Techno–economic optimisation of hydrogen geological storage in UK depleted gas reservoirs

Abstract

Long-duration energy storage is becoming critical in the UK to manage renewable intermittency, prolonged low-generation periods, and energy curtailment. Depleted natural gas reservoirs offer a promising option for large-scale underground hydrogen storage because of their substantial capacities, established containment, and well-characterised geology. However, a systematic assessment linking reservoir-scale behaviour to cost-optimal UK storage portfolios remains lacking. Here, we formulate a cost-aware portfolio optimisation framework that combines compositional reservoir simulations, surrogate modelling, and techno-economic optimisation across representative UK reservoir properties and operating conditions. The simulations identify permeability, porosity, reservoir pressure, and density contrast between H 2 and cushion gas as the dominant controls on recovery, while injection rate and cycle duration have comparatively lower influence. These results support a high-accuracy surrogate model that enables rapid evaluation of feasible storage configurations for delivery requirements from 5 to 200 TWh. By linking reservoir-dependent recovery to H 2 losses, purification, and storage-system costs, the framework determines cost-optimal combinations of depleted gas reservoirs and operating strategies. The optimised portfolios produce long-term levelised storage costs of approximately 30–60 $ MWh −1 . Higher delivery requirements generally increase costs because fewer annual cycles are available to distribute infrastructure and inventory costs. When purification costs approach H 2 production costs, cushion-gas ratios of 2–4 are favoured for the 5 TWh case, decreasing to 0–1 for requirements of 100 TWh and above; inexpensive purification shifts the preferred ratio towards zero. Across scenarios, selected reservoirs consistently exhibit permeabilities of 10–30 mD, porosities of 0.10–0.15, and pressures of 250–300 bar, conditions that reduce buoyant mixing while maintaining practical deliverability.