Research and analysis

The geomechanics of hydrogen storage in salt caverns: environmental considerations: summary

Published 2 September 2025

Applies to England

1. Chief Scientist’s Group report summary

This project explored how the structural integrity of underground salt caverns is affected by using them to store hydrogen. The project is based on a review of literature and supplementary discussions with practitioners from industry, academics and regulators. These findings will help the Environment Agency understand the uncertainties and environmental risks associated with storing hydrogen in salt caverns.

1.1 Background

The transition to net zero will require increased use of renewable technologies to generate energy. Hydrogen is used both as a fuel and for storing surplus energy. Naturally occurring salt caverns (cavities that are made from salt deposits in the subsurface dissolving) are good for storing gas because they form good seals. Salt caverns have been used to store hydrogen as a chemical feedstock in the UK since 1971. However, there will be new challenges in how salt caverns are used for large-scale hydrogen storage. These challenges relate to the scale of the storage and the frequency with which hydrogen is “cycled” into and out of the cavern.

The aim of this project was to understand how the structure of underground salt caverns might behave in response to them being used for hydrogen storage purposes. The project considered possible environmental and structural impacts throughout the lifetime of a salt cavern, and how these risks could be reduced.

1.2 Approach

This project involved a review of published scientific and grey literature, as well as supplementary discussions with industry practitioners, academics and regulators to gain insights from ongoing projects, including unpublished findings. The review sought to understand the geomechanical considerations for storing hydrogen in salt caverns at four stages of the salt cavern lifetime: planning, construction, operation and decommissioning.

1.3 Results

The geology of the salt deposit determines factors such as the depth, shape and size of the salt cavern. For large-scale storage, multiple caverns may be developed, and it will be important to keep sufficient distance between caverns to ensure cavern stability. During operation, pressure within a cavern needs to be kept within an optimal range to prevent fracturing, roof falls, or cavern closure. Changes in pressure and temperature from cycling hydrogen into and out of the cavern could lead to fatigue of the walls and loss of integrity, although relatively little is known about this. To decommission a salt cavern, hydrogen is removed and the cavern filled with brine. Pressure within the cavern is equilibrated with the surrounding pressure to prevent the cavern closing or fluid escape owing to the cavern being under- or overpressure.

Loss of salt cavern integrity could result in two main environmental impacts: geological (for example, land subsidence or seismicity) or gas release from the cavern or borehole to the surrounding environment (for example, groundwater, surface water or atmosphere). As a small, mobile molecule, hydrogen could potentially impact the environment due to its flammability and because it is a secondary greenhouse gas.

Risks can be managed through suitable geological characterisation, appropriate salt cavern design and operational parameters. Ongoing pressure and temperature monitoring and regular surveys of the evolution of the cavern also reduce risk.

1.4 Conclusions

This report highlights several possible geomechanical effects from storing hydrogen in salt caverns that could have environmental impacts. Understanding and managing these effects, particularly in relation to the scale and cyclic nature of hydrogen storage, will be essential for operators to successfully manage large-scale hydrogen storage sites. It also assists the Environment Agency to work with operators, using its advisory and regulatory role to reduce potential environmental impacts.

1.5 Publication details

This summary relates to information from project SC240045, reported in detail in the following output:

• Report: SC240045/R
• Title: The geomechanics of hydrogen storage in salt caverns: environmental considerations
• Project managers: Helen Brooks and Sian Loveless, Chief Scientist’s Group. Research undertaken and report written by Doug Smith, British Geological Survey, on a short-term placement to the Environment Agency.

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

© Environment Agency