Evolution patterns of temperature field in key strata during underground coal gasification process in deep coal mining

To investigate the significant influence of high-temperature field evolution on the structural behavior of key strata during deep underground coal gasification (UCG), a theoretical heat-conduction model for the roof strata above a UCG cavity was established by combining theoretical derivation with numerical simulation. A convection-conduction coupling reduction factor was introduced to account for the coupled effects of convective heat transfer and radiative heat transfer at the cavity wall, as well as heat conduction within the surrounding rock mass. The evolution of the temperature field and the thermal stress response of the key strata were subsequently analyzed. The results indicate that, owing to the low thermal conductivity and thermal resistance of the rock mass, the theoretically predicted temperature rise in the main key stratum located 15.43 m above the top of the gasification cavity is less than 1.00 K, while the numerical simulation yields a temperature rise of approximately 0.80 K. The high-temperature-affected zone is concentrated in the rock strata adjacent to the gasification channel, and the temperature decreases rapidly within a vertical distance of 20.00 m from the gasification cavity. The vertical heat diffusion rate is substantially lower than the horizontal advance rate of the gasification working face. The temperature rise in the key strata is insufficient to reach the thresholds for mineralogical alteration or significant thermal-stress-induced damage. Therefore, the conventional key-strata criterion developed under ambient-temperature conditions remains applicable to deep UCG operations. These findings provide a theoretical basis for roof control and surface subsidence prediction in UCG engineering.