Effect of temperature on the stability of supercritical CO2 foam stabilized with a betaine surfactant at high pressure

Abstract

Aiming at improving the thermal stability of CO2 foam under reservoir conditions, four different types of surfactants were evaluated through high temperature and pressure foaming apparatus. Supercritical CO2 (SC-CO2) foam stabilized with betaine surfactant EDSB has best stability among the surfactants. Effect of temperatures on CO2 foam properties were investigated and the stabilization mechanism of foam film was explored through molecular dynamics simulation. The results showed that the apparent viscosity in the capillary tube was up to 30 mPa·s at 15 s−1 at 120 ℃ and the resistance factor was up to 40 in the core. EDSB stabilized CO2 foam had lower C/W interfacial tension (IFT) due to the regular and tight molecular arrangement at the C/W interface. Covalence rate of CO2 foam stabilized with EDSB was lower than SDS at high temperature, which was attributed to large numbers of hydrophilic headgroups of EDSB molecule including sulfo groups, amino group and ethoxyl groups. They can bond more water molecules, forming thicker film than SDS. EDSB surfactant was also more difficult to be desorbed from the C/W interface than SDS, thereby further improving the foam film stability. The findings of this study can help for better understanding of the stabilization mechanism of CO2 foam film and optimizing the appropriate CO2 foam agents at high temperature.