key strata characteristics controlling the integrity of deep wells in longwall mining areas abstract the damage of vertical oil gas wells in longwall mining areas is mainly a result of strata movement induced by coal extraction strata with contrasting lithology vary dramatically in their movement and potential for well damage with some special combinations of strata in particular having the greatest potential for damage this study investigates the effects of specific combinations of strata transition structures i topsoil bedrock ii a thin weak interlayer sandwiched above and below by two stiff beds and iii the key stratum sandwiched above and below by two soft beds on the magnitude severity and distribution of various anticipated well deformations and explores the optimal drilling path for wells to maximize well integrity results indicate that 1 effects of various combinations of strata on well deformation lie essentially in the mismatch in the mechanical properties of the strata and weak interfaces with the stratum thickness and vertical distance from the coal seam to the stratum interface also exerting a significant influence 2 wells in the upper part of the topsoil are subject to horizontal tension while the lower part is laterally compressed following the extraction of either one panel or both panels large lateral tensile strains normally arise at the upper part of the hard strata which directly underlie the soft strata large lateral compressive strains are concentrated in the strata within 5 m above and below the coal seam and peak in the seam longitudinal well deformation is dominated by compression in soft strata especially in the upper part of the layer and is dominated by tension in stiff strata within the lower portion in particular vertical compression at the interface is larger below the key stratum and peaks at the interface between the coal seam and its immediate roof well distortions in soft strata are 3 to 5 times those of ones in stiff strata 3 well deformations developing both at interfaces and within layers significantly intensify in the vicinity of the seam an integrated consideration of various deformations of five candidate well paths indicates that the optimal position for well stability is the one that deviates from the pillar centerline and is close to the second mined panel

coalbed methane completions a world view abstract cbm wells are cheap because they are usually shallow deeper wells tend to have lower coal permeability and productivity low permeability is the weak point achilles heel for cbm ventures and success will entail finding regions of enhanced permeability utilizing horizontal wells with the option of fracturing these wells and possibly in creating permeability by new paradigm methods such as shear stimulation and branch fracturing this paper discusses the role of permeability in choosing cbm completions as well as examples of those completions from around the world the guidelines offered are new and practical including perm bands and a decision tree and should benefit any cbm completion strategy

an analytical coal permeability model for tri axial strain and stress conditions coal permeability is sensitive to the effective stress and is therefore coupled to the geomechanical behaviour of the seam during gas migration as coal shrinks with gas desorption and swells with adsorption understanding this coupling to geomechanical behaviour is central to interpreting coal permeability existing coal permeability models such as those proposed by shi and durucan 2004 and palmer and mansoori 1996 simplify the geomechanical processes by assuming uni axial strain and constant vertical stress however it is difficult to replicate these conditions in laboratory tri axial permeability testing and during laboratory core flooding tests for enhanced coal bed methane often laboratory tests involve a hydrostatic stress state where the pressure in the confining fluid within the tri axial cell is uniformly applied to the sample exterior in this experimental arrangement the sample is allowed to undergo tri axial strain this paper presents two new analytical permeability model representations derived from the general linear poroelastic constitutive law that include the effects of tri axial strain and stress for coal undergoing gas adsorption induced swelling a novel approach is presented to the representation of the effect of coal sorption strain on cleat porosity and thus permeability this involves distinguishing between the sorption strain of the coal matrix the pores or cleats and the bulk coal the developed model representations are applied to the results from a series of laboratory tests and it is shown that the models can predict the laboratory permeability data as part of this characterisation the various sorption strains are identified and it is shown that the pore strain is significantly larger than approximately 50 times the bulk sorption strain the models also provide further insight into how coal permeability varies with coal shrinkage and swelling and how the permeability rebound pressure depends upon the effective stress applied

shelf response to intense offshore wind this is the accepted version of the following article grifoll m aretxabaleta a espino m shelf response to intense offshore wind journal of geophysical research setembre 2015 vol 120 num 9 p 6564 6580 which has been published in final form at http onlinelibrary wiley com doi 10 1002 2015jc010850 full

seal evaluation and confinement screening criteria for beneficial carbon dioxide storage with enhanced coal bed methane recovery in the pocahontas basin virginia abstract the geological storage of carbon dioxide in appalachian basin coal seams is one possible sink for sequestration of greenhouse gases with the added benefit of enhanced coal bed methane ecbm recovery the pocahontas basin part of the central appalachian basin of southwestern virginia is a major coal bed methane cbm province with production mostly from coal beds in the lower pennsylvanian pocahontas and new river formations as part of the southeast regional carbon sequestration partnership s phase ii research program a co 2 injection demonstration well was installed into lower pennsylvanian coal bed methane producing strata in southwest virginia samples of siliciclastic lithologies above coal beds in this oakwood field well and from several other cores in the nora field were taken to establish a baseline of the basic confinement properties of overlying strata to test seal competency at local and regional scales strata above cbm producing coal beds in the pocahontas and new river formations consist of dark gray shales silty gray shales heterolithic siltstones sandstones and shales lithic sandstones and quartzose sandstones standard measurements of porosity permeability and petrography were used to evaluate potential leakage hazards and any possible secondary storage potential for typical lithologies both lithic and quartz rich sandstones exhibit only minor porosity with generally low permeability 2 ecbm traps one of the most promising confining intervals above the major coal bed methane producing interval is the hensley shale member analyses of 1500 geophysical logs in southwest virginia indicate that this unit is moderately thick 50 ft 15 m laterally continuous 3000 km 2 and a homogenous shale which coarsens upward into siltstone and sandstone or is truncated by sandstone calculations from two mercury injection capillary porosimetry tests of the shale indicate that a displacement entry pressure of 207 psi 1427 kpa would generate an estimated seal capacity of 1365 ft 416 m of co 2 before buoyant leakage scanning electron microscopy indicates a microfabric of narrow pore throats between quartz grains floating in a clay matrix modeled median pore throat size between micro fabric matrix grains for the shale is estimated at 0 26 m these characteristics indicate that the shale where fractures and joints are limited would be an adequate regional confining interval for deeper co 2 storage with ecbm

geologic and hydrological controls on coal reservoir water production in marine coal bearing strata a case study of the carboniferous taiyuan formation in the liulin area eastern ordos basin china abstract coalbed methane cbm is commercially explored and produced in the continental permian shanxi formation of the southern qinshui and eastern ordos basins of china however cbm production in marine carboniferous taiyuan formation is hindered by a lack of knowledge about the controlling factors on water production the liulin area of the eastern ordos basin is one of the trail areas for cbm development in china in this study water yield characteristics and their influencing factors during cbm production in the liulin area were investigated by fluid inclusion studies core slice observations and stable isotope analyses of groundwater the results demonstrated that the recharge area for this limestone aquifer of the taiyuan formation is the exposed carbonate in the northeastern liulin area the thickness along with the dissolved pores and fractures of the limestone aquifer were closely related to the water production of the cbm well from an engineering point of view hydraulic fracturing allows the direct movement of water from coal seams to the roof limestone aquifers which was a key factor in the high water yield of cbm wells in the liulin area finally based on the structure and distribution of roof limestone as well as water production data the geologic scenarios for water production in the taiyuan formation was divided into four types these divisions indicated that the best prospective target areas for cbm production should have low numbers of faults small limestone thicknesses relatively large burial depths and normal reservoir pressures and temperatures the results of this study are helpful for cbm exploration and production in the marine coal bearing strata of china

permeability variations within mining induced fractured rock mass and its influence on groundwater inrush this paper is concerned with the evaluation of permeability of fractured rock mass due to the cover stress re establishment which is a major factor in controlling water and gas flow rate induced by mining operations in fractured rock the case study considered in this paper is based on the results of observations of groundwater inrush and a decrease in water inflow from the fractured roof strata due to mining advancing in the taiping coalmine shandong province china a conceptual model of an effective porous media was used to assess the permeability distribution in the fractured zone induced by coal mining the cover stress re establishment in gob fractured rock mass was evaluated using an empirical formula based on the surface subsidence a simplified conceptual model of the fractured zone was used to evaluate the deformation of fractured zone along with the evaluation of changes in the rock permeability above the gob due to the cover stress re establishment these data were then used to calculate the water inflow rate into the panel predicted water inflow rates have been found to be in good agreement with those from monitoring data this study improved the understanding of the mechanisms of the post mining cover stress re establishment on permeability change of the overburden fracture rock strata these results can then be applied for numerical simulations of the process of overburden failure and consequent groundwater inrush due to coal mining

multiple cold trap pyrolysis gas chromatography a new technique for modeling hydrocarbon generation abstract the newly developed multiple cold trap pyrolysis gas chromatography mctp gc technique allows us to calculate activation energies for the generation of individual hydrocarbons from source rocks this improves our ability to predict the timing of oil generation and the compositional changes of oil at the different stages of kerogen conversion the activation energies for n c 12 and n c 24 for a type ii kerogen toarcian shale are 57 5 0 8 kcal mol and 51 2 2 2 kcal mol with frequency factors of 8 71 10 16 min and 1 15 10 15 min respectively the relative rates of alkane generation are n c 24 n c 18 n c 12 n c 2 c 5 by comparing the rates of generation from kerogen and asphaltenes for monterey source rocks we conclude that normal alkanes can be generated directly without going through an asphaltene intermediate

