Research on Nanopore Characteristics and Gas Diffusion in Coal Seam

The nanopore structure of five coal samples was analyzed using low-temperature nitrogen adsorption method. Then, the gas desorption experiments were carried out. Combining the experimental results and pore structure characteristics, the rules of gas diffusion in coal seam were further investigated. The results show that the Knudsen number decreases with the gas pressure and increases with temperature. The type of gas diffusion varies between different rank coals. Gas diffusion model in most coals mainly concentrates on transitional diffusion. However, for the highly developed microporous coal samples (anthracite), the diffusion type is closer to the Knudsen diffusion. Whereas, the main diffusion type is Fick diffusion for macroporous coals, such as lignite. With the increase of pressure, the gas diffusion model will undergo Knudsen diffusion, transition diffusion and Fick diffusion state.