Synergistic mechanisms of plant derived silica nanoparticles, gemini surfactants and low salinity water in enhanced oil recovery

Carbonate reservoirs pose substantial challenges for enhanced oil recovery (EOR) due to their inherently oil-wet surfaces and complex brine-rock interactions, necessitating environmentally benign yet high-efficiency solutions. To address this, a mechanistically designed ternary nanofluid system was developed, integrating Equisetum-derived nanosilica (NS), a novel cationic gemini surfactant (GS), and sulfate-enriched low-salinity brine (Na₂SO₄) to achieve multi-scale interfacial modification. Experimental procedures included comprehensive physicochemical characterization of the components, zeta potential and adsorption analyses, interfacial tension (IFT) measurements, contact angle (CA) evaluation, and spontaneous imbibition tests under controlled salinity conditions. Zeta potential results showed tunable surface charge from approximately - 70 mV to + 30 mV through sulfate-mediated adsorption and double-layer compression. The optimized ternary formulation achieved ultralow IFT of 0.51 mN/m at 5500 ppm Na₂SO₄ and significant wettability alteration with CA reduction from 138° to 34° at 2000 ppm Na₂SO₄. Langmuir adsorption modeling confirmed cooperative binding between NS and T14S3, and spontaneous imbibition demonstrated that the 2000 ppm Na₂SO₄ blend recovered 25.4% of OOIP, over twice the baseline brine performance. These results confirm that wettability alteration becomes the dominant recovery mechanism once IFT reaches the sub-1 mN/m range. The integration of NS, bio-based polymers, and low critical micelle concentration (CMC) GSs offers a potentially scalable and environmentally conscious framework for EOR, aligning with principles of resource efficiency and long-term reservoir management.