geological controls on gas saturation in the yanchuannan coalbed methane field southeastern ordos basin china abstract the paper investigates lateral variation of gas saturation and its geological controls of the no 2 coal seam in the permian shanxi formation based on coal samples from 21 exploration wells in the yanchuannan coalbed methane cbm field southeastern ordos basin china the data set reveals that gas saturation of the no 2 coal seam shows a high lateral variation from 32 44 to 89 69 and that there is an overall trend in gas saturation with depth overprinted by four other factors 1 influence of faults 2 secondary biogenic gas generation 3 local top seal conditions and 4 variations in coal properties the reverse faults f1 and f2 are effective barriers horizontally for the hydraulic communication and divide our study area into relatively closed and recharge zones gas saturation of the relatively closed zone is generally higher than that in the recharge zone in the recharge gas saturation increases generally along the flow pathway of groundwater with the exceptions of the areas affected by secondary biogenic gas the stable isotope compositions suggest that late stage biogenic methane was generated via co 2 reduction associated with meteoric water recharge which significantly contributes to higher gas saturation than expected meanwhile the biogenic gas generation was is restricted to shallow depths the apparent variations in local areas of lithology of the overlying stratum next to the coal seam suggest that the top seal conditions are deteriorative which can cause gas dissipation and reduce gas saturation remarkably integrally for the variations in coal properties gas saturation has a general positive relationship with coalification and weak negative correlations with moisture content and ash yield but the relationships lacks statistical significances gas saturation is not associated with coal maceral in the study area

variations in pore characteristics in high volatile bituminous coals implications for coal bed gas content abstract the seelyville coal member of the linton formation pennsylvanian in indiana was studied to 1 understand variations in pore characteristics within a coal seam at a single location and compare these variations with changes occurring between the same coal at different locations 2 elaborate on the influence of mineral matter and maceral composition on mesopore and micropore characteristics and 3 discuss implications of these variations for coal bed gas content the coal is high volatile bituminous rank with r 0 ranging from 0 57 to 0 60 bet specific surface areas determined by nitrogen adsorption of the coals samples studied range from 1 8 to 22 9 m 2 g bjh adsorption mesopore volumes from 0 0041 to 0 0339 cm 3 g and micropore volumes determined by carbon dioxide adsorption from 0 0315 to 0 0540 cm 3 g the coals that had the largest specific surface areas and largest mesopore volumes occur at the shallowest depths whereas the smallest values for these two parameters occur in the deepest coals micropore volumes in contrast are not depth dependent in the coal samples examined for this study mineral matter content influenced both specific surface area as well as mesopore and micropore volumes it is especially clear in the case of micropores where an increase in mineral matter content parallels the decrease of micropore volume of the coal no obvious relationships were observed between the total vitrinite content and pore characteristics but after splitting vitrinite into individual macerals we see that collotelinite influences both meso and micropore volume positively whereas collodetrinite contributes to the reduction of mesopore and micropore volumes there are large variations in gas content within a single coal at a single location because of this variability the entire thickness of the coal must be desorbed in order to determine gas content reliably and to accurately calculate the level of gas saturation

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

evolution of methane sorption capacity of coal seams as a function of burial history a case study from the campine basin ne belgium based on extensive data sets of high pressure sorption isotherms and canister desorption data from two central european coal basins campine and ruhr basins a computational scheme has been developed to calculate the maximum coal bed methane cbm sorption capacity of coal seams as a function of pressure temperature and coal rank in addition the effects of in situ moisture content and maceral composition have been tentatively implemented using this algorithm it is possible to explicitly take into account variations in sorption capacity of the coal seams in sedimentary basins over geologic time as a function of burial history and thermal evolution the procedure has been applied to model the evolution and the present day coal bed methane content of the campine basin ne belgium it is demonstrated how the present day gas content of the campine basin is controlled by the burial history of the coal layers throughout geologic time the maximum gas sorption capacity typically occurs at a depth range between 500 and 1000 m during periods of uplift and erosion 250 and 90 ma before present the uppermost coal layers have lost methane due to a reduction of gas storage capacity while their storage capacity has increased during periods of burial 300 and 180 ma ago and present additionally the present day gas content is controlled by the gas generation history coal layers which have lost storage capacity during geologic time will stay undersaturated if not replenished by late stage e g microbial gas the gas content profile of test well kb206 in the ne campine basin established from canister desorption tests can be reproduced by assuming that undersaturation of the coals is due to erosion and re burial and that no significant gas generation e g microbial gas has taken place after the time of maximal burial isotopic data d 178 13c 59 indicate the presence of a small portion of microbial gas the absolute gas contents in this well are lower than the calculated maximum present day sorption capacity this may be due to an underestimation of the effect of water content on sorption capacity or result from degassing via nearby faults enforced by fluid circulation

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

coalbed methane producibility from the mannville coals in alberta canada a comparison of two areas the mannville coals in the fenn area alberta plains have desorbed gas content averaging 8 57 cm3 g 275 scf t which is similar to the same coals in the corbett creek area almost 400 km away vitrinite reflectance values are also similar although the coals at corbett creek are situated about 300 m shallower which points to a rank excursion from hilt s burial law curves at corbett creek coals from both areas are within the oil window the medicine river seam in the fenn area has higher total inertinite content and greater proportions of inertodetrinite and detrovitrinite suggesting that peat deposition occurred in swamps and marshes and were prone to periodic flooding at corbett creek the mannville coal seams are characterized by greater concentrations of telo inertinite which contributes to coal meso porosity and the potential for free gas storage in the open cell lumens and to an increased gas flow along lithotype boundaries horizontal permeability non fluorescing vitrinite was present mostly in the upper medicine river seam which was deposited in a regressive environment the lower medicine river seam which formed during a marine transgressive phase contained greater amounts of fluorescing vitrinite the mannville coals in the fenn area are moderately under pressured in relation to those at corbett creek which may have an impact on gas retention capacity the difference in absolute coal permeability 1 3 5 md at fenn versus 3 4 md at corbett creek which is likely the result of higher in situ stresses in the deeper mannville coals at fenn has had an effect on both gas and water production rates from these coals however the largest impact on gas production volumes has been made by the application of horizontal drilling technology initially at fenn and more recently by multiple horizontal wells drilled at corbett creek

