Dissolved CO2 Injection to Eliminate the Risk of CO2 Leakage in Geologic Carbon Storage
Geologic carbon storage is usually viewed as injecting, or rather as storing, CO2 in supercritical phase. This view is very demanding on the caprock, which must display: (1) high entry pressure to prevent an upward escape of CO2 due to density effects; (2) low permeability to minimize the upwards displacement of the brine induced by the injected CO2; and (3) high strength to ensure that the fluid pressure buildup does not lead to caprock failure. We analyze the possibility of injecting dissolved CO2 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 CO2 downhole. Mixing at depth reduces the pressure required for brine and CO2 injection at the surface. We find that dissolved CO2 injection is feasible and eliminates the risk of CO2 leakage because brine with dissolved CO2 is denser than brine without dissolved CO2 and thus, it sinks towards the bottom of the saline aquifer.
KeywordsCO2 storage Dissolved CO2 Leakage Caprock Buoyancy
The authors acknowledge financial support from the “TRUST” project (European Community’s Seventh Framework Programme FP7/2007-2013 under grant agreement n 309607) and from “FracRisk” project (European Community’s Horizon 2020 Framework Programme H2020-EU.220.127.116.11 under grant agreement n 636811).
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