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

kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone shale sequences abstract based on water rock interaction modelling and kinetic considerations the present study is aimed at testing the impact of organic matter maturation on two kinds of diagenetic reactions leading to the alteration of the petrophysical properties of sandstones 1 clay mineral conversion to illite with k feldspar being a local potential source of k and 2 dissolution precipitation processes produced in sandstones by the action of water soluble organic species derived from adjacent shales assuming firstly that the chemical reactions take place in closed systems the nature and timing of diagenetic reactions in marine sandstone shale formations were modelled for a 50 120 c temperature range in order to improve understanding of the factors that control the illitization reaction with k feldspar coexisting with aluminous clay illite is modelled here as a muscovite type mineral we tested the effects of an energy barrier on illite growth by allowing or preventing the muscovite illite precipitation reaction to occur while using several illitization reaction rates we also compared the stable mineral parageneses predicted for organic material free systems with those predicted in the case of organic diagenesis release of co 2 ch 4 acetic and oxalic acids similarities and discrepancies between numerical results and natural mineral assemblages suggest that the illitization reaction depends on the nature of the reacting clays kaolinite conversion to end member illite involves high energy conditions 2 kcal mol 1 which are not met when the pore water equilibrates with the mineral matrix from undersaturated conditions in a closed system to overcome this barrier the fluid should be oversaturated with respect to k feldspar an external source of k or a ph increase in an open system is necessary for this reaction no particular effect of organic diagenesis on this reaction was found in the present study on the other hand smectite to illite conversion involves a lower energy barrier and can operate in closed systems where k feldspars are the source of k the maturation of organic matter may speed up the smectite to illite conversion rate by increasing the gibbs free energy of illite growth interactions between sandstone and shale were examined by modelling the transfer of aqueous species of organic origin from shale to sandstone fluid expulsion from shale had little or no effect on diagenesis in adjacent sandstones during each flushing cycle mainly because organic protons and ligands were neutralized in the source rock however the diffusion of shale derived cations through sandstone as organometallic complexes mg ca fe al appears to be an efficient process during carbonate cementation in sandstones where oxidizing conditions enhance the decomposition of such complexes

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

an integrated thermal and isotopic study of the diagenesis of the brent group alwyn south u k north sea abstract the petrography fluid inclusion thermometry and isotope geochemistry of diagenetic cements are used to reconstruct the pore fluid history of the middle jurassic brent group reservoir sandstones in the alwyn south area of the u k north sea the study focuses on a relatively limited area of three adjacent reservoir compartments at successively higher structural levels the cement assemblage of kaolinite quartz and illite has resulted in severe deterioration of otherwise good reservoir quality early precipitation of vermiform and late blocky kaolinite was succeeded by a period of relatively intense illite precipitation temperature estimates for kaolinite precipitation of 80 c and 18o of 15 3 suggest co existing fluids of 18o 3 quartz cementation overlapped both kaolinite and illite formation fluid inclusion data indicate that quartz cementation took place at temperatures of 109 7 c pore fluid salinities were 4 wt nacl with a h2o o isotopic composition of 1 o 0 5 smow the fluids which precipitated coexisting illite were compositionally homogeneous with equilibrium 18o water compositions of 0 5 smow illite sd values range from 33 to 50 smow these fluid inclusion and isotopic data suggest that both quartz and illite were precipitated from pore waters with a uniform marine signature this is consistent with the predominantly marine to paralic depositional context of the brent group in alywn south illite precipitation was followed by hydrocarbon emplacement between the middle eocene and lower oligocene

sandstone diagenesis in the pattani basin gulf of thailand history of water rock interaction and comparison with the gulf of mexico abstract in the pattani basin a failed rift basin extensive water rock interaction has occurred between subquartzose alluvial sandstones of miocene age and their pore fluids diagenetic rates and pathways have been strongly influenced by high geothermal gradients high co 2 fugacities and low pore water salinities depositional pore water was fresh to brackish depending on the depositional environment of the sediments chloride concentrations in modern formation water are believed primarily to reflect the proportions of river and sea water in the depositional environment however the concentration of other important solutes and the isotopic composition of the formation waters can not be explained by roportional mixing of these two end member waters dissolution of detrital plagioclase an 3 and k feldspar are reactions of major significance that are reflected chemically in the na cl and k cl ratios of the formation water despite the high temperature of the sandstones 120 200 c diagenetic albite does not occur geochemical calculations indicate the formation water is undersaturated with respect to both orthoclase and albite this style of feldspar diagenesis differs significantly from that of sandstones of similar composition in other basins and has probably influenced other aspects of silicate diagenesis important authigenic minerals are 1 locally abundant calcite cement 13 c 12 8 18 o 17 3 pdb an early diagenetic phase that formed at about 60 c 2 pore filling kaolinite 18 o 9 9 d 83 5smow that was closely associated with feldspar dissolution and formed over a range of temperatures and 3 fibrous pore lining and pore bridging illite 18 o 9 8 d 86 7 smow the last significant cement formed at temperatures of 120 to 150 c potassium argon dates on illite indicate that sandstone diagenesis took place during a period of rapid sedimentation in the first two thirds of the burial history comparison of pattani basin diagenesis with diagenesis of sandstones of similar age in other sedimentary basins demonstrates that chemical diagenesis relative to mechanical compaction has been especially rapid in the pattani basin this reflects the effect of high temperatures on reaction rates the net effect is a high average rate of porosity loss with burial 11 km