geostatistical modeling of the gas emission zone and its in place gas content for pittsburgh seam mines using sequential gaussian simulation determination of the size of the gas emission zone the locations of gas sources within and especially the amount of gas retained in those zones is one of the most important steps for designing a successful methane control strategy and an efficient ventilation system in longwall coal mining the formation of the gas emission zone and the potential amount of gas in place gip that might be available for migration into a mine are factors of local geology and rock properties that usually show spatial variability in continuity and may also show geometric anisotropy geostatistical methods are used here for modeling and prediction of gas amounts and for assessing their associated uncertainty in gas emission zones of longwall mines for methane control this study used core data obtained from 276 vertical exploration boreholes drilled from the surface to the bottom of the pittsburgh coal seam in a mining district in the northern appalachian basin after identifying important coal and non coal layers for the gas emission zone univariate statistical and semivariogram analyses were conducted for data from different formations to define the distribution and continuity of various attributes sequential simulations performed stochastic assessment of these attributes such as gas content strata thickness and strata displacement these analyses were followed by calculations of gas in place and their uncertainties in the pittsburgh seam caved zone and fractured zone of longwall mines in this mining district grid blanking was used to isolate the volume over the actual panels from the entire modeled district and to calculate gas amounts that were directly related to the emissions in longwall mines results indicated that gas in place in the pittsburgh seam in the caved zone and in the fractured zone as well as displacements in major rock units showed spatial correlations that could be modeled and estimated using geostatistical methods this study showed that gip volumes may change up to 3 mmscf per acre and in a multi panel district may total 9 bcf of methane within the gas emission zone therefore ventilation and gas capture systems should be designed accordingly in addition rock displacements within the gas emission zone are spatially distributed from an engineering and practical point of view spatial distributions of gip and distributions of rock displacements should be correlated with in mine emissions and gob gas venthole productions

cross formational flow of water into coalbed methane reservoirs controls on relative permeability curve shape and production profile coalbed methane cbm wells tend to produce large volumes of water especially when there is hydraulic connectivity between coalbed and nearby formations cross formational flow between producing coal and adjacent formations can have significant production and environmental implications affecting economic viability of production from these shallow reservoirs such flows can also affect how much gas can be removed from a coalbed prior to mining and thus can have implications for methane control in mining as well the aim of this paper is to investigate the impact of water flow from an external source into coalbed on production performance and also on reservoir variables including cleat porosity and relative permeability curves derived from production data analysis a reservoir model is constructed to investigate the production performance of a cbm well when cross formational flow is present between the coalbed and the overlying formation results show that cleat porosity calculated by analysis of production data can be more than one order of magnitude higher than actual cleat porosity due to hydraulic connectivity water saturation within coalbed does not considerably change for a period of time and hence the peak of gas production is delayed upon depletion of the overlying formation water saturation in coalbed quickly decreases rapid decline of water saturation in the coalbed corresponds to a sharp increase in gas production as an important consequence when cross flow is present gas and water relative permeability curves derived from simulated production data have distinctive features compared to the initial relative permeability curves in the case of cross flow signatures of relative permeability curves are concave downward and low gas permeability for a range of water saturation followed by rapid increase afterward for water and gas respectively the results and analyses presented in this work can help to assess the impact of cross formational flow on reservoir variables derived from production data analysis and can also contribute to identifying hydraulic connectivity between coalbed and adjacent formations

coal bed reservoir simulation with geostatistical property realizations for simultaneous multi well production history matching a case study from illinois basin indiana usa abstract coal seam degasification is a means to recover energy from the methane gas retained in coal and is also a supplementary measure to ventilation which is proven to be one of the most effective ways to reduce methane emissions to a safe level in coal mines reservoir simulation is probably the most effective way to assess the coal seam as a gas reservoir and thereby its fluid storage and flow related properties this objective is achieved by taking advantage of history matching of wellbore production reservoir simulation with multi well history matching is a tedious process as important coal properties that affect wells production characteristics are spatially variable across the seam the common practice is to change various properties at the well blocks during the history matching process and assume that they are uniform across the domain of interest this process however often does not produce realistic and effective results for well or coal reservoir management in this work a multi level approach to coal bed reservoir simulation is demonstrated for a group of coalbed methane wells in the illinois basin producing from the seelyville coal member of the linton formation of the carbondale group pennsylvanian in indiana this approach includes in order gas and water deliverability analyses of wells geostatistical simulation and co simulation and coal bed reservoir simulation it is shown that a reservoir model which utilizes the geostatistical maps of important coal properties is effective for simultaneous history matching of all wells and eliminates the need for guessing and changing values of coal properties at and around individual well blocks this methodology also provides realistic distributions of reservoir parameters and how they change during gas depletion and thus aids in coal seam and coal gas management

an accurate method for permeability evaluation of undersaturated coalbed methane reservoirs using early dewatering data abstract accurate determination of permeability is critical for the efficient development of coalbed methane cbm reservoirs permeability determination is mainly based on the feature straight line analysis method and the plate fitting method requiring pressure build up data although few analytical methods only require dynamic production data they usually have limitations in application due to complicated solution processes or insufficient consideration of cbm reservoir characteristics this study improves the previous method for determining the permeability of undersaturated cbm reservoirs firstly mathematical models are established for calculating permeability of undersaturated cbm reservoirs with constant permeability and variable permeability due to pulverized coal output blockage matrix shrinkage and stress dependence during the production process secondly the proposed models are validated by numerical simulation analytical and pressure build up test methods finally the models are applied to the muai cbm reservoir in sichuan basin china high middle and low permeability zones of the muai reservoir are classified the results show that when bottom hole pressure and water production data of cbm wells during single phase water flow period are processed by the proposed method and plotted in a rectangular coordinate system a strong linear relationship can be obtained for cbm reservoirs with constant permeability and variable permeability the slope of the fitted equations can be used to determine permeability efficiently and accurately compared with previous methods the new method provides better interpretation results for cbm wells with strongly fluctuating production data since the use of the integration of fluctuating data and cumulative water production reduce the effect of production fluctuation on the results due to its conciseness this method can rapidly calculate reservoir permeability around a large number of production wells and obtain permeability distribution in the reservoir providing guidance for cbm productivity forecasting and development policy adjustment

mining induced strata stress changes fractures and gas flow dynamics in multi seam longwall mining abstract this paper presents key findings from a recent comprehensive study of longwall mining induced strata movement stress changes fractures and gas flow dynamics in a deep underground coal mine in anhui china the study includes field monitoring of overburden displacement stress and water pressure changes at the longwall panel 1115 1 of the guqiao mine in addition 3d modelling of strata behaviour at the longwall panel using a 3d finite element code and goaf gas flow simulations with a cfd code are carried out this research has resulted in many new insights into the complex dynamic interaction between mining induced strata stress changes fractures and gas flow patterns based on the findings from the field monitoring and numerical modelling a three dimensional annular shaped overlying zone along the perimeter of the longwall panel is identified for optimal methane drainage during mining a practical method that helps define the geometry and boundary of this zone is proposed this study provides a new methodology and a set of engineering principles for the design of optimal co extraction of coal and methane

probabilistic modeling using bivariate normal distributions for identification of flow and displacement intervals in longwall overburden abstract gob gas ventholes ggv are used to control methane emissions in longwall mines by capturing it within the overlying fractured strata before it enters the work environment in order for ggvs to effectively capture more methane and less mine air the length of the slotted sections and their proximity to top of the coal bed should be designed based on the potential gas sources and their locations as well as the displacements in the overburden that will create potential flow paths for the gas in this paper an approach to determine the conditional probabilities of depth displacement depth flow percentage depth formation and depth gas content of the formations was developed using bivariate normal distributions the flow percentage displacement and formation data as a function of distance from coal bed used in this study were obtained from a series of borehole experiments contracted by the former us bureau of mines as part of a research project each of these parameters was tested for normality and was modeled using bivariate normal distributions to determine all tail probabilities in addition the probability of coal bed gas content as a function of depth was determined using the same techniques the tail probabilities at various depths were used to calculate conditional probabilities for each of the parameters the conditional probabilities predicted for various values of the critical parameters can be used with the measurements of flow and methane percentage at gob gas ventholes to optimize their performance

production characteristics and reservoir analysis of coalbed methane reservoirs abstract six appalachian coalbed methane cbm projects are reviewed and evaluated in terms of reservoir engineering techniques and cbm recoverability these include three non mine related projects in the northern appalachian basin one non mine related and two mine related projects in the central appalachian basin of southwestern virginia generally low production rates and low cbm reserves are characteristic of the central and northern appalachian basin therefore minimizing production costs is fundamental to the economic success of a cbm project in these regions well deliverability is determined through permeability testing and through production data analysis using a reservoir simulator to history match historic production data all of the non mine related projects utilize vertical wells with well spacings of 60 to 100 acre 0 23 0 40 km 2 that produce from multiple coalbeds at depths as much as 762 m the targets are coalbeds of the pocahontas and new river formations and correlative lee formation in the nora field of virginia equitable resources developer well spacing is 60 acre 0 23 m 2 and recoverability is high 30 60 of initial gas in place well stimulation is by foam or water as the fracture medium the average gas in place is 675 mmscf well 1 and the expected lifetime of the wells is 30 years cost of water disposal is a major economic factor in cbm development in the appalachian basin water disposal is accomplished by using water disposal holes injection wells rather than surface water discharged which is generally not permitted water disposal in the central appalachian basin involves relatively low volumes of water 30 stb day 1 declining to 1 to 2 stb day 1 in the northern appalachian basin in indiana county pa belden and blake developer vertical cbm holes penetrate six to eight allegheny formation coalbeds water and a sand proppant are used for stimulation production levels are low 1 well 1 the life of a vertical cbm hole drilled in advance of mining is 3 to 5 years this type of hole may be converted to a gob hole after mining is completed gob gas is recovered mainly from coalbeds above the mined coalbed and has high recoverability of as much as 10 mmscf day 1 well 1 horizontal cbm holes produce almost pure methane and typically have 1 year of production

analysis of gob gas venthole production performances for strata gas control in longwall mining longwall mining of coal seams affects a large area of overburden by deforming it and creating stress relief fractures as well as bedding plane separations as the mining face progresses stress relief fractures and bedding plane separations are recognized as major pathways for gas migration from gas bearing strata into sealed and active areas of the mines in order for strata gas not to enter and inundate the ventilation system of a mine gob gas ventholes ggvs can be used as a methane control measure the aim of this paper is to analyze production performances of ggvs drilled over a longwall panel these boreholes were drilled to control methane emissions from the pratt group of coals due to stress relief fracturing and bedding plane separations into a longwall mine operating in the mary lee blue creek coal seam of the upper pottsville formation in the black warrior basin alabama during the course of the study pratt coal s reservoir properties were integrated with production data of the ggvs these data were analyzed by using material balance techniques to estimate radius of influence of ggvs gas in place and coal pressures as well as their variations during mining the results show that the ggvs drilled to extract gas from the stress relief zone of the pratt coal interval is highly effective in removing gas from the upper pottsville formation the radii of influence of the ggvs were in the order of 330 380 m exceeding the widths of the panels due to bedding plane separations and stress relieved by fracturing material balance analyses indicated that the initial pressure of the pratt coals which was around 648 kpa when longwall mining started decreased to approximately 150 kpa as the result of strata fracturing and production of released gas approximately 70 of the initial gas in place within the area of influence of the ggvs was captured during a period of one year

