Influence of Extreme Temperature on the Pore and Fracture Development of High-Rank Coal

Pore and fracture structures in coals and their distribution features play an important role in the enrichment and osmosis migration of coalbed methane (CBM). The modification and antireflection of pore and fracture in coal reservoir through ultrahigh and ultralow temperature stress, such as liquid nitrogen frozen-induced cracking and thermal antireflection of coal reservoir, have attracted wide research attention. This study conducted a nuclear magnetic resonance (NMR) experiment of pore and fracture features of coal samples under two extreme temperatures (100°C, −196°C) using the Meso MR23-060H-I low-field NMR and imaging instrument. The influencing law of ultrahigh and ultralow temperature stress on pore and fracture development in high-rank coal was discussed. Results demonstrated that temperature can influence pore and fracture development of high-rank coal samples. The pore volume, porosity, and permeability of the coal sample increase after low-temperature (−196°C) treatment. The proportion of microspores decreases, the proportion of small pores increases, the proportion of mesopores remains the same, and the proportion of macrospores increases to some extent. The pore volume of coal sample decreases after high-temperature (100°C) treatment. Porosity and permeability decrease. The proportion of mesopores declines, the proportion of mesopores remains basically same, and the proportion of macrospores decreases.

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