytical approximations and numerical solutions were obtained for typical cases the results suggest that differential transport of ch4 and co2 in a water saturated coal seam is mainly controlled by their adsorption equilibrium in coals and solubilities in water although co2 is about 20 times more soluble than ch4 in water at temperatures lower than 50c the transport of co2 from a coal seam is only several times more efficient than that of ch4 because of the stronger adsorption of co2 than ch4 in coals preferential transport of co2 over ch4 by groundwater advection can substantially accumulate more gas rich in co2 at downstream or near discharge zones if gas trapping structures exist and it may cause low total gas content of ch4 near recharge zones which may explain the co2 and ch4 distribution in the san juan and powder river basins and the undersaturation of gas in many other coals the separation and redistribution of coalbed gas by transport processes may also be complicated by late stage biogenic gas generation with infiltration of meteoric water with nutrients and gas producing microbes into the coal beds as suggested for some basins overall hydrogeologic systems strongly influence the distribution of coalbed gas content and composition in coal seams

coal petrology and coal seam gas contents of the walloon subgroup surat basin queensland australia abstract core exploration and appraisal drilling over the last four years have targeted the juandah upper and taroom lower coal measures of the middle jurassic walloon subgroup of the injune creek group these wells have shown that the high volatile bituminous perhydrous coals of the walloon subgroup have gas contents of between 1 and 14 m 3 t and some wells have encountered gas flows at rates of over 30 000 m 3 day this recent work has confirmed the initial supposition that the coals within the walloon subgroup contain sufficient quantities of gas to be economically viable as a coal seam gas source coal volumes depth and structure have also been confirmed from the initial work what has become apparent during this work is the variability in gas content across each of the seams in the juandah and taroom coal measures and the variability in coal petrographic composition of these two units are controlled by many factors what has also become apparent is that the taroom coal measures have a lower average gas content than the overlying juandah coal measures the obvious conclusion is that the difference in gas content is related to a difference in coal petrology not only do the gas contents of these coal intervals differ their gas adsorption capacities also differ with the taroom coal measures coals displaying on average lower gas content and lower gas adsorption capabilities again the obvious cause would be coal petrological differences but the juandah and taroom coal measures coals have similar maceral percentages an understanding of the relationship between gas desorption gas adsorption and coal composition is vital in determining which areas in the basin offers the most economically viable targets for the commercialisation of coal seam gas in the surat basin

leaching of inorganics in the cretaceous greymouth coal beds south island new zealand abstract leaching processes are believed to be responsible for the unusually low ash content sometimes less than 1 of the thick up to 35 m cretaceous coals located in the greymouth coalfield south island new zealand although leaching of inorganics in peat is a generally accepted process little is known about leaching after burial the main and e seams in the greymouth coalfield show good correlation between low ash and bed thickness the ash content however is often less than 1 which is lower than most known modern analogues i e peat there are several lines of evidence that suggest that mineral matter may have been removed from the coal not only in the peat stage but also after burial for example etching features found in quartz grains and clay aggregates indicate that some leaching processes have taken place in addition liptinitic material e g bitumen in the cleat networks supports the conclusion that there has been some movement of solutions through the coal after burial these solutions may have helped to remove some of the inorganics originally within the greymouth coals

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

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

hydrogeologic factors affecting gas content distribution in coal beds gas content in coal is not fixed but changes when equilibrium conditions within the reservoir are disrupted therefore gas content distribution in coal varies laterally within individual coal beds vertically among coal beds in a single well and within thicker coal beds major hydrogeologic factors affecting gas content variability include gas generation coal properties and reservoir conditions gas generation affects gas content variability on a regional scale whereas coal properties influence gas content distribution on a regional and local scale reservoir conditions affect gas content more locally within specific fields or individual wells the potential for high gas content is controlled directly by the amount of thermogenic and secondary biogenic gases generated from the coal which in turn are controlled by burial history maceral composition and basin hydrodynamics variability in mineral matter ash and moisture content sorption behavior among macerals diffusion coefficients and permeability result in heterogeneous gas content distribution gas content decreases with decreasing pressure and temperature and coal beds become undersaturated with respect to methane during basin uplift and cooling gas content generally increases where conventional and hydrodynamic trapping of coal gases occur and may decrease in areas of active recharge with downward flow potential and or convergent flow where there is no mechanism for entrapment

influence of groundwater flowpaths residence times and nutrients on the extent of microbial methanogenesis in coal beds powder river basin usa water and natural gas samples were collected from coalbed methane wells and a surface coal mine in the powder river basin prb and analyzed for solute chemistry isotopes and gas composition to test hypotheses about the timing and source of recharge importance of nutrient influx and extent of microbial methanogenesis in coalbeds recharge to the wyodak anderson coal zone in the central portions of the prb appears to be from the southern basin margin based on 18o h2o values and hydraulic gradients coal zones along the eastern margin near the coal outcrop represent mixing between surface water and deeper circulating groundwater coalbeds along the northwestern basin margin may contain high elevation recharge from the bighorn mountains with flow patterns likely affected by local faults detectable 14c 0 39 to 4 13 pmc in coal waters throughout the prb indicates they were recharged 50 000 bp correlation of d ch4 and d h2o values suggests that methane has accumulated since the late pleistocene nutrient concentrations c n and p species are low throughout the prb and do not correlate to groundwater flowpaths or methanogenic pathways nutrients may be sourced from in situ leaching of coals carbon isotope values of ch4 and co2 likely indicate the extent of methanogenesis i e early versus late stage rather than the dominant metabolic pathway i e acetate fermentation versus co2 reduction coal gasses from the northwestern margin of the basin are isotopically depleted and suggest early stage methanogenesis where the reactant carbon reservoir has not been significantly fractionated due to relatively rapid groundwater flow coal gasses from the central basin and southeastern margin are isotopically enriched and suggest late stage methanogenesis where the reactant carbon reservoir has been significantly depleted likely due to longer groundwater residence times