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

themis observations of substorms on 26 february 2008 initiated by magnetotail reconnection 1 on 26 february 2008 the themis satellites observed two substorms that occurred at about 0405 and 0455 ut angelopoulos et al 2008 made a comprehensive study of the second event in this paper we display detailed features of the two substorms with emphasis on the first in both substorms a distinct auroral intensification occurred during the earliest stage of onset about 1 to 2 min after midtail reconnection began this initial intensification was weak and localized and thus had the signatures of a pseudobreakup in both substorms a second major intensification occurred next in the substorm onset sequence followed by rapid and extensive poleward expansion this second intensification had the features of the major expansion onset and was nearly coincident with observations of earthward flows and magnetic dipolarization in the near earth tail during the growth phase of the two substorms open magnetic flux accumulated in the polar cap in the expansion recovery phase the polar cap open flux was quickly reduced these observations are in agreement with the assertion that tail reconnection initiates the initial pseudobreakup and the ensuing major expansion and releases and transports energy to eventually cause near earth dipolarization and the expansion phase onset of these two substorms

reply to comment on the poleward leap of the auroral electrojet as seen in auroral images by edward w hones jr un decrochement du cote pole de l electrojet auroral est il une signature des dernieres etapes de la phase d expansion d un sous orage

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

geochemical modelling of late diagenetic processes in the brent sandstone alwyn south area east shetland basin north sea abstract this study simulates the third diagenetic stage of the brent sandstone in the alwyn south area through modelling of water rock interactions at temperatures of 120 and 140 c as determined by the fluid inclusion method simulation results are compared to those from petrographic analyses the major diagenetic events are recognized petrographically but data on the chemical speciations of the invading fluid are not available thus the geochemical simulations test both seawater and dilute water a solid solution model is used in order to test the precipitated complex clay phase and its influence on the chemical composition of the reacting fluid the best agreement with petrographic analyses is from rock interaction with seawater that is depleted in magnesium

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

stepwise tailward retreat of magnetic reconnection themis observations of an auroral substorm auroral stepwise poleward expansions were clarified by investigating a multiple onset substorm that occurred on 27 february 2009 five successive auroral brightenings were identified in all sky images occurring at approximately 10 min intervals the first brightening was a faint precursor the second brightening had a wide longitude thus it represented the akasofu substorm onset other brightenings expanded poleward thus they were interpreted to be auroral breakups these breakups occurred stepwise that is later breakups were initiated at higher latitudes corresponding reconnection signatures were studied using time history of events and macroscale interactions during substorms themis satellite observations between 8 and 24 re down the magnetotail the akasofu substorm onset was not accompanied by a clear reconnection signature in the tail in contrast the three subsequent auroral breakups occurred simultaneously within a few minutes with three successive fast flows at 24 re thus these were interpreted to be associated with impulsive reconnection episodes these three fast flows consisted of a tailward flow and two subsequent earthward flows the flow reversal at the second breakup indicated that a tailward retreat of the near earth reconnection site occurred during the substorm expansion phase in addition the earthward flow at the third breakup was consistent with the classic tailward retreat near the end of the expansion phase therefore the tailward retreat is likely to have occurred in a stepwise manner we interpreted the stepwise characteristics of the tailward retreat and poleward expansion to be potentially associated by a stepwise magnetic flux pileup

