Monitoring Offshore CO2 Storage Using Time-lapse Gravity and Seafloor Deformation

Combined 4D-gravity and seafloor-deformation surveys have been performed for monitoring hydrocarbon production in seven fields on the Norwegian continental shelf. In one of them, Sleipner, CO2 storage has also been monitored. The experience from that case demonstrates that gravity provides quantitative information on the lateral distribution of mass changes, which can be used to estimate CO2 density and the fraction of CO2 that is dissolved in brine. Surface deformation monitoring has been a focus of interest in recent years, due to increasing attention on fault activation and induced seismicity. The onshore In Salah CO2 storage project demonstrates that frequent and high resolution surface deformation data allow studying potential fault reactivation. This abstract reviews the principles behind the 4D-gravity and seafloor-deformation monitoring technology, and then discusses the value of gravity and surface deformation data for CO2 storage, by describing the cases of Sleipner and In Salah. An outlook on the recent and future developments of the technology is provided.