Coupled Hysteresis and Variogram-Controlled Heterogeneity Effects on Underground Hydrogen Storage in Saline Aquifers.

Hydrogen is projected to be a critical component in worldwide efforts to transition toward low-carbon energy systems. As hydrogen generation capacities rise to meet climate goals, parallel advancements in scalable, high-efficiency storage infrastructure are urgently required. Accurately assessing the storage capacity of saline aquifers is critical for deploying underground hydrogen storage (UHS) on the scale necessary for the energy transition. Conventional assessments, however, often rely on static reservoir properties, such as porosity and permeability, which fail to capture the complex realities of subsurface fluid behavior. This study demonstrates that neglecting crucial dynamic parameters, such as hysteresis, leads to a significant overestimation of recoverable gas. Our numerical simulations reveal that relative permeability hysteresis is one of the dominant factors, causing substantial residual gas trapping that reduces the hydrogen recovery factor by nearly 30% in the initial cycles. The heterogeneous nature of the reservoir adversely affects hydrogen storage operations by promoting preferential flow paths, reducing sweep efficiency, and leading to uneven hydrogen distribution and storage within porous media. Optimal selection of the production rate is crucial for balancing the hydrogen recovery and water management. In heterogeneous models, by optimizing flow rates, recovery improved by ∼10% and water production decreased by ∼20%, underscoring the need for reservoir-specific flow-control strategies. This research underscores the imperative of a dynamic, physics-based approach to designing efficient and cost-effective UHS projects. Moving beyond static assumptions is not just an improvement; it is essential for unlocking the true potential of saline aquifers for large-scale hydrogen storage.