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

three dimensional effects of hydraulic conductivity enhancement and desaturation around mined panels changes in the three dimensional hydraulic conductivity field that accompany undermining by a longwall panel are evaluated to define the potential for changes in flow patterns and desaturation relations linking changes in conductivity with the mining induced strain field that develops around the advancing face are defined through the assumption of an equivalent porous medium with the strain partition between fractures and matrix apportioned relative to respective deformation constants model results are validated against behavior recorded at a well instrumented field site replicating the complex steady flow pattern that develops around an advancing longwall face significant hydraulic conductivity increases are restricted to strata at shallow depth ahead of the advancing face and to deep zones behind the face particularly in the caving zone and abutment shear zones these very large increases in conductivity at depth that include the out of section conductivity enhancement that develops along the panel rib exercise primary control on induced water level changes and the potential for saturation zones of desaturation are readily defined with these enabling locations of well vulnerability to water loss to be identified these zones of vulnerability are directly above the panel with their extent potentially modulated by the presence and the location of flatlying layers of low conductivity the complex response recorded in the near face region mandates use of three dimensional models to adequately represent observed behavior

comparison of rate constants for some molecular tracers generated during artificial maturation of kerogens influence of kerogen type abstract the purpose of this work is to carry out artificial maturation of various kerogens under isothermal conditions in open and closed systems and to derive kinetic parameters for specific molecular tracers such as n c 12 and n c 24 alkanes results show that individual normal alkane generation from type i and type ii kerogens follows first order kinetics in both open and closed pyrolysis systems however the normal alkanes generated from type iii samples do not follow a first order mechanism for type i and type ii kerogens slightly different rate constants are obtained for n c 12 and n c 24 generation whereas for the two type iii kerogens n c 24 is produced much faster than n c 12 combining the rate constants derived from open and closed system pyrolysis arrhenius plots were obtained for the four samples under study from which accurate sets of kinetic parameters were calculated

three dimensional mineral grade distribution modelling and longwall mining of an underground bauxite seam abstract a multi step interpolation approach was proposed to model the three dimensional grade distribution and to demarcate orebody in a thin and anfractuous bauxite seam a pre mining demonstration procedure was established to virtually perform fully mechanized longwall mining in the modelled bauxite seam meanwhile a comprehensive evaluation function expressed by the sum of dilution and loss rates of bauxite was utilized to determine the optimal cutting heights 1 71 2 69 m and a suitable diameter 1 5 m for the cutting drums mounted on a double drum shearer to achieve no waste and high recovery mining of the demarcated 106 026 m3 bauxite orebody in addition a numerical model of strata containing geological defects a karst cave and fault discontinuities joints and stratifications and a mountain was established to simulate the discontinuous motion and overburden fracturing disturbed by the longwall mining in the modelled bauxite seam the results indicated that the overburden presented reliable stability and impermeability in which no large scale caving in goaf no water influx no cave collapse no fault slip and no mountain slope landslide occurred this was due to arched roofs above the karst cave and the mining induced fractured zone the subcritical condition of the longwall panel in the dip section and support from the protective pillar between two adjacent panels

a formalism to compute permeability changes in anisotropic fractured rocks due to arbitrary deformations abstract the liu elsworth 1997 formalism that predicts permeability in deformed fractured rock has been highly useful and successful in numerous engineering situations involving mining coal bed methane and shale gas extraction the formalism assumes the rock s fractures are aligned with three orthogonal axes and that the rock is subjected to strains along these three directions only here we relax these assumptions our proposed formula yields the permeability tensor for an anisotropic arbitrarily fractured rock subjected to arbitrary deformations unlike the original liu elsworth approach our formula may therefore be used confidently in situations involving any stress and strain states including those that are non diagonal and with rocks with any distribution of fracture orientations including those that are non orthogonal this is advantageous in numerical simulation and in mining situations that frequently involve such situations our formula adds no discernible computational load to numerical simulations our proposal agrees with lab and in situ direct and indirect tests of permeability

void fraction distribution in overburden disturbed by longwall mining of coal voids in overburden disturbed by coal mining provide channels for transfer of heat methane groundwater oxygen exhaust gas and fire fighting materials in the underground environment based on expressions of strata and ground subsidence a group of void fraction distribution models are proposed including porosity in the caved zone the fracture ratio in the bed separation zone and the fissure ratio in the ground subsidence zone combined with a case study of the antaibao coal mine china theoretical calculation and numerical simulation indicate that porosity distribution in the caved zone is u type and the transverse void fractions in the bed separation zone and ground subsidence zone have m type distributions additionally the longitudinal void fraction distribution changes from type to m type along the strike and dip of the coalbed after the complete subsidence of ground the distribution of fractures in the disturbed overburden of the goaf presents a fractured arch and fracture density gradually decreases from arch foot to crown fire prone zones propagating paths of coalbed fires areas prone to water influx and outlets of boreholes used for fire fighting all usually appear around the perimeter of disturbed overburden the transverse void fractions distribution in the bed separation zone changes from type to m type with an increase in the size of the goaf it is suggested that the inlets of gob vent boreholes should be arranged near the center of the bed separation zone in the early stages of longwall mining and around the perimeter in middle to late stages of mining

the use of coal cuttings from underground boreholes to determine gas content of coal with direct desorption method abstract in underground coal mining operations gas content in a coal seam is used to assess the risk of coal and gas outbursts a broadly standard procedure has been adopted to estimate the gas content with coal core in the coal mining industry in soft or friable or geologically complex sections of coal seams it has proven to be extremely troublesome in taking coal cores as cores can be severely fragmented or sometimes it is simply impossible to core with conventional coring methods due to poor borehole stability leaving coal cuttings from boreholes as the only practical alternative for sampling when coal core is replaced with coal cuttings concerns have been raised about the validity and accuracy of the procedure used for gas content determination with coal core in particular with respect to the sampling method of coal cuttings and gas content calculation due to faster initial gas desorption rates of coal cuttings the standard procedure for gas content determination with coal core has been modified to determine gas content of coal with coal cuttings from underground boreholes this paper describes the modified method and presents and discusses the results when it was trialed in a soft coal seam at huainan china

circulation and haline structure of a microtidal bay in the sea of japan influenced by the winter monsoon and the tsushima warm current mooring and hydrographic surveys were conducted in tango bay a microtidal region of freshwater influence rofi in the sea of japan in order to clarify the circulation pattern in the bay and its driving forces monthly mean velocity records at four stations revealed an inflow and outflow at the eastern and northern openings of the bay respectively indicating an anticyclonic circulation across the bay mouth the circulation was significantly intensified in winter in accordance with the prevailing nw wind component of the winter monsoon the anticyclonic circulation at the bay mouth was connected to an estuarine circulation that was evident near the mouth of the yura river at the bay head surface salinity just offshore of the river mouth was closely related to the yura river discharge whereas in lower layers the offshore water had a stronger influence on salinity prior to a seasonal increase in the yura river discharge summer salinity decreased markedly through the water column in tango bay possibly reflecting intrusion of the changjiang diluted water transported by the tsushima warm current in contrast with the traditional assumption that estuarine circulation is controlled mainly by river discharge and tidal forcing the circulation in tango bay is strongly influenced by seasonal wind and the tsushima warm current the narrow shelf may be responsible for the strong influence of the tsushima warm current on circulation and water exchange processes in tango bay

horizontal and residual circulations driven by wind stress curl in tokyo bay this study investigates the horizontal and residual circulations in tokyo bay using field observations numerical simulations and theoretical analysis numerical simulations show that the observed deepening of isopycnals and associated anticyclonic horizontal circulation in the bay head are mainly driven by negative wind stress curl the effects of river discharge surface heat fluxes and tides are found to be small under strong wind events the wind stress curl over the bay head can be large enough to make the surface ekman layer strongly nonlinear theoretical and numerical analyses show that under large negative wind stress curl the nonlinearity tends to induce positive pumping velocity at the base of the surface mixed layer that counteracts the ekman pumping however the typical duration of wind events in the bay head is not long enough to induce positive pumping under negative wind stress curl these results and historical wind data suggest that the average horizontal circulation and residual circulation immediately below the surface mixed layer in tokyo bay are respectively cyclonic and convergent in summer but anticyclonic and divergent in winter

gas emission prediction and recovery in underground coal mines abstract strata gas can be released and captured from non active and active gas resources either from virgin or relaxed strata both prior to and when mining activities take place the high and irregular gas emissions associated with high production longwall mining have provided a need to optimise the methods used to predict these gas levels and the ventilation requirements for gas dilution a forecast of gas emissions during development drivage and longwall mining indicated possible gas and ventilation problems requiring the introduction of various gas drainage techniques and in maintaining the necessary air quantities in ventilation systems to satisfy the statutory gas limitations for various coal production rates although there are sound principles used in world recognised methods of gas emission prediction a new approach developed from long term practical experience in underground gassy coal mine practices and gas rock mechanics studies appear most suitable for local conditions and mining systems in use the lunagas floorgas and roofgas geomechanical and gas emission models offer an effective solution to these problems both programs are the most advanced engineering numerical tools available to calculate gas source contributions to total gassiness and improve the accuracy and quality of gas control gas capture technologies and ventilation system design

