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Measurements of sorption isotherms and transport properties of carbon dioxide (CO 2 ) in coal cores are important for designing enhanced coalbed-methane/CO 2 -sequestration field projects. Sorption isotherms measured in the laboratory can provide the upper limit on the amount of CO 2 that might be sorbed in these projects.Because sequestration sites will most likely be in unmineable coals, many of the coals will be deep and under considerable lithostatic and hydrostatic pressures. These lithostatic pressures may reduce the sorption capacities and/or transport rates significantly. Consequently, we have studied apparent sorption and diffusion in a coal core under confining pressure. A core from the important bituminous coal Pittsburgh #8 was kept under a constant, 3D effective stress; the sample was scanned by X-ray computer tomography (CT) before, then while, it sorbed CO 2 . Increases in sample density because of sorption were calculated from the CT images. Moreover, density distributions for small volume elements inside the core were calculated and analyzed. Qualitatively, the CT showed that gas sorption advanced at different rates in different regions of the core, and that diffusion and sorption progressed slowly. The amounts of CO 2 sorbed were plotted vs. position (at fixed times) and vs. time (for various locations in the sample). The resulting sorption isotherms were compared to isotherms obtained from powdered coal from the same Pittsburgh #8 extended sample.The results showed that for this single coal at specified times, the apparent sorption isotherms were dependent on position of the volume element in the core and the distance from the CO 2 source. Also, the calculated isotherms showed that less CO 2 was sorbed than by a powdered (and unconfined) sample of the coal. Changes in density distributions during the experiment were also observed. After desorption, the density distribution of calculated volume elements differed from the initial distribution, suggesting hysteresis and a possible rearrangement of coal structure because of CO 2 sorption.

Measurements of sorption isotherms and transport properties of CO 2 in coal cores are important for designing enhanced coalbed methane/CO 2 sequestration field projects. Sorption isotherms measured in the lab can provide the upper limit on the amount of CO 2 that might be sorbed in these projects.Because sequestration sites will most likely be in unmineable coals, many of the coals will be deep and under considerable lithostatic and hydrostatic pressures. These lithostatic pressures may significantly reduce the sorption capacities and/or transport rates. Consequently, we have studied apparent sorption and diffusion in a coal core under confining pressure. A core from the important bituminous coal Pittsburgh #8 was kept under a constant, three-dimensional external stress; the sample was scanned by X-ray computer tomography (CT) before, then while it sorbed, CO 2 . Increases in sample density due to sorption were calculated from the CT images. Moreover, density distributions for small volume elements inside the core were calculated and analyzed. Qualitatively, the computerized tomography showed that gas sorption advanced at different rates in different regions of the core, and that diffusion and sorption progressed slowly. The amounts of CO 2 sorbed were plotted vs. position (at fixed times) and vs. time (for various locations in the sample). The resulting sorption isotherms were compared to isotherms obtained from powdered coal from the same Pittsburgh #8 extended sample.The results showed that for this single coal at specified times, the apparent sorption isotherms were dependent on position of the volume element in the core and the distance from the CO 2 source. Also, the calculated isotherms showed that less CO 2 was sorbed than by a powdered (and unconfined) sample of the coal. Changes in density distributions during the experiment were also observed. After desorption, the density distribution of calculated volume elements differed from the initial distribution, suggesting hysteresis and a possible rearrangement of coal structure due to CO 2 sorption.

