Integrated Technology for Large-Scale Underground Hydrogen Storage in Porous Media

Global efforts toward low-carbon energy have increased the demand for large-scale hydrogen storage. Such storage is needed to balance the fluctuation of renewable energy supply and demand. Among different options, Underground Hydrogen Storage (UHS) in porous media provides large capacity, good safety, and economic potential. However, compared with Underground Gas Storage (UGS) , UHS still faces key challenges. The small molecular size, low viscosity, and high diffusivity of hydrogen lead to complex flow behavior, unstable cushion gas performance, and strong water invasion. This study builds an integrated framework that connects basic mechanisms with engineering practice for large-scale UHS. First, the feasibility of converting UGS to hydrogen storage is analyzed, showing advantages in construction, geological stability, and operation. Second, compositional and molecular simulations are developed to study how depth affects hydrogen storage performance under different pressure and temperature conditions. Third, pore-network and numerical simulations are used to examine the mechanisms and selection of cushion gases, including natural gas, nitrogen, carbon dioxide, and air. The results show that CO₂ improves hydrogen recovery by reducing interfacial tension and stabilizing pressure, while nitrogen offers higher gas purity with moderate cost benefits. To reduce water invasion and increase the working gas volume, this study introduces a new gel-barrier technology. This technology is modeled using coupled mass, energy, and reaction equations. Simulation results show that gel barriers can block water pathways, keep the storage pressure stable, and raise hydrogen recovery by 10–25% in water-bearing reservoirs. A techno-economic analysis based on a capital cost, an operating cost, net present value, and an internal rate of return confirms that combining cushion gas with gel barriers is technically reliable and economically feasible for field use. Overall, this research builds a unified framework that links theory and engineering for safe and efficient underground hydrogen storage in porous media. The findings provide scientific support and practical guidance for future UHS projects in porous media.