Designing a Monitoring Plan for the Endurance CO2 Store, Southern North Sea, UK

The Endurance CO2 store is a saline aquifer anticlinal structural trap in the Triassic Bunter Sandstone Formation in the Southern North Sea (SNS). Injection of 100 Mt of dense-phase CO2 is planned over 25 years as the first phase of development for the Northern Endurance Partnership (NEP). A detailed monitoring plan has been developed for Endurance with the site-specific risk assessment in mind. The plan covers pre-injection baseline data acquisition for several technologies, monitoring activity during the 25 years of CO2 injection (100 Mt CO2) and the post-closure period. Several objectives besides verifying CO2 containment are considered, as well as a requirement to be economic and efficient from a cost perspective. It also links closely to the Corrective Measures Plan, which describes how the operator will deal with instances of monitoring observations that are not in line with expectations. The plan relies on mature, core technologies that have a proven track record of surveillance in hydrocarbon fields (e.g., 4D seismic, pressure/temperature gauges, flowmeters), but also provides for maturation of options for new or alternative technologies. These may, in time, displace other monitoring activity to achieve the same objectives more efficiently or more effectively.