Measurements of sorption isotherms and transport properties of CO 2 in coal cores are important for designing enhanced coalbed methane/CO 2 sequestration field projects. Sorption isotherms measured in the lab can provide the upper limit on the amount of CO 2 that might be sorbed in these projects.Because sequestration sites will most likely be in unmineable coals, many of the coals will be deep and under considerable lithostatic and hydrostatic pressures. These lithostatic pressures may significantly reduce the sorption capacities and/or transport rates. Consequently, we have studied apparent sorption and diffusion in a coal core under confining pressure. A core from the important bituminous coal Pittsburgh #8 was kept under a constant, three-dimensional external stress; the sample was scanned by X-ray computer tomography (CT) before, then while it sorbed, CO 2 . Increases in sample density due to sorption were calculated from the CT images. Moreover, density distributions for small volume elements inside the core were calculated and analyzed. Qualitatively, the computerized tomography showed that gas sorption advanced at different rates in different regions of the core, and that diffusion and sorption progressed slowly. The amounts of CO 2 sorbed were plotted vs. position (at fixed times) and vs. time (for various locations in the sample). The resulting sorption isotherms were compared to isotherms obtained from powdered coal from the same Pittsburgh #8 extended sample.The results showed that for this single coal at specified times, the apparent sorption isotherms were dependent on position of the volume element in the core and the distance from the CO 2 source. Also, the calculated isotherms showed that less CO 2 was sorbed than by a powdered (and unconfined) sample of the coal. Changes in density distributions during the experiment were also observed. After desorption, the density distribution of calculated volume elements differed from the initial distribution, suggesting hysteresis and a possible rearrangement of coal structure due to CO 2 sorption.

Permeability is a key property for injectivity of carbon dioxide in enhanced coalbed methane/carbon sequestration projects. In addition to cleat spacing and connectivity, permeability is affected by the in situ stresses, the geomechanical properties (Young's modulus, Poisson's ratio) of the coal, the amounts and compositions of the fluids (e.g., CH4, CO2) sorbed by the coal matrix, and the dependence of the matrix swelling on the amounts and compositions of the sorbed fluids. In this paper, we have tested bituminous coal coal cores from the Upper Freeport formation, Marshall County, West Virginia in the Appalachian Basin. This coal has generated considerable interest, because of a current industry/DOE/NETL sponsored project to inject carbon dioxide into this seam for the purpose of developing and testing carbon sequestration. The cores were tested in a composite core holder allowing hydrostatic confinement and X- ray computerized tomography (CT). Permeabilities for helium, methane, and carbon dioxide were measured using a conventional method of simultaneous pressure-drop and flow-rate measurements. Compressibility and carbon dioxide sorption of the sample were calculated from CT measurements of density variations in the core. Permeability was reduced considerably by increases of effective stresses in the coal, and by sorption of carbon dioxide in the coal. Due to the heterogeneous nature of the coal, its sorption and elastic properties varied greatly among different locations within the core. As a corollary, samples from the same well and coal seam may show large variations in methane content, carbon dioxide storage capacity, permeability, and mechanical properties. Introduction The Upper Freeport coal sits in the Allegheny formation, consisting of inter-bedded sandstones, siltstones, shales, limestone and coalbeds, as illustrated by Figure 1. Coalbed methane is produced from Lower and Upper Freeport, Kittaning and Clarion coals. The total gas in place for Allegheny coalbeds was estimated at 50.5 tcf, out of an estimated 61 tcf for all coals of the Northern Appalachian coal basin, which includes parts of southwestern Pennsylvania, northwestern West Virginia, and western Ohio (West Virginia Geological and Economic Survey, 1996). The National Energy Technology Laboratory (NETL) and industrial partners (Consol) are performing a field pilot in Marshal Co., WV, in the Upper Freeport formation to develop CO2 sequestration /enhanced coalbed methane technologies (Cairns, 2003). The production of gas from coal seams, and the injectivity and storage of CO2 into coal, are highly dependent on two parameters: permeability, and storage. Coal seams are treated as dual porosity reservoirs with the majority of the gas stored in the primary porosity system (coal matrix), while the permeability of the coal seam is governed by the natural fractures and cleats in coal that constitute the secondary porosity system (Mavor, 2006). The natural fracture (or cleat) porosity and permeability are dependent on location, pressure in the reservoir, and geomechanical properties (Young's modulus, Poisson's ratio) of the coal, the amounts and compositions of the fluids (e.g., CH4, H2O, CO2) sorbed by the coal matrix, and the dependence of the matrix swelling on the amounts and compositions of the sorbed fluids.