Optimizing geological hydrogen storage in bedded salt formations: Assessing permeation and leakage dynamics

Hydrogen, as a leading candidate for the future energy revolution due to its promise as an environmentally friendly energy source, presents significant potential for global energy systems. Among various storage methods, salt caverns stand out due to their inert environments and stable physical configurations, making them the most promising option for future hydrogen storage. In this study, we first elucidate the physical and chemical properties of hydrogen, emphasizing its low molecular weight, low solubility, high diffusion rate, and strong permeability. Detailed analyses of salt rock properties reveal their low permeability, favorable creep, and self-healing characteristics. A 3D geological model of salt cavern hydrogen storage is constructed to analyze the impact of various injection-production frequencies and operational pressure intervals on the tightness of salt caverns. An index system composed of permeation range, pore pressure distribution, pore pressure evolution, and leakage amount is used to assess the tightness of the caverns. Key findings from our research indicate the suitability of salt caverns for hydrogen storage, the minimal impact of injection-production frequency on hydrogen permeation range, and the significant influence on pore pressure in the near-field surroundings of the cavern. Elevating operation pressure markedly increases the permeation range and cumulative leakage amount. A broader range of pressure fluctuations correlates with increased variability in leakage rates. Over a 30-year operational period for a specific salt cavern, each 1 MPa increase in operation pressure results in a 20-ton increment in hydrogen leakage. Therefore, salt caverns are well-suited for hydrogen storage applications with flexible injection and production frequencies. However, while increasing operational pressure significantly enhances energy capacity, it also elevates the risk of hydrogen leakage. Therefore, it is crucial to determine an appropriate pressure interval for hydrogen storage. This research provides valuable insights for evaluating the sealing effectiveness of salt cavern hydrogen storages, contributing to the optimization of their design and operation for sustainable energy systems.