a sequence stratigraphic model for reservoir sand body distribution in the lower permian shanxi formation in the ordos basin northern china abstract the lower permian shanxi formation is the main gas bearing stratigraphic unit in the northeastern ordos basin china based on an integrated investigation of well logs seismic data cores and outcrops the lower member of the shanxi formation has been subdivided into three third order sequences from base to top namely sq1 sq2 and sq3 the three sequences consist primarily of stacked lowstand systems tracts with little deposition of transgressive systems tracts and or highstand systems tracts detailed sedimentological and stratigraphic analyses indicated that the entire sequence is characterized by a regional transgression with incised valleys and channel fills marking the bases of each retro gradational sequence and swamp or inter channel bay mudstone and coal deposits capping each sequence the three sequences retracted source ward sequentially from the sandstone dominated sq1 to the mudstone dominated sq3 the spatial and temporal distributions of the reservoir sandstones was primarily controlled by retro gradational stacking patterns channel sand bodies formed during the lowstand systems tracts of sq1 sq2 and sq3 are excellent reservoirs which form excellent reservoir cap rock assemblages with the overlying fine grained sediments the unique sequence stacking patterns control the accumulation of hydrocarbons the reservoir quality of the sq1 sq2 and sq3 sequences become worse gradually from base to top within each sequence channel or incised valley fill of the lowstand systems tracts remain potential good expiration targets

coalbed gas systems resources and production and a review of contrasting cases from the san juan and powder river basins coalbed gas has been produced commercially from the northern appalachian basin since the 1930s and from the san juan basin since the early 1950s however the magnitude and economic sig nificance of coalbed gas resources were realized only in the 1970s and early 1980s when the u s bureau of mines u s department of energy the gas research institute and oil and gas operators made a concerted effort to demonstrate commercial production of coalbed gas from vertical wells exploration and development ex panded in the late 1980s and early 1990s due partly to an uncon ventional fuels tax credit by 2000 coalbed gas accounted for 8 8 of the reserves 15 7 tcf 0 44 tm3 and 9 2 of the annual pro duction 1 38 tcf 40 gm3 of dry gas in the united states from 1989 through 2000 cumulative united states coalbed gas produc tion was 9 63 tcf 272 gm3 today coalbed gas development has spread to about a dozen basins in the united states and exploration is progressing worldwide coal beds are self sourcing reservoirs that can contain ther mogenic migrated thermogenic biogenic or mixed gas coalbed gas is stored primarily within micropores of the coal matrix in an adsorbed state and secondarily in micropores and fractures as free gas or solution gas in water the key parameters that control gas resources and producibility are thermal maturity maceral compo sition gas content coal thickness fracture density in situ stress permeability burial history and hydrologic setting these param eters vary greatly in the producing fields of the united states and the world in 2000 the san juan basin accounted for more than 80 of the united states coalbed gas production this basin contains a gi ant coalbed gas play the fruitland fairway which has produced more than 7 tcf 0 2 tm3 of gas the fruitland coalbed gas system and its key elements contrast with the fort union coalbed gas play in the powder river basin the fort union coalbed play is one of the fastest developing gas plays in the united states its production escalated from 14 bcf 0 4 gm3 in 1997 to 147 3 bcf 4 1 gm3 in 2000 when it accounted for 10 7 of the united states coalbed gas production by 2001 annual production was 244 7 bcf 6 9 gm3 differences between the fruitland and fort union petroleum systems make them ideal for elucidating the key elements of contrasting coalbed gas petroleum systems

hydrochemistry weathering and weathering rates on madeira island madeira island consists of miocene to pleistocene lavas and pyroclasts major rock types are alkali basalts basanites and hawaiites principal soil types are leptosols andosols and cambisols our main objective was to link the chemistry of ground waters to weathering reactions and rates we collected 40 shallow groundwater samples remote from human activities with a few exceptions the ranges of electrical conductivities were 29 176 ms cm and of ph 5 8 8 5 the calculated pco2 was generally higher than the atmospheric value the contribution of sea salt to the water chemistry was 30 9 corrected for sea salt the cation concentrations in meq l decrease in the order ca 2 mg 2 na k the concentrations of so42 and no3 are very low we calculated that the total annual chemical denudation rate in the studied area amounts to 37 12 g m 2 consuming 0 86 0 38 mol co2 m 2 to achieve our main objective a set of mole balance equations ax b was used where a is a composite matrix of coefficients including ratios between stoichiometric coefficients as determined by the weathering reactions and coefficients accounting for unconstrained contributions b is the vector with a water composition and x is the set of mole fractions of dissolved primary minerals plus the residual concentrations of the unconstrained contributions olivine ol pyroxene py and plagioclase pl were considered to be the major primary minerals and smectite vermiculite halloysite allophane gibbsite and hematite the secondary minerals in the weathering reactions using iterative procedures whereby mixtures of secondary products as well as the composition of plagioclase are allowed to change we selected one best fit set of weathering reactions for each spring by checking all possible solutions of the mole balances against predefined boundary conditions at odds with goldich 1938 sequence our model results indicate for most best fit sets a weathering rate sequence of pl ol py but such reverse order is not unique on average the annual weathering rates in mol ha y vol mineral are 44 19 pl 29 14 ol and 22 13 py q 2003 elsevier b v all rights reserved

tectonic and stratigraphic controls of hydrocarbon systems in the ordos basin a multicycle cratonic basin in central china the ordos basin is the oldest and still an important hydrocarbon province in central china it is a typical cratonic basin developed on the archean granulites and lower proterozoic greenschists of the north china block the development of the ordos basin during the paleozoic mesozoic can be divided into three evolutionary stages cambrian early ordovician cratonic basin with divergent margins middle ordovician middle triassic cratonic basin with convergent margins and late triassic early cretaceous intraplate remnant cratonic basin two hydrocarbon systems are present in the basin the paleozoic gas and mesozoic oil systems in the paleozoic gas system the lower ordovician marine carbonates and pennsylvanian lower permian coal measures serve as source rocks the lower ordovician karst modified dolomites and pennsylvanian bauxitic mudstones form a significant reservoir seal association and the pennsylvanian lower permian deltaic sandstones and upper permian lacustrine mudstones form another effective reservoir seal association in the mesozoic oil system the upper triassic lacustrine mudstones are mature source rocks the upper triassic deltaic sandstones and overlying shallow lacustrine and swamp mudstones form a reservoir seal association and the lower jurassic fluvial sandstones and overlying shallow lacustrine and swamp mudstones form another reservoir seal association in both hydrocarbon systems the stratigraphic variations provide the principal traps the ordos basin is characterized by a stable tectonic setting that controlled the distribution of depositional systems and the development of erosional surfaces and ultimately governed the distribution of oil and gas fields and trap types

