Characteristics of Nanometer Pore Structure in Coal Reservoir

In order to study the characteristics of nanometer pore structure of coal, the heterogeneous structures of nano pores of different rank coals were investigated by using SEM, liquid nitrogen adsorption and small angle X ray. It is found that the mesopore shows the multimodal division, mainly concentrated in the 2-10 aperture and nm. The adsorption capacity of coal low-temperature nitrogen adsorption experiments of coal samples is 3.676 cm³/g, and coal sample surface area is 1.416 m²/g. By analyzing the most probable aperture, the range of experimental pressure can be found out, and the most probable pore size will be increased with the adsorbent pressure. Gas diffusion model in most nanoscale pore structure model prefers coals mainly concentrated on transitional diffusion. In more developed microporous coal samples (anthracite), the diffusion type is closer to the Knudsen diffusion. In much less developed coal samples, the main diffusion type is closer to Fick diffusion. The Knudsen number is negatively related to temperature, and Knudsen number tends to be stable when the temperature is higher than 250 K, which is positively correlated with the pressure. The diffusion will be easier with the increase of pressure.