Greensand focused seismic monitoring for offshore CO₂ pilot injection

The Greensand consortium, led by INEOS Energy Denmark, is preparing a CO₂ pilot injection to inject up to 15.000 tons of CO₂ into the depleted Nini West oil field, Danish North Sea. The operation lasts 90 days and include 14 shipments of CO₂ to the Nini site. The injection is cyclic and will be accompanied by three focused seismic acquisitions with the objective to detect and monitor the CO₂ plume and to proof the concept of focused seismic offshore. Rock physical modelling implies that the seismic surveys can detect injected CO₂ in the reservoir exceeding 4% saturation. The maximum CO₂ saturation at the injection well after the last injection cycle will reach up to 55% and will radially migrate up-dip, being dissolved in formation brine and trapped in the reservoir. Such focused and repeated seismic surveys have the potential to replace conventional 4D seismic for CO₂ plume migration monitoring requirements, reducing the monitoring costs and environmental footprint during the entire storage field life including the post-closure period of 20 years. If successful, this focused seismic monitoring concept would have positive impact on the commercial viability and environmental footprint of the Greensand project and possibly other offshore CCS site as well.