Study on coal full pore aperture distribution characteristics considering coal matrix compression effect

The single pore structure characterization method can only characterize the pore structure within a certain pore aperture range, the combined Mercury intrusion porosimetry and low-temperature liquid nitrogen adsorption method can characterize the full pore aperture distribution characteristics of coal. However, the coal matrix compression effect will bring errors to the pore aperture distribution measurement results, and the current research has not considered the impact of coal matrix compression effect on the pore aperture distribution measurement results. In order to study the full pore aperture distribution characteristics of coal with different metamorphic degrees, Mercury intrusion porosimetry and low-temperature liquid nitrogen adsorption experiments are carried out on four kinds of coal samples. When the mercury pressure is 0.124-20 MPa, the coal matrix is compressed and the pore structure is deformed. With the increase of mercury pressure, the compression effect of coal matrix becomes obvious and the deformation degree of pore structure increases gradually. When the mercury pressure is 20-206 MPa, the compression effect of coal matrix is significant, and the pore structure is destroyed. Considering the impact of coal matrix compression effect, a joint pores analysis principle is proposed. The boundary point of the joint pores is set at 62.35 nm (the corresponding pore aperture is 62.35 nm when the mercury pressure is 20 MPa). When the pore diameter is less than 62.35 nm, the pore volume and specific surface area are analyzed by low-temperature liquid nitrogen adsorption. When the pore aperture is greater than 62.35 nm, the cumulative mercury intrusion volume measured by mercury intrusion method is corrected in combination with the compressibility coefficient of coal matrix so as to analyze the pore volume and specific surface area. The results show that micropore and transition pore contribute the most to the surface area, mesopore and macropore contribute the most to the pore volume. The greater the degree of coal metamorphism, the greater the contribution of micropores and transition pores to the specific surface area, and the greater the contribution of mesopores and macropores to the pore volume.