LI W B, LI F, SHI L Y, et al. Differences in pore development characteristics and methane adsorption/desorption performance among various macrolithotypes in low-rank coals[J]. Journal of Henan Polytechnic University (Natural Science), 2024, 43(2): 57-67.

doi:10.16186/j.cnki.1673-9787.2021110078

Received:2022/11/19

Revised:2022/12/14

Published:2024/03/25

Differences in pore development characteristics and methane adsorption/desorption performance among various macrolithotypes in low-rank coals

LI Weibo1,  LI Fei1,  SHI Liyan1,  ZHOU Shaowei1, MA Dongmin2, WANG Chuantao3, CHEN Yue2

1. Shaanxi Geological Science and Technology Center, Xi’an 710054， Shaanxi， China； 2.College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, Shaanxi， China； 3. School of Chemistry and Chemical Engineering, Yan’an University, Yan’an 716000, Shaanxi， China

Abstract: Objectives The heterogeneity of coal reservoirs is significant,and the differences in material composition and pore structure among different macrolithotypes lead to marked differences in the adsorption and desorption performance of coalbed methane and the characteristics of gas-water migration. Methods This study focuses on the low-rank coal from the Yan’an Formation in the Binchang mining area of the Huanglong Coalfield. The components of vitrinite and durain were collected and separated. Comprehensive testing methods, including microscopic component determination, elemental analysis, mercury intrusion, low-temperature liquid nitrogen adsorption, and adsorption-desorption experiments were employed to investigate the differences in porosity development characteristics between low-rank vitrinite and durain, and their impact on methane adsorption/desorption performance. Results The findings indicate that: (1) The mass fractions of vitrinite, volatile matter, and the elements H, O, N and S in vitrinite are higher than those in durain, while the mass fractions of inertinite, chitinite, minerals, ash, fixed carbon, and element C are lower in vitrinite than in durain; (2) The porosity of the coal samples ranged from 2.92% to 10.29%, indicating that the overall pore development is relatively significant. The porosity of durain is slightly higher than that of vitrinite, with thicker pore throats, more developed macropores, and better connectivity. The BET specific surface area and BJH total pore volume of vitrinite are slightly larger than those of durain, with micropores more developed, predominantly in semi-closed and ink bottle shapes; (3) Vitrinite exhibits more developed micropores, a larger specific surface area, and stronger adsorption capacity. Conclusions The methane adsorption/desorption process in coal generally exhibits desorption hysteresis, with durian showing relatively better pore connectivity. The degree of desorption hysteresis in  durian is lower than that in vitrinite, resulting in higher theoretical desorption efficiency compared to vitrinite. The results of this study provide valuable insights into the physical properties of low-rank coalbed methane reservoirs in the Binchang mining area.

Key words: Huanglong Coalfield;  low-rank coal;  coal lithotype;  pore structure;  adsorption/desorption