Evolution of full-scale pore structure characteristics of long-flame coal and influencing factors

Abstract

China has vast long-flame coal reserves containing abundant coalbed methane (CBM) resources. Understanding the evolution of full-scale pore structure characteristics of this coal and their influencing factors are vital for the CBM development. However, researches on these topics are limited. Herein, 17 long-flame core coals were collected from southern Junggar Basin to accurately characterize the specific surface area (SSA), total pore volume (V_t), and full-scale pore size distribution (FPSD) using mercury intrusion porosimetry (MIP) along with N₂/CO₂ adsorption experiments. Results demonstrate that the FPSD generally exhibits a bimodal characteristic, with abundance of micropores and macropores but scarcity of mesopores, which hinders the efficient transport of CBM. The full-scale pore structure characteristics are closely linked to coal's thermal evolution. As R_{o, max} rises, V_t, mesopore volumes (V_me), and macropore volumes (V_ma) initially decrease to a minimum at a R_{o, max} of ∼0.55 % and then increase. Conversely, micropore volumes (V_mi) exhibit an inverted U-type correlation with R_{o, max}, peaking almost at the same R_{o, max}. Ash yield negatively affects pore volumes and SSAs, particularly for macropores. Inertinite-rich long-flame coals, particularly those with higher semifusinite and fusinite contents, develop more micropores and mesopores, whereas increasing vitrinite content is negatively correlated with their development.