Effects of amphoteric surfactants on the dispersibility of TiO2 nanoparticles and experimental study of enhanced oil recovery

As a new type of flooding technology, the application of nano-surfactant fluids in the petroleum industry has received much attention in recent years. Stability of the nanofluids, which requires the nanoparticles to remain dispersed in the base fluid during flowing in porous media, is vital for enhanced oil recovery (EOR). In this paper, the feasibility of using amphoteric surfactants to promote the dispersion stability of TiO2 nanoparticles in aqueous solution for EOR was investigated for the first time. The dispersion effects of four major classes of surfactants (cationic, anionic, non-ionic, and amphoteric) on TiO2 nanoparticles were compared. When the ultrasonication time was 10 min, the concentration of TiO2 nanoparticles and surfactant was 0.002 and 0.1 wt%, respectively, and the amphoteric surfactant disodium cocoamphodiacetate (CAD) had better dispersion stability for TiO2 nanoparticles compared with other surfactants. The Zeta potential of the CAD/TiO2 dispersion system was −47.53 mV, and the average particle size was 40 nm. Moreover, a nanofluid flooding system of CDEA-CAD/TiO2, with good dispersion stability and remarkable oil displacement performance, was constructed by compounding CAD with the non-ionic surfactant alkanolamide (CDEA). In the core flooding test, the CDEA-CAD/TiO2 nanofluid effectively enhanced oil recovery by 13.3%, which was mainly attributed to the outstanding wettability reversal, interfacial and emulsifying properties of the nanofluid. This study would help further supplement the research on the dispersibility of TiO2 nanoparticles and construct an efficient nanofluid flooding system to enhance oil recovery.