Water wettability alternation of CO2-water-shale system due to nanoparticles: Implications for CO2 geo-storage

•The ability of SiO2 and Al2O3 nanoparticles to retain wettability reversal of CO2-water-shale system is studied.•The wettability-enhancing effect of SiO2 and Al2O3 nanofluid with different nanofluid concentrations and aging time on contact angles is obtained.•The effect of SiO2 and Al2O3 nanoparticles on water wettability and functional groups of shale after a period of ScCO2 treatment is elaborated.•SiO2 nanofluid showed better performance compared to Al2O3 nanofluid in wettability reversal after ScCO2 treatment.•SiO2 and Al2O3 nanoparticles can recover CO2 structural trapping and increase mineral trapping potential in shale formation.