Effects of tectonism on the pore characteristics and methane diffusion coefficient of coal

The diffusion coefficient of methane in coal is a key parameter that influences the methane extraction effect. Former studies on the methane diffusion coefficient mainly paid attention to the intact coal. The diffusion coefficient of tectonic coal is different from that of intact coal, which may be caused by the effect of tectonism on the pore characteristics. In this study, the pore characteristics of the intact coal and tectonic coal were tested using mercury intrusion porosimetry (MIP) and the physisorption method, while the counterdiffusion experiments were adopted to measure the methane diffusion coefficients of both coal samples. The results indicate that the methane diffusion coefficient of the tectonic coal is higher than that of the intact coal, and the diffusion coefficients decrease with the increasing methane pressure. The tectonism increases the volumes of mesopores and macropores and the porosity of coal, which is the main reason for the higher methane diffusion coefficient of the tectonic coal. The pore structure of coal becomes more winding or complicated by tectonism, thus showing a higher tortuosity of the tectonic coal. The tectonism makes it easier to extract methane, and coal mining in the tectonic region should receive more attention.