reservoir rock properties of coal measure strata of the lower monongahela group greene county southwestern pennsylvania from methane control and production perspectives abstract the methane emission rate into an underground mine environment from overburden strata during longwall mining is impacted by reservoir and geomechanical characteristics of the coal measure rocks in the overlying strata as well as the presence of any coal seam the reservoir characteristics and how they change during mining potentially affect the performance of gob gas ventholes which consequently impacts the efficiency of methane control in the mining environment this study presents reservoir and elastic properties of coal measure rocks in the lower monongahela group in greene county southwestern pennsylvania of the northern appalachian basin since the source of methane in this region from underground mining is located between the sewickley coal and the pittsburgh coal a specific emphasis was given to this interval core analyses were performed in the laboratory to determine rock porosity and permeability geophysical logging data gamma density sonic obtained from two exploration boreholes were used for evaluating formation boundaries shale contents log porosities and geomechanical properties of formations permeability was also calculated using density log data and empirical equations and compared with laboratory measurements and slug tests performed in isolated intervals of boreholes the results presented in this study can be used as data sources for reservoir studies related to the production and control of methane

diagnostic study on the vertical circulation and the maintenance mechanisms of the cyclonic gyre in lake biwa lake biwa in japan has a stable cyclonic gyre during seasons of thermal stratification a vertical circulation consisting of downwelling in the central area and upwelling near the rim of the gyre is calculated by the diagnostic model the energetics in the model indicate that this vertical circulation corresponds to the decay process of the gyre tracking of drifters in summer supports the presence of a vertical circulation though its magnitude is about 50 less than that estimated by the diagnostic model this is explained from the ratio of kinetic energy and available potential energy of the gyre the realistic value of the vertical eddy viscosity is estimated to be 0 8 2 1 cm2 s 1 in summer monthly variations of the horizontal and vertical circulations are calculated by the diagnostic model using the monthly mean density fields the gyre and the vertical circulation are maximal in september the characteristic decay time scale of the gyre is estimated to be about 10 days the effect of topographic differential heating is considered to be one of the maintenance mechanisms of the gyre in early summer and the wind stress curl to be the important maintenance force for the gyre from late summer to late fall

permeability changes in coal analytical modeling abstract permeability changes can be very large during depletion of coalbed methane wells up to 100 times in the san juan basin analytic models of permeability increase during depletion are accessible easy to use and practical they are more transparent and less complicated than coupled numerical models however there are minor differences between the analytic models and these are reviewed here there are also discrepancies in attempting to match field data which is the final test of a model and these are discussed two different sets of san juan data have been modeled after suppressing the pressure dependent permeability with reasonably consistent reservoir parameters the matching parameters appear to be justifiable the small porosities do not seem to be ruled out by reservoir experts and the changes of elastic parameters including pore volume compressibility with depletion do not seem unreasonable the analytic models are used in reservoir simulators to model and predict injection of greenhouse gases in coal seams only when we can match the permeability increase of coalbed methane wells during depletion will we have the confidence to use the analytic models in reservoir simulators to match or predict sequestration of greenhouse gases such as co2

analysis of longwall goaf gas drainage trials with surface directional boreholes abstract surface directional boreholes sdb were recently trialled at two australian coal mines as a new application to longwall goaf gas drainage this method has become increasingly attractive for use at coal mines where surface access to drill large numbers of vertical goaf wells are limited or restricted to demonstrate the performance and effectiveness of the sdb and help improve future design and implementation results of the field trials at the two australia coal mines are analysed and presented in this paper the sdbs drilled with medium radius drilling techniques had different configuration parameters including number of branches diameter and relative locations above the mining seam and from the tailgate no borehole stability issues were encountered during the gas drainage operation the drainage methane flow rate varied in all sdbs however if applied properly they can gain a consistent high flow rate of methane at about 1000 l s it was observed that the drainage effectiveness and efficiency were significantly influenced by local geological settings borehole horizontal and vertical placement branching and water filling the key to having high and consistent gas flow in a sdb is to maintain a sufficient connection with the mining induced fracture zone in addition drilling quality control for such boreholes is also crucial to avoid any concave sections that might fill with groundwater and block the borehole the trial results demonstrate that sdbs have the potential to become a common method of longwall goaf gas drainage

comparison of generative capacities for bitumen and gas between carboniferous coals from donets basin ukraine and a cretaceous coal from sabinas piedras negras basin mexico during artificial maturation in confined pyrolysis system abstract the goal of this work is to study the ability of two immature carboniferous coals from donets basin ukraine to act as source for oil heating experiments in confined medium were performed to compare the thermal behavior of these coals 1l1 dim r r 0 55 h c at 0 79 and 2c10yd r r 0 65 h c at 0 80 relative to a mature cretaceous coal from sabinas basin olmos r r 0 92 h c at 0 77 macerals analysis carried out on starting materials showed that olmos is exhausted in liptinite contrary to 2c10yd 20 vol and 1l1dim 6 vol the vitrinite content is lower for 2c10yd 59 vol than for olmos 84 vol and 1l1dim 80 vol solid bitumen occurs often dispersed in the raw coals both petrographic and geochemical analyses on starting materials revealed that the selected carboniferous donets coals have better potentialities for bitumen generation than the cretaceous sabinas coal the presence of long chain n alkanes n c 8 in the pyrolysis gc chromatograms indicates that the two raw carboniferous coals from donets basin can yield non volatile hydrocarbons under further thermal maturation it is speculated that some vitrinite macerals present in hydrogen rich carboniferous coals from donets basin can act as source rocks for oil as a matter of fact results showed that the oil window occurs between 1 0 r r and 2 0 r r for both cretaceous sabinas and carboniferous donets coals during confined pyrolysis as expected from geochemical and petrographic analyses of starting samples the carboniferous donets coals yielded more bitumen and hydrocarbons than cretaceous sabinas coal during artificial maturation low proportions of solid bitumen r r and 1 5 r r during confined pyrolysis of coals two solid bitumen groups have been identified which correspond to distinct phases of neo formation the drop in the solid bitumen content at higher ranks indicates that it contributes to generation of gas during experimental simulation moreover their morphology and porosity change with the level of maturity the porosity of the vitrinite matrix increases as well as the pore size with increasing maturity a relationship has been observed between the porosity and the weight loss the higher pore content of carboniferous donets coals is correlated with a higher generation of gas compared to cretaceous sabinas coal

hydraulic conductivity changes and influencing factors in longwall overburden determined by slug tests in gob gas ventholes abstract this study presents the results of core log analyses from the exploration boreholes the analyses of face advance rates and the results of downhole monitoring studies performed in gob gas ventholes for calculation of changes in hydraulic properties in the longwall overburden at a mine site in southwestern sw pennsylvania section of northern appalachian basin in the first part of the study coal measure rocks in overburden strata were analyzed and the locations where possible fractures and bedding plane separations would occur were evaluated in the second part the hydraulic conductivities were computed by two different slug test analyses methods using the water level changes measured in gob gas ventholes as longwall face approached hydraulic conductivities were analyzed with respect to the changes in overburden depth the locations of the borehole and mine face advance rates these data were used to interpret the potential productivities of the gob gas ventholes as a result of fracturing and changes in hydraulic conductivities the general results showed that the probability of fracturing and bedding plane separations in the overburden increase between strong and weak rock interfaces also the probability of bedding plane separations increases as the interface is close to the extracted coal seam evaluation of slug tests showed that the hydraulic conductivity developments in the boreholes and their potential production performances are affected by the underground strata and the roof materials in situations where the roof material is stiff and thick the development of high permeability fractures around the borehole will be less results also indicated that borehole location with respect to face position affects the fracturing time and permeability evolution as well greater overburden depths generally cause earlier fracturing as longwall face approaches but eventually result in lower hydraulic conductivities and potentially less effective boreholes increasing mining rates also resulted in generally lower hydraulic conductivities in the overburden the results of this study were intended to improve the interpretation of gob gas venthole performance and to provide better siting of these boreholes

two phase rate transient analysis of a hydraulically fractured coal seam gas well a case study from the ordos basin china abstract apart from implications related to coal seam gas csg reservoir engineering such as stress and desorption dependent permeability 2 phase flow of gas and water adds further complications to rate transient analysis rta techniques in csg reservoirs this paper introduces the concept of area of influence ai to calculate water saturation in transient formation linear flow for 2 phase rta in hydraulically fractured csg wells the relevant equations are derived and discussed and the application of the ai is demonstrated using reservoir simulation the area of influence allows a superior estimation of water saturation compared to the dynamic drainage area dda in under saturated csg reservoirs and hence improves the estimation of fracture half length a practical workflow is also developed and presented to estimate reservoir and hydraulic fracture properties using 2 phase rta for hydraulically fractured vertical wells the presented workflow works in a reverse order by first analysing boundary dominated flow regime and then proceeds to other existing flow regimes developed at earlier production history of the well although analysis of each flow regime provides a standalone method to calculate some of reservoir properties the full development of all flow regimes allows crosschecking and brings more confidence into calculation in this workflow the reservoir properties derived from later flow regimes feeds earlier flow regimes to extract other reservoir variables such as fracture half length a hydraulically fractured csg well from the ordos basin china is analysed using ai and the proposed workflow to demonstrate the field application of this study

