Fatty alcohol polyoxyethylene ether sulfonate for foam flooding in high-salinity and high-temperature reservoir conditions

Abstract Foam flooding can significantly improve the sweep efficiency of gas flooding by avoiding or weakening gas segregation, viscous fingering and gas channeling through areas of high permeability. However, most conventional anionic surfactants are not suitable to be used as foaming agents due to low tolerance to either high salinity or high temperature. In this paper, an anionic-nonionic combined surfactant, fatty alcohol polyoxyethylene (3) ether sulfonate (AEO3-HS) was synthesized, and its foaming performances at different conditions were examined. The results show that the foaming performance of the AEO3-HS is sensitive to crude oil which behaves as a defoaming agent. But this can be improved by mixing with cetyl dimethyl hydroxypropyl sulfobetaine (C16HSB). In mild reservoir conditions such as dissolved in simulated Daqing connate water (45 ℃, total salinity of 6778 mg/L, pH = 8–9) the AEO3-HS/C16HSB binary mixture at an optimal mole fraction ratio (0.6/0.4) and an optimal total concentration (4 mM) gives the maximum composite foaming index of 1100 Ls by shaking 10 mL solution with 0.25 g oil in a 100 mL cylinder. Moreover, the AEO3-HS/C16HSB binary mixture is well soluble in brine with 5000 mg/L CaCl2 + 100,000 mg/L NaCl at 60 °C, and does not hydrolyze in aqueous solution when stored at 90 °C for 3 months. In addition, the AEO3-HS and C16HSB molecules show attraction in mixed monolayer and the crude oil can be easily emulsified as small oil droplets dispersed in foaming solution during foaming process, which ensures the stabilization of the pseudo-emulsion films and thereby the foam stability in the presence of crude oil. The AEO3-HS synthesized is therefore a good candidate as foaming agent for high salinity and high temperature reservoirs.