Interfacial Activity and Surface Behavior of Oleic Acid-Based Surfactants for Improved Oil Recovery in Sandstone Reservoirs

Abstract

This study presents a comprehensive evaluation of two newly designed oleic acid–derived surfactants (SMP-02 and SMP-04) in combination with natural polymer (guar gum) for Enhanced Oil Recovery (EOR) applications. The surfactants possess very good thermodynamic and surface characteristics with Gibbs free energy of adsorption (ΔGads) higher than that of micellization (ΔGmic), favoring interfacial adsorption over bulk micellization. Evaluation of key EOR parameters, including interfacial tension, emulsification, and wettability alteration, revealed that the surfactants reduced crude oil–water IFT to 0.36 mN/m for SMP-02 and 0.11 mN/m for SMP-04 at their respective critical micelle concentrations and an optimal salinity of 1 wt %. Both surfactants formed stable emulsions at the optimal salinity and effectively converted oil-wet rock surfaces to water-wet. Microscopic and DLS analyses of SMP-04 emulsions revealed good colloidal stability and a reduced particle size, thereby enhancing pore-scale mobility. Rheological studies of emulsions revealed pseudoplastic shear-thinning behavior that increased reservoir injectivity. Lower adsorption of both surfactants onto the rock surface proved their economic viability for EOR application. The SMP-04-guar gum formulation delivered superior tertiary recovery, achieving 29.39% OOIP with a residual oil saturation of 14.35% in core-flooding tests, confirming that optimized surfactant–polymer systems markedly enhance sweep efficiency and oil recovery in heterogeneous sandstone reservoirs.