The CO2-in-water foam stabilized with the mixture of CO2-soluble surfactant and nonionic surfactant

Abstract

In recent years, many studies focused on the foam behavior with CO2-soluble surfactants. However, it would be better if the mixing surfactants solution could increase the foam viscosities further and keep the considerable solubility in CO2 comparing with single CO2-soluble surfactant. In this paper, the synergism of the mixture of CO2-soluble surfactant composed of 2 ethoxylated amine headgroups with cocoalkyl tails (C12NEO2) and nonionic surfactant with high degree ethoxylation (C13EO12) was investigated quantitatively by interfacial tension measurement, including micelles in water phase and monolayer at CO2-water interface. Lower critical micelle concentration (CMC) and negative interaction parameters βσ represented the positive synergism clearly after adding nonionic surfactant to the switchable CO2-soluble surfactant. Importantly, the solubility in CO2 and the foam viscosity in porous media were analyzed comparably to confirm the engineering applicability. Even though the C13EO12 is hard to dissolve in CO2 solely, 0.2 wt% surfactants mixture (C13EO12 proportion was lower than 30%) could dissolve in CO2 absolutely to form transparent single-phase at 60 °C and 16 MPa. Limited to the mixture solubility in CO2, which means that the α(C13EO12) <0.3, the optimum surfactants ratio to get the best foam was C12NEO2:C13EO12 = 8:2, where the bulk foam stability and viscosity increased 1.5 and 2.5 times separately. It was attributed to that the positive synergism leaded to more compact surfactants adsorption layers at the interface, then more stable foam. With increasing brine salinity, the enhancement of foam viscosity diminished to a great extent, while the counter ions in brine could help to get more viscous foam stabilized with C12NEO2 alone.