Changes to interfacial characteristics by low salinity water/nanoparticle flooding in carbonate reservoir

Nano-enhanced oil recovery (nano-EOR) and low salinity water flooding (LSWF) has been considered a promising EOR method. We investigated the interfacial properties between the nanofluid, oil, and rock when both methods were applied simultaneously to the carbonate reservoir. SiO₂ and Al₂O₃ nanoparticles (NPs) were used, and interfacial tension (IFT) and contact angle were measured using a drop shape analyzer to investigate the effect of each NP and low salinity water (LSW). In addition, to analyze the complex oil recovery mechanism caused by each interfacial property change, we generated a capillary pressure curve using IFT and contact angle. As a result, LSW significantly reduced contact angle due to the charge screening effect, which increases the NP adsorption on the rock surface. SiO₂ NPs with a negative zeta potential considerably decreased contact angle by electrostatic attraction with carbonate rock which has a positive zeta potential, but its effects on IFT were minimal. Meanwhile, Al₂O₃ NPs, which have relatively weak hydrophilicity than SiO₂, migrated to oil after vortexing and significantly reduced the IFT. Although each NP improved the recovery by a different mechanism, they considerably decreased the capillary pressure that oil can be displaced more efficiently. In this study, Al₂O₃ NPs are more appropriate for carbonate rock due to their high IFT reduction effect, but additional experiments are essential for the various NPs and salinity conditions in the perspective of the interfacial property alteration.