Evaluation of the density and thickness of adsorbed methane in differently sized pores contributed by various components in a shale gas reservoir: A case study of the Longmaxi Shale in Southeast Chongqing, China

To investigate the densities and thicknesses of adsorbed methane in a shale gas reservoir, the Lower Silurian Longmaxi Shale in Southeast Chongqing was selected as a case study to establish models of the pore size distributions contributed by various components (PSDCVC), the amounts of methane adsorbed by various components (AMAVC) and the density and thickness of methane adsorbed by various components (DTMAVC). Based on the results of total organic carbon, carbon content in organic matter (OM), X-ray diffraction, methane isothermal adsorption and low-temperature nitrogen adsorption measurements, the pore size distributions and the amount of methane adsorbed by OM, clay and other minerals were calculated using the PSDCVC and AMAVC models. The average densities and thicknesses of adsorbed methane in pores with widths of < 2 nm, 2-5 nm, 5-10 nm, 10-20 nm, 20-50 nm, 50-100 nm and 100-200 nm associated with OM, clay and other minerals under various conditions (i.e., temperatures of 30-70 degrees C and pressures of 1-10 MPa) were calculated using the DTMAVC model. The calculated data for the three analyzed samples using the PSDCVC and AMAVC models were compared with experimental results to determine the uncertainties of the two models. The density and thickness values of adsorbed methane in pores with various widths associated with OM, clay and other minerals decrease with increasing temperature and pore width and increase with increasing pressure. At the same temperature, pressure and pore width, the density and thickness values of adsorbed methane differ significantly among pores contributed by OM, clay and other minerals, exhibiting a decreasing trend from OM to clay to other minerals.