Methane Adsorption Characteristics and Adsorption Model Applicability of Tectonically Deformed Coals in the Huaibei Coalfield

Abstract

Based on methane isothermal adsorption experiments, the supercritical methane adsorption characteristics of middle-rank tectonically deformed coals (TDCs) screened from the Huaibei coalfield were analyzed. The applicability of different adsorption models to different kinds of TDCs was discussed using the standard deviation method, and the mechanism of methane adsorption in TDCs was explored. The following results were obtained. First, the experimental maximum adsorption capacity of TDCs increases gradually with enhanced tectonic deformation, and the experimental maximum adsorption capacity of ductile TDCs is significantly higher than those of primary coal and brittle TDCs. The adsorption potential of TDCs gradually decreases with increasing adsorption space, and the adsorption potential of ductile TDCs is generally higher than those of primary coal and brittle TDCs. Second, for the applicability of adsorption models to TDCs, the highly applicable models of primary, cataclastic, and scaly coals are the Toth, Langmuir–Freundlich, and Dubinin–Astakhov models; the highly applicable models of schistose coals are the Langmuir, Toth, Langmuir–Freundlich, three-parameter Brunauer–Emmett–Teller, Dubinin–Radushkevich, and Dubinin–Astakhov models; the highly applicable models of wrinkle coals are the Toth, Langmuir–Freundlich, Dubinin–Radushkevich, and Dubinin–Astakhov models; and the highly applicable models of mylonitic coals are the Langmuir, Toth, Langmuir–Freundlich, expand-Langmuir, three-parameter Brunauer–Emmett–Teller, and Dubinin–Astakhov models. Third, the three-parameter Brunauer–Emmett–Teller model is suitable to study the adsorption state of TDCs. As the deformation degree increases, the adsorption state of TDCs transforms from monolayer unsaturated adsorption to multilayer adsorption. TDCs have larger adsorption potential and adsorption space with the enhancement of tectonic deformation, which increases the number of adsorption layers on the coal surface.

Prediction of gas pressure in thin coal seams in the Qinglong Coal Mine in Guizhou Province, China

“…The greater the burial depth of the coal seam, the larger the in-situ stress and the greater the distance of gas escape, which is also conducive to gas sealing. The greater the thickness of the coal seam, the more conducive it is to gas preservation (Lu et al 2018b;Kang et al 2020;Li et al 2020b). However, some studies have shown that the depth effect is no longer obvious when the depth of coal seam exceeds the critical point of 800-900 m (Li et al 2020a).…”

A method to determine nuclear magnetic resonanceT2cutoff value of tight sandstone reservoir based on multifractal analysis

“…Therefore, it is of great theoretical and practical significance to carry out micro‐nano pore evaluation of tight reservoirs. In recent decades, the main experiments that can be used to quantitatively determine pore structure are capillary pressure curve method, binary image computer analysis (PIA), displacement method, and the pore three‐dimensional space shape computer reconstruction method . As classical high‐precision experiments for pore structure analysis, mercury intrusion analysis has been widely used.…”

“…In recent decades, the main experiments that can be used to quantitatively determine pore structure are capillary pressure curve method, binary image computer analysis (PIA), displacement method, and the pore three-dimensional space shape computer reconstruction method. [1][2][3][4][5][6][7][8][9][10][11] As classical high-precision experiments for pore structure analysis, mercury intrusion analysis has been widely used. However, it has many defects, such as core damage, environmental pollution and high cost, so it is difficult to carry out on a large scale.…”

Variation of Surface Free Energy in the Process of Methane Adsorption in the Nanopores of Tectonically Deformed Coals: A Case Study of Middle-Rank Tectonically Deformed Coals in the Huaibei Coalfield

“…Coal is a stress-sensitive porous medium. − Tectonically deformed coal (TDC) with various structures will form under different stress–strain environments. − TDCs occur in almost all major coal-producing countries in the world. − TDCs develop widely in Chinese coal-bearing basins as China has experienced multistage tectonic movements . Various TDCs have different pore structures and methane adsorption characteristics, which affect the recovery of coalbed methane (CBM) and the prevention of coal and gas outburst. , For example, the brittle deformation sequence of TDCs may be the target layer for CBM recovery, and the occurrence of mylonitic coal may lead to the coal and gas outburst in the underground coalmine .…”