Corrected Pore Size Distribution and Structure Parameters in Anthracite Coal from Mercury Intrusion and Nitrogen Adsorption

The coal reservoir characteristics are mainly affected by pore structures and, therefore, influence safe exploration and development of coal and coalbed methane (CBM) resources. The pore size distribution and structure parameters of coals measured by traditional mercury intrusion porosimetry (MIP) experiments are much more accurate for big pores, while they are erroneous for small pores due to high mercury pressure. Therefore, this paper proposes a corrected method for pore size distribution and structure parameters using comprehensive measurements of MIP and low-temperature liquid nitrogen adsorption (LTLNA) for six high-rank anthracite coal samples. The pore size distributions obtained by two measurements in the range of 1–100 nm exhibit similar trends, and the developed pores in sizes of about 5, 50, and 100 nm coincide roughly. A ratio is introduced in this paper to match the developments of small pores measured by MIP and LTLNA. A corrected percentage is introduced as well to adjust the measurement deviation caused by MIP. After correction, the porosity for six samples varies from 4.17 to 13.97%, with an average of 6.29%. The average volumetric percentages for micropores, mesopores, and macropores are 17.24%, 20.05%, and 62.72%, respectively. A higher corrected percentage brings a lower deviation, resulting in more accurate measurement results by MIP. Therefore, it is much more accurate for MIP measurements under conditions of a larger average radius, low vitrinite reflectance, and a high volumetric percentage of macropores. Meanwhile, if the porosity is about 10%, the deviation measured by MIP is the biggest.