CCS at Depleted Gas Fields in North Sea: Network Analysis

Abstract

As part of development of the Dutch North Sea for CO2 storage, this study presents an investigation into offshore transport and storage network design. With depleted gas fields providing storage capacity, the low post-production reservoir pressures pose challenges to defining safe injection procedures. Pressure and temperature profiles are computed for a range of mass flow rates for well – reservoir combinations that are typical for gas fields in the Dutch part of the North Sea. These profiles illustrate the trade-offs that exist between injection of CO2 in gas phase versus injection of liquid CO2. In the latter case the injection rates that can be achieved are significantly higher, but limitations to the temperature in the well often lead to a significant minimum flow rate that limits flexibility of operations. The limitations arise from wellhead integrity and from hydrate formation at bottomhole or close to the well in the reservoir. Three potential networks of depleted fields are used to compare overall feasible injection rates over timeline of 30 years. While all networks can store the assumed target rates, the different well and reservoir properties result in substantial differences in well and reservoir count and, by consequence, in effort required to re-develop fields and wells for CO2 storage. The networks have different levels of operational flexibility, arising from flow constraints, and of network complexity, related to field and well count. The results from this study show that a network of depleted gas fields can be used to reach the injection rates commonly associated with large-scale CO2 capture and that the challenges related to low reservoir pressure can be managed.