Effects of aquifer salinity on underground hydrogen storage

Underground hydrogen storage (UHS) is considered a promising technology for enhancing clean energy resilience. Deep saline aquifers, with their abundance and ample storage capacity, are favorable candidates for UHS. Although the technical feasibility of UHS in saline aquifers has been widely studied, the impact of aquifer salinity (ratio of dissolved salt mass to total brine mass) on storage performance remains poorly understood. To address this gap, we conduct high-fidelity reservoir simulations to evaluate the effects of salinity on three UHS performance metrics: maximum reservoir pressure buildup, liquid–gas ratio of produced fluids, and hydrogen withdrawal efficiency. Our results show that salinity strongly impacts UHS performance. Hydrogen injection desiccates the near-well region, causing salt precipitation that reduces porosity and permeability. In aquifers with salinity ≤ 10%, most precipitated halite is redissolvable, causing only minor permeability reductions. Within this range, increasing salinity decreases the produced liquid–gas ratio and improves hydrogen withdrawal efficiency without significantly increasing reservoir pressure buildup. By contrast, at salinities ≥ 15%, halite accumulates over successive storage cycles, clogging near-well zones, drastically reducing hydrogen withdrawal efficiency and elevating pressure buildup. These findings indicate that aquifer salinity is a critical factor for UHS performance and should be carefully considered in site selection and operational design. • Hydrogen injection causes near-well dry-out and salt precipitation. • Salt precipitation lowers porosity and permeability as halite saturation increases. • Salinity affects salt precipitation and hydrogen storage performance.