Optimization and effectiveness of the extended amphoteric-Gemini surfactant combination flooding for low-permeability reservoirs

Addressing the issue of low oil recovery in low-permeability reservoirs, the prepared extended amphoteric surfactant (C12P3E3NS) was combined with Gemini surfactants (C14-3–14) to form an optimized formula. The surface tensions, examined by a surface tensiometer, were determined to obtain the mixtures with C12P3E3NS mole fractions of 40% (named C23) and 50% (named C11), exhibiting stronger synergistic effect. The interfacial tensions (IFTs) of two mixtures, determined by an interfacial tensiometer, can reach ultra-low level (10−3 mN·m−1) at 10 wt.% salinity. Meanwhile, the emulsification ability of C23 with smaller emulsion droplet size is better than that of C11 due to its larger Zeta potential value, measured by a Zeta potential instrument, and interfacial film's strength, obtained by an automated drop tensiometer. Additionally, the wettability of slice surface, obtained by a contact angle measuring instrument, can be altered by surfactant mixtures from oil-wet to water-wet due to the removal of oil and covering of surfactants, thus conducive to stripping the residual oil and transforming the capillary resistance to driving force. Due to the synergistic effect of ultra-low IFT, wettability alteration ability, and emulsification, the depressurization rate of C23, across the coreflooding experiment, is 10.3% and its corresponding oil recovery factor is 12.2%, which are larger than those of C11. These results show that the extended amphoteric-Gemini surfactant combination can provide an alternative approach in low-permeability reservoirs.