Perenco, Carbon Catalyst and Harbour Energy have successfully wrapped up the UK’s first offshore CO₂ injection test at the Poseidon project in the North Sea. The project involved injecting liquid CO₂ into a heavily depleted North Sea gas field, achieving injection rates above 1 million tonnes per annum (Mtpa).

“This technical feat wasn’t just an operational success – it was a critical derisking milestone for both the Poseidon project and the broader CCS industry, providing concrete evidence that repurposing the UK’s mature offshore infrastructure for CO₂ storage is not only possible, but commercially viable,” said the project partners.

The Leman gas field, the UK’s largest legacy gas field, located at the southern edge of the Southern North Sea (SNS), has produced over 14 trillion cubic feet (Tcf) of gas. Leman now has an estimated storage capacity of 1 billion tonnes of CO₂.

“Sitting within reach of some of the UK’s major emission hubs – including London and the South East – Poseidon is also ideally positioned to receive CO₂ from Europe’s industrial corridors, such as the German Rhine Valley, the Netherlands, Belgium and Northern France,” said the partners.

Over a three-month trial, the team executed a rigorous CO₂ injection programme into the Leman H fault panel, utilising the Leman Hotel unmanned wellhead platform and a previously suspended gas well.

The goals of the injection test were to generate hard data on the viability of storing CO₂ in offshore depleted gas reservoirs at commercial rates of injection; confirm the potential for repurposing existing infrastructure, from topsides to well completions, for cost-effective CCS deployment; introduce advanced Measurement, Monitoring, and Verification (MMV) technologies capable of tracking CO₂ flow, pressure changes and well integrity; demonstrate stable CO₂ injection at scale across gas, super-critical and liquid phases; test the boundaries around the CO₂ fluid properties and behaviour as it flows from well head to bottom hole and then into the geological store; and assess the operability of the system and its capacity to maintain liquid-phase injection at Mtpa levels.

A total of 4000 tonnes of food-grade CO₂ was sourced from Air Liquide’s Netherlands facility. From there, it was shipped across the North Sea via the Atlantic Carrier supply vessel to Petrodec’s ERDA jack-up rig, which had been outfitted with a CO₂ injection package including 24 cryogenic ISO tanks. These 20-ft tanks enabled the controlled injection of 400-ton liquid CO₂ batches into the reservoir via the adjacent wellhead.

“This complex setup not only enabled continuous, high-rate injections but also tested the practicality of offshore liquid-phase transport and storage – key learnings for future commercial deployment,” said the partners.

The partners secured the first CO₂ well test consent from the North Sea Transition Authority (NSTA) and Offshore Petroleum Regulator for Environment and Decommissioning (OPRED).

Poseidon’s MMV programme included Vertical Seismic Profiling (VSP) using Distributed Acoustic Sensing (DAS), passive seismic monitoring, and seabed DAS via telecom cables already laid on the seabed. “These techniques aimed to understand the capabilities of geophysics to track the pressure front as it moved through the reservoir, providing real-time insights into CO₂ migration and model conformance – crucial for long-term storage safety and regulatory compliance,” said the partners.

More than 15 full injection cycles were executed with stable injection achieved across all CO₂ phases – gaseous, super-critical, and liquid. Commercial- scale injection rates of 1 Mtpa were achieved, limited only by topside facility constraints.

“The results point to a viable commercial case for repurposing depleted reservoirs,” said the partners.

Test data will be integrated into the front-end engineering design (FEED) for a commercial-scale development. Meanwhile, discussions continue with the UK Government on an appropriate business model. A CCS storage permit application is expected in 2026, with a Final Investment Decision (FID) targeted for 2027. First injection is slated for 2029.