Numerical simulation of solid-fluid-thermal coupling in the heating stage of in-situ injection of supercritical water for hydrogen production from coal

Hydrogen production via in-situ injection of supercritical water into underground coal seams is a new coal conversion technology. This study proposes a solid-fluid-heat coupling mathematical model for the heating stage of the injection of supercritical water into the coal seam and studies the evolution law of the temperature distribution, pore pressure, solid deformation, and other aspects of the coal seam, the roof strata, and the floor strata using numerical simulation. The results showed that after the injection of supercritical water, the temperature and flow rate near the injection well increased rapidly, gradually decreased, and expanded outwards. Subsequently, the temperature rose to about 1050°C and the flow rate decreased slightly near the injection well. The flow rate near the production well showed a negative exponential growth pattern six months prior; however, the temperature and flow rate remained constant after six months. The temperature around 700 m from the injection well changed little over one year. A large compression deformation zone may form above the injection well and the maximum uplift displacement of the deformation zone within one year can reach 8 mm. The extreme value of vertical stress was located in the surrounding rock layer closest to the coal seam and its maximum value can be 17 MPa.