General – CO2 Wells
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 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.
Since CO₂ injection requires different conditions than gas extraction, the wells and the platform had to be technically upgraded for their new purpose. A new production system was thus designed and installed—referred to as completion—to adapt the wells for CO₂ injection. This system uses modern technology to continuously monitor pressure and temperature.
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 – ‘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 conversion was carried out using the Valaris123 jack-up drilling rig.