coal reservoir saturation impact of temperature and pressure methane adsorption isotherms measured for a series of coals with varying rank at a wide range of temperatures and pressures allows the prediction of the change in sorption capacity as a function of tectonic history changes in sorption capacity in response to declining pressure and temperature associated with uplift may increase or decrease the capacity of the coal and if the coal is initially saturated result in excess gas or a deficiency of gas undersaturation assuming reasonable geothermal and pressure gradients our data indicate that the sorption capacity will generally decrease with uplift and associated exhumation suggesting that an initially gas saturated coal will desorb gas during uplift of the reservoir the desorbed gas would be available for migration and or potentially resaturation of an undersaturated coal our results argue against the generally accepted theory that undersaturation of coal reservoirs results from an increase in the sorption capacity with uplift except for coals at such high pressures that the isotherms are essentially flat or for very high pressure and geothermal gradients

biostratigraphic and aminostratigraphic constraints on the age of the middle pleistocene glacial succession in north norfolk uk considerable debate surrounds the age of the middle pleistocene glacial succession in east anglia following some recent stratigraphical reinterpretations resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north western europe the orthodox consensus that all the tills were emplaced during the anglian marine isotope stage mis 12 has recently been challenged by a view assigning each major till to a different glacial stage before during and after mis 12 between trimingham and sidestrand on the north norfolk coast datable organic sediments occur immediately below and above the glacial succession the oldest glacial deposit happisburgh till directly overlies the sidestrand unio bed here defined as the sidestrand hall member of the cromer forest bed formation dating of these sediments therefore has a bearing on the maximum age of the glacial sequence this paper reviews the palaeobotany and describes the faunal assemblages recovered from the sidestrand unio bed which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland there are indications from the ostracods for weakly brackish conditions significant differences are apparent between the sidestrand assemblages and those from west runton the type site of the cromerian stage these differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at sidestrand and a much younger age this conclusion is suggested by the higher proportion of thermophiles at sidestrand and the occurrence of a water vole with unrooted molars arvicola rather than its ancestor mimomyssavini with rooted molars amino acid racemisation data also indicate that sidestrand is significantly younger than west runton these data further highlight the stratigraphical complexity of the cromerian complex and support the conventional view that the happisburgh till was emplaced during the anglian rather than the recently advanced view that it dates from mis 16 moreover new evidence from the trimingham lake bed sidestrand cliff formation above the youngest glacial outwash sediments briton s lane formation indicates that they also accumulated during a middle pleistocene interglacial probably mis 11 all of this evidence is consistent with a short chronology placing the glacial deposits within mis 12 rather than invoking multiple episodes of glaciation envisaged in the new glacial stratigraphy during mis 16 12 10 and 6 copyright 2009 john wiley sons ltd

evaluating the coalbed methane potential of the gething coals in ne british columbia canada an example from the highhat area peace river coalfield abstract lower cretaceous coals from the gething formation in the highhat area of ne british columbia were analyzed for gas content as part of an exploration program samples of continuous wireline core and cuttings were processed vitrinite reflectance and dry ash free volatile matter both indicate that the rank of the coal is low volatile bituminous the coals are well cleated and contain shear fractures as seen in the core description and in the fmi logs coal cuttings were screened to remove a very fine fraction 200 mesh and then treated in heavy liquid sg 1 75 g cm 3 to remove inorganic lithologies for the cores total gas content ranges from 516 9 to 876 8 scf t 16 1 27 4 cm 3 g adb with a mean value of 671 1 scf t 20 9 cm 3 g at 20 5 ash adb for the cuttings all desorbed gas was assigned to the 200 mesh float 1 75 sg weight fraction on this recalculated basis total gas content for the processed cuttings ranges from 651 8 scf t 20 4 cm 3 g to a high value of 2083 6 scf t 65 1 cm 3 g adb weight yields after screening floating are generally low for samples yielding very low values 3 g adb with a mean value of 760 4 scf t 23 8 cm 3 g at 15 5 ash adb the desorbed gas is predominantly methane 98 99 air free and acid free basis and average carbon dioxide is about 6 methane is thermogenic based on isotopic analysis methane adsorption isotherm analysis at reservoir conditions shows that the gething coals are at least 95 gas saturated using 1300 m as a depth cut off and an average gas content of 672 scf t 21 cm 3 g gip gas in place in the highhat prospect area is estimated to be 270 bcf billion cubic feet this translates to 24 5 bcf section a section is equal to a square mile or 640 acres for the 11 sections of land in the vicinity of the corehole or to 3 bcf m mile 2 the low absolute permeability of the coals 0 5 md is the main limiting factor for producibility and commercial development of the resource even at today s high natural gas prices these coals are not economically viable

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

geology of coalbed methane reservoirs in the southeast qinshui basin of china abstract the no 15 coal seam of the pennsylvanian taiyuan formation and the no 3 coal seam of the permian shanxi formation in the southeast qinshui basin are relatively thick 3 m laterally continuous and are of anthracite rank ro 2 2 4 5 the depth of these coal seams is generally between 200 and 700 m a tectonic thermal event during the jurassic to cretaceous yanshanian orogeny controlled coalification and thermogenic hydrocarbon generation because the generation of late stage bacterial gas coalbed methane in the southeast qinshui basin occupies two zones which are the mixed thermogenic and late stage bacterial gas zone near the basin margins and the dominantly thermogenic gas zone in the structurally deep part of the basin basin hydrodynamics causes low gas content in the shallow subsurface 20 m3 t because cleats are rare and are mostly filled with calcite the permeability of the coalbed methane reservoir is controlled by shear fractures the recharge and flow of groundwater not only control gas content but also control reservoir pressure abnormally high pressure reservoir in the deep stagnant zone is a favorable area for coalbed methane exploration and development the current coalbed methane wells are generally completed in the deep stagnant zone

sulige field in the ordos basin geological setting field discovery and tight gas reservoirs abstract the sulige gas field in central ordos basin is one of the largest gas fields in china with about 860 7 billion cubic meters bcm of proven gas reserve this field covers an area of about 500 km 2 with largely tight clastic reservoirs the upper carboniferous lower permian deltaic sandstones and upper permian lacustrine mudstones deposited in a stable cratonic tectonic setting form an effective petroleum system that is favorable for gas accumulation in large scale stratigraphic lithologic traps based on wire line log response drilling stem test and core data a generalized classification system was developed for the gas reservoirs of the sulige field thus type i and ii rocks are capable of gas production without natural and or artificial fracturing type iii rocks are capable of gas production after artificial fracturing and type iv rocks are too tight to produce at commercial rates even with artificial fracturing the discovery of the sulige field not only adds large gas reserve in the ordos basin but strongly indicates the overlook potential of both tight sandstone reservoir rock and relatively porous and permeable sweet spots in it