buoyancy driven current during cooling periods in ise bay japan 1 the cooling effect on buoyancy driven current is studied in the coastal embayment of ise bay japan by applying knowledge derived from studies of convection in a rotating fluid this convection process is highly sensitive to the presence of inhomogeneities in the preexisting stratification and to differential buoyancy loss on freshwater input the bay water is divided into two regions that differ in their response to the cooling from the surface one region represents a river plume which in effect shields the deeper regions from the cooler surface in the other region convective mixing is active although the mixed water forms and becomes extensive in this convection region the mixed water hardly develops in the river plume region the subsequent differential deepening of the mixed water causes gravitational circulation and yields a mixed water lens which has a reversed dome shape and rotates anticyclonically in a thermal wind balance in the mixed water lends nonvanishing stratification remains because of the rotational effect the location of the mixed water lens and associated anticyclonic circulation determines the basin wide circulation during cooling periods

reservoir simulation based modeling for characterizing longwall methane emissions and gob gas venthole production abstract longwall mining alters the fluid flow related reservoir properties of the rocks overlying and underlying an extracted panel due to fracturing and relaxation of the strata these mining related disturbances create new pressure depletion zones and new flow paths for gas migration and may cause unexpected or uncontrolled migration of gas into the underground workplace one common technique to control methane emissions in longwall mines is to drill vertical gob gas ventholes into each longwall panel to capture the methane within the overlying fractured strata before it enters the work environment thus it is important to optimize the well parameters e g the borehole diameter and the length and position of the slotted casing interval relative to the fractured gas bearing zones this paper presents the development and results of a comprehensive dynamic three dimensional reservoir model of a typical multi panel pittsburgh coalbed longwall mine the alteration of permeability fields in and above the panels as a result of the mining induced disturbances has been estimated from mechanical modeling of the overlying rock mass model calibration was performed through history matching the gas production from gob gas ventholes in the study area results presented in this paper include a simulation of gas flow patterns from the gas bearing zones in the overlying strata to the mine environment as well as the influence of completion practices on optimizing gas production from gob gas ventholes

effect of stair step and piecewise linear topography on internal wave propagation in a geophysical flow model 1 the paper describes the effect of a stair step representation of bottom topography common in most numerical models on the propagation of internal waves in a geophysical flow an analytical solution was used to predict the effect of stair step and piecewise linear representations of topography on the reflection and transmission of internal waves the estuary lake and coastal model elcom was used to simulate the transmission of a train of small amplitude internal gravity waves propagated along a variable depth rectangular channel containing a linearly stratified fluid the effect of the different obstacle approximations was examined in terms of the interference of the resulting wave number content and hence the associated reflection coefficients which could be directly compared to the analytical theory it was shown that for gaussian obstacles of varying lengths and heights the full bottom cells and partial bottom cells solutions from elcom agree with the stair step and piecewise linear solutions from the theory respectively it was shown that when gaussian obstacles with weak slopes are represented by stair steps an aliasing that is similar to that in discrete fourier transform can occur resulting in reflection coefficients that are much higher than the exact solution on the other hand piecewise linear approximations produce significantly attenuated aliasing an immersed boundary technique that enforces a no flux condition at the actual sloping bottom similar to that of the analytical solution is found not to produce better numerical results

compaction characteristics of the caving zone in a longwall goaf a review broken rock and coal residual coal plus material from the immediate roof and overlying strata fill in the goaf in an area termed the caving zone due to its high porosity and permeability the caving zone contains gas and water which may have originated from the mined coal seam the adjacent unmined coal seam or from any aquifer or surface river thus studying the compaction characteristics of the caving zone can help understand gas and mine water drainage and identify steps to prevent spontaneous combustion of residual coal the stability characteristics of the caving zone after mining are affect surface subsidence as well as water and gas build up and use the caving zone is a potential underground storage of greenhouse gases therefore the time space relationship of caving zone compaction characteristics in the goaf has become an area for research focus in recent years in this study the formation height determination and compaction characteristics of a caving zone are examined reduction in block size and rearrangement of the fill are the main factors affecting the compaction process as re crushing and rearrangement of the broken coal and rock mass affect the secant modulus and pore size of the caving zone causing the secant modulus to gradually increase and pore size to decrease this in turn affects the macroscopic stress strain curve and seepage characteristics of the caving zone the strength and fracturing mode of the caving blocks are the main factors affecting the re crushing and rearrangement of the caving blocks the applicability and reliability of present research results and research methods are analyzed and the focus areas for future studies are identified using a combination of research methods including theoretical analysis laboratory testing numerical simulation and field measurement the compaction characteristics of a caving zone in longwall goaf can be accurately calculated

current status and geological conditions for the applicability of cbm drilling technologies in china a review abstract coalbed methane cbm drilling technology is critical in achieving efficient cbm development the geological conditions for cbm development in china are complex including special terrain high rank coal areas deep coal seams multiple superposed coal seams and coal measure gas symbiosis areas steeply inclined coal seam areas and tectonic coal seam areas therefore it is critical to apply the optimum drilling technology in each different area this paper first reviews the current cbm drilling technologies and gas production behaviors in china it is found that although vertical wells and cluster well groups are common well types for cbm development in china u v and l shaped horizontal wells and multilateral horizontal wells have been favored for cbm development in recent years the paper then discusses the applicability of different well types to geological conditions and proposes a modification method for well design in various geologic conditions this method uses the coal structure ro in situ stress and ratio of critical desorption pressure to the reservoir pressure as the main inputs

investigation of longwall goaf gas flows and borehole drainage performance by cfd simulation abstract to reduce methane emissions into the workings of a longwall panel the mechanisms of gas emissions and migration within the longwall goaf must first be understood additionally high performance drainage boreholes must be designed many variables affect the goaf gas flow and borehole drainage efficiency namely the gas release characteristics of gas sources the heights of caved and fractured zones of the goaf the location of the drainage borehole and the position of the effective drainage section the portion of the perforated case and the uncased open hole this paper illustrates how these variables influence the goaf gas flow patterns and borehole performances through cfd simulations a permeability model and a gas release curve which reflect observations from experiments geomechanical modellings mine site monitoring and borehole drainage data were constructed for the mining disturbed strata and incorporated into the cfd model the cfd model was calibrated with the actual drainage data from the surface boreholes at a coal mine simulation results show that the gas drainage velocities around the perimeter of the panel goaf are higher than in the central goaf which is consistent with the overlying annular fracture zone model established from csiro previous research boreholes located within the annular area drew methane at a higher flow rate than those located in the central area leading to a significant reduction of methane emissions to the ventilation system goaf geometry with higher caved and fractured zones has lower pressure and methane concentration but higher gas flow velocity the location of the effective drainage section of the borehole has significant influence on drainage performance boreholes with the bottom end located in the lower region of the fractured zone 20 m above the roof can draw more methane than those located in the upper region of the fractured zone 70 m above the roof and those located in the caved zone 2 m above the roof

numerical experiments on stratified wind induced circulation in tokyo bay japan during summer in tokyo bay the upwelling of the anoxic water strongly affects eggs and larvae of fish and shellfish the northerly wind causes the upwelling along the eastern coast and near the bay head and downwelling along the western coast numerical experiments were carried with a three dimensional model to explain the wind induced circulation in tokyo bay when a uniform north easterly wind is imposed at the sea surface the circulation almost reaches steady state due to geostrophic adjustment after one inertial period from the beginning of the computation a forced internal kelvin wave propagating with the land on the right is found to have a great effect on the development of the steady state when the observed variable wind is given as the surface boundary condition the results of the numerical experiment agree qualitatively with data from both the sea surface temperature obtained by satellite images and field measurements at moored stations in the bay

biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of opalinus clay and posidonia shale in northern switzerland abstract samples from two argillaceous formations opalinus clay and posidonia shale of near identical maturity from northern switzerland were subjected to a geochemical characterisation of organic matter and to confined system pyrolysis experiments throughout the study area the characteristics of organic matter are similar indicating a spatially homogeneous sedimentary facies posidonia shale contains marine organic matter deposited in a reducing environment while a predominantly terrigenous source and a more oxidising environment of deposition was identified for opalinus clay in the western and central parts of the study area organic maturity is close to the onset of oil generation in the easternmost part a higher maturity has been reached due to a deeper burial below thick tertiary molasse deposits isothermal pyrolysis experiments were conducted at temperatures between 250 and 390 c over 24 h bitumen yields increase along similar pathways for both opalinus clay and posidonia shale but the maximum values are displaced by 10 20 c data pertaining to maturity were determined from gc ms analyses of saturated hydrocarbons and specific attention was given to c 29 sterane and c 32 hopane isomerisation ratios the evolution of these parameters with rising temperature is slightly different in the two formations which is attributed to the contrasting organic facies the pyrolysis data together with literature data from natural basins were used to calculate kinetic parameters for c 29 sterane and c 32 hopane assuming a single step isomerisation scheme according to the arrhenius law the resulting values based on pyrolysis data alone are very similar to those based on the combination of pyrolysis and natural data activation energies are similar in both formations while the frequency factors are up to one order of magnitude higher for posidonia shale when compared to opalinus clay for the benken site maximum temperature during cretaceous burial was calculated on the basis of the kinetic data using the tti approach the resulting temperatures of 75 80 c are 5 10 c below those derived in the literature from apatite fission track analysis vitrinite reflectance and basin modelling

modeling circulation in lakes spatial and temporal variations the influence of spatial and temporal variations in wind forcing on the circulation in lakes is investigated using field data and the three dimensional estuary and lake computer model elcom applied to lake kinneret lake kinneret field data from six thermistor chains and eight wind anemometers deployed during july 2001 are presented internal wave motions are well reproduced by the numerical model when forced with a spatially uniform wind taken from a station near the lake center however simulated seiche amplitudes are too large especially vertical mode 2 and lead observations by 3 10 h for a 24 h period wave at different locations around the lake consideration of the spatial variation of the wind field improves simulated wave amplitude and phase error at all stations is reduced to less than 1 5 h this improvement is attributable to a better representation of the horizontally averaged wind stress and can be reproduced with a spatially uniform wind that has the same horizontally averaged wind stress as the spatially varying wind field however a spatially varying wind field is essential for simulating mean surface circulation which is shown to be predominantly directly forced by the surface layer averaged wind stress moment

