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Advanced low-salinity aqueous formulations have shown promising results for rock wettability modification and interfacial tension reduction. Additives, such as surfactant and nanoparticles, can be used for such formulations. The interaction of these novel formulations with different fluid phases and the rock surface is, however, yet to be understood in detail. Thus, an experimental study was conducted in this study to investigate the interfacial tension and wettability of carbon dioxide and anionic surfactant (SDBS, 1.435 mM) at high pressure and temperature. The results show that the anionic surfactant (SDBS, 1.435 mM) augmented the effect of zirconia (ZrO 2 ) nanoparticles (100−2000 mg/L concentration) at low-salinity conditions and proved to be an effective wettability and interfacial tension modifier when used at appropriate divalent cation/sulfate ion ratios. Low-salinity surfactant nanofluids may thus be applied for wettability alteration and interfacial tension reduction for recovering residual oil, carbon dioxide-enhanced oil recovery, as well as carbon dioxide geosequestration. We also demonstrate in this study that the ratio of divalent cations to sulfate ions (0 ≤ M 2+ /SO 4 2− ≤ 4.427) has a significant role in interfacial tension reduction and wettability modification. We further show using contact angle wettability measurements that initial weak water− wet quartz surfaces can turn to more water−wet when zirconia nanoparticles used in the low-salinity formulation are in the range of 100−1000 mg/L. Interestingly, further incremental nanoparticle concentration decreases the water wettability but further reduces the carbon dioxide/brine interfacial tension.

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