Engineering the Wettability Alteration of Sandstone Using Surfactant-Assisted Functional Silica Nanofluids in Low-Salinity Seawater for Enhanced Oil Recovery

The application of nanoparticles for enhanced oil recovery (EOR) has been shown to be advantageous over conventional methods. Wettability alteration of reservoir rock from oil-wet to water-wet is one of the main factors in improving oil recovery from matured reservoirs. The sandstone reservoirs are generally negatively charged, and hence, a proper selection of the surface charge of nanoparticles is important. In this work, a novel nanofluid is prepared using the synergistic effect of an oppositely charged Ludox CL silica nanoparticle (positive) and an anionic Aerosol-OT (AOT) surfactant in low-salinity seawater (LSW). The positively charged Ludox CL silica nanoparticle can readily adsorb on the Berea sandstone core due to electrostatic attraction, altering the wettability. The interfacial tension (IFT) and three-phase contact angle are measured to study the effect of the nanofluid on the IFT of the crude oil–nanofluid system and the wettability of the sandstone core. At a low AOT surfactant concentration, the nanoparticles are hydrophobic because of the monolayer adsorption of AOT with a higher tendency to sit at the oil–water interface, causing a reduction in the IFT. Moreover, scanning electron microscopy and energy-dispersive X-ray analyses were used to show the adsorption of nanoparticles on the Berea core surface and the desorption of crude oil from the core. The efficiency of different imbibition fluids was evaluated via a spontaneous imbibition technique using Amott cells. Experimental results showed that the oil recovery due to spontaneous imbibition of the nanofluid conducted on the Berea core yielded the highest oil recovery rate as compared to deionized water, LSW, pure silica nanoparticles, and a pure surfactant (AOT), respectively. The nanofluid showed excellent stability, significant wettability alteration, greater reduction of IFT, and great potential as an imbibition agent for EOR applications.