A sensitivity study of hydrogen mixing with cushion gases for effective storage in porous media

This study investigates the impact of methane, carbon dioxide, nitrogen, and their mixtures on hydrogen storage and recovery in depleted oil and gas reservoirs, with a focus on gas mixing and diffusion behaviour. Using the MATLAB Reservoir Simulation Toolbox (MRST), this research evaluates the effects of geological parameters such as permeability and porosity on hydrogen recovery and purity. Our results indicate a significant decline in hydrogen purity after 250 days of withdrawal, with methane providing the highest recovery rates but also exhibiting the greatest mixing with hydrogen. Permeability and porosity distributions were found to influence recovery and mixing dynamics in distinct and contrasting ways. While hydrogen purity and recovery were more sensitive to permeability, the computed mixing zone showed a marked sensitivity to the formation's porosity. By applying various control strategies for well injection rates and bottom hole pressures during injection and withdrawal phases, the optimal conditions for maximizing hydrogen recovery while minimizing gas mixing were identified. This study provides valuable insights into the optimization of hydrogen storage in subsurface geological formations, contributing to the advancement of sustainable energy solutions.