CO2 in water foam stabilized with CO2-dissolved surfactant at high pressure and high temperature

The CO2 flooding is a popular method for enhanced oil recovery, even though viscous fingering and gravity override always reduce the displacement efficiency. Foam agent can improve the gas sweep efficiency depending on foamability and foam stability, but harsh conditions destroy foam performance seriously. In this paper, tallow ethoxylated amine surfactants are used to generate and stabilize CO2 foam at high pressure and high temperature. Meanwhile, the surfactant solubility in CO2, aqueous phase behavior, bulk foam stability and apparent viscosity in porous media were presented in detail. C16-18 N(EO)(5) can be soluble easily in CO2 with low cloud pressure and solubility comes up to 0.5 wt% without co-solvents, which is much higher than CMC and enough for stabilize foam at 20 MPa and 80 degrees C. High pressure and temperature is favorable for surfactant solubility in CO2 from the cloud pressure results and protonated quaternary amine group can ensure C16-48 N(EO)(5) dissolved in high salinity brine saturated with CO2 at 120 degrees C. From the results of bulk foam half-life, the foam stability stabilized with C16-18 N(EO)(5) was better than C12-14 N(EO)(5) at same conditions and higher salinity could enhance foam stability since counter irons decrease repulsion of surfactant head groups. In porous media, high foam apparent viscosities, up to 120 mPa s at 80-90% foam quality, demonstrated the tallow ethoxylated amine would be an alternative foam agent at high pressure and high temperature. Strong foam can form with fewer injecting volume when surfactants were injected with CO2 phase, ensure the surfactants could utilize more efficient to stabilize foam. Therefore, injecting C16-18 N(EO)(5) into underground with CO2 phase would be useful method to decrease gas mobility with forming stable foam in situ with residual water in reservoir.