Foaming systems for foam flooding with both high foaming performance and ultralow oil/water interfacial tension

In foam flooding ultralow oil/water IFT and superior foaming performance are usually not compatible, because both are achieved by surfactants at different conditions. In this paper we constitute a mixed surfactant system which can achieve both ultralow oil/water IFT and high foaming performance concurrently by means of synergistic effects between different surfactants. Aiming at the reservoir conditions of Daqing oilfield, China (45 degrees C, total salinity 6,778 mg/L, pH = 8-9), a ternary surfactant mixture SDS/DTAB/APG at a mole fraction ratio of 0.36/0.24/0.4 was found to be an optimal surfactant system by which ultralow IFT and high foaming performance could be achieved concurrently at wide total concentrations (2-6.5 mM). Specifically, at a total concentration of 5 mM the IFT can be reduced to as low as 2.9 x 10(-5) mN/m whereas the composite foaming index in the presence of crude oil can reach as high as 936 Ls. The SDS/DTAB binary mixture dominates the mixed monolayer at both air/water and oil/water interfaces as indicated by a high pseudo mole fraction of 0.94. The strong attraction between anionic/cationic surfactants endows densely packed monolayers which are responsible for the achievement of low surface tension and ultralow IFT, whereas the nonionic surfactant APG behaves as a solubilizer of the SDS/DTAB binary mixture in bulk as well as a stabilizer of the bubbles and emulsified oil droplets, which synergistically endows a high foaming performance to the ternary surfactant system. Based on the relevant principle more mixed surfactant systems may be found which are significant for improving efficiency of foam flooding. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This paper proposes a mixed surfactant system that can achieve both ultralow oil/water interfacial tension and high foaming performance simultaneously. Under the reservoir conditions of Daqing oilfield, the ternary surfactant mixture SDS/DTAB/APG was found to be the optimal surfactant system. The study demonstrates that this surfactant system can achieve ultralow interfacial tension and high foaming performance over a wide range of total concentrations.