westward traveling surges sliding along boundary arcs and distinction from onset arc brightening 1 after onset auroral brightening rapidly spreads azimuthally along the onset arc typically but not always extending substantially farther westward than eastward expansion phase auroras also expand poleward and can contact an arc along the auroral poleward boundary for such events we find that poleward expansion of the region of active aurora accelerates after contact forming a bulge region that protrudes into the preexisting polar cap and expands westward as the westward traveling surge this westward motion is slower than and initiates later than the azimuthal spreading of the onset arc brightening the poleward boundary arc remains connected to the surge as the surge slides along the equatorward moving edge of the boundary arc and this connection appears to set off the westward traveling poleward protruding activity of the surge via localized polar cap flow adjacent to the boundary arc ground magnetic signatures show a relatively weak h component depression moving westward with the onset arc brightening and a delayed substantially larger depression moving with the westward propagating surge that must be associated with a substantially larger westward ionospheric current the clear distinction between onset arc brightening and the westward traveling surge seen in auroral and magnetometer current signatures implies that their underlying processes are very different evidence suggests that flow channels adjacent to the boundary arc possibly feed surge development these results are consistent with current wedge formation being more associated with post onset activity than with onset and with flow channels from the polar cap being important for surge bulge development

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

geology and coal bed methane resource potential of the gondwana barapukuria coal basin dinajpur bangladesh abstract with an area of 5 16 km2 the barapukuria coal deposit is one of the five largest gondwana coal basins in bangladesh and is located in the north west of the country close to the towns of dinajpur and saidpur the existence of the basin was initially indicated by a negative gravity anomaly in oil and gas exploration exploration for the deposit was commenced by the geological survey of bangladesh gsb with seven surface boreholes that confirmed the existence of a significant coal deposit the deposit occurs as an asymmetrical synclinal structure with an axis striking approximately n s the deposit is limited to the east by a large normal fault which has displaced archaean metamorphics against the gondwana sediments the coal bearing sediments are comprised of gondwana permian age sandstones siltstones subordinate carbonaceous shales and six correlated coal seams the gondwana sediments are unconformably overlain by tertiary and quaternary deposits against which the coal seams are successively subcropped to the west within the structural limits of the basin approximately 377 mt coal in situ has been quantified in the six coal seams that range in depth from 118 to 518 m below surface due to the synclinal nature of the deposit the upper coal seams designated i to v occur over diminishing areal extent with decreasing depth the principal seam of interest is the lowermost seam vi with a variable thickness across the deposit from 22 m in the northern part of the deposit to more than 42 m in the southern and eastern areas development of the barapukuria mine the country s first coal mine commenced in 1996 with the construction of two vertical shafts coal production from seam vi began in 2005 and continues at the present time seam vi coal is high volatile b bituminous rank about 34 mt of coal has been estimated as recoverable resources utilising descensional multi slice longwall mining the mine design and development have been severely constrained by adverse seam gradients and the presence of the overlying water bearing tertiary dupi tila sediments the potential of coal bed methane extraction has been investigated as an alternative to underground mining the study considers the barapukuria deposit in terms of its geological structure geothermal gradient and the rank porosity and permeability of the coal seams as determined by several phases of exploration of the area the methane content of the bituminous coal at barapukuria varies within the range 6 51 12 68 m3 t representing a potential resource of more than 5 gm3 of gas

trinidad mud volcanoes where do the expelled fluids come from abstract in order to establish the origin of fluids expelled from mud volcanoes in trinidad we analyzed their major element trace element and isotopic h o sr compositions the mineralogical chemical and sr isotope compositions of associated expelled muds were also determined on the basis of their chemical and sr isotope compositions the fluids were divided into two groups those southwest and northeast of a major right lateral wrench fault the los bajos fault that both controls the chemical quality of the fluids and acts as a drain strontium isotopes were derived via mixing between a radiogenic source 0 71135 and a nonradiogenic source 0 70671 for both southwest and northeast groups however the nonradiogenic source possibly feeding the northeast group showed a lower sr concentration than that of the southwest group h and o isotope data show that the fluids became enriched in 18 o through interaction with wall rocks the fluids were originally oceanic but their properties were subsequently modified by diagenesis as evidenced by chemical data and mixing between fluids issued from two deep seated reservoirs and surface aquifer end members the gas phase expelled with the mud and the fluid through the mud volcanoes is composed mainly of methane with minor carbon dioxide the amount of expelled gas seems the same in samples from both sides of the los bajos fault the almost unique methane content of the gas phase and the large positive 18 o shifts of the reservoir end member as well as b li and ba contents reveal that the fluids from the deep seated reservoirs inherited their chemical compositions at high temperature fluid rock interactions estimates of equilibrium temperatures of the two deep seated reservoirs suggest that to acquire the estimated higher temperature 150 c the mud volcanoes must have been fed partly by a reservoir located at a depth of more than 3 km this depth corresponds to previous geologic information which located the deep seated reservoir in miocene sediments at such a comparable depth the mixing of the original fluids with a less deep seated reservoir and meteoric waters on the ascending path suggests the presence of a recharge mechanism and contributes to the dynamics of the expulsion itself

