Molecular Simulation of the Pore Structure and Adsorption Properties of Coal under Compression Stress

The deformation of the macromolecular structure of coal under compression stress may affect the pore structure and adsorption properties. In this study, the Grand Canonical Monte Carlo and molecular dynamics methods were used to investigate the effects of compression stress on the pore structure and adsorption properties of coal, and the coupling relationships between stress, strain, pore structure, and adsorption properties were explored. A macromolecular model of coal was constructed, and uniaxial compression simulation was conducted. The increase of compression stress reduces the pore volume, specific surface area, and connectivity of coal and concentrates the pore size distribution in pores with smaller sizes. The increase of stress leads to a different degree of reduction in the adsorption performance of coal on CH4 and CO2, and the stress sensitivity of CH4 is slightly stronger than that of CO2. The results of adsorption configurations in the pores under different strains indicate that the reduction of adsorption properties is controlled by the pore volume and pore connectivity. The adsorption performance of CH4 and CO2 in coal at different strains has a good linear relationship with the volume and specific surface area of the pores; the smaller the volume and specific surface area of the pores, the weaker the adsorption performance of coal. This study clarifies the control of the strain response under compression stress on the pore structure and adsorption properties of coal and provides guidance for the study of adsorption, desorption, and diffusion of CBM.