Effect of carbon dioxide adsorption on permeability and mechanical strength of coal powders

Abstract

Enhanced coalbed methane recovery (ECBM) is a method to produce methane gas while storing carbon dioxide (CO2) in coal seams. We examined the effect of CO2 adsorption on the mechanical properties and permeability of coal powder samples using a modified triaxial strength apparatus. A sub-bituminous coal sample obtained from east Kalimantan, Indonesia and an anthracite coal sample from Kyung-Dong, Korea were used in this study. Permeability of the coal powder sample during CO2 adsorption was measured before conducting triaxial strength testing. As the CO2 adsorption pressure increased from 1 MPa to 2 MPa, the permeability decreased by ~75%. Upon the completion of CO2 adsorption, a series of triaxial strength tests were performed on a dry coal powder sample under a consolidated-drained (CD) condition. Our results revealed that the shear strength of the coal powder was reduced due to CO2 adsorption, where the internal friction angle decreased from 25° to 22° and the cohesion intercept decreased by ~50% under the CO2 adsorption pressure of 1 MPa. Our results suggest that CO2 adsorption heavily affects the mechanical and hydraulic properties of coals.