Enhanced stability and high temperature-tolerance of CO2 foam based on a long-chain viscoelastic surfactant for CO2 foam flooding

CO2 switchable foams have gained increasing attention recently for their smart properties. However, their performance at high temperature and high pressure has been less documented. In this study, a long-chain viscoelastic surfactant, N1-(3-aminopropyl)-N3-octadecylpropane-1,3-diamine bicarbonate (ODPTA) has been studied as a CO2 foam agent for its application in CO2 flooding in complex and harsh reservoir conditions, and the foam performance under static and dynamic conditions was tested up to 160 degrees C and 10.5 MPa using a visualized foam-meter and in sand-pack flooding experiments. The viscosity of the ODPTA and conventional surfactant solutions saturated with dissolved CO2 was measured using a long coiled-tube viscometer at HTHP, and its effect on the high temperature-tolerance of CO2 foams has been analyzed. The experimental results show that CO2 foam generated using ODPTA is much more stable than the conventional surfactants (such as SDS and alkylphenol ethoxylates) and has high temperature-tolerance up to 160 degrees C, and has also exhibited excellent mobility control in CO2 flooding experiments. The viscosity of the ODPTA-CO2 bulk phase can be maintained as high as 12 mPa s under 160 degrees C and 10.5 MPa, which is much higher than that of the conventional surfactant solutions (similar to water). ODPTA's good foam performance with extremely high temperature-tolerance can be attributed to its high bulk phase viscosity in the brine water saturated with CO2.