Assessment of CO2 injection into the south Utsira-Skade aquifer, the North Sea, Norway

Abstract

To estimate the capacity of CO2 storage in a southern part of Utsira/Skade aquifer, a reservoir model was built to simulate the long-term behavior of CO2 injection. The model covers 1600 km2 in the southern part of the Norwegian sector. The study illustrates potential migration and to forecast possible migration of CO2 from the Skade Formation into the Utsira Formation above. CO2 from Skade sand can penetrate through a clay layers into Utsira sand if the clay between Skade sand and Utsira sand has permeability from 0.1 mD and higher. About 170 Mt (million tonne) CO2 can be injected in Utsira sand in the segment model with 4 horizontal wells over 50 years, BHP (bottom-hole pressure) change of 10 bars, no water production. After 8000 years of storage, the dissolved part is nearly 70%, residual trapping is less than 1% and mobile CO2 has decreased to 29% of total amount of injected CO2. These results are based on a residual saturation of CO2 of 0.02. If a residual saturation of CO2 is 0.3, CO2 trapped by residual mechanisms is 13% of total CO2 injected after 8000 years. Mineral trapping by geochemical reactions was not considered in the simulation, but will add additional storage capacity.