carboniferous coals of the zonguldak basin northwest turkey implications for coalbed methane potential we investigated the carboniferous coals in the zonguldak basin northwest turkey using a multidisciplinary approach including petrographical and geochemical analyses gas adsorption and gas content measurements artificial maturation experiments on selected coals and one dimensional 1 d modeling of the basin evolution and hydrocarbon generation the main emphasis was set on the definition of coalbed methane cbm generation capability and adsorption capacity of the coals considering these properties of coals and the amount and composition of gas within the coal seams we carried out a comprehensive evaluation of the cbm potential of the basin three areas in the basin namely armutcuk zonguldak and amasra were investigated separately for their cbm potential from the standpoint of petroleum oil and or gas generation the coals in the armutcuk and amasra areas are located within the oil generation window the coals of the zonguldak area are located within the oil and gas generation window computer aided basin modeling using a basin specific kinetic data set of hydrocarbon generation from coals suggests that significant quantities of gas have been generated only in the zonguldak area modeling results also indicate that major gas generation from the base of the westphalian a kozlu formation in the zonguldak area occurred between 80 and 42 ma during the late cretaceous early eocene prior to basin inversion that started at 42 ma and continues at present the predicted amount of generated coalbed gas from coal seams in the gas generation zone is several times higher than the adsorption capacity of the respective seams a certain amount of this gas controlled by the adsorption capacity is stored within the coal seams where it is generated gas generated in excess of storage capacity obviously would have been expelled from the coal part of the expelled gas is accumulated in coal seams located above the gas generation zone however the coal seams within and above the gas generation zone are undersaturated with respect to their adsorption capacity the undersaturation is probably caused by remigration of gas that is desorbed because of pressure decrease during basin inversion of more than 2500 m 8203 ft over the last 42 m y the rest of the gas generated within the coal seams and expelled first because of the overflow of adsorption capacity and then because of the desorption during basin inversion has either migrated to source conventional gas reservoirs or has been lost to the surface during basin inversion because the basin has not been explored for conventional gas reservoirs a conclusive mass balance cannot yet be performed despite basin inversion and remigration of gas some coal seams still contain gas amounts of up to 10 cm 3 g of coal indicating a cbm potential

correlation of carbon dioxide abundance with temperature in clastic hydrocarbon reservoirs relationship to inorganic chemical equilibrium the mol co2 of gas reservoired in sandstones tends to increase with increasing temperature along both the us gulf coast and the norwegian continental shelf each of these provinces displays identical linear correlations between temperature and the log of the partial pressure of co2 i e pco2 in the reservoir fluid that is the product of the mol co2 the reservoir pressure this correlation is the same both in gulf coast reservoirs younger than 17 ma and in norwegian reservoirs of jurassic to triassic age 144 245 ma indicating that it is not dependent on reaction kinetics norwegian shelf data indicate that the same correlation also applies for gas condensate and oil reservoirs we suggest that the log pco2versus temperature correlation is the result of inorganic chemical equilibria between feldspar clay and carbonate minerals a trend of decreasing ph with increasing temperature is fixed by equilibria between aluminosilicate minerals feldspar kaolinite at lower temperatures followed by various reactions between kaolinite illite chlorite and feldspar as temperatures exceed 110 140 c responding to the ph set by the aluminosilicate system co2 activity in the formation water and thereby co2 partial pressure in any gas phase present is controlled by equilibrium with carbonate minerals this model predicts that co2 released by organic maturation will in general result in precipitation of carbonate minerals below 100 120 c and that there should be widespread carbonate dissolution at higher temperatures

multistation observations of auroras polar cap substorms double wavelength 630 0 and 427 8 nm all sky imagers were operated at the automatic geophysical observatory ago sites p1 and p4 magnetic latitude 80 south pole station magnetic latitude 74 and p3 magnetic latitude 72 during the austral winter of 1994 and 1995 a new data format was developed to present the 24 hour auroral displays from the station arrays which provided 24 hour optical data during the antarctic winter night for several months auroras at these stations exhibit the typical magnetic local time mlt features of high latitude precipitation on the nightside mlt substorm poleward expansions were observed to reach very high latitudes a typical event june 3 1994 0400 0500 ut started equatorward from the south pole and propagated to the high latitude limit of the field of view at p1 and p4 the morphological appearance of these high latitude auroral substorm features was similar to that of substorm auroras observed at lower latitudes the intense 427 8 nm emission accompanied by a weak 630 nm emission showed that the particles were energetic the interplanetary magnetic field imf bz component was slightly negative before and during this event emphasizing that these were substorm auroras and not polar cap auroras which tend to occur during times of prolonged positive imf bz statistical analysis of the 1995 ago optical data shows that over 20 of substorms are seen to penetrate to regions greater than 80 of latitude

