Green Gemini Surfactants from Glycine Max for Enhanced Oil Recovery Under Harsh Reservoir Conditions

Objectives Surfactants are widely used in enhanced oil recovery (EOR) for reducing interfacial tension (IFT), altering wettability, and improving displacement efficiency. However, conventional surfactants suffer from poor stability at elevated temperatures and high salinity. This study reports the synthesis of sustainable Gemini surfactants from Glycine max (soybean), engineered for stability in harsh reservoirs. Structural variations were systematically evaluated to determine their effect on IFT reduction, wettability alteration, adsorption behaviour, emulsion stability, and oil recovery performance. Methods Two nonionic Gemini surfactants were synthesized using soybean oil with systematically varied spacer groups. The chemical structure of the synthesized Gemini surfactants was confirmed by FTIR. Surface activity was evaluated through the determination of critical micelle concentration (CMC), micellization thermodynamics, and interfacial studies with crude oil. IFT was measured under variable temperature and salinity. Emulsion stability tests were conducted under high-temperature conditions. Wettability alteration was quantified using contact angle measurements on sandstone and carbonate, while surfactant adsorption on both rock samples was determined to assess retention. Core flooding experiments were conducted using the SoyGS-TETA to assess actual oil recovery performance in both sandstone and carbonate core samples. Results and Observations The synthesized Gemini surfactants exhibited strong surface activity with low CMC values (0.223-0.278 mmol/L) and significantly ultra-low IFT values, which are sufficient to mobilize capillary-trapped oil. IFT remained significantly low (in the range of ~10−3 mN/m), even at elevated salinity levels of 15 wt% NaCl and temperatures of up to 90°C, applied for 7 days. Emulsion studies demonstrated the formation of stable emulsions to support effective displacement. Wettability alteration rapidly shifted contact angles from ~121° to ~20° within 1200 seconds. Adsorption values were low (0.74-0.93 mg/g), supporting efficient transport through porous media. Core flooding experiments demonstrate substantial incremental oil recovery, 31.1% and 29.6% of the original oil in place (OOIP), in sandstone and carbonate cores, respectively. These findings validate the potential of the synthesized Gemini surfactants for EOR under harsh reservoir environments. Novelty This study introduces novel Gemini surfactants derived from soybean with tuneable structural features that enable performance optimization under harsh reservoir conditions. The ability to achieve ultra-low IFT, rapid wettability alteration, low adsorption, and OOIP tertiary recovery establishes these surfactants as next-generation candidates for sustainable EOR. This work contributes a practical pathway toward environmentally responsible oil recovery in challenging reservoirs, also aligns with industry goals, and is naturally derived, reducing the chemical footprint.