Synergistic Application of a Plant-Derived Surfactant and CO ₂ Foam for Enhanced Oil Recovery: Linking Interfacial Phenomena to Core-Scale Performance

Externally pregenerated CO2 foam is a promising approach for improving sweep efficiency in enhanced oil recovery (EOR) while enabling subsurface CO2 utilization. In this study, the stability and displacement efficiency of externally generated CO2 foam stabilized by the plant-derived surfactant (Acacia concinna) were investigated through core-scale flooding experiments under simulated reservoir conditions. Berea sandstone cores (porosity 10–11.6%, permeability 97–488 mD) were subjected to sequential surfactant flooding followed by CO2 foam injection at 50 °C and 100 psi injection pressure. Surface and interfacial characterization showed that the natural surfactant reduced surface tension from 72 to 12.11 mN/m and decreased oil–water interfacial tension from 3.5 to ∼2.1 mN/m, facilitating improved oil mobilization. Wettability measurements revealed a transition from oil-wet (94.98°) contact angle to near water-wet conditions (34.87°) at higher surfactant concentrations. Core-flooding results showed that secondary water flooding recovered 50–54% of the original oil in place (OOIP), while tertiary surfactant flooding provided an additional 10–21% OOIP recovery. Subsequent CO2 foam flooding further enhanced displacement efficiency, resulting in cumulative oil recovery of up to 89.7% OOIP at an optimal surfactant concentration of 1.5 wt %. The externally generated foam system improved sweep efficiency by delaying gas breakthrough and increasing pressure differentials across the core. Furthermore, a dimensionless correlation based on the Buckingham Pi theorem was developed to predict surfactant-driven oil recovery trends, yielding excellent agreement between experimental and predicted values (R2 = 0.995). The results demonstrate that Acacia concinna functions as an environmentally benign surfactant capable of stabilizing CO2 foam and enhancing oil recovery, offering a scalable and sustainable alternative to conventional synthetic surfactant systems for mature sandstone reservoirs.