carbon dioxide in clastic rocks and silicate hydrolysis the amount of carbon dioxide in clastic rocks in sedimentary basins increases with depth organic matter dissolved organic species and dissolution of carbonate minerals have been suggested as sources of co sub 2 which increases in abundance with depth and temperature isotopic compositions of aqueous hco sub 3 sup minus gaseous co sub 2 and calcite from conventional hydrocarbon wells and steam assisted recovery of heavy oil suggest that calcite or other carbonate minerals are the source of co sub 2 particularly at higher temperatures detailed examination of the stability of diagenetic minerals such as kaolinite smectite and analcime among others relative to the coexisting waters indicates that silicate hydrolysis is the driving force for dissolution of carbonate minerals and the ultimate source of abundant co sub 2 in clastic rocks in diagenetic environments at temperatures over approximately 100 c

temperature and pressure characteristics of ordovician gas condensate reservoirs in the tazhong area tarim basin northwestern china this paper investigates the temperature and pressure distribution characteristics and their evolution in the upper ordovician strata in the tazhong area tarim basin northwestern china based on hundreds of temperature data from boreholes the present day temperature ranges from 100 c to 130 c increasing from the southeast to the northwest and having a cool belt in the central fault horst pore pressures in the upper ordovician reservoirs range from 35 to 62 mpa 5076 to 8992 psi overpressures developed in the southwestern region and along the eastern segment of the central fault horst to the northern slope the lower ordovician reservoirs in the east reached 140 c during the late ordovician but those in the west heated continuously and reached the maximum temperature 130 c during present day paleopressures reconstructed from fluid inclusion data indicate that overpressures caused by hydrocarbon generation were formed in the areas away from fault belts but were absent in the area around the no 1 fault belt the temperature evolution indicates that the middle lower cambrian source rocks reached gas generation stage vitrinite reflectance ro 2 0 at the end of the ordovician whereas the middle upper ordovician source rocks are still in the high maturity stage ro 1 3 at the present day deep oil and gas migration is driven by overpressure and commercial reservoirs are predominantly distributed in the normally pressured zones along the no 1 fault belt the formation of gas condensate is controlled by specific temperature and pressure characteristics

total gas in place gas composition and reservoir properties of coal of the mannville coal measures central alberta abstract the lower cretaceous mannville coal measures in south central alberta host one of the most successful horizontal coal methane developments yet the contribution of thin coal seams and other organic rich strata to total gas in place and producible gas remains unaccounted in this study well log core fluid and gas analyses in the mannville coal measures are evaluated in order to quantify and characterise the total gas in place resource that may be accessed by a horizontal well completed in the main coal seam which is the usual practise regionally the estimated gas capacity and content of the coals increases from northeast to southwest in parallel with the depth of burial and the level of organic maturation rank although local variations exist the isotopic composition of the methane of coals currently at depths greater than 1500 m have a strong thermogenic signature shallower coals have a mixed biogenic thermogenic signature and the shallowest coals have a strong biogenic signature the trend in gas composition is less well defined with the highest carbon dioxide contents occurring in the area of the lowest and highest ranks generally the percentage of heavier gases c 2 c 5 increases with maturity depth of burial but some low rank coals ro 0 30 in eastern alberta and saskatchewan contain significant c 2 c 5 hydrocarbons the origin of the heavier gases in the low rank coals is unclear migration from a deeper source is the most likely explanation the gas adsorption capacity of the coals varies regionally with depth of burial pressure coal rank and ash content the highest adsorption capacity at reservoir pressure and temperature approaches 400 1 scf t but most coals have values between 260 and 320 scf t the gas content of the coals as measured by desorption ranges from 230 to 350 scf t and averages 310 scf t most of the coals are saturated with gas within the accuracy of the analyses notable exceptions occur adjacent to the saskatchewan border where the lower rank coals may be markedly under saturated the amount of methane in solution calculated at a reservoir pressure of 1000 psig 6 9 mpa is calculated to be between 7 and 10 scf t 3 of total gas currently mannville coal gas production is limited to an area in central alberta of about 2200 km 2 850 miles 2 outside the producing fairway sustained commercial production has not been achieved due to low permeability in the producing and prospective fairway the net thickness of the coal within 20 m of the main coal seam varies from 0 to 10 8 m and averages 5 1 m here the thickest coal seam ranges up to 4 7 m thick and averages 1 9 m due to limited gas content data from core for all seams and wells a protocol was developed to extrapolate existing core data to non cored seams and wells through petrophysical logs the protocol takes into consideration the correlation between gas and ash content and the maturity of the coals the total coal gas resource density in the current area of production and prospective areas determined by applying this protocol for the average well has a low estimate of 5 4 bcf mi 2 2 m 3 km 2 a median estimate of 5 9 bcf mi 2 and a high estimate of 6 1 bcf mi 2

