The Rheological Enhancement of an Internal Olefin Sulphonate Surfactant upon Interactions with Cationic Surfactants...

Enhanced oil recovery (EOR) methods traditionally rely on polymer solutions to improve viscosity and elasticity; however, their effectiveness is limited under high-temperature, high-salinity, and high-shear conditions, leading to elevated operational costs. Anionic/cationic formulations have been studied in terms of interfacial tension reduction for EOR applications. This study presents a novel approach to EOR by enhancing the rheological properties of an anionic internal olefin sulfonate surfactant through interactions with cationic surfactants, eliminating the need for polymer molecules. This research demonstrates that cationic surfactants can induce micellization changes, resulting in substantial viscosity enhancement and viscoelasticity development. The effect is found to depend on the hydrocarbon chain length and concentration of the cationic surfactants, with longer chains yielding higher viscosity and more pronounced non-Newtonian behavior. Additionally, this study reveals that the addition of NaCl alters micellar organization, with the order of component additions playing a critical role in rheological performance. This kinetic-dependent micellization behavior, rarely explored in EOR applications, highlights the potential of counterion surfactants as viscosity enhancers in surfactant-based flooding processes. Oscillatory rheology confirms that cationic/anionic surfactant systems in this study exhibit stable viscoelastic behavior, making them potentially more suitable for harsh reservoir environments than polymer-based EOR fluids. These findings open new avenues for the development of cost-effective and tailored surfactant formulations, offering an alternative to polymer solutions under challenging reservoir conditions.