Offshore CO2 storage: Sleipner natural gas field beneath the North Sea

Sleipner is the world's longest-running industrial-scale storage project and the first example of underground CO2 storage arising as a direct response to environmental legislation. It began in 1996, injecting around one million tonnes (1 Mt) of CO2 per year into the Utsira Sand, a relatively shallow saline aquifer. By late 2011 over 13 Mt of CO2 had been securely stored. A comprehensive research-focused monitoring programme was carried out with multiple time-lapse surveys; predominantly 3D seismic but also 2D seismic, gravimetry and controlled-source electromagnetics (CSEM). The time-lapse seismic data image the CO2 plume clearly in the reservoir with very high detection capability and show no evidence of CO2 migration from the storage reservoir. Although not specifically designed for this purpose, the monitoring programme fulfils most of the requirements of the recently developed European regulatory framework for CO2 underground storage.