The Porthos Project: How to Manage CO2 Injection in a Heavily Depleted Gas Field

The Porthos project is located in the Dutch part of the North Sea and is under construction. Injection is planned to start in 2026 at an average rate of 2.5 MTPA into depleted reservoirs. Injection of CO2 needs careful management to avoid low temperatures, measures have been taken:

1. All wells will be reused and worked-over to materials that can tolerate low temperatures
2. The offshore pipeline is thermally insulated to make use of the compressor heat to keep the pipeline in single phase operation
3. The reservoir pressure will be increased to 50 bar by means of gaseous CO2 injection before switching to supercritical CO2 injection. Continuous evolution of system operating setpoints will ensure that injection capacity limits will remain constant while reservoir pressure is increasing
4. For short and long term forecast, EBN has developed a fully coupled network, wells and reservoirs physics based simulation tool called CALYSTO (Carbon Low enthalpY Simulation TOol). This in-house simulator provides a global overview of CO2 thermodynamical conditions along its entire pathway from emitters down to the underground stores
5. All of this is complemented with operating guidelines and extensive monitoring using downhole gauges and fibre optics for DTS and DAS surveys