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

isotopic geochemistry and habitat of the natural gases from the upper carboniferous žacleř coal bearing formation in the nowa ruda coal district lower silesia poland the nowa ruda coal district is located in the se part of the lower silesian coal basin the analysed coals have vitrinite reflectance from 1 12 to 1 56 and 13c values from 24 6 to 23 2 natural gases accumulated in coal seams reveal considerable variability of molecular and isotopic compositions geochemical indices and stable isotope ratios vary in the following ranges c2 wet gas index from 0 6 to 40 7 carbon dioxide methane index cdmi from 1 9 to 99 9 13c methane from 66 1 to 28 6 d methane from 256 to 211 13c carbon dioxide from 24 4 to 7 0 and 13c ethane from 27 8 to 25 5 stable isotope studies allow distinction between thermogenic endogenic magmatic and or upper mantle derived and probably even bacterial gases the intensity of migration mixing and accumulation of the natural gases of various origins appear to be variable in time and space the variability of both the molecular and the isotopic compositions of the analysed gases probably results from the specific primary reactions active during the generation of the thermogenic gases in coal seams decomposition of coal seam matrix and or cracking of n alkanes and or in humic dispersed organic matter of coaly mudstones an isotopic fractionation may also develop during the migration of the natural gases through the ultra fine pores of coals the results of this paper suggest that in the case of gases connected with coal seams the existing gas classifications cannot be directly applied to their genetic interpretation

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

factors influencing the methane content of coal beds of the czech part of the upper silesian coal basin czech republic the article is one of the results of long term efforts of the team of authors to evaluate the reserves of raw materials for energy purposes in the czech part of the upper silesian coal basin and to assess possibilities of their realistic utilisation a relatively large program of exploratory drilling to determine the content of coal bed methane cbm in the czech part of the upper silesian coal basin upper mississippian to lower pennsylvanian was undertaken in the 1990s the possibility of extracting cbm from coal beds undisturbed by mining was also investigated numerous analyses of the gas contents of coal beds by the borowski and usbm methods and other parameters that affect the sorption of cbm were made the relationships between these factors are described and discussed in the present paper factors governing the occurrence and spatial distribution of cbm in the czech part of the upper silesian coal basin are divided into those of primary nature the degree of coalification the chemical and physical properties of the coal its maceral composition and pore structure and those of secondary nature gas migration erosion tectonic setting the ten most important factors are defined however in the area of all the czech part of the upper silesian coal basin the degree of their importance which varies in individual boreholes cannot be unambiguously determined future geological exploration for cbm in coal basins should be guided by the essential factors identified in this study the application of them could contribute to solving a long term known discrepancy between the amount of reserves and the question of their exploitability

produced fluids and shallow groundwater in coalbed methane cbm producing regions of alberta canada trace element and rare earth element geochemistry abstract the production of coalbed methane cbm represents a vital new source of natural gas supply in western canada there are however concerns over potential negative environmental impacts on groundwater resources caused by potential contamination with fluids and gases from coal bearing strata this paper provides a brief description of the geochemistry and a detailed discussion of trace element and rare earth element ree concentrations of the produced fluids from two major coal deposits in western canada the mannville formation and the horseshoe canyon belly river group hscn brg and shallow groundwater sgw in this region it evaluates how the depositional environment redox conditions and water rock interactions influence the trace element and rare earth element distributions in the produced fluids and sgw of the study area produced waters from the mannville formation are a saline na cl type and a high boron content is indicative of a brackish marine depositional environment in contrast the hscn brg produced fluids are a na hco3 water type and have lower total dissolved solids tds and lower boron concentrations shallow groundwater has a na hco3 to na hco3 so4 water type with often high concentrations of sulphate and low tds some groundwater samples many hscn brg and all mannville fluids had low sulphate concentrations often with elevated 34s values indicating that bacterial sulphate reduction had occurred making the redox environment suitable for methanogenesis dissolved gas from the mannville formation had a notable thermogenic component whereas dissolved gas from the hscn brg and free gas in shallow groundwater contained methane predominantly or exclusively of biogenic origin mannville produced waters are up to 70 times more concentrated in trace elements compared to the hscn brg waters and up to 300 times more concentrated than shallow groundwater in the mannville fluids trace elements such as as se and pb occurred in concentrations often exceeding drinking water guidelines 5 g l 10 g l and 10 g l respectively whereas most samples in the hscn brg contained only se above drinking water guidelines and a few samples contained as and pb slightly above the maximum allowable concentrations for drinking water therefore the potential risk of trace metal contamination of shallow groundwater with hscn brg swabbing fluids is low because of their comparatively low trace metal content rare earth elements in the mannville produced fluids indicate interaction with silicate dominated host rocks in contrast the rees of the hscn brg produced fluids show interaction with carbonate rich material the shallow groundwater shows a similar pattern to the hscn brg suggesting that rees are not a suitable parameter to monitor potential contamination of shallow groundwater with cbm fluids from the hscn brg however several other geochemical and isotopic parameters are sufficiently distinct between shallow groundwater hscn brg and mannville fluids so that cross contamination with produced fluids or gases should be identifiable with a suitable geochemical monitoring program

developmental geology of coalbed methane from shallow to deep in rocky mountain basins and in cook inlet matanuska basin alaska u s a and canada abstract the rocky mountain basins of western north america contain vast deposits of coal of cretaceous through early tertiary age coalbed methane is produced in rocky mountain basins at depths ranging from 45 m 150 ft to 1 981 m 6 500 ft from coal of lignite to low volatile bituminous rank although some production has been established in almost all rocky mountain basins commercial production occurs in only a few despite more than two decades of exploration for coalbed methane in the rocky mountain region it is still difficult to predict production characteristics of coalbed methane wells prior to drilling commonly cited problems include low permeabilities high water production and coals that are significantly undersaturated with respect to methane sources of coalbed gases can be early biogenic formed during the early stages of coalification thermogenic formed during the main stages of coalification or late stage biogenic formed as a result of the reintroduction of methane generating bacteria by groundwater after uplift and erosion examples of all three types of coalbed gases and combinations of more than one type can be found in the rocky mountain region coals in the rocky mountain region achieved their present ranks largely as a result of burial beneath sediments that accumulated during the laramide orogeny late cretaceous through the end of the eocene or shortly after thermal events since the end of the orogeny have also locally elevated coal ranks coal beds in the upper part of high volatile a bituminous rank or greater commonly occur within much more extensive basin centered gas deposits which cover large areas of the deeper parts of most rocky mountain basins within these basin centered deposits all lithologies including coals sandstones and shales are gas saturated and very little water is produced the interbedded coals and carbonaceous shales are probably the source of much of this gas basin centered gas deposits become overpressured from hydrocarbon generation as they form and this overpressuring is probably responsible for driving out most of the water sandstone permeabilities are low in part because of diagenesis caused by highly reactive water given off during the early stages of coalification coals within these basin centered deposits commonly have high gas contents and produce little water but they generally occur at depths greater than 5 000 ft and have low permeabilities significant uplift and removal of overburden has occurred throughout the rocky mountain region since the end of the eocene and much of this erosion occurred after regional uplift began about 10 ma the removal of overburden generally causes methane saturation levels in coals to decrease and thus a significant drop in pressure is required to initiate methane production the most successful coalbed methane production in the rocky mountain region occurs in areas where gas contents were increased by post eocene thermal events and or the generation of late stage biogenic gas methane generating bacteria were apparently reintroduced into the coals in some areas after uplift and erosion and subsequent changes in pressure and temperature allowed surface waters to rewater the coals groundwater may also help open up cleat systems making coals more permeable to methane if water production is excessive however the economics of producing methane are impacted by the cost of water disposal