the poleward leap of the auroral electrojet as seen in auroral images this paper discusses a recently published series of 12 successive images of the northern auroral oval obtained by the university of iowa s auroral imager on de 1 during a substorm on november 8 1981 the images showed a sudden within 12 min thickening and poleward expansion of the midnight sector of the oval that occurred at the maximum epoch of the substorm i e as auroral zone bays reached their peaks and began to subside about 90 min after the expansive phase onset we propose that this was the auroral manifestation of the poleward leap of the auroral electrojet that has been reported on many occasions to coincide with thickening of the plasma sheet in the outer magnetotail beyond 15 re late in a substorm the plasma sheet thickening is thought to be associated with a tailward retreat of the substorm magnetic neutral line we note evidence that the neutral line s tailward retreat influences auroral currents and particle precipitation even at low auroral latitudes modifications of the present auroral substorm model are suggested

variable gas content saturation and accumulation characteristics of weibei coalbed methane pilot production field in the southeastern ordos basin china using diverse geologic and geophysical data from recent exploration and development and experimental results of analysis of gas content gas capacity and gas composition this article discusses how geologic structural and hydrological factors determine the heterogeneous distribution of gas in the weibei coalbed methane cbm field the coal rank of the pennsylvanian no 5 coal seam is mainly low volatile bituminous and semianthracite the total gas content is 2 69 to 16 15 m3 t 95 00 570 33 scf t and gas saturation is 26 0 to 93 2 burial coalification followed by tectonically driven hydrothermal activity controls not only thermal maturity but also the quality and quantity of thermogenic gas generated from the coal gas composition indicates that the cbm is dry and of dominantly thermogenic origin the thermogenic gases have been altered by fractionation that may be related to subsurface water movement in the southern part of the study area three gas accumulation models are identified 1 gas diffusion and long distance migration of thermogenic gases to no flow boundaries for sorption and minor conventional trapping 2 hydrodynamic trapping of gas in structural lows and 3 gas loss by hydrodynamic flushing the first two models are applicable for the formation of two cbm enrichment areas in blocks b3 and b4 whereas the last model explains extremely low gas content and gas saturation in block b5 the variable gas content saturation and accumulation characteristics are mainly controlled by these gas accumulation models

gas saturation and co2 enhancement potential of coalbed methane reservoirs as a function of depth the influence of moisture temperature coal rank and differential enthalpy on the methane ch4 and carbon dioxide co2 sorption capacity of coals of different rank has been investigated by using high pressure sorption isotherms at 303 318 and 333 k ch4 and 318 333 and 348 k co2 respectively the variation of sorption capacity was studied as a function of burial depth of coal seams using the corresponding langmuir parameters in combination with a geothermal gradient of 0 03 k m and a normal hydrostatic pressure gradient taking the gas content corresponding to 100 gas saturation at maximum burial depth as a reference value the theoretical ch4 saturation after the uplift of the coal seam was computed as a function of depth according to these calculations the change in sorption capacity caused by changing pressure temperature conditions during uplift will lead consistently to high saturation values therefore the commonly observed undersaturation of coal seams is most likely related to dismigration losses into adjacent formations and atmosphere finally we attempt to identify sweet spots for co2 enhanced coalbed methane co2 ecbm production the co2 ecbm is expected to become less effective with increasing depth because the co2 to ch4 sorption capacity ratio decreases with increasing temperature and pressure furthermore co2 ecbm efficiency will decrease with increasing maturity because of the highest sorption capacity ratio and affinity difference between co2 and ch4 for low mature coals

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

detailed analysis of a substorm event on 6 and 7 june 1989 1 growth phase evolution of nightside auroral activities and ionospheric convection toward expansion phase onset 1 we have analyzed in detail the evolution of nightside auroral activities and ionospheric convection during the growth phase of an isolated substorm the following three characteristic auroral activities were identified by meridian scanning photometers msp at ground stations 1 proton main oval 2 fast equatorward moving fem arc and 3 near plasma sheet boundary layer npsbl aurora the proton main oval corresponds to the main part of the proton auroral region and was located at the equatorward most region of the electron auroral emissions and gradually moved equatorward during the growth phase the fem arc was a discrete auroral arc having a clear longitudinally elongated form it appeared about 20 min before the onset on the high latitude side of the auroral region and moved equatorward toward the proton main oval its equatorward motion gradually slowed as it approached the proton main oval as the fem arc moved equatorward the location of the peak velocity in the nightside return flow of the two cell convection also moved equatorward the auroral breakup occurred in a localized area around the demarcation region between the two return flows close to the latitude of the fem arc this was observed by the uv imager aboard the akebono satellite the npsbl aurora appeared a few minutes before the onset around the poleward most region of the aurora and continued even after the onset our detailed analysis of these phenomena can give us important clues as to how the growth phase proceeds toward the expansion phase onset

