Stability and Flow Properties of Oil-Based Foam Generated by CO2

Foam flooding is an important method used to protect oil reservoirs and increase oil production. However, the research on foam fluid is generally focused on aqueous foam, and there are a few studies on the stability mechanism of oil-based foam. In this paper, a compound surfactant consisting of Span (R) 20 and a fluorochemical surfactant is determined as the formula for oil-based foam. The foam volume and half-life in the bulk phase are measured to be 275 mL and 302 seconds, respectively, at room temperature and atmospheric pressure. The stability mechanism of oil-based foam is proposed by testing the interfacial tension (IFT) and interfacial viscoelasticity. The lowest IFT of 18.5 mN/m and the maximum viscoelasticity modulus of 16.8 mN/m appear at the concentration of 1.0 wt%, resulting in the most-stable oil-based foam. The effect of oil viscosity and temperature on the properties of oil-based foam is studied. The foam stability increases first and then decreases with the rising oil viscosity, and the stability decreases with rising temperature. The apparent viscosity of oil-based foam satisfies the power-law non-Newtonian properties, and this viscosity is much higher than that of the phases of oil and CO2. The flow of oil-based foam in porous media is studied through microscopic-visualization experiments. Bubble division, bubble merging, and bubble deformation occur during oil-based-foam flow in porous media. The oil-recovery efficiency of the oil-based-foam flooding is 78.3%, while the oil-recovery efficiency of CO2 flooding is only 28.2%. The oil recovery is enhanced because oil-based foam reduces CO2 mobility, inhibits gas channeling, and improves sweep efficiency. The results are meaningful for CO2 mobility control and for the application of foam flooding for enhanced oil recovery (EOR).