CO2 has been stored in the Utsira Formation of the North Sea at the Sleipner field since 1996, and at the end of 2009, more than 11 million tonnes had permanently been placed underground. Injection has been going on with high regularity during these 13 years. CO2 enters the formation at supercritical (dense phase) conditions. The geophysical monitor data consists of a base seismic survey from 1994 and six high-quality repeat surveys, giving a unique “movie” of the development of the subsurface CO2 plume. The seismic images are unusually bright, caused by the large contrast in compressibility between fully water-saturated rocks to CO2-saturated rocks. Rock velocity reduces from 2050 m/s to about 1400 m/s and formation fluid density is reduced from about 1030 kg/m3 to around 730-770 kg/m3 on average for the subsurface CO2. The CO2 plume consists of nine different identifiable layers of CO2, interpreted as thin CO2 accumulations trapped below the sealing cap rock and below thin intra-Utsira shale layers. The 4D seismic defines the geometry and growth of the plume well, and show with high confidence that all of the injected CO2 stays in the primary storage formation, without any leakage. Seafloor gravity monitoring has successfully been applied in 2002, 2005 and 2009, showing separable time-lapse signals from both the CO2 plume and the hydrocarbon gas reservoir beneath. These data give the best estimate of plume average density (and temperature). The data interpretation shows that the CO2 plume is growing in all directions. The flow seems to be mainly topographically controlled. The storage capacity and efficiency of the primary anticline benefits from a large rock volume receiving CO2. Even if the CO2 is not permanently trapped, a significant part will stay as residual saturation. Focus in recent years has been on demonstration of seal integrity and lack of any leakage. This is important for this high profile project, which is the first, longest-running and largest CCS (Carbon Capture and Storage) project world-wide.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error