Thermal-hydraulic-mechanical coupling effects on CBM extraction from heat-injected coal seams in basis of numerical simulation and experimental study

This paper presents a coupled thermal-hydraulic-mechanical model, which was established and solved to investigate the effect of coalbed heat injection on CBM production. The simulation results indicated that gas production rate increases linearly and then gradually decreases, while the water production rate decreases gradually, consistent with the 'large water and small gas' rule during drainage and 'small water and large gas' rule during stable production. Additionally, the study explored the impact of temperature, ground stress, moisture content, and permeability on CBM production. The model's accuracy was further verified by measuring the permeability of coal samples under different conditions, revealing that permeability decreases with increasing temperature and surrounding pressure. Furthermore, the study found that the higher the moisture content, the greater the increase in permeability after hot steam treatment, which can significantly enhance the permeability of water-bearing coalbed. [Received: July 4, 2022; Accepted: May 21, 2023]