the effect of sedimentary redbeds on coalbed methane occurrence in the xutuan and zhaoji coal mines huaibei coalfield china abstract the lithologies and permeabilities of caprocks have significant effects on coalbed methane cbm preservation to study the controlling effects of redbeds deposits on cbm occurrence in the xutuan and zhaoji coal mines of the huaibei coalfield in china the variations in mineralogical composition microstructure pore structure permeability and diffusion among the redbeds caprock samples neogene clay rock and ordinary coal measure strata sandstone mudstone and siltstone have been investigated the results indicate that redbeds are porous rocks with weaker sealing capabilities than coal strata caprocks allowing cbm to escape from the coal seam the formation of the lithological properties of the redbeds is closely related to their mineralogical composition and diagenesis redbeds are mainly composed of illite 57 64 calcite 25 33 quartz 6 12 muscovite 3 8 and pyrite

geochemistry of coalbed gas a review coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource coal mining operations such as ventilation of coalbed gas from underground mines release coalbed ch4 into the atmosphere an important greenhouse gas whose concentration in the atmosphere is increasing because of these energy and environmental issues increased research attention has been focused on the geochemistry of coalbed gas in recent years this paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances

uncertainty of gas saturation estimates in a subbituminous coal seam abstract to assess the commercial viability of a coalbed methane prospect two of the key geological parameters measured are gas content desorbed gas and gas holding capacity adsorption capacity these two measures together with reservoir pressure give an estimate of the gas saturation of the reservoir typically gas saturation has been assessed by collecting one adsorption isotherm sample and assuming it is representative of the whole seam reservoir conditions this study addresses that assumption to understand the level of variation and thus the inherent uncertainty in saturation one core jasper 1 from the huntly coalfield in new zealand was analysed in detail ten samples representing the whole coal seam were placed into gas desorption canisters and desorbed for ten days and then analysed for adsorption capacity desorption analyses for total measured gas content average in situ basis ranged from 2 32 to 2 89 m 3 t standard deviation sd 0 18 and gas adsorptive capacity at 4 mpa average in situ basis from 2 11 to 3 51 m 3 t sd 0 38 resulting in saturations ranging from 66 to 120 sd 15 determination of how many samples are required to make a realistic assessment of average reservoir properties requires a consideration of i the level of accuracy desired ii the limit of accuracy possible which is governed by the magnitude of experimental error and iii the innate variability of the seam it was found that a minimum of five samples each for adsorption and desorption were required in order to significantly decrease the uncertainty in gas saturation estimates for a subbituminous coal

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

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

water rock interaction in tertiary sandstones san joaquin basin california u s a diagenetic controls on water composition three water types are recognized among petroleum associated waters of the southern san joaquin basin 1 meteoric water 2 diagenetically modified connate water and 3 mixed meteoric modified connate water the diagenetically modified connate marine water can be further subdivided into three types 1 fully mg depleted mg 1 mole of the sum of na k ca and mg 2 partially mg depleted and 3 ca enriched enrichment in ca which is the sharpest chemical divide found for the diagenetically modified connate water is the result of feldspar albitization the ca enriched waters are also rich in total dissolved al up to 6 mg l 1 and exhibit lighter 18o values than other diagenetically modified connate waters the total dissolved al abundance in these waters may be due to the presence of organic complexing agents simple and aromatic organic acids and phenolics the lighter 18o values are probably due to both albitization and the lack of substantial clay diagenesis illitization of smectite

chemistry of oil field brines in relation to diagenesis of reservoirs 2 reconstruction of palaeo water composition for modelling illite diagenesis in the greater alwyn area north sea abstract input data for water composition are required in order to numerically simulate diagenetic episodes in rock dominated closed system modelling the composition of water initially present in the pores has at most only a minor influence on the stability of the system and is controlled by the mineral composition in open system modelling the composition of infiltrating water can play an important role brent water salinities of the greater alwyn area exhibit a regional trend from the north to the south the k cl ratio of these waters varies along two trends it is higher in the north than in the south alkalinity and published pco2 values are used to calculate ph under subsurface conditions very few silica measurements are available aluminium analyses of pore water are not available some reservoirs of the greater alwyn area experienced a major reduction in permeability due to illite and quartz precipitation coeval with kaolinite and k feldspar dissolution saturation of present day brent waters with respect to these minerals is examined the method proposed in part 1 is applied to reconstruct a range of possible compositions for ancient waters in brent reservoirs between several extreme conditions one of these extremes is provided by buffering water with a set of minerals chosen from petrographic considerations the other extremes correspond to reasonable states of over saturation with respect to particular minerals e g quartz and concern the values of dissolved si and al which are the least well characterised concentrations from the routine analyses of formation waters

