Novel Foam Stabilized by Fatty Amine Polyether Carboxylate and AOS Binary Blend for Enhanced Oil Recovery

A novel fatty amine polyether carboxylate (RNEC) surfactant with dicarboxylate groups is designed as a foam booster to enhance alpha-olefin sulfonate (AOS) surfactant foam properties for enhanced oil recovery in order to increase gas or steam sweep efficiency under high-temperature conditions. Compared with AOS only, an AOS/RNEC binary blend can generate stronger foam faster at 80-150 degrees C in sandpack. The foam strength can be improved with the addition of inorganic salts, and good foam performance is maintained over a wide range of salinity between 5791 and 65 255 mg/L and divalent ion concentration between 110 and 3140 mg/L. Three factors lead to the generation of strong foam by the AOS/RNEC binary blend in porous media. First, the salt tolerance of AOS is improved significantly by adding the RNEC foam booster. Second, a greatly negative zeta potential for AOS/RNEC reduces surfactant adsorption and retardation on the silica sand. More importantly, lower surface area and lower critical micelle concentration (CMC) of AOS/RNEC compared with AOS itself lead to more surfactant molecules adsorbed at the gas-water surface. As a result, foam can propagate further in porous media, even in low surfactant concentrations. Third, an intermolecular attraction between AOS and RNEC leads to the formation of a compacted monolayer, thereby increasing the film thickness and improving the viscoelasticity of the foam. Surface thickness is increased from 2.05 nm for AOS to 2.85 nm for the surfactant blend. Meanwhile, the hydrophobic chain of the blend is oriented more perpendicular to the surface, with tilt angles of 33 degrees from the view of the molecular level. The compacted and ordered arrangement of the surfactant molecules at the surface improved the dilatational modulus and surface viscosity by 2.5 times and 1.7 times at an oscillation frequency of 0.1 Hz, respectively. As a consequence of the enhanced film properties, the foam generated by the AOS/RNEC binary blend is more stable and efficient during flowing in porous media.