hydrodynamics of coalbed methane reservoirs in the black warrior basin key to understanding reservoir performance and environmental issues abstract the black warrior basin of the southeastern united states hosts one of the world s most prolific and long lived coalbed methane plays and the wealth of experience in this basin provides insight into the relationships among basin hydrology production performance and environmental issues along the southeast margin of the basin meteoric recharge of reservoir coal beds exposed in an upturned fold limb exerts a strong control on water chemistry reservoir pressure and production performance fresh water plumes containing na hco3 waters with low tds content extend from the structurally upturned basin margin into the interior of the basin northwest of the plumes coal beds contain na cl waters with moderate to high tds content carbon isotope data from produced gas and mineral cements suggest that the fresh water plumes have been the site of significant bacterial activity and that the coalbed methane reservoirs contain a mixture of thermogenic and late stage biogenic gases water produced from the fresh water plumes may be disposed safely at the surface whereas underground injection has been used locally to dispose of highly saline water wells in areas that had normal hydrostatic reservoir pressure prior to development tend to produce large volumes of water and may take up to 4 a to reach peak gas production in contrast wells drilled in naturally underpressured areas distal to the fresh water plumes typically produce little water and achieve peak gas rates during the first year of production environmental debate has focused largely on issues associated with hydrologic communication between deep reservoir coal beds and shallow aquifers in the coalbed methane fields of the black warrior basin a broad range of geologic evidence suggests that flow is effectively confined within coal and that the thick intervals of marine shale separating coal zones limit cross formational flow

production waters associated with the ferron coalbed methane fields central utah chemical and isotopic composition and volumes this study investigated the composition of water co produced with coalbed methane cbm from the upper cretaceous ferron sandstone member of the mancos shale in east central utah to better understand coalbed methane reservoirs the ferron coalbed methane play currently has more than 600 wells producing an average of 240 bbl day well water water samples collected from 28 wellheads in three fields buzzards bench drunkards wash and helper state of the northeast southwest trending play were analyzed for chemical and stable isotopic composition water produced from coalbed methane wells is a na cl hco3 type water from the drunkards wash field has the lowest total dissolved solids tds 6300 mg l increasing in value to the southeast and northeast in the helper state field about 6 miles northeast water has the highest total dissolved solids 43 000 mg l and major ion abundance indicates the possible influence of evaporite dissolution or mixing with a saline brine in the southern buzzards bench field water has variable total dissolved solids that are not correlated with depth or spatial distance significant differences in the relative compositions are present between the three fields implying varying origins of solutes and or different water rock interactions along multiple flow paths stable isotopic values of water from the ferron range from 0 9 to 11 4 18o and 32 to 90 2h and plot below the global meteoric water line gmwl on a line near but above values of present day meteoric water isotopic values of ferron water are consistent with modification of meteoric water along a flow path by mixing with an evolved seawater brine and or interaction with carbonate minerals analysis of isotopic values versus chloride conservative element and total dissolved solids concentrations indicates that recharge water in the buzzards bench area is distinct from recharge water in drunkards wash and is about 3 c warmer these variations in isotopes along with compositional variations imply that the ferron reservoir is heterogeneous and compartmentalized and that multiple flow paths may exist

geological and hydrological controls on the producibility of coalbed methane geological and hydrological comparison of two united states coalbed methane basins the prolific san juan basin and the marginally producing sand wash basin indicates that coal distribution and rank gas content permeability ground water flow and depositional and structural setting are critical controls on coalbed methane producibility a complex interplay and moreover a synergy amongst these controls determines high productivity this paper proposes a basin scale explanation for the prolific and marginal production in the two basins and that can be applied to evaluation of coalbed methane potential in coal basins worldwide high productivity is governed by 1 thick laterally continuous coals of high thermal maturity 2 basinward flow of ground water through coals of high rank and gas content orthogonally toward no flow boundaries regional hingelines fault systems facies changes and or discharge areas and 3 conventional trapping along those boundaries to provide additional gas beyond that sorbed on the coal surface

coal reservoir characteristics and coalbed methane resource assessment in huainan and huaibei coalfields southern north china abstract the huaibei and huainan coalfields in southern north china contain abundant coalbed methane cbm resources 1 1 10 12 m 3 net accumulated thicknesses of all minable coal seams are 18 32 m in huainan and 8 18 m in huaibei coalfields coal rank in the huainan coalfield high volatile a and b bituminous r o 0 65 0 85 is generally controlled by geothermal metamorphism in comparison coal rank in the huaibei coalfield varies from high volatile a bituminous to semi anthracites 0 8 to 2 8 r o and is controlled by the influence of the cretaceous yanshanian magmatic metamorphism in both coalfields coal reservoirs have low permeability values of 0 0013 0 224 md and porosity of 0 9 10 9 pores in coals are dominated by those with diameter 2 in both coalfields the abundance of microfractures in coals is related to the coal structures commonly more abundant in sheared coals 200 per 9 cm 2 than in the normally structured coals 2 the in place gas content is generally 8 16 m 3 t in huaibei and 10 30 m 3 t in huainan coalfields these data yield an estimated in place cbm resource of 375 247 10 9 m 3 for the huaibei and 722 677 10 9 m 3 for the huainan coalfields based on the cbm resource investigation and reservoir evaluation the most prospective target areas for cbm production are evaluated which include the nanping taoyuan mines of the southern suxian deep coal district and zhuxianzhuang and luling mines in eastern suxian area of the huaibei coalfield and the area around the panji 2 mine in panji xieqiao coal mining districts in the huainan coalfield

