Numerical Modelling of Gas Mixing in Salt Caverns During Cyclic Hydrogen Storage

This study presents the development of a robust numerical model for simulating underground hydrogen storage (UHS) in salt caverns, with a particular focus on the interactions between original gas-methane (CH4) and injected gas represented by hydrogen (H2). Using the Schlumberger Eclipse 300 compositional reservoir simulator, the cavern was modelled as a highly permeable porous medium to accurately represent gas flow dynamics. Two principal mixing mechanisms were investigated: physical dispersion, modelled by numerical dispersion, and molecular diffusion. Multiple cavern configurations and a range of dispersion–diffusion coefficients were assessed. The results indicate that physical dispersion is the primary factor affecting hydrogen purity during storage cycles, while molecular diffusion becomes more significant during long-term gas storage. Gas mixing was shown to directly impact the calorific value and quality of withdrawn hydrogen. This work demonstrates the effectiveness of commercial reservoir simulators for UHS analysis and proposes a methodological framework for evaluating hydrogen purity in salt cavern storage operations.