Study on the multi-field coupling evolution law of coal spontaneous combustion–methane coupled hazards in the goaf of ultra-long working faces

This study systematically investigates the multi-field coupling evolution of coal spontaneous combustion–methane coupled hazard in the goaf of ultra-long working faces through an integrated approach combining theoretical analysis, numerical simulation, and field measurements. For the first time, a comprehensive numerical model was developed that integrates coal oxidation heat release, oxygen consumption, methane desorption, and leakage-driven gas flow with dynamic working face advancement, three-dimensional zonal porosity–permeability structures, and multi-physics coupling, enabling dynamic interaction and feedback among all physical fields. Considering working face burial depth and roof–floor lithology, the model quantitatively characterizes their regulatory effects on methane migration and multi-field evolution. Parameter sensitivity verification was performed to evaluate the influence of key model parameters, providing quantitative guidance for optimizing critical engineering parameters such as advancing speeds and working face air volume. Using COMSOL simulations, the spatiotemporal evolution of the hazard under different advancing speeds and working face air volume conditions was analyzed. Results indicate that at 4 m/d, multi-field coupling achieves an optimal balance, with oxygen transport, methane release, and convective heat transfer dynamically coordinated. When working face air volume is 2604 m3/min, methane peak concentration is significantly reduced, and oxygen and temperature distributions are synchronously optimized, achieving a globally optimal multi-field coupling state. This study reveals the regulatory mechanisms of key controlling parameters, offering robust and quantifiable engineering guidance for coal spontaneous combustion–methane coupled hazard risk prediction, operational parameter optimization, and precise hazard prevention in ultra-long working faces.