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

relationships between water and gas chemistry in mature coalbed methane reservoirs of the black warrior basin water and gas chemistry in coalbed methane reservoirs of the black warrior basin reflects a complex interplay among burial processes basin hydrodynamics thermogenesis and late stage microbial methanogenesis these factors are all important considerations for developing production and water management strategies produced water ranges from nearly potable sodium bicarbonate water to hypersaline sodium chloride brine the hydrodynamic framework of the basin is dominated by structurally controlled fresh water plumes that formed by meteoric recharge along the southeastern margin of the basin the produced water contains significant quantities of hydrocarbons and nitrogen compounds and the produced gas appears to be of mixed thermogenic biogenic origin late stage microbial methanogenesis began following unroofing of the basin and stable isotopes in the produced gas and in mineral cements indicate that late stage methanogenesis occurred along a co2 reduction metabolic pathway hydrocarbons as well as small amounts of nitrate in the formation water probably helped nourish the microbial consortia which were apparently active in fresh to hypersaline water the produced water contains nh4 and nh3 which correlate strongly with brine concentration and are interpreted to be derived from silicate minerals denitrification reactions may have generated some n2 which is the only major impurity in the coalbed gas carbon dioxide is a minor component of the produced gas but significant quantities are dissolved in the formation water degradation of organic compounds augmented by deionization of nh4 may have been the principal sources of hydrogen facilitating late stage co2 reduction

coalbed methane potential of the paleocene fort union coals in south central wyoming usa abstract the paleocene age wasatch and fort union formations in the study area contain numerous coal seams that are interbedded with shale sandstone and conglomerates individual seam thickness ranges from 2 to 15 ft 0 6 4 6 m and aggregate thickness ranges from 64 to 163 ft 19 5 49 7 m the coals are of sub bituminous to high volatile c b bituminous rank ro ran 0 47 to 0 59 and are found at depths from 3 g arb which is higher than expected for the coal rank the coals appear to be close to full saturation based on a comparison of adsorption isotherms with desorption data the coals pinch out updip in the subsurface forming a stratigraphic trap which may explain the high gas content and the mixed biogenic thermogenic origin supported by isotopic analysis gas composition is 97 methane with 3 inerts and the gas has a heating value of 990 btu ft 3 the coals are relatively clean average ash content is 15 wt and have fast diffusivity 63 of total gas desorbs in 3 with wells drilled on 80 acre spacing which translates to a gross eur of 1 4 bcf per well for the 500 well locations identified in the developable acreage based on numerical simulation using the simplistic fekete tm model peak coal gas rate is expected to be 320 mcf d 9014 m 3 per day after 36 months and production should remain at that level for 12 months before declining at a rate of 10 per year conventional gas potential also exists in numerous intervals within the upper fort union and wasatch formations sandstones at depths shallower than 2000 ft 526 m few wells drilled decades ago having perforations in these sands showed ip initial production rates ranging from 500 mcf d 14 084 m 3 per day to 12 mmcf d 338 028 m 3 per day a 24 inch 60 cm diameter pipeline that has an operating pressure of 800 1000 psig a tap and a capacity of 275 mmcf d 7 74 million m 3 per day crosses the study area the pipeline is connected to the colorado interstate gas mainline which provides gas to markets in the eastern united states

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

controls on methane sorption capacity of indian coals details of methane sorption properties of some indian coals ranging in rank from high volatile bituminous c 0 62 ro max to medium volatile bituminous coal 1 46 ro max were investigated to determine the major factors influencing gas adsorption capacity and desorption rate variables studied included moisture content mineral matter content rank and coal type maceral composition adsorption isotherm analysis of dry coals showed that adsorption capacity followed a second order polynomial trend with rank equilibrium moist samples showed a linear increase in adsorption capacity with rank and had a significantly reduced adsorption capacity compared to the dry coals with the reduction being related to the moisture content mineral matter acted as a simple diluent to the gas adsorption capacity of the coals and was found to be nonadsorbent adsorption capacity moist was reduced by 0 32 cm3 g 10 ft3 gas t for every 1 increase in the ash yield bright and dull coal lithotypes showed strong separation in their adsorption capacities on an as analyzed basis with the bright coals adsorbing greater quantities of gas on a dmmf basis however no relationship was observed between coal type and gas storage capacity comparison of maceral composition with adsorption capacity dry confirmed this observation effective diffusivity de of methane through the coal was seen to be affected by coal type and rank effective diffusivity de decreased as rank increased which is related to the increasing microporous nature of the coal bulk coals tested had 2 3 times larger effective diffusivities than bright coals and dull coals had intermediate rates the larger de values for the bulk coals may be related to the presence of collodetrinite coupled with mineral matter which acts as higher permeability pathways for the gas compared with the high ash dull coals dominated by inertinite macerals differences were noted with similar age permian australian coals where methane adsorption capacities were larger and coal type had a stronger influence on adsorption capacity begin page 202

noble gas tracing of groundwater coalbed methane interaction in the san juan basin usa the san juan basin natural gas field located in northwestern new mexico and southwestern colorado in the usa is a case type coalbed methane system groundwater is thought to play a key role in both biogenic methane generation and the co2 sequestration potential of coalbed systems we show here how noble gases can be used to construct a physical model that describes the interaction between the groundwater system and the produced gas we collected 28 gas samples from producing wells in the artesian overpressured high production region of the basin together with 8 gas samples from the underpressured low production zone as a control stable isotope and major species determination clearly characterize the gas in the high production region as dominantly biogenic in origin and the underpressured low producing region as having a significant admix of thermogenic coal gas 3he 4he ratios increase from 0 0836ra at the basin margin to 0 318ra towards the center indicating a clear but small mantle he signature in all gases coherent fractionation of water derived 20ne 36ar and crustal 4he 40ar are explained by a simple rayleigh fractionation model of open system groundwater degassing low 20ne concentrations compared to the model predicted values are accounted for by dilution of the groundwater associated gas by desorbed coalbed methane this rayleigh fractionation and dilution model together with the gas production history allows us to quantify the amount of water involved in gas production at each well the quantified water volumes in both underpressured and overpressured zones range from 1 7 103 m3 to 4 2 105 m3 with no clear distinction between over and underpressured production zones these results conclusively show that the volume of groundwater seen by coal does not play a role in determining the volume of methane produced by secondary biodegradation of these coalbeds there is no requirement of continuous groundwater flow for renewing the microbes or nutrient components we furthermore observe strong mass related isotopic fractionation of 20ne 22ne and 38ar 36ar isotopic ratios this can be explained by a noble gas concentration gradient in the groundwater during gas production which causes diffusive partial re equilibration of the noble gas isotopes it is important for the study of other systems in which extensive groundwater degassing may have occurred to recognize that severe isotopic fractionation of air derived noble gases can occur when such concentration gradients are established during gas production excess air derived xe and kr in our samples are shown to be related to the diluting coalbed methane and can only be accounted for if xe and kr are preferentially and volumetrically trapped within the coal matrix and released during biodegradation to form ch4

