Mechanism of Synergistically Changing Wettability of an Oil-Wet Sandstone Surface by a Novel Nanoactive Fluid

Various methods, including zeta potential, infrared (IR), quartz crystal microbalance (QCM), contact angle, and spontaneous imbibition measurements, were used to investigate the micromechanism of synergistically changing the wettability of oil-wet sandstone surfaces by the employed nanoparticles and gemini surfactants in this paper. Results show that the absolute value of the surface potential of the sandstone after the treatment of the studied nanoactive fluid was above 30 mV, indicating that the studied system was in a stable state. As a result of a higher ion-pair-forming ability and desorption capacity, the intensity of the carbonyl absorption peak of crude oil for the IR spectrum of the employed nanoactive fluid is lower than that of the gemini surfactant, indicating that synergy exists between the used calcium carbonate nanoparticle and gemini surfactant. QCM experiments show that, when the surfactant concentration increases (>0.003 wt %), the frequency drop becomes smaller for the studied system as a result of the desorption of ion pairs and the frequency drops for the studied nanoactive fluid are smaller than those for the used gemini surfactant. A complex is formed by the surfactant molecules and calcium carbonate nanoparticles as a result of the polar dipole interaction, promoting the formation of ion pairs formed by the gemini surfactants and carboxylic acid groups of crude oil. The balanced contact angles of oil droplets on the aged oil-wet surfaces treated by the studied gemini surfactant and nanoactive fluid were 45 degrees and 36 degrees, respectively, indicating that the used nanoactive fluid has a better effect on changing the wettability of oil-wet sandstone surfaces. In addition, the ultimate imbibition recovery of the nanoactive fluid is higher than that of the studied gemini surfactant. Thus, the synergistic mechanism of wettability alteration of oil-wet sandstone surfaces by the nanoparticles and gemini surfactants was indirectly confirmed by the contact angle and spontaneous imbibition determinations.