05 February 2026

Milestone reached: Porthos wells ready for CO₂ injection

At the end of January, an important step was taken in the offshore work for the Porthos project: work on the wells in the North Sea was successfully completed. Four former gas production wells have been converted into CO₂ injection wells. Three other wells have been sealed and permanently removed. This means that the underground access points are now ready for the injection and safe storage of CO₂ deep beneath the seabed.

The wells are vertical pipes that connect the P18-A platform to the depleted gas fields in porous sandstone, three to four kilometres below the seabed. These were previously used for gas production. As CO₂ injection involves different conditions than gas extraction, the wells – as well as the platform – had to be technically modified for their new function. A new production system was therefore designed and installed – known as completion – to make the wells suitable for CO₂ injection. This system incorporates modern technology to continuously monitor pressure and temperature.

A second life as injection wells
The work differed per well, with the safety of the system being paramount in all cases. Some pipe sections showed wear and tear – the wells have been in use for around 30 years – and were replaced. In other wells, part of the existing installation could be retained. Technical challenges, such as corrosion in older components, were successfully resolved.

The conversion of the wells took place in several carefully executed phases. First, the reservoir was secured at great depth by placing an isolation plug above it, so that no more natural gas could rise. The well was then filled with liquid for extra safety and to clean it. After that, the existing pipes and installations were disconnected and removed from the well. Materials that were still suitable were reused in other projects where possible.

The condition of each well was then thoroughly checked. Ultrasonic measuring equipment was lowered into the well on an electric cable – a technique known as “logging” – to examine the quality of the steel and cement in particular. Once it had been established that the wells were in good condition, new pipes and equipment were installed. Finally, new production valves were installed, collectively referred to as the X-mas tree because of their characteristic shape, which is reminiscent of a Christmas tree.

The Valaris123: a unique workplace at sea
The conversion was carried out using the Valaris123 jack-up drilling rig, a football field-sized installation that can lift itself above the water for maximum stability. With its own cranes, power supply, workspaces and accommodation, work could be carried out 24 hours a day, seven days a week. TAQA, the former owner of the platform and wells during the gas production period, acted as the main contractor and managed dozens of specialised parties. The work was completed without a single incident: everyone returned home safely and there was no impact on the environment.

Ready for CO₂ injection
Four wells have been successfully converted for CO₂ injection. Two wells outside the platform have been safely sealed and removed, and one well from the platform; multiple tests have confirmed that this has been done successfully. The reservoirs into which the injection will take place have remained untouched. Extensive inspections show that the steel and cement of all wells are in excellent condition. This means that they can be used safely throughout the project.

In short: the wells are ready for CO₂ injection. Work on the platform and onshore will continue in the coming period. The first CO₂ injection is planned for the autumn of 2026.