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CO 2 foam can be used for mobility control and blocking gas breakthrough channels during CO 2 injection for enhanced oil recovery, and specially designed and formulated foam agents are needed to enhance the stability of the foams especially under reservoir conditions. In this study, the performance of CO 2 foams with various surfactants has been investigated, including amide based surfactants (e.g. coconut monoethanol amide (CMEA), lauryl diethanol amide (LDEA)), amine based surfactants (cocoacyl propyl dimethylamine (UC 11 AMPM)), sodium dodecyl sulfate (SDS) and its mixtures with the amides and amines. A visualized high pressure and high temperature foam meter and a sand-pack flooding setup were used to assess the foam's performance, along with the surface tension measurement of the surfactant solutions in the presence of CO 2. The influence of temperature, the surface tension of the aqueous solution, and SDS on CO 2 foam performance of amide and amine based surfactant were investigated. The experimental results indicate that the amide or amine based surfactant alone all show poor foam performance, while their CO 2 foam stability and their mobility control capability can be greatly enhanced at high temperature up to 100 °C with the salinity of 50000 mg/L. After adding SDS to CMEA, LDEA, or UC 11 AMPM, an excellent synergistic effect can be formed among the molecules, which can reduce the surface tensions of individual surfactant solution and enhance the stability of CO 2 foams. • The CO 2 foam performance of amine and amide based surfactants were tested at HTHP conditions. • Stable CO 2 foams can be generated by amine surfactant with SDS at temperature up to 130 °C. • The synergistic effect of amine based surfactant with SDS has been demonstrated for CO 2 foams at high temperature. [ABSTRACT FROM AUTHOR]

Amine-surfactant can be converted to be cationic surfactant in water solution saturated with CO 2 , which can enhance their foaming ability and foam stability, and the foaming ability can be switched off or on by CO 2 or replacing with N 2 with heating, so the amine-surfactants have great potential for smart mobility control to gas channeling during CO 2 flooding. In this study, three alkyl propyl dimethylamines with different carbon chain length (R = 11, 17 and 22, named as UC 11 AMPM, UC 17 AMPM, and UC 22 AMPM, respectively), were investigated as CO 2 responsive foam agent, and their foam performance under static and dynamic condition was tested up to 130 °C and 10.5 MPa using a visualized foam meter and a sand-pack flooding setup. The influence of carbon chain length on bulk solution viscosity, surface activity, foaming ability, and foam quality on bulk foam stability were measured and analyzed. The experimental results indicate that the three amine surfactants all demonstrate well CO 2 responsibility and CO 2 foaming ability, and show well switchable by CO 2 and N 2 at high temperature and high pressure (HTHP) condition. With the carbon chain length increasing, the surfactant shows higher absorption on the foam films, and bulk solution has a higher viscosity, which can decrease de-foam velocity and enhance the foam stability, as a result, the surfactant shows higher mobility control ability. • The CO 2 foam performance of three amine surfactants were tested at HTHP conditions. • The influence of carbon chain length on foam performance, bulk viscosity, surface active and foam quality was analyzed. • Alkyl propyl dimethylamines have well mobility control ability to CO 2 at high temperature-tolerance (up to 130 °C). [ABSTRACT FROM AUTHOR]