Dissolved CO 2 injection to eliminate the risk of CO 2 leakage in geologic carbon storage

Abstract

Geologic carbon storage is usually viewed as injecting, or rather as storing, CO 2 in supercritical phase. This view is very demanding on the caprock, which must display: (1) high entry pressure to prevent an upward escape of CO 2 due to density effects; (2) low permeability to minimize the upwards displacement of the brine induced by the injected CO 2 ; and (3) high strength to ensure that the fluid pressure buildup does not lead to caprock failure. We analyze the possibility of injecting dissolved CO 2 and, possibly, other soluble gases for cases when the above requirements are not met. The approach consists of extracting saline water from one portion of the aquifer, reinjecting it in another portion of the aquifer and dissolving CO 2 downhole. Mixing at depth reduces the pressure required for brine and CO 2 injection at the surface. We find that dissolved CO 2 injection is feasible and eliminates the risk of CO 2 leakage because brine with dissolved CO 2 is denser than brine without dissolved CO 2 and thus, it sinks towards the bottom of the saline aquifer.