Synergistic Integration of CTAB-Modified Silica Nanoparticles and Low-Salinity Water for Enhanced Oil Recovery in Carbonate Reservoirs

Abstract Nanoparticles can improve conventional enhanced oil recovery (EOR) techniques; however, they are not stable. Surface modification offers a promising strategy to enhance nanoparticle stability and performance in EOR. To address this impediment, a minimal amount of surface-active agent can be introduced to the nanoparticle surface to improve their dual wettability potential. This study presents a comprehensive analysis of the mechanisms that enhance oil recovery when cetyltrimethylammonium bromide (CTAB) is adsorbed onto silica nanoparticles to formulate a CTAB-silica-based nanofluid using low-salinity water (LSW). Various experiments, including nanofluid formulation and characterization, interfacial tension (IFT) measurements, wettability assessment using contact angle, spontaneous imbibition, nuclear magnetic resonance (NMR) measurements, and core flooding experiments, were performed on limestone core plugs with low (50 mD) and high (200 mD) permeability. The experiments evaluated oil recovery during injections of formation brine, LSW, silica nanoparticles, CTAB, and CTAB-modified silica nanoparticles. Our results showed that the main mechanism controlling oil recovery is IFT reduction, especially at higher pH, which resulted in an increase in the capillary number from 10–6 to 10–3. Furthermore, although contact angle measurements indicated a significant shift from oil-wet to water-wet, Amott index and NMR measurements indicated no significant wettability change. The core flood experiments showed that for the 200 mD cores, CTAB alone could recover an extra 22.4% while CTAB-modified silica nanoparticles at a higher pH (SE) could recover 34.7%. For the 50 mD case, CTAB alone could recover 15%, while the modified system (SE) could recover an additional 20% after water flooding. Thus, CTAB-modified silica nanoparticles at higher pH present an efficient approach for implementing surfactant-nanoparticle solutions in carbonate reservoirs with low and high permeability.