Monitoring of CO2 Injected at Sleipner Using Time Lapse Seismic Data

Abstract

Since October 1996, Statoil and its Sleipner partners have injected CO2 into a saline aquifer, the Utsira Sand, at a depth of approximately 1000 m. The aquifer has a thickness of more than 200 m near the injection site and is sealed by thick shales. A multi-institutional research project, SACS (Saline Aquifer CO2 Storage), was formed to predict and monitor the migration of the injected CO2. To this end, two time-lapse seismic surveys over the injection area have been acquired, one in October 1999, after 2.3 million tonnes of CO2 had been injected, and the second in October 2001, after approximately 4.4 million tonnes of CO2 had been injected. Comparison with the base seismic survey of 1994 prior to injection provides insights into the development of the CO2 plume. This chapter presents some selected results of the seismic interpretation of the CO2 plume at the two different time-steps.The overall effect of the accumulated CO2 on the seismic signal is significant. At several depth levels within the Utsira Sand, a large increase in reflectivity has been observed on the time-lapse seismic data caused by individual CO2 accumulations under the intra-reservoir shale layers.