separation and fracturing in overlying strata disturbed by longwall mining in a mineral deposit seam abstract mining induced fractures influence the stability of overburden and may provide pathways for transferring heat and mass in underground environment a novel approach was proposed to quantify the separation and fracture evolution in the undermined overburden consisting of 1 theoretical distribution models of the void ratios of fractures vrfs based on analytical evaluation of key strata subsidence and 2 numerical modeling using the universal distinct element code and a sequence of image post processing procedures for a longwall mining panel both theoretical calculations and numerical simulations indicated that vrf first increased rapidly then gradually decreased and finally stabilized to a minimum from the surrounding edges of disturbed strata to their centers and gradually decreased from deep to shallow strata the fractures exhibited a fracture rich arch distribution type along a vertical section numerous fractures occurred around the arch feet near the perimeters of mined out area and or arch crown near the center of disturbed strata the distributions of vrfs show the heights shapes and damage intensities of fractured zones and can also be used as porosity parameters to determine the permeabilities of mining disturbed overburdens therefore the vrf models can be used as a quantitative parameter to assess the extent of possible risk zones e g for water inflow into the mine or escape of hazardous fluids to the surface

preservation of lateral pressure disequilibrium during the uplift of shale reservoirs a pressure gradient increase from normal pressure in oil zones to overpressure in dry gas zones indicates a lateral disequilibrium of pore pressure in many shale reservoirs in this work conditions for the preservation of the lateral pressure disequilibrium during uplift and erosion are investigated numerical simulations were conducted by coupling pressure volume temperature pvt and fluid dynamic calculations results show that temperature decrease and pore volume expansion during erosion tends to increase the pressure gradient in the gas or condensate zone and tends to decrease the pressure gradient in the black oil zone therefore the pvt effect tends to enhance lateral pressure disequilibrium during erosion low permeability is crucial for the preservation of the lateral pressure disequilibrium the persistence of disequilibrium over geological time tens of millions of years requires extremely small vertical permeability sub picodarcy range and horizontal permeability 10 nd or even lower the horizontal permeability is 10 100 times smaller than laboratory measurements on shale plugs indicating a discontinuity of laminations and fractures within a shale formation

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

breaking of internal kelvin waves shoaling on a slope in stratified flow breaking of internal waves over slopes induces resuspension of bottom sediments and transport of mass when internal waves shoal and break flow dynamics and mass transport diff

possible controls of hydrogeological and stress regimes on the producibility of coalbed methane in upper cretaceous tertiary strata of the alberta basin canada the coalbed methane potential and producibility of any coal bearing strata are strongly affected by the hydrogeological regime of formation waters and by coal permeability which in turn depends on the effective stress regime of the coals peat that accumulated in the alberta basin during the late cretaceous and early tertiary led to the formation of coal deposits that may contain significant coalbed methane resources the flow of formation waters plays an important role in the maintenance and producibility of this resource the present day flow is driven by gravity topography and erosional rebound and is controlled by rock permeability and the presence of gas saturated sandstones the estimated gas in place in the tertiary upper cretaceous coals decreases significantly with stratigraphic age ranging between less than 2 bcf mi2 in the lower coal zones and 12 bcf mi2 in the uppermost coals the gas content especially of the deeper coals is lower than would be expected for the corresponding coal rank and burial depth most likely because the underpressuring has caused the release of gas from the coals and accumulation in adjacent sands the shallow coals although of low rank may contain important amounts of late stage biogenic methane the salinity of formation water in shallow coal seams where the flow is driven by topography is low generally less than 1500 mg l although in places it reaches 3000 5000 mg l the salinity of formation water in the deeper underpressured strata in the west central part of the basin is significantly higher reaching 18 000 mg l this affects treatment and or disposal strategies with regard to the water produced concurrent to coalbed methane the producibility of this resource depends on coal permeability which decreases west southwestward with increasing burial depth from the order of several darcys in the shallow zones to millidarcys in the deep zones the minimum effective stress which affects coal permeability by closing fractures increases west southwestward from zero at the erosional edge of these strata to approximately 20 mpa near the rocky mountain deformation front fractures including those in coal seams will generally be vertical and will propagate on a southwest northeast axis along the direction of the maximum horizontal stress in a direction generally perpendicular to the rocky mountain deformation front considering the hydrogeological and stress regimes in conjunction with estimations of the gas content in coals the region with probably good coalbed methane potential and producibility are the ardley coal zone in the scollard formation and maybe to a lesser extent the coal zones of the stratigraphically deeper edmonton and belly river groups along their respective subcrop in central and southern alberta the deep edmonton and belly river strata in western and central alberta have most likely a reduced coalbed methane potential as a result of lower gas content and of low permeability these regional considerations need to be applied against local studies of coal thickness rank permeability and gas content to identify the best targets for coalbed methane exploration and production

determination of sealing depth of in seam boreholes for seam gas drainage based on drilling process of a drifter abstract in order to determine a reasonable sealing depth for seam gas drainage boreholes an innovative method is proposed to study the geological conditions in the coal seam by monitoring the response of the drift while drilling the boreholes based on the investigation of the in situ tests on the drift we found that the idle pressure of the hydraulic motor which features a rapid increase at the depth of approximately 14 to 16 m from the roadway wall appeared to be suitable for characterizing the coal mass condition then a numerical simulation was performed to investigate the reason for the response of the idle pressure it reveals that high stress and gas pressure are the main factors accounting for the rapid increase of the idle pressure accordingly the rapid increase of idle pressure becomes an indication for high stress and gas pressure next for determining the sealing depth the gas drainage process with different sealing depths was studied via numerical simulation and a simplified theoretical analysis was conducted to comprehend the flow of air from the roadway to the borehole the analysis reveals that the reasonable sealing depth should be several meters larger than the stress concentration area which is indicated in practice by the idle pressure then a sealing depth of 16 to 18 m is determined for the iii1011 mining face in the haizi coal mine this research provide a real time method to determine the sealing depth for in seam boreholes

organic geochemistry and petrology of posidonia shale lower toarcian western europe the evolution from immature oil prone to overmature dry gas producing kerogen abstract kerogen concentrates as well as whole rock samples of the lower jurassic posidonia shale representing a complete maturity series from immature to highly overmature were analyzed using organic petrography palynology bulk geochemical analysis ft ir and curie point pyrolysis gc ms cp py gc ms in order to investigate changes in kerogen composition with increasing maturation vitrinite reflectance vrr ranges from 0 5 to 3 hi values reflect the maturity trend very well with little scatter in contrast tmax oi and pi values show more scatter and greater differences between kerogen concentrates and whole rock samples ft ir spectra show a decrease in functional group bands with increasing maturation which has been quantified cp py gc ms analyses indicate an increase in hydrocarbons especially for short and medium length n alkanes with a strong predominance of short length alkanes at highest maturities about 3 vrr this effect however depends also on the applied pyrolysis temperature where higher temperatures 920 c as compared to 650 c favor generation of short length n alkanes especially for samples at high levels of maturation ratios of aromatic over aliphatic hydrocarbons or alkenes over alkanes show a non steady evolution depending also on the applied pyrolysis temperatures indicating that higher pyrolysis temperatures are needed for pyrolytic alkene formation with a maximum alkene formation for samples within early overmature maturities 1 4 vrr aromaticity first decreases but increases at high levels of maturation finally weathering of the highly overmature sample 3 vrr resulted in strong oxidation of organic matter with impact on rock eval ftir and curie point pyrolysis data

formation of fractured zones in overburden due to longwall mining the fractured zones caused by mining were studied in the overburden of the torezko snezhnyanskaya area ukraine through the change in natural gas emission from these zones during longwall coal excavation zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings the maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19 41 and 53 92 times the thickness of the coal seam respectively it was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof it is shown that the growth of the zone of interconnected fractures occurred during 17 39 days at an average rate of 0 94 1 97 m day 1 and it was accompanied by increasing methane emission from overburden observation shows that the formation of separate horizontal fractures began only 11 49 5 days after the height of the zone of interconnected fractures reached its maximum value formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone sandy shale layer interfaces in the direction of the ground surface

methane drainage from roof strata using an overlying drainage gallery abstract methane drainage is conducted in polish coal mines to reduce mine methane emissions and to keep methane concentrations in mines within safety limits this article describes a method of methane drainage conducted during mining in polish coal mines the method is based on driving a drainage gallery into a coal seam situated above or below the worked seam prior to its extraction by a longwall method this article shows the influence of a typical ventilation system on the drainage efficiency at longwall panel b 11 in seam 348 with an overlying drainage gallery at this longwall measurements of the methane emissions and efficiency of the methane capture were conducted these measurements consisted of gauging the methane concentration air velocity absolute air pressure and the amount of methane captured by the drainage system the experimental data were used to estimate the variations in the total methane release methane release into the ventilation system and most importantly the efficiency of methane drainage the results obtained were analysed statistically and the influence of different factors on the total methane release and the amount of methane captured into the drainage system were determined

high temperature gc evidence for the early formation of c 40 n alkanes in coals abstract high temperature gc analyses were performed on a coal sourced waxy oil from the toka 1 well in the taranaki basin and on three bitumens extracted ultrasonically with boiling toluene from coals from the tara 1 well in the great south basin new zealand the coals represent an evolutionary trend from immature to post oil expulsion in all samples the c 40 alkanes were characterised by dominant straight chain members up to about c 65 which decreased significantly in abundance in bitumen with increasing maturity they are present at an early stage of maturity prior to the main phase of n alkane generation and may be liberated from cutan cutin sources within kerogen by thermal decarboxylation of esters or have an earlier origin in the bitumen inherited from diagenesis an odd over even predominance in the c 40 n alkanes was most marked in the c 51 c 57 range and decreased with increasing maturity suggesting that minor amounts of c 40 n alkanes with a cpi approaching 1 are also generated during catagenesis however the observed c 40 n alkane distributions may be affected to a degree by decreasing efficiency of solvent extraction with increasing n alkane molecular weight and by further long chain n alkanes generated during catagenesis being partially inaccessible to solvent extraction

