We propose a new strategy for carbon storage in which CO2 is injected into a geologic formation after emplacement of brine containing dispersed surface-modified nanoparticles. This strategy increases the sweep efficiency of CO2 storage in aquifers and enhances the aquifer storage security. The most likely mechanism is the generation of nanoparticle stabilized CO2/water foam which securely traps the injected CO2 for long periods of time.
As a consequence of low density and viscosity of CO2 at typical geologic storage conditions, CO2 injection into aquifers suffers from low sweep efficiency which manifests as the gravity override and viscous fingering. Here, we show that nanoparticles can reduce the mobility of the injected CO2 as it displaces brine, and therefore, increase the sweep efficiency. Further we show that displacing the injected CO2 with brine increases residual phase saturations, and therefore enhance the capillary trapping of CO2.
We conducted core flooding experiments in which liquid CO2 was used to displace brine with and without suspended nanoparticles. Sandstone cores with different degrees of heterogeneity were used to capture the effect of heterogeneity on the efficiency of the proposed technique. Saturation distributions and pressure drops were measured in real time with a modified medical CT scanner and pressure transducers. The use of nanoparticles is shown to render about 90% of the injected CO2 immobile and increases the sweep efficiency up to 20% when compared to the base brine case.