Carbon Dioxide Transport and Sorption Behavior in Confined Coal Cores for Enhanced Coalbed Methane and CO2 Sequestration.

Abstract

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.

The Stress and Gas Adsorptive Effect on Coal Densities in Laboratory CBM/ECBM Processes

“…Therefore, coal core can not relax into its original status even the pressure load is removed at the final stage. Similar observation was noticed by Jikich et al (16) . They used x-ray CT to study the CO 2 adsorption in coal core.…”

“…In literature there are limited studies related to the flow, storage mechanisms, and structure and property variation of coal. Several authors have demonstrated that x-ray CT can be a useful tool in studying the distributions of coal density (10) , minerals and cleat/fracture distribution (11,12,13) , and coal adsorption and swelling by CO 2 (2,14,15,16) . With the help of other image tools, x-ray CT can be used to investigate the gas storage and transport properties of coal (17,18,19) .…”

Visual Representation of Carbon Dioxide Adsorption in a Low-Volatile Bituminous Coal Molecular Model

“…This would then impart enhanced molecular sieving in this region. To compare the loading level of CO 2 and CH 4 within the molecular representation, the same number of molecules (25) was added to the structure to visualize where in the structure the molecules would reside (Figures 5 and 7). Again, the methane molecules were false-colored yellow to aid in visualization.…”

On the Physical Insight into the Barotropic Effect in the Interfacial Behavior for the H2O + CO2 Mixture

“…In the last few years, disposal of carbon dioxide (CO 2 ) in permeable, porous subsurface rock formations (often known as geological sequestration) has been identified as a viable option for reducing greenhouse gas emissions into the atmosphere. Potential subsurface systems considered for geological sequestration include depleted oil and gas reservoirs, 1,2 coalbed methane and shale gas reservoirs, 3,4 and deep aquifers. 5,6 Though each of these disposal systems has its advantages, deep aquifers (mostly filled with nonpotable or brackish waters) have the greatest potential for large CO 2 sequestration programs, primarily because of their relative abundance in most sedimentary basins and their large effective capacities.…”

“…In the last few years, disposal of carbon dioxide (CO 2 ) in permeable, porous subsurface rock formations (often known as geological sequestration) has been identified as a viable option for reducing greenhouse gas emissions into the atmosphere. Potential subsurface systems considered for geological sequestration include depleted oil and gas reservoirs, , coalbed methane and shale gas reservoirs, , and deep aquifers. , Though each of these disposal systems has its advantages, deep aquifers (mostly filled with nonpotable or brackish waters) have the greatest potential for large CO 2 sequestration programs, primarily because of their relative abundance in most sedimentary basins and their large effective capacities. , Successful selection of the potential of CO 2 deep aquifer sequestration sites, however, requires an understanding of all the physical and chemical trapping mechanisms by which CO 2 may be retained, where the stratigraphic/structural and residual fluid mechanisms have the largest and most immediate impact on trapping or retaining CO 2 in aquifers . A common attribute between the stratigraphic/structural and residual fluid mechanisms is the dependence on capillary pressure characteristics of the aquifer seal and formation, in which the capillary pressure characteristics are the strong functions of both the interfacial tension (IFT) properties of the water plus carbon dioxide (H 2 O + CO 2 ) system and the behavior of CO 2 -rich phase density.…”