coalbed methane characteristics of gates formation coals northeastern british columbia effect of maceral composition the majority of research reported on methane adsorption characteristics of coal seams has focused on vitrinite rich coals however western canadian coals are more inertinite rich than those of the western united states and are shown to differ in gas adsorption characteristics the influence of maceral composition upon gas adsorption characteristics of medium volatile coal samples from the middle cretaceous gates formation of northeastern british columbia was investigated lithotype coal facies samples were analyzed for surface area maceral and mineral composition and methane adsorption standard coal analyses were also performed proximate low temperature ash and equilibrium moisture the vitrinite content of the samples analyzed ranges from 18 to 95 vol min ral matter free the ash yield varies from 4 4 to 33 7 wt both maceral composition and mineral matter content have an important influence on adsorption characteristics as indicated by carbon dioxide surface areas and methane adsorption isotherms on a mineral matter free basis the amount of methane adsorbed generally increases with vitrinite enrichment the lowest methane adsorption occurs in the sample with the highest inertinite content carbon dioxide surface areas of the lithotypes range from 87 to 176 m2 g on a raw coal basis and from 99 to 184 m2 g on a mineral matter free basis surface area generally decreases with increased mineral matter content and increases with increased vitrinite content the increase in adsorption of both methane and carbon dioxide with increased vitrinite concentration is interpreted a resulting from differences in the pore size distribution of vitrinite and inertinite vitrinite is predominantly microporous whereas inertinite is meso to macroporous the monolayer volumes of carbon dioxide as calculated from the dubininradushkevich equation are higher than those of methane as determined from the langmuir equation but are correlated the methane adsorption isotherms and surface area data indicate that the maceral compositional variations in coal are at least as significant as coal rank in determining the potential volume of adsorbed methane and thus the coalbed methane potential of a deposit

high heat flow effects on a coalbed methane reservoir east kalimantan borneo indonesia abstract the balikpapan formation miocene age in sangatta east kalimantan is thick 1500 m containing abundant coal seams that range in thickness from less than a meter to over 5 m coal seams are distributed throughout the section and may represent 5 to 7 of the total formation thickness measured gas contents range from

hydrodynamic and stratigraphic controls for a large coalbed methane accumulation in ferron coals of east central utah abstract upper cretaceous coals within the ferron sandstone member of the mancos shale contain large volumes of coalbed methane coals at the northern end of the 80 mile long 129 km ferron trend have produced more than 200 billion cubic feet bcf 5663 10 6 m 3 of coalbed methane with daily production of 260 million cubic feet per day mmcfd 7 36 10 6 m 3 day from 470 wells during november 2000 core data from exploratory wells drilled along trend to the south indicate that the gas content of the coals decreases dramatically from north to south even though the rank and maturity of the coals decreases only slightly the area with lowest gas content correlates with the outcrop of the ferron coals hydrodynamic studies have shown that the ferron coals are aquifers that are recharged from the wasatch plateau to the west regional mapping indicates that the productive fields are large stratigraphic traps where the coals pinchout updip into tight marine shales to the east much of the produced gas is secondary biogenic gas and migrated thermogenic gas that has moved from the wasatch plateau and south margin of the uinta basin respectively further south near the town of emery coals are present at the surface but most of the gas has been flushed out of the coals due to reduction of reservoir pressure and active water flow from the west therefore the entire ferron trend probably contained tremendous volumes of stratigraphically trapped coalbed methane before uplift and erosion exposed the southern coals to the atmosphere

preliminary evaluation of the coalbed methane production potential and its geological controls in the weibei coalfield southeastern ordos basin china article i nfo the coalbed methane cbm geology resource and production potential in the weibei coalfield southeastern ordos basin are studied based on geological surveys and laboratory measurements the results showed that coal rank varies both laterally and vertically and changes from volatile bituminous coals in the margin to anthracites towards the basin 1 6 2 5 ro coals are composed of 60 85 vitrinite 15 40 inertinite and a trace amount of minerals methane isothermal adsorption measurements of 20 coal samples revealed that the maximum adsorption capacity on a dry and ash free basis of coals which are affected by coal rank coal maceral coal lithotype and especially to the moisture content varies from 13 91 to 29 54 m 3 t estimated gas contents range from 0 to 15 m

on the effects of petrographic composition on coalbed methane sorption abstract the effect of petrographic composition on the methane sorption capacity has been determined for a suite of coals and organic rich shales subbituminous and bituminous coals were separated into bright and dull lithotypes by hand picking the methane sorption capacities range between 0 5 and 23 9 cm 3 g at a pressure of 6 mpa the low volatile bituminous canmore coal and the anthracite sample have the highest capacities with the natural coke having the lowest for low rank coals there is no significant difference between bright and dull samples except for one coal with the dull sample having a greater sorption capacity than its bright equivalent for higher rank coals the bright samples have a greater methane capacity than the dull samples and the difference between sample pairs increases with rank the boghead coal samples have the highest sorption capacities in the liptinite rich coals suite and are higher than subbituminous to medium volatile bituminous samples pore size distribution indicates that methane is held as solution gas in liptinite rich coals and by physical sorption in micropores in liptinite poor coals these contrasting processes illustrate that liptinite rich samples need to be independently assessed the positive relationship between reactive inertinite content and methane sorption capacity occurs within the subbituminous to medium volatile bituminous coals because the reactive inertinite is structurally similar to vitrinite and have a higher microporosity than non reactive inertinite reactivity of inertinite should be assessed in cbm studies of dull coals to provide a better understanding of petrographic composition effects on methane capacity

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

variable gas saturation in coalbed methane reservoirs of the black warrior basin implications for exploration and production abstract gas saturation is highly variable in carboniferous coalbed methane reservoirs of the black warrior basin usa and diverse geologic data derived from more than three decades of exploration and development provides insight into the origin of this variability and the consequences for production performance coalbed methane is produced from numerous thin 0 3 to 95 importantly this range of variation is commonly developed among closely spaced seams within the same well exploration has to date been successful where coal seams are in the thermogenic gas window geochemical evidence indicates that thermogenic gases have been altered by subsurface water movement and may have been augmented with late stage biogenic gases particularly in areas affected by fresh water recharge adsorption isotherms of coal samples in the black warrior basin typically have langmuir volume between 15 and 30 cm3 g and langmuir pressure between 2 and 6 mpa both langmuir pressure and langmuir volume correlate significantly with coal rank in deep normally pressured coal beds where reservoir pressure is substantially above langmuir pressure even a small degree of undersaturation can necessitate prolonged dewatering before a large reservoir volume can reach the critical desorption pressure permeability moreover decreases exponentially with depth which can make dewatering coal seams deeper than 800 m difficult where reservoir pressure is relatively low however isotherm geometry indicates that significantly undersaturated reservoirs can be near the critical desorption pressure consequently areas of underpressure favor high gas production along with minimal water production