magnetic mapping effects of substorm currents leading to auroral poleward expansion and equatorward retreat magnetotail fast flows magnetic field dipolarization and its relaxation are linked to auroral brightening poleward expansion and equatorward motion during substorm onset expansion and recovery respectively while auroral brightening is often attributed to the field aligned currents produced by flow vorticity and pressure redistribution the physical causes of auroral poleward expansion and equatorward retreat are not fully understood simplistically such latitudinal changes can be directly associated to the tailward motion of the flux pileup region and the earthward flux transport toward the dayside that depletes the near earth plasma sheet however because the equatorial magnetic field profile and the magnetospheric field aligned current system change significantly mapping is severely distorted to investigate this distortion we superimpose a substorm current wedge model dynamically driven by ground based observations on the global tsyganenko model t96 during an isolated substorm on 13 february 2008 observed by the time history of events and macroscale interactions during substorms and goes 10 spacecraft and by ground all sky imagers we validate our model by showing that the timing and ionospheric projection of the flux pileup region and flow bursts observed at the spacecraft match auroral activations we then use the improved mapping enabled by the model to demonstrate that in this event auroral poleward expansion and equatorward retreat are mainly caused by substorm current wedge induced mapping changes

pore characterization and methane sorption capacity of over mature organic rich wufeng and longmaxi shales in the southeast sichuan basin china abstract currently the upper ordovician wufeng o3w and lower silurian longmaxi s1l formations in southeast sichuan basin have been regarded as one of the most important target plays of shale gas in china in this work using a combination of low pressure gas adsorption n2 and co2 mercury injection porosimetry mip and high pressure ch4 adsorption we investigate the pore characteristics and methane sorption capacity of the over mature shales and discuss the main controlling factors for methane sorption capacity and distribution of methane gas in pore spaces low pressure co2 gas adsorption shows that micropore volumes are characterized by three volumetric maxima at about 0 35 0 5 and 0 85 nm the reversed s shaped n2 adsorption isotherms are type with hysteresis being noticeable in all the samples the shapes of hysteresis loop are similar to the h3 type indicating the pores are slit or plate like mesopore size distributions are unimodal and pores with diameters of 2 16 nm account for the majority of mesopore volume which is generally consistent with mip results the methane sorption capacities of o3w s1l shales are in a range of 1 63 3 66 m3 t at 30 c and 10 mpa methane sorption capacity increase with the toc content surface area and micropore volume suggesting organic matter might provide abundant adsorption site and enhance the strong methane sorption capacity samples with higher quartz content and lower clay content have larger sorption capacity our data confirmed that the effects of temperature and pressure on methane sorption capacity of shale formation are opposite to some extent suggesting that during the burial or uplift stage the gas sorption capacity of hydrocarbon reservoirs can be expressed as a function of burial depth based on the adsorption energy theory when the pore diameter is larger than 2 nm much methane molecular will be adsorbed in pores space with distance to pore wall less than 2 nm while free gas is mainly stored in the pore space with distance to pore wall larger than 2 nm distributions of adsorption space decrease with the increasing pore size while free gas volume increase gradually assuming the pore are cylindrical or sphere particularly when the pore size is larger than 30 nm the content of adsorbed gas space volume is very low and its contribution to the all gas content is negligible

geochemical modelling of sandstone diagenesis and its consequences on the evolution of porosity abstract geochemical modelling of fluid rock interaction is one theoretical approach that can be used for understanding diagenetic processes and their effects on reservoir quality results of successive modelling of dissolution and heating using two specific path calculation codes dissol and thermal from 25 to 160 c are presented if one considers one volume of reacting solution the diagenetic effects are very important for fluid chemistry while mass transfers have little effect on porosity only cumulative effects due to the circulation of fluids in reservoirs may explain the extent of diagenetic processes on minerals comparison between the computed data this study and available data from the north sea from gulf coast sandstones from pattani basin gulf of thailand from san joaquin basin california u s a and from a triassic sandstone reservoir in the rhine graben cronenbourg france show interesting similarities in the chemical evolution of the fluid the modelling has interesting implications for the relations between ph p co 2 conditions and the diagenetic stability of calcic plagioclase

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined