Mechanistic evaluation of static and dynamic adsorption of Brassica juncea derived gemini surfactants: implications to enhanced oil recovery

Abstract

The adsorption of surfactants onto reservoir rock surfaces significantly affects the efficiency of enhanced oil recovery (EOR), as high retention reduces the effective concentration of surfactants during flooding. In the present study, the adsorption behaviour of synthesized Gemini surfactants (GS) on sandstone and carbonate rocks was evaluated using UV-vis spectroscopy under static and dynamic conditions. Equilibrium isotherm and kinetic models were applied to interpret the adsorption trends and assess the governing adsorption pathways. FESEM-EDX was employed to assess surface morphology and elemental mapping, while zeta potential measurements indicated charge modification. The static adsorption results showed that surfactant retention systematically decreased with increasing spacer length, indicating reduced packing efficiency for longer spacer Gemini structures. Dynamic adsorption shows very low surfactant retention, with maximum adsorption capacities of 0.013 mg g⁻¹ for sandstone and 0.0087 mg g⁻¹ for carbonate using Hexamine GS. Excessive surfactant adsorption during flooding causes chemical loss, but controlled surface adsorption is necessary for wettability alteration, as it facilitates a shift from oil-wet to water-wet conditions, thereby enhancing oil recovery. In this study, wettