An Innovative Approach to Reducing Upfront Costs in Hydrogen Storage via Cushion–Working Gas Separation

Hydrogen is an expensive and relatively scarce commodity. However, its storage—both to increase renewable energy efficiency by reducing curtailment and to support a zero-carbon energy system that reduces reliance on energy imports—appears inevitable. This raises a key question: how can the high upfront costs and substantial hydrogen volumes required for subsurface storage be reduced? One of the main cost drivers is the need for hydrogen cushion gas, which, depending on the techno-economic analysis, can account for up to 80% of the initial investment costs.

In this talk, we present two approaches to improve the competitiveness of hydrogen storage. First, drawing on lessons learned from the ACT Acorn CO₂ storage project, we explore the potential of a staged investment strategy. The central idea is to initiate storage operations at a small scale, requiring relatively modest volumes of cushion gas, while retaining the option to upscale if early phases prove successful and safe, efficient storage is demonstrated.

Second, we introduce a new conceptual model that allows hydrogen cushion gas to be replaced with cheaper and more readily available alternatives. The primary function of cushion gas is to provide compression during working gas injection and pressure support during production. We propose a strategy in which cushion gas (in this case CO₂) and working gas are spatially separated, preventing mixing or chemical reactions while still delivering the pressure support required for efficient operation.

We use the Long Clawson field in the East Midlands, UK, as a case study to demonstrate the theoretical feasibility of this approach. The field of interest is relatively shallow (approximately 680 m) and comprises several reservoir layers with an average thickness of ~10 m. Using an efficient black-oil simulator, reservoir modelling is employed to test and optimise the feasibility of cyclic hydrogen storage within these layers.

This work forms part of the East Midlands Storage (EMStor) project, a Strategic Innovation Fund–supported feasibility study focused on the development of hydrogen storage in repurposed hydrocarbon fields.