conceptual exploration targeting for microbially enhanced coal bed methane mecom in the walloon subgroup eastern surat basin australia abstract the sustainable in situ regeneration of microbial biogenic methane or microbially enhanced coal bed methane mecom is an emerging concept being investigated globally promising results and recommendations of a preliminary culture study of walloon subgroup co produced coal seam gas csg waters from the surat basin queensland established the presence of viable methanogens and suggested that in situ methanogenesis could be stimulated using physical and chemical reservoir treatments this paper represents the culmination of a stepwise basin analysis project ultimately aimed at siting potential in situ bioreactor locations in the eastern surat basin the integration of stratigraphically located data on the molecular and isotopic composition of desorbed gases host coal properties and spatially associated waters through the core production zone has allowed the spatial variability and relative influence of hydro geological factors on methanogenesis to be evaluated in detail for the first time higher gas contents and systematically enriched ch 4 and co 2 carbon isotopic compositions in the stratigraphically central coal seams oldest youngest in the upper taroom coal measures tangalooma sandstone lower juandah coal measures are best explained by increased rates of microbial co 2 reduction and substrate depletion there is a building case to trial mecom in the central coal seams in a depleted underperforming well in an area of high permeability integrated microbiological chemical engineering hydro chemical and geological studies are ongoing to further enhance understanding of walloon subgroup csg and the bioreactor potential of the surat basin

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

determination of rank and petrographic composition of jurassic coals from eastern surat basin australia abstract petrographic analysis and rank determination were carried out on coals from a jurassic sequence in eastern surat basin australia the coals consist mainly of exinite rich clarite with desmocollinite as dominant maceral of the vitrinite group petrographically there is no significant variation in the composition of the coals a herbaceous swamp type free from severe oxidation dehydration appears to have been a dominant depositional environment during the peat accumulation the coal rank ranges from sub bituminous b to high volatile bituminous c b vitrinite reflectance depth profile shows a uniform increase in coalification with depth of burial

variability of geochemical properties in a microbially dominated coalbed gas system from the eastern margin of the illinois basin usa this study outlines gas characteristics along the southeastern margins of the illinois basin and evaluates regional versus local gas variations in seelyville and springfield coal beds our findings suggest that high permeability and shallow 100 250 m depths of these indiana coals allowed inoculation with methanogenic microbial consortia thus leading to widespread microbial methane generation along the eastern marginal part of the illinois basin low maturity coals in the illinois basin with a vitrinite reflectance ro 0 6 contain significant amounts of coal gas 3 m 3

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

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

mio pliocene adakite generation related to flat subduction in southern ecuador the quimsacocha volcanic center abstract new geochemical and geochronological data on the miocene pliocene quimsacocha volcanic center qvc have led to the recognition of adakitic lavas generated by slab melting related to the flat slab subduction in southern ecuador and northern peru the qvc located in the presently inactive southern part of the ecuadorian arc was built up during three distinctive volcanic phases the first phase generated a basal edifice with mainly andesitic lava flows while the second phase is characterized by the emplacement of cryptodomes domes and related outflow breccias comprised of andesites and some dacites the last phase released rhyolitic ignimbrites associated with the formation of a large caldera which was later partly filled by dacitic rhyolitic domes geochemical data for the qvc indicate higher al2o3 tio2 na2o zr and sr contents and lower fe2o3 mgo y mree and hree abundances compared to other eruptive rocks of the plio quaternary volcanic front of ecuador such geochemical features as well as the frequent presence of an associated epithermal gold deposit are characteristic of the involvement of slab melts also known as adakites 1 2 in the generation of these magmas after a calc alkaline arc magmatism phase slab horizontalization in response to the subduction of a buoyant oceanic plateau results in increased involvement of a slab melting component in the magmas produced however pristine adakites were generated and emplaced during a relatively short period as indicated by zircon fission track ages then volcanic activity stopped and a volcanic gap formed the identification of these adakites their location and age support a model of slab melting associated with flat slab subduction m a gutscher et al geology 28 2000 535 538

stable isotope and water quality analysis of coal bed methane production waters and gases from the bowen basin australia abstract coal bed methane cbm is a significant growing industry in queensland s energy sector it is however a relatively new industry with little local water quality data and stable isotope compositions of production waters and gases available in the public domain this study aims to determine whether water quality and stable isotope data can be correlated with gas and groundwater production and flow pathways and identify zones of recharge and water mixing stable isotope analysis and accessory water quality tests were conducted on cbm production gas and water samples collected from two cbm producing bituminous coal seams within a single field in the bowen basin in the production field the reservoir seams are gently folded with eastwardly dipping fold axes and compartmentalised by an ene normal fault on the flank of a broad central anticline that contains minor faults for one seam splitting and a change in coal quality parallels the fault and fold axes although virgin reservoir conditions were similar differing production performance north and south of the main fault suggests it acts as a barrier to water and gas flow along strike the stable isotope analysis on the production water showed that waters with more positive d and 18o compositions were associated with areas of higher water production and shallower depths whereas more negative d and 18o compositions were associated with lower water production and high gas production the gas isotope analysis showed that production gases had both biogenic and thermogenic origins and that secondary biogenic gas generated through co2 reduction comprises a significant portion of the cbm produced from this field more negative ch4 13c values characterize the zones of meteoric recharge in shallow up dip areas gas production data and co2 13c values suggest that this may result from 13ch4 stripping by the recharge waters and or increased biogenic activity in this area smaller co2 ch4 carbon isotopic fractionation values characterized zones of meteoric recharge whereas higher isotopic fractionation values characterized the high gas production domain