Enhancing surfactant desorption through low salinity water post-flush during Enhanced Oil Recovery

Low Salinity Water (LSW) incorporates in surfactant Enhanced Oil Recovery (EOR) as a pre-flush is a common practice aiming to reduce the formation salinity, affecting surfactant adsorption. However, in a field implementation, the adsorption of surfactant is unavoidable, thus, a scheme that detaches the trapped surfactant is important. To address this, LSW was considered to enhance the desorption of surfactant. LSW solely formulated from NaCl (1 wt.%), Sodium Dodecylbenzene Sulfonate (SDBS) was chosen as the primary surfactant at its critical micelle concentration (CMC, 0.1 wt.%). Injecting LSW as post-flush achieved up to 71.7% of SDBS desorption that lower interfacial tension against oil to 1.3 mN/m, hence, bring the total Recovery Factor (RF) to 56.1%. This result was 4.9% higher than when LSW injecting as pre-flush and 5.2% greater than conventional surfactant flooding (without LSW). Chemical analysis revealed salinity reduction induced Na⁺ ion adsorption substitution onto pore surface resulting in an increment in surfactant desorption. The proposed scheme resolved the problems of adsorbed surfactant after EOR, and further improve the economic viability of surfactant EOR.