Storage of CO2 in saline aquifers–Lessons learned from 10 years of injection into the Utsira Formation in the Sleipner area

The ongoing CO2 injection at Sleipner has demonstrated that 2/3 of the injected CO2 has not reached the top of the Utsira Formation, but has instead migrated laterally below imperfect intra-reservoir seals. The CO2 trapping below the structural spill point in the Utsira Formation is due to local mini traps, capillary flow resistance, and the hydrodynamic drive of the injection. About 40% of the CO2 that has entered the pore systems will remain as residually trapped CO2, whereas an unknown fraction of the remaining CO2 will migrate towards the top of the reservoir.