Thermo-hydro-chemical coupled numerical modeling of hydrogen-thermal co-development in hydraulically fractured peridotite

Hydrogen generation through serpentinization reactions in peridotite formations under high temperature conditions represents a promising avenue for subsurface hydrogen production. However, the thermal energy in the formation environment have not been sufficiently considered. To integrate hydrogen production with thermal energy development, this study develops a thermo-hydro-chemical coupled numerical model, which is used to investigate hydrogen-thermal co-development in hydraulically fractured peridotite. Given that the hydrogen-thermal co-development process involves fluid flow, heat transfer and serpentinization reactions, the governing equations are formulated based on Darcy flow and energy conservation equations, with serpentinization kinetics incorporated through the reactive source terms. To evaluate hydrogen production and thermal energy recovery under varying formation and injection fluid temperatures, the coupled system is solved numerically. The results show that under high geothermal temperature conditions, continuous high-temperature injection combined with moderate natural fracture development can sustain stable high production during long-term operation. When the contribution of thermal energy is neglected, the total system energy output decreases significantly, highlighting the necessity of hydrogen-thermal co-development. This study further identifies the optimal injection temperature range under high geothermal conditions. Under normal geothermal conditions, hydrogen production is limited by reaction temperature, and high-level production cannot be maintained solely through thermal stimulation. Sensitivity analysis reveals that reaction kinetics are the dominant factor controlling system hydrogen productivity, and enhancing them can increase hydrogen production by nearly an order of magnitude. This work establishes a quantitative framework for artificial hydrogen generation and provides theoretical guidance for engineering design and the operational parameter optimization of hydrogen-thermal co-development systems.