Impact mechanisms of injection temperature and pressure on multi-field evolution and gas production characteristics in in-situ coal-to-hydrogen

The quantitative regulation mechanisms of injection temperature and pressure on the spatiotemporal multi-field evolution in in-situ coal-to-hydrogen (ISCH) conversion remain poorly understood. We developed a coupled thermal–hydraulic-chemical (THC) model and performed full-factorial simulations to elucidate the competitive interactions between these parameters. Results demonstrate a distinct functional differentiation: injection pressure serves as the decisive lever for the spatial expansion rate, where increasing pressure from 8 MPa to 10 MPa surged the average expansion rate by 200.0%; conversely, injection temperature predominantly governs the induction period, with an increase from 673.15 K to 873.15 K reducing the initiation time by 59.2%. While the system exhibited convergence toward a quasi-steady configuration regardless of initial conditions, high-energy injection strategies effectively suppressed the localized accumulation of carbon byproducts by intensifying fluid transport. Crucially, this study identifies “heat–mass spatial decoupling”—characterized by the spatiotemporal mismatch between the high-temperature core and the reactant field—as the fundamental bottleneck restricting initial hydrogen production efficiency, rather than thermal energy depletion. Accordingly, this study suggests that enhancing spatiotemporal overlap through dynamic pressure modulation and gradient steam-to-oxygen regulation is essential for maximizing ISCH yield.