Applicability of mercury intrusion method and nitrogen adsorption method in characterizing pore structure of high-rank coal

The coal reservoirs in the southern Qinnan Basin are typical high-rank coal reservoirs in China, and they are vital for coalbed methane extraction. The characterization of coal pore structure in this area plays a crucial role in coalbed methane extraction, CO₂ sequestration, and the assessment of gas outburst hazards. Samples from the Qinshui Basin were selected, and the pore size distribution and pore morphology of the coal samples were tested and calculated using the mercury intrusion method and nitrogen adsorption method, respectively. The results indicate that compared to mercury intrusion method, the change rate of pore volume measured by nitrogen adsorption method increases slowly with the increase of pore size, and the dV/dlgD-D value corresponding to pore size is low, which better conforms to the characteristics of micro-pores in high-rank coal. By comparing the pore morphology tested by mercury intrusion method and nitrogen adsorption method, and combining the measured pore size values, and combining the measured pore size value with the pore characteristics of high-rank coal in typical mining areas, it was found that the pore shape measured by the nitrogen adsorption method can better characterize the characteristics of micro-pores in high-rank coal. Therefore, the low-temperature nitrogen adsorption method is suitable for characterizing the pore structure of high-rank coal with pore sizes ranging from 5 to 50 nm. These research findings provide theoretical basis and practical experience for finely characterizing pore structure in high-rank coal reservoirs in the southern part of the Qinshui Basin.