Leakage fears see old Midlothian gas field site ruled out for safe storage of explosive hydrogen

Concerns over the safety of underground storage for hydrogen, for use as a green fuel, have been raised after studies suggest the highly explosive gas would leak out of rock formations and escape into the wider environment, posing a danger to people living nearby.

The findings come following investigations at a decommissioned onshore gas field just outside Edinburgh.

Professor John Underhill from the University of Aberdeen and Malcolm Butler at the UK Onshore Geophysical Library (UKOGL), who led the research, have concluded that the Cousland gas field in Midlothian fails to meet the criteria for safe subsurface storage.

Hydrogen is being pushed as an eco-friendly replacement for climate-polluting fossil fuels because it can be generated using green electricity and produces only water when burned.

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Cousland, near Dalkeith, produced natural gas for around a decade before being decommissioned in the 1960s

The site has been highlighted in other academic studies as a potential contender for large-scale hydrogen storage to help achieve national environmental ambitions.

However, closer analysis of its geology has highlighted numerous barriers to its suitability for the purpose, including a lack of evidence of the nature of subsurface sedimentary rocks and the structure of the field.

Hydrogen is seen as a greener alternative to climate-polluting fossil fuels, with potential for use to power everything from planes, trains and automobiles to heating for homes

The findings have sparked fears that the gas could easily escape, presenting a danger to the local environment and surrounding communities.

“Hydrogen has been proposed as a possible green energy vector in the transition, but it forms a small, nimble molecule and is very difficult to contain,” said Professor Underhill, who is director of the university’s Centre for Energy Transition.

“It can be stored safely in subsurface geological sites, but so far these have largely been limited to man-made hermetically sealed soluble caverns in halite (rock salt) deposits.

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Professor John Underhill, director of the University of Aberdeen's Centre for Energy Transition, co-led research into the suitability of Cousland gas field, in Midlothian, as a site for safe subsurface storage of hydrogen

“The absence of salt deposits onshore in Scotland is what has led to the proposal that former and now depleted hydrocarbon fields such as the Cousland gas field could be used.

“However no natural hydrogen has been discovered in any existing onshore or offshore fields in the UK, which raises the question of whether it was once there and leaked – and, crucially, if it would stay underground if it was injected into a subsurface site.”

The research team used geological data, available through the UKOGL, to critically evaluate Cousland’s potential for hydrogen storage, but concluded that it “fails to meet the criteria for safe subsurface storage, is a poor site for a hydrogen repository and should not be used for this purpose”.

Professor Underhill says the study demonstrated the need for independent evaluation of subsurface sites proposed for use in the green energy transition.

“In this particular case, it emphasises the storage challenges associated with porous media in general and in subsurface sites in onshore areas in particular,” he said.

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“It also underlines the University and Centre for Energy Transition’s role as an independent technical evaluator of subsurface technologies, and its willingness to identify unforeseen hurdles and seek workable solutions as we steer a pathway to net zero.”

Dr Butler, chair of UKOGL, added: “This study would not have been possible without access to the large volume of well data, seismic records and crucial unpublished historic reports and correspondence archived by UKOGL and now available for free download from its website.2

The study has been published in the journal Earth Science, Systems and Society.