Hydrogen geological storage in saline aquifers based on seasonal and hourly cyclic profiles and the effects of integrating cushion gas

Abstract

Underground hydrogen storage (UHS) in saline aquifers is a scalable solution to balance renewable energy intermittency. This study evaluates the techno-operational feasibility of UHS through dynamic numerical simulations using a 3D heterogeneous synthetic model representing real reservoir properties of a saline aquifer. Two operational cyclic profiles (seasonal and hourly) were developed based on real energy data in Portugal and tested over a 10-year period. The simulations demonstrate that terawatt-hour (TWh) scale storage is achievable under both profiles, with the hourly profile showing improved pressure stability, 30% lower water production, and higher withdrawal efficiency (up to 74%) with pre-injected hydrogen cushion gas. Pre-injection enhances early-cycle performance and increases cumulative recovery by over 1.3 TWh. Results also highlight the effects of reservoir heterogeneity on well performance and pressure constraints. This study also highlights that optimized cyclic operation and cushion gas strategies can enhance UHS feasibility in saline aquifers, supporting large-scale energy storage.