An Integrated Experimental and Simulation Study for the Feasibility of Underground H Production from Natural Gas Reservoirs.

The rising global energy demand and environmental concerns necessitate sustainable alternatives to fossil fuels. Hydrogen (H) is a promising clean energy carrier with high energy density and minimal environmental impact, yet current production methods, such as steam methane reforming (SMR) and coal gasification, remain carbon intensive. In situ H production (IHP) in oil and gas reservoirs has emerged as a novel approach, leveraging existing infrastructure to generate H while sequestering CO. This method has been extensively explored in heavy oil reservoirs through the so-called in situ combustion gasification (ISCG). However, its application in natural gas reservoirs is limited. This study examines the feasibility of in situ H generation from depleted natural gas reservoirs through process simulation and experimental validation using a custom autoclave reactor. Process simulation predicted a high H yield due to the dominant role of the water-gas shift (WGS) reaction at the reservoir temperature (200 °C). The experimental results confirmed H production but to a lesser extent due to the low steam-to-carbon (S/C) ratio. This is aggravated by methanation reactions, which consume H, especially under low-temperature and high-pressure conditions. The presence of rock samples inhibited H generation, yet a better H yield is observed due to mechanochemical H generation. Compared with the simulation results, the experimental yield at 200 °C is significantly lower, highlighting the need for catalysts and higher temperatures (500-800 °C) to improve efficiency. High temperatures can be achieved through exploring geothermal or other heating methods for process optimization. However, this process can be very energy efficient if such high H yield as predicted by the process simulation can be achieved practically.