maturity related variation in the bulk transformation kinetics of a suite of compositionally related new zealand coals abstract bulk hi transformation kinetics were determined by open system pyrolysis for a suite of compositionally related late cretaceous to paleocene coals from tara 1 well great south basin new zealand these coals span a maturity range encompassing the onset of significant oil generation and expulsion kinetic parameters were also obtained for one of the immature samples following artificial maturation by hydrous pyrolysis kinetic models were based on three modes of optimisation of kinetic parameters discrete e act distribution with single variable a value discrete e act distribution with fixed a 10 14 s 1 and gaussian e act distribution with single variable a value hi transformation rate vs temperature envelopes for the naturally matured coals exhibited an abrupt jump to higher temperature near rank s r 12 5 apparently coinciding with the onset of significant paraffinic oil expulsion for all optimisation modes the artificially matured sample does not predict this shift in transformation envelopes which suggests that certain of the reactions that occur under natural maturation do not occur during laboratory pyrolysis the structural rearrangements occurring up to the expulsion threshold some or all of which are responsible for the increase in hi up to rank s r 11 are not manifested in changes in hi transformation rate envelopes however the presence of adsorbed bitumen may mask the influence of structural rearrangements during optimisation of the kinetic data which could explain the behaviour of the transformation rate envelopes in the rank s r 11 0 12 5 range obtained from the discrete e act free a optimisation this behaviour involves a regression in transformation rate envelopes to lower temperatures as the amount of retained bitumen increases prior to expulsion the almost perfect nesting of transformation rate envelopes subsequent to oil expulsion suggests either that any further structural rearrangement does not produce a significant change in the a and e act distributions of hydrocarbon generating bonds or that the expulsion drastically reduces the degree of further rearrangements involving hydrocarbon generating moieties within the kerogen it follows that kinetic parameters for immature coals should not be considered ideal for modelling the whole phase of hydrocarbon generation nevertheless the kinetic parameters for the least mature tara coal rank s r 8 5 reproduced the normalised hi trend for the entire suite of coals with reasonable accuracy over the maturity range considered rank s r 8 5 15 0 only slightly underestimating conversion at the lower maturity levels and overestimating it slightly at the higher levels

prediction of the height of destressed zone above the mined panel roof in longwall coal mining abstract longwall mining is one of the most widely used underground mining methods most suitable in relatively flat lying thick and uniform coalbeds due to extraction of the coal seam the panel roof strata above the mined zone will be destressed and then the roof loads will be redistributed and transferred to the front abutment and neighboring solid sections with higher load bearing capacity where the adjacent access tunnels and the corresponding barrier pillars are located the height of destressed zone hdz in this paper is taken as equivalent to the combined height of the caving and fracturing zones above the mined panel roof induced due to longwall mining the height of destressed zone plays a vital role in accurate determination of the amount of loads being transferred towards front abutment and panel sides the paper describes the mechanism of development of the height of this zone finally five new simple yet conclusive mathematical approaches to estimate the height of destressed zone are presented the results of the methods proposed are compared with each other and with the comparable methods the methods proposed are further compared and verified with in situ measurements reported in the literatures the comparative results confirm the agreement that exist among the methods and those with the in situ measurements as well finally the methods have shown that in short term the height of destressed zone ranges from 6 5 to 24 times the extraction coal seam height while in long term the height of destressed zone ranges from 11 5 to 46 5 times the extraction coal seam height therefore beyond this height the overburden pressure will be transferred towards the front abutment the adjacent access tunnels the intervening barrier pillars as well as the panel rib sides

coal seam porosity and fracture heterogeneity of macrolithotypes in the hancheng block eastern margin ordos basin china abstract heterogeneity in cleats and pore size distribution within coal macrolithotypes bright semi bright semi dull and dull coals determined from the overall relative luster and percentage of bright components impact coalbed methane cbm extraction however few studies have investigated the characteristics of macrolithotypes across multiple length scales here the macrolithotype description was performed for the no 3 5 and 11 coal seams in the hancheng block of ordos basin the cleats were characterized by optical microscopy and x ray computed tomography ct while pores and their connectivity were determined from mercury intrusion porosimetry n 2 and co 2 adsorption and low field nuclear magnetic resonance nmr of water saturated cores evaluated both cleats and pores the ch 4 adsorption capacity of coal samples scraped from the surface of the macrolithotype layers was also determined dull lithotypes semi dull and dull were dominant followed by bright lithotypes bright and semi bright in these seams the bright lithotype coal has a higher microfracture density averaging 339 microcleats per 9 cm 2 m mm better connectivity and a larger fractal dimension averaging 1 7 from optical microscopy the dull lithotype has a lower average microfracture density 272 microcleats per 9 cm 2 and a smaller fractal dimension 1 6 this higher connectivity observation was consistent with x ray ct observations and low field nmr of the water saturated cores and the transition upon water removal from the fractures and larger pores also the ease of mercury injection from cores also supported higher connectivity in the bright lithotypes both the semi bright and semi dull lithotypes have equivalent pore proportions micro to macropores and good apparent connectivity at the nm m scale despite mineral occlusions based on the ch 4 adsorption capacities of the macrolithotypes the bright coal has the greatest gas adsorption capacity due to the largest smaller micropores

residual circulation due to internal waves shoaling on a slope we describe the residual circulation induced in a two layer system when internal waves with a wave length equal to or longer than the slope length propagate over a sloping bottom and either reflect or break for the case of no wave breaking scaling is used to derive boussinesq type equations the solution of which leads to an expression for the residual circulation adjacent to the sloping bottom this residual circulation is maintained by a weak slope on the density interface for breaking waves laboratory experiments and numerical modeling were used to ascertain the details of the residual circulation arising from the formation of gravitational intrusions results from these three investigative tools were used to determine as a function of bottom slope and incident wave amplitude the internal wave reflection coefficient and the strength of the residual circulation pattern with and without wave breaking the ocean and most lakes are thermally stratified for at least part of the year in stratified fluids the density anomaly associated with the thermal stratification supports internal waves with a range of vertical modal structures antenucci et al 2000 antenucci and imberger 2001 antenucci and imberger 2003 the gravest or first vertical mode induces a large current over the lake or ocean bottom and when the bottom slopes the waves shoal causing them to break and lose energy to dissipation the associated currents and turbulence can often lead to sediment resuspension and mixing of the water column gloor et al 1994 pierson and weyhenmeyer 1994 steinman et al 1997 the gravitational motions in turn induced by the mixing may combine with secondary internal wave motions to drive a residual circulation that may transport resuspended and dissolved material to the central area of a lake hakanson 1982 ostrovsky et al 1996 inall 2009 also demonstrated mass transport due to intrusion caused by internal wave breaking in the fjord loch etive by using a fluorescent dye tracer such intrusions have been observed but their dynamics do not seem to have received any attention in this paper the processes leading to residual circulation are described when a continuous train of internal waves with an individual wavelength equal to or longer than the slope length supported by a two layer stratification impinges perpendicularly onto a sloping bottom two cases were investigated when the waves break and when they are reflected perfectly without breaking internal waves and their associated mass transport in lakes fjords and coastal oceans are reviewed in ostrovsky and stepanyants 1989 and huthnance 1989 whereas solitary internal waves are reviewed by brown and christie 1998 lamb 2002 and grue et al 2000 regarding mass transport lamb 2002 investigated shoaling of largeamplitude internal waves and demonstrated that trapped

kinetics of oil generation from brackish lacustrine source rocks in the southern bohai sea east china abstract oil generation c14 hydrocarbons of three type ii kerogen samples isolated from brackish lacustrine mudstones from palaeogene strata ed3 es1 es3 in the southern bohai sea was simulated by closed system gold tube experiments in addition a series of complementary analyses rock eval pyrolysis total organic carbon vitrinite reflectance trace element x ray diffraction and flash pyrolysis gas chromatography mass spectrometry were also performed to identify the bulk geochemistry palaeo environment and chemical composition of the kerogen the aim of this study was to achieve a better understanding of the kinetics of oil generation from lacustrine source rocks in the southern bohai sea the results show that the three samples are type ii source rocks deposited in similar palaeo environments hot and arid climates anoxic conditions and brackish water in shallow to semi deep lakes with consequent similarity in the chemical compositions of their kerogens the organic matter inputs are predominantly composed of lacustrine microalgae with a relatively small contribution from land plants the activation energies of oil generation from these samples show a range of 44 52 kcal mol with a frequency factor varying from 1 116 1014 to 1 274 1014 s 1 due to the similar palaeo environments and chemical composition samples in this study exhibit strong consistencies in kinetic parameters transformation ratio tr evolution curves of oil generation from the three samples calculated under a linear heating rate 3 k ma exhibit a slight difference which varies within 4 c at a given tr due to the great similarities of the three kinetic models an average kinetic model for the type ii brackish lacustrine source rocks in the southern bohai sea was established this model integrates the characteristics of the three kinetic models and is still dominated by activation energy of 52 kcal mol the geological temperature of the oil generation phase for the average model in the southern bohai sea is from 92 to 137 c

localization of mining induced horizontal fractures along rock layer interfaces in overburden field measurements and prediction the locations of mining induced horizontal fractures along rock interfaces in the overburden of donetsk coal basin were identified using an original experimental device the device traps methane from horizontal fracture zone 100 fold coal seam thickness over an active longwall mining excavation presence or absence of horizontal fractures along rock layer interfaces is correlated with physical characteristics of the overburden such as thickness uniaxial compressive strength of overburden rock layers location of rock layer interfaces and thickness of extracted coal seams as a result a combined criterion based on these physical characteristics is proposed to predict the presence of overburden horizontal fracturing in coal mine operations

