Synergistic influence of nanoparticles and surfactants on interfacial tension reduction, wettability alteration and stabilization of oil-in-water emulsion

Abstract

In this study, the synergistic interaction of nanoparticles and surfactants were explored for oil-water interfacial tension (IFT) reduction, alteration of rock wettability, and stabilization of oil-in-water emulsion. The interfacial properties were investigated using drop-shape analyzer (DSA 25) while the pore scale visualization studies were conducted using the etched glass micromodels. The most stable surfactant-stabilized emulsion was formed in presence of cetyltrimethylammonium bromide (CTAB) while the order of increasing emulsion stability in presence of nanoparticles was obtained as follows: carbon nanotubes >copper oxide> silicon dioxide> aluminum oxide > titanium dioxide. Compared to pure nanofluids or surfactant solutions, the nanoparticles-surfactant solutions demonstrated promising tendency for significant reduction in oil-water interfacial tension and alteration of rock wetting properties. Specifically, the carbon nanotubes (CN) based nanofluids, reduced the contact angle of the rock from 68.73° to 65.5° (4.7%) while the Triton X-100 (TX 100) and CN-TX100 solutions reduced the contact angles to 10.65° (84.5%) and 7.0° (89.8%) respectively. The dominant mechanism of resident oil mobilization from the micro and dead-end pores was identified as emulsification-entrainment. A correlation exists between influence of nanoparticles-surfactant solutions on interfacial properties and resident oil mobilization from the micro and dead-end pores. The CN-CTAB solution that was the most effective in mobilization of the resident oil from the micro and dead-end pores significantly reduced the crude oil-water IFT to 0.63 mN/m. The mechanisms of IFT reduction, wetting properties alteration, as well as emulsion stabilization have been identified as the orientation of the particles at the interface and the electrostatic interaction between the nanoparticles and surfactant molecules. These procedures could be exploited to achieve significant reduction in IFT, rock wettability alteration and emulsion stabilization than could be achieved using pure nanofluids or surfactant solutions only.