Dual sensor streamer technology used in Sleipner CO2 injection monitoring

CO2 has been injected into the saline aquifer Utsira Fm at the Sleipner field since 1996. In order to monitor the movement of the CO2 in the sub-surface, the seventh seismic monitor survey was acquired in 2010, with dual sensor streamers which enabled optimal towing depths compared to previous surveys. We here report both on the time-lapse observations and on the improved resolution compared to the conventional streamer surveys. This study shows that the CO2 is still contained in the subsurface, with no indications of leakage. The time-lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the time-lapse effects of the CO2 at Sleipner, and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine CO2 saturated layers with improved thickness estimates of the layers. In particular we have estimated the thickness of the uppermost CO2 layer based on an analysis of amplitude strength together with time-separation of top and base of this layer and found the maximum thickness to be 11 m. This refined interpretation gives a good base line for future time-lapse surveys at the Sleipner CO2 injection site.