Chemically Enhanced Carbon Dioxide Geosequestration Using Silica Nanofluid: Detailed Study on the Wettability Alteration and Adsorption

Abstract CO2 geo-sequestration in the subsurface is a promising method to mitigate global warming. Among the reported trapping mechanisms, residual trapping, in which supercritical CO2 (Sc.CO2) is trapped by capillary forces within the pores of rocks, is considered highly effective to secure Sc.CO2 in short to medium time flame. The efficiency of this process depends on rock wettability, which can be altered using colloidal silica nanoparticles (C-SNPs). Previous research showed that C-SNPs could enhance CO2 trapping by up to 80.6%. This study further investigated the effect of C-SNPs on wettability using the Amott wettability index with Berea sandstone and carbonate cores. Also, the adsorption behavior of C-SNPs with good or poor brine stability to the quartz was investigated by Quartz crystal microbalance and dissipation (QCM-D). To evaluate the Amott wettability index, isoparaffin was used as an analog fluid of Sc.CO2 and glycerol were mixed with brine to mimic the mobility of Sc.CO2/brine in a reservoir. Berea sandstone cores were aged with stearic acid in advance to alter the wettability to intermediate wet. All processes for the Amott wettability index were conducted at room temperature and 800 psi of confining pressure. It was found that just 0.01 PV of C-SNPs significantly improved wettability and enhanced CO2 trapping efficiency. In the case of sandstone cores, the wettability was altered by C-SNPs from 0.50 to 0.62, suggesting the sandstones became more water-wet. Effluent analysis revealed that all of the C-SNPs were adsorbed or trapped within the sandstone. Also, C-SNPs increased the Amott wettability index of carbonate cores from 0.50 to 0.60. QCM-D analysis revealed that the adsorption of C-SNPs could start immediately after contacting the quartz's surface. The adsorption behavior was different depending on the brine stability of C-SNPs; The mass of adsorbed C-SNPs with high brine stability reached the equilibrium, whereas that of C-SNPs with poor brine stability continuously went up. This result indicated that there was a low risk of causing blockage in the stratus when injecting the stable C-SNPs. We verified the potential of C-SNPs to alter the wettability both in sandstone and carbonate layers with a very small amount. Also, a novel analytical method, QCM-D, gave insights into the behavior of nanoparticles in the reservoir. We believe this study could accelerate the application of nanoparticles to alter the wettability and enhance CO2 geo-sequestration.