Construction of multi-field coupling model based on desorption hysteresis effect and response mechanism of CBM extraction

Numerical simulation is a core method for coalbed methane (CBM) extraction research, but existing models generally neglect the ubiquitous desorption hysteresis effect and rely on the conventional reversible Langmuir equation, which significantly impairs the accuracy of simulation results. In this study, a thermal–hydraulic-mechanical (THM) dual-porosity model incorporating desorption hysteresis is developed. The desorption hysteresis index (HI) is introduced to quantify hysteresis magnitude, and governing equations are formulated for gas–water two-phase flow, temperature variation, coal matrix deformation and pore evolution, establishing the quantitative linkage between microscopic desorption hysteresis and macroscopic CBM extraction responses. Eight coal samples of varying metamorphic degrees across multiple coal ranks are tested using CH 4 adsorption/desorption and low-temperature liquid nitrogen adsorption experiments, and key hysteresis parameters are derived through data fitting. The results demonstrate that: The governing effect of pore size distribution and pore morphology on desorption hysteresis intensity outweighs that of total pore volume. Comparative simulations demonstrate that the deviation in CBM production prediction shows a strong linear correlation with HI. Desorption hysteresis suppresses the coal seam cooling induced by CH 4 desorption and enhances the CH 4 adsorption capacity of the coal matrix. Neglecting this effect leads to significant overestimation of fracture dilation and subsequent permeability evolution.