It is the first carbon storage appraisal well to be drilled on acreage licensed by the North Sea Transition Authority (NSTA) as part of the world’s first large-scale carbon storage licensing round in 2023.
The appraisal well, operated by global energy company Eni, is an important step towards assessing the carbon storage potential of the UK continental shelf (UKCS). The basin has up to 78 gigatonnes of potential storage capacity in depleted reservoirs and saline aquifers, enough to sequester all the CO2 emitted in the UK since the industrial revolution.
The NSTA estimates that up to 100 stores may need to be appraised to identify the best candidates for storage and help the UK reach its net zero target by 2050.
Hewett, 18 miles off the Norfolk coast, was one of the UKCS’s longest serving gas fields. Its original operator, Phillips, started production from the field in 1969, making Hewett only the third North Sea field to reach this stage, after West Sole and Leman. The field had produced 3.5 trillion cubic feet of gas by the time it permanently shut down in 2023.
Now Eni wants to give Hewett a new lease of life as a carbon store. It is thought to be capable of storing up to 10 million tonnes of CO2 per year emitted from the Bacton and wider Thames Estuary area, as well as potentially offering decarbonisation solutions for emitters across the European Union.
Eni contracted the Valaris 72 rig to drill the well – and work got under way in May 2025. Extensive data sampling was conducted, including cutting 270 ft of core and performing a nitrogen injection test, before plugging and abandoning it.
The data collected will inform the development plans for the Bacton CCS project by enabling the operator to build a fuller picture of the reservoir’s post-production characteristics and conditions, including reservoir pressures, possible injection rates, wellbore integrity and leakage risk.
In time, the data will be made available on the NSTA’s National Data Repository, helping to provide a richer data set to all operators looking to evaluate and derisk similar stores.
The Valaris 72 rig
The NSTA awarded permits for the UK’s first two carbon storage projects to the Northern Endurance Partnership in December 2024 and Liverpool Bay CCS, also operated by Eni, in April 2025. Together, they could store more than 200 million tonnes of CO2, equivalent to taking 110 million cars off the road for a year. The permits also unlocked £6 billion worth of supply chain contracts and 4,000 construction jobs.
In May, the NSTA put out a call for nominations for potential carbon storage locations to encourage companies to focus on areas where they have already done some technical work, leading to higher quality applications and likely cutting time to project delivery.
The NSTA offered 21 licences in the UK’s inaugural carbon storage licensing round, which concluded in September 2023. Licence CS008, which covers Hewett, is held by Bacton CCS Limited, a subsidiary of Eni CCUS Holding.
The well on Hewett is also the first to be consented as a dedicated carbon storage appraisal well via the Well Operations Notifications System.
Andy Brooks, NSTA Director of New Ventures, said, “The carbon storage industry has entered an exciting period of delivery, with two multibillion-pound projects getting the go-ahead in the past year, unlocking thousands of supply chain jobs. Long-held ambitions for this industry, which is essential to the UK’s energy transition, are rapidly becoming reality.”
“The appraisal well on Hewett – the first to be drilled on acreage awarded by the NSTA as part of the world’s first large-scale carbon storage licensing round – is yet another important milestone for the sector as it looks to assess further stores which should progress towards development. The NSTA continues to work with licensees to ensure that their plans are the right ones.”
Offshore Energies UK welcomed the news, saying the UK is making significant strides on the path to becoming a global leader in carbon capture and storage. Enrique Cornejo, OEUK Head of Energy Policy said, “This Hewett appraisal well is a powerful signal of industry’s commitment to invest in the UK’s net zero future. It shows how our existing energy infrastructure and expertise are being repurposed to deliver climate solutions.”
“But for commercial carbon capture and storage to succeed at scale, government must accelerate a clear route to market for projects like Bacton CCS which are outside the government’s planned cluster sequencing process. The Hewett appraisal well is a tangible example of industry stepping up, and now it’s time for policy to keep pace.”
