UK CO2 storage plans yet to be proved viable, top geologist warns

The UK's plans to store CO2 beneath the North Sea as part of a drive to net-zero have yet to resolve questions over leakage, while a rapid wind farm build-out risks obstructing the monitoring of storage sites and industry activity generally, a leading geologist has said.

Decisions taken during the UK's hosting of COP26 climate talk as part of efforts to lower emissions leave significant questions unresolved, Professor John Underhill of Heriot-Watt University in Edinburgh, who takes up a new role as director of Aberdeen University's Interdisciplinary Centre for Energy Transition on March 1, said in an interview.

The UK plans to store billions of tons of CO2 from sites such as refineries and chemical plants in rock formations under the North Sea. Industry group Oil & Gas UK (OGUK) envisages at least 100 million mt of CO2 stored annually by 2050, and two sites in northwest and northeast England have been awarded 'Track-1' status by the authorities.

OGUK points to Norway's Sleipner project as a model: it has stored 1 million mt/yr since 1996. But Underhill pointed to mixed results from CO2 storage around the world and called for independent studies into the Track-1 projects — Hynet North West, led by Italy's Eni, and the East Coast Cluster led by BP.

He urged a "forensic and critical, independent evaluation of the sites before any injection takes place," adding that "if we identify challenges or problems and if either of those sites go wrong, the issue will be people will lose confidence in CO2 storage, and that will then be an industry problem and a UK-wide problem."

"It's really important that policy-makers and others are aware of how their aspiration and wishes for net-zero can or can't be met based upon and governed by our understanding of the geoscience currently."

Underhill called for closer collaboration between wind farm regulator the Crown Estate and hydrocarbon regulator the Oil & Gas Authority, saying wind farm expansion, including recent Scottish lease offers, could obstruct the seismic survey ships that would have to monitor stored CO2.

Hornsea 4 is one wind farm project set to overlap a CO2 storage site, the Endurance site proposed for the East Coast Cluster, Underhill said, adding access for regular 3D seismic surveys would be needed if more expensive 'ocean bottom' monitoring is to be avoided.

He raised several geological questions, including the possibility some formations may not be sufficiently sealed due partly to the 'tilt' of the British Isles, and said formations where CO2 is already present may be safer than those where it is not, with the Track-1 sites among the latter.

"We do need to know where the plume of CO2 is migrating and to ensure there is no leakage through the sealing cap rock and its overburden," he said.

West coast sites such as the depleted Hamilton field in Liverpool Bay under consideration for Hynet could prove too shallow to ensure the pressures and temperatures needed to keep CO2 in the supercritical form required to maximize volumes stored and reduce leakage risk, he said, describing Hamilton as "much more challenged" than generally realized, with a new study awaiting publication.

A further risk is of CO2 reacting with water to form carbonic acid, which could threaten cap rocks at storage sites and the cement used to seal decommissioned oil wells, Underhill said.

"There is a need for a robust technical assessment... so that we select the right sites for the right reasons," he said, adding current choices of site were driven by commercial considerations such as which fields are coming up for decommissioning.

OGUK defended the UK plans, telling S&P Global Platts that thorough risk assessments would be carried out, and projects in operation would be subject to annual verification as part of the UK emissions trading scheme.

OGUK energy policy manager Will Webster cited Norway's Sleipner and said: "Natural trapping mechanisms such as CO2 trapping within the pore space... coupled with the transferrable reservoir engineering skills and subsurface expertize from the oil and gas industry, have all ensured permanent storage of CO2, and prevented the migration of CO2 from the store to the surface."

Licensing restart

Underhill went on to address industry setbacks such as Shell's decision to drop the West of Shetland Cambo project, which he said need not be a "sacrificial lamb" signifying the end of the industry. Cambo is geologically "difficult and marginal" because of inter-bedded volcanic rock found at the formation, a problem also for the nearby Rosebank field, he said.

However, he called on the government to relaunch offshore licensing after a pause announced in 2020 to align the process with climate goals. Having thought "very long and hard" about banning exploration the UK appears to have heeded Norway's example of maximizing hydrocarbon recovery while curbing emissions, and a relaunch is expected with a built-in 'climate compatibility checkpoint,' he said.

Having a 33rd licensing round with climate compatibility test would be "a very strong signal... that the UK Continental Shelf is still open for business for oil and gas exploration," he said, describing gas as a "crucial component of the transition."

Demand reality

On the UK's fraught energy politics, Underhill called for a "difficult, but important discussion" about the UK's need for hydrocarbons — confirmed by the International Energy Agency and the UK Climate Change Committee — and the obligation to avoid fuel poverty, enshrined in UN development goals.

Efforts to curb emissions from the upstream production process mean the UK Continental Shelf "offers a reliable, low-carbon option" with the potential to reuse fields and infrastructure for both CO2 and gas storage, he said.

"There is an urgent need to address the energy trilemma of sustainability, affordability, and security of supply. Oil, gas, coal, nuclear and renewable technologies like wind, solar and hydro all have to be part of the discussion," he said.

"The key question... is: are we comfortable to be reliant on imports and the security of those supply routes, the carbon footprint they bring, the intermittency of renewables and the lack of [gas storage]? If [not], we need a full, frank and open discussion with all options on the table."