coalbed methane resource potential and current prospects in pennsylvania abstract coalbed methane gas content analyses from exploratory coal cores and existing data indicate that gas content generally increases with increasing depth and rank the coal beds studied are from the main bituminous field of pennsylvania which currently contains 24 coalbed methane pools and the northern and southern anthracite coal fields they range from the middle pennsylvanian allegheny group to the late pennsylvanian early permian dunkard group previous us bureau of mines studies revealed gas contents from 0 4 to 13 8 cm 3 g at depths of 99 to 432 m for the bituminous coal beds of the allegheny group more recent core data from the allegheny group yielded gas contents from 2 2 to 8 9 cm 3 g at depths from 167 to 387 m in the anthracite region of eastern pennsylvania the little data that are available show that gas content is anomalously high or low gas yields from test holes in eastern pennsylvania are low with or without artificial stimulation mainly due to the lack of a good cleat system overall estimates of coalbed methane resources indicate there may be 1 7 tm 3 61 tcf of gas in place contained in the northern appalachian coal basin the amount of technically recoverable coalbed methane resources is projected by the us geological survey national oil and gas resource assessment team us geological survey national oil and gas resource assessment team 1996 1995 national assessment of united states oil and gas resources results methodology and supporting data us geological survey digital data series dds 30 cd rom denver co 80 pp and lyons lyons p c 1997 central northern appalachian coalbed methane flow grows oil and gas journal 95 27 76 79 at 0 3 tm 3 11 48 tcf this includes portions of pennsylvania ohio west virginia and a small part of maryland consequently a mapping investigation was conducted to evaluate the regional geology of the bituminous coal bearing intervals in southwestern pennsylvania and its influence on coalbed methane potential phase i of this study involved the entire pennsylvanian coal bearing interval of southwestern pennsylvania phase ii focused on a stratigraphic delineation and evaluation of allegheny group coal beds and associated sandstones several prospective coal beds and associated facies relationships with channel fill sandstones were determined possible non coal scenarios for coalbed methane include erosional contacts between coal beds and overlying channel fill sandstones and areas of stacked channel fill sandstones repetitive sequences of coal accumulation are stacked commonly with shale interburden and are also potential coalbed methane targets additional pennsylvania geological survey drilling coalbed methane sampling occurred in armstrong beaver cambria greene lawrence somerset and washington counties raw coalbed methane desorption data tables graphical displays of gas contents versus depth thickness and time and average composition and heating values from coal beds of the allegheny group to the dunkard group are available at the pennsylvania geological survey further information on cross sections isopleth maps isopach maps raw drillhole data and ownership issues can also be obtained from the same source

horizontal structure and excitation of primary motions in a strongly stratified lake a modal analysis in the horizontal plane was extended to a layer stratified basin with irregular bathymetry and the theory was applied to lake biwa to investigate the horizontal structure and excitation of the basin scale internal waves and gyres the horizontal structure of the basin scale internal waves consisted of cyclonic and anticyclonic elliptic cells each of which appeared to follow the dispersion relationship of kelvin and poincare waves in elliptic basins the internal waves were preferentially excited depending on the arrangement of the cells and the wind direction but the spatial distribution of wind stress curl over the lake primarily determined the horizontal structure of the ensuing gyres decoupled evolutionary equations for the individual modes provided a good approximation for excitation of the internal waves and early stages of excitation of the gyres before nonlinear effects and damping become significant the modal decomposition of hydrodynamic simulation results also showed that the primary action of the wind was to excite the internal waves however these internal waves were damped within a few days and the dynamics during calm periods were dominated by the gyres illustrating the importance of internal waves on mixing and gyres on long term horizontal transport

quantitative modelling of hydrocarbon expulsion and quality grading of tight oil lacustrine source rocks case study of qingshankou 1 member central depression southern songliao basin china the quality of source rocks plays an important role in the distribution of tight and conventional oil and gas resources despite voluminous studies on source rock hydrocarbon generation expulsion and overpressure a quality grading system based on hydrocarbon expulsion capacity is yet to be explored such a grading system is expected to be instrumental for tight oil and gas exploration and sweet spot prediction this study tackles the problem by examining late cretaceous lacustrine source rocks of the qingshankou 1 member in the southern songliao basin china by evaluating generated and residual hydrocarbon amounts of the source rock the extent of hydrocarbon expulsion is modelled through a mass balance method the overpressure is estimated using petromod software through correlation between the hydrocarbon expulsion and source rock evaluation parameters total organic carbon toc kerogen type vitrinite reflectance ro and overpressure three classes of high quality effective and ineffective source rocks are established high quality class contains toc 2 type i kerogen ro 1 0 overpressure 7mpa sharp increase of hydrocarbon expulsion along with increasing toc and overpressure and high expulsion value at ro 1 source rocks with toc and ro 0 8 type ii2 iii kerogen overpressure 3mpa and low hydrocarbon expulsion volume are considered ineffective rocks with parameters between the two are considered effective the high quality class shows a strong empirical control on the distribution of tight oil in the songliao basin this is followed by the effective source rock class the ineffective class has no measurable contribution to the tight oil reserves because the hydrocarbon expulsion efficiency of source rocks is controlled by many factors the lower limits of the evaluation parameters in different basins may vary however the classification method of tight source rocks proposed in this paper should be widely applicable

relative effects of wind stress curl topography and stratification on large scale circulation in lake michigan 1 this paper uses the results from two multiseason numerical model simulations of lake michigan hydrodynamics to examine the relative effects of wind stress curl topography and stratification on large scale circulation the multiseason simulations provide a period long enough to encompass the full range of atmospheric and thermal conditions that can occur in the lake the purpose of this paper is to diagnose the relative importance of various mechanisms responsible for the large scale circulation patterns by analyzing the vorticity balance in the lake on a monthly timescale five different model scenarios are used to isolate the predominant mechanisms 1 baroclinic lake spatially variable wind stress 2 barotropic lake spatially variable wind stress 3 baroclinic lake spatially uniform wind stress 4 barotropic lake spatially uniform wind stress and 5 barotropic lake linearized equations spatially uniform wind stress by comparing the results of these five model scenarios it is shown that the cyclonic wind stress curl in the winter and the effect of baroclinicity in the summer are primarily responsible for the predominantly cyclonic flow in the lake topographic effects are also important but are not as significant as wind stress curl and baroclinic effects nonlinear effects are much smaller

an analysis of reservoir conditions and responses in longwall panel overburden during mining and its effect on gob gas well performance abstract niosh conducted a cooperative research study to provide direct measurements of changing reservoir conditions in longwall panel overburden the field measurements documented changes in permeabilities methane concentrations fluid pressures and the effects of adjacent gob gas ventholes ggvs on niosh boreholes drilled in the study panel three different stratigraphic horizons were monitored by the niosh boreholes results indicated that the gob gas venthole fracture network formed 24 to 46 m 80 to 150 ft ahead of the mining face overburden permeabilities within the same overburden test zones were 1 md prior to undermining increasing to hundreds or thousands of md during undermining permeabilities measured seven months after undermining showed additional increases the relationship between changing reservoir conditions longwall face position and surface movement is discussed recommendations are made to optimize ggv performance by evaluating changes in subsidence produced by mining resulting in rock stresses that substantially influence induced fracture permeability mechanisms to account for the observed changes in reservoir conditions are reported

experimental research on the permeability of high rank coal under a varying stress and its influencing factors abstract in order to investigate the permeability behavior of high rank coal during early depletion of cbm and its influencing factors we collected 14 coal samples from ordos basin in northwest china and determined their air permeability under a varying effective stress of 2 5 20 mpa in laboratory we used effective confining pressure to simulate effective stress it turns out that high rank coal permeability is susceptible to effective stress permeability of coal samples declines exponentially with the rise of effective stress on the whole when effective confining pressure variation ranges from 2 5 mpa to 10 mpa permeability varies dramatically when effective confining pressure rises to above 10 mpa the curve of permeability decline gets gentle and the stress sensitivity becomes relatively weak coal permeability is also affected by coal moisture maceral fracturing and metamorphism degree permeability rises with the increase of vitrinite content and fracturing degree and decreases with the increase of moisture content permeability of wet and fractured coal samples is more sensitive to effective stress than dry intact ones and the irreversible permeability loss rate of fractured coal cores is significant over 80 comparison of tests results of medium and low rank coal samples and high rank ones shows that the stress sensitivity coefficient decreases with the increase of the maximum reflectance of vitrinite if experiencing the same load relief process the irreversible permeability loss rate of low rank coal is less than that of medium and high rank coals

summer circulation and temperature structure of lake kinneret a three dimensional lake model driven by wind stress and heat flux fields derived from an atmospheric model is applied to lake kinneret israel the summer wind field over the lake has a strong diurnal and large spatial variation due to complex terrain surrounding the lake the sharp temperature contrast between the arid land and the lake and due to the penetration of the mediterranean sea breeze msb into the lake area the daily mean wind curl field which is predominantly determined by the penetration of the msb is responsible for the generation of three lake gyres one of them dominates most of the lake and rotates counterclockwise it is flanked to the north and to the south by two smaller ones that rotate clockwise during the summer the diurnal variation of the wind over the lake is repeated daily due to consistent forcing conditions during that season numerical tests show that the rectified flow induced by the diurnal winds plays a minor role in the lake circulation the thermocline oscillation which was believed to be the free propagation of internal kelvin waves mainly responds to the surface elevation set up by the time dependent winds and it appears that no systematic counterclockwise propagating waves with large thermocline displacements exist in the lake the intense msb over the lake in the late afternoon pushes the heated surface water toward the east forcing the deep cooler water to be advected westward and creating strong mixing over the shallow western shore this results in higher temperature off the eastern shore and lower temperature off the western shore however a strong mean flow is constantly eliminating the temperature difference by counterclockwise transfer of the western cooler water eastward the results are in good agreement with available observations