Pore Size Distribution, Compressibility, and Strain Kinetics upon Exposure to Methane of Four Bituminous Coal Specimens from Kaiping Basin, China

Abstract Gas migration through coal matrix and cleats not only includes gas sorption and desorption but also leads to coal strain development. In this article, a series of experiments were carried out to investigate the strain development in four unconfined bituminous coal samples exposed to methane at various pressures. The dominant factors for sorption/desorption-induced deformation were associated with pore characteristics. Pore size distribution for all samples was determined by mercury intrusion porosimetry, nitrogen adsorption, and carbon dioxide adsorption techniques. The results show that there were differences in the pore surface area, pore shape, and pore size distribution of coal samples. Coal swelled when methane was injected and shrank when gas was released. The coal radial strains were always larger than axial strains at adsorption and desorption phases because the samples were drilled along coal cleat. The residual strain remaining after the adsorption–desorption cycle may be positive or negative. The strains of coal samples were different even with the same injected gas pressure. The total pore volume is not a dominant factor for sorption/desorption strain and rate. The pore size distribution and pore type also should be comprehensively considered.