Design of CO2 -in-Water Foam Stabilized with Switchable Amine Surfactants at High Temperature in High-Salinity Brine and Effect of Oil

The design of surfactants for CO2-in-water (C/W) foams in carbonate reservoirs above 100 degrees C has been limited by thermal instability of surfactants, surfactant adsorption to mineral surfaces, and challenges in generating and stabilizing the foams. Here, we have identified a diamine surfactant, C12-14N(CH3)C3N(CH3)(2) (Duomeen CTM), with good thermal stability (>1 month at 135 degrees C), that stabilizes viscous C/W foam with an apparent viscosity of up to similar to 35 cP at 120 degrees C in 22% total dissolved solid (TDS) brine. Strong foams with excessively high viscosity were reported to be generated with longer-tailed C16-18N(CH3)C3N(CH3)(2) (Duomeen TTM) that formed a viscoelastic aqueous phase. Here, the tail length was shorter for C12-14N(CH3)C3N(CH3)(2) and thus a viscoelastic aqueous phase was not formed, resulting in a weaker CO2 foam with a more appropriate viscosity for the proposed applications. Moreover, at the lowest superficial velocity studied (4 ft/day), the apparent viscosity for C12-14N(CH3)C3N(CH3)(2) was similar to 20 fold lower than that of C16-18N(CH3)C3N(CH3)(2), consistent with the lower viscosity for the aqueous phase. Not only the foam viscosity with C12-14N(CH3)C3N(CH3)(2) was high enough for CO2 mobility control in enhanced oil recovery (EOR) but also it was low enough to be more favorable with regard to the injection pressure than the excessive high flow resistance associated with C16-18N(CH3)C3N(CH3)(2). In addition, viscous C/W foam was maintained at low fractions of dodecane (model oil) and broke in the presence of large fractions of dodecane, both of which are beneficial to EOR. The oil/water (O/W) emulsions formed with C12-14N(CH3)C3N(CH3)(2) were unstable and broke in 30 min, and the O/W partition coefficient depended greatly on pH at 120 degrees C in 22% TDS brine. All of these factors suggest that the surfactant C12-14N(CH3)C3N(CH3)(2) is a good candidate for further evaluation and scale up for CO2 EOR, CO2 sequestration, and hydraulic fracturing at high salinities and temperatures.