The effect of interfacial tension on CO2 oil-based foam stability under different temperatures and pressures

Abstract

Gas channeling easily occurs in CO2 flooding, leading to lower oil production efficiency. CO2 oil-based foam can effectively control gas channeling, so it is particularly important to study the stability of CO2 oil-based foam to improve oil recovery. In this paper, an oil-based foam system was constructed by evaluating many different surfactants, and then the viscosity of the base oil and the type of gas were changed to study their influence on the stability of the oil-based foam. The stability of CO2 oil-based foam under high temperature and high pressure was analyzed. Finally, the influence of CO2-oil interfacial tension (IFT) on the stability of oil-based foam was investigated. The results show that the CO2 oil-based foam system composed of compound foaming agent FS with a total concentration of 2 wt% and a ratio of FCO-80 to Span 20 of 3:7 and an oil phase with a viscosity of 2.98 mPa·s have excellent foaming performance. In Zones I and II, the CO2-oil IFT is too low, a miscible or near miscible system is formed, and the system cannot generate foam. Although the IFT in Zone III is low, the film’s strength is low, which leads to no foam in the system. The temperature and pressure conditions in zone IV are suitable for an oil-based foam system to generate foam. Under the same foam system, there is a critical CO2-oil IFT at different temperatures, which can be used as a standard to criterion whether the system can foam. This paper has meaningful guiding significance for improving the stability mechanism of CO2 oil-based foam under different temperatures and pressures and controlling gas channeling in the process of CO2 flooding.