evaluation of coalbed gas potential of the seelyville coal member indiana usa abstract the seelyville coal member of the linton formation in indiana potentially contains 0 03 trillion m3 1 1 tcf of coalbed gas the gas content determined by canister desorption technique ranges from 0 5 to 5 7 cm3 g on dry ash free basis 15 4 to 182 2 scf ton the controls on gas content distribution are complex and cannot be explained by the coal rank alone ash content and the lithology of the overlying strata among other factors may influence this distribution

geological controls on coalbed methane reservoir capacity and gas content the influence of coal composition and rank on coalbed methane reservoir capacity gas content and gas saturation have been investigated for a series of australian canadian and united states coals globally there is no or little correlation between coal rank and methane adsorption capacity as commonly assumed although in particular basins there are general trends with rank and composition micropore1 capacity and surface area determined from low pressure carbon dioxide adsorption isotherms 0 c decrease and then increase with rank passing through a minimum in the high volatile bituminous coal rank there is no consistent variation in modal micropore size or size distribution with rank for suites of isorank coals there is a poor permian bulli and wongawilli seams australia to good positive correlation gates formation coal seams lower cretaceous canada between vitrinite content and methane adsorption capacity dry ash free and as received bases for each isorank coal suite there is a good correlation between micropore capacity and abundance of vitrinite and high pressure methane adsorption capacity comparison of coals of similar composition but from different isorank suites indicates however that the coals with the highest methane adsorption capacity do not necessarily have the highest micropore capacity such results are counterintuitive most pore volume available for methane adsorption is generally assumed to be microporosity it is suspected that moisture prevents methane from accessing some microporosity or competes with methane for adsorption space carbon dioxide micropore capacity which is performed on a dry basis may thus not reflect the microporosity available for gas adsorption in moisture equilibrated coals alternatively because of differing physical and chemical properties of carbon dioxide and methane apparent microporosity available to carbon dioxide due to greater energy of adsorption may not be available to methane total desorbed gas from canister analyses of sydney basin australian coals suggests that most coals are under saturated for a small data set the degree of saturation is negatively correlated with permeability r 0 78 suggesting preferential gas leakage from the higher permeability coals which are vitrite rich some degree of under saturation is probably the result of increased reservoir capacity as a consequence of uplift of the coal seams and thus lower temperatures following gas generation rates of desorption are correlated with total gas content r 0 79 but do not correlate with rank or any compositional parameter

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

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

numerical simulation of coalbed methane generation dissipation and retention in se edge of ordos basin china abstract this paper presents a numerical study on the formation history of coalbed methane cbm reservoir in the southeast edge of ordos basin china the coal seams studied belong to the late palaeozoic coal bearing series these coal seams have a burial history and experienced the process of subsidence rapid subsidence alternated with uplift and then uplift sequentially and underwent the geothermal actions at normal extremely high and then normal temperatures respectively coal organic matter of the coal seams matured in the triassic period and in the late jurassic to early cretaceous period the results from numerical simulation reveal that cbm reservoir evolution history can be classified into five stages namely primary initial stagnant active and dissipative stages in the first primary stage coal rank was very low and there was little methane generated and stored in the coal seams in the second initial stage the coal was converted to middle high volatile bituminous coal as a result a certain amount of methane was generated and began to accumulate in coal seams except part of it escaped from coal seams by diffusion and cap outburst in the third stagnant stage generation of methane was almost stagnant due to the temperature of the coal seam that dropped slightly and the maturation of coal organic matter stopped meanwhile cbm would keep dissipating through diffusion in the fourth active stage coal rank varied from high volatile bituminous coal a to semianthracite which accelerated pyrolysis gas formation and resulted in a large amount of methane generated at a high speed during this period cbm was increasingly accumulated in coal seams although there would be considerable amounts of gas dissipated from the coal seams in the last dissipative stage due to coal seams uplifted at various rates and no more methane generated cbm was continuously dissipated by diffusion throughout the whole coal seams and by permeation at some local areas the simulation provides insights for further interpretation of how many factors that control or affect the cbm reservoir formation history and cbm accumulation these factors include features of coal bearing series characteristics of coal seams physical properties of coal reservoir tectonic evolution history burial history and geothermal conditions etc in particular tectonic evolution history and gas generation are critical under given conditions cbm reservoirs in the study area were developed in different ways and the cbm was accumulated in the reservoirs at different levels for example the west part of study area is favourable for cbm accumulation as a result the gas content of the main coal seams in this region has a maximum of about 28 m3 t at depths of 900 1100 m and generally increases with the increasing of burial depth from the east to the west the coal reservoir is under saturated in the east part where the burial depth is shallower than about 500 m while the west part is saturated there is a close correlation of the lateral distribution of both gas content and saturation to the gas generation in the geological history

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

isotopic fingerprints of shallow gases in the western canadian sedimentary basin tools for remediation of leaking heavy oil wells abstract thousands of wells have been drilled in northeastern alberta and adjacent saskatchewan in order to develop the heavy oil reservoirs of the lower cretaceous mannville group in a large number of these wells vertical migration of gas from unknown sources to the surface via well casings and surrounding soils represents a serious environmental problem mud samples from new wells drilled in the area were collected at approximately 50 m intervals from the surface to the completion depth and the gases contained within the muds mud gases were analyzed for 13c 12c composition gases from the various mannville group sands do not show unique isotopic signatures they comprise bacterial methane 13cc1 70 to 60 pdb with trace c2 components that are residues from biodegradation processes gases from each of the overlying upper cretaceous colorado group shale units are however isotopically distinct the 13c of methanes in the shales have values equivalent to those within the mannville sands but the 13c of the c2 components are unambiguously different c2 gases from the shallower colorado shales are incipient thermal gases and fit the isotopic maturity diagram of james a t 1983 aapg bull 67 1176 1191 and also of chung h m gormly j r squires r m 1988 chem geol 71 97 103 we believe these gases may include the most immature suite of thermogenic gases reported 13cc2 63 to 32 13cc3 42 to 22 13cnc4 37 to 23 carbon isotope fingerprints from mud gases are used to identify specific source depths of migrated gases comparisons between the isotopic characteristics of the shallow gases and the migrated gases collected near surface infer that most of the migrated gases are actually generated in the colorado group shales and not the mannville sands in which the wells were completed the ability to estimate the source depth of the migrated gases greatly aids remediation of leaking wells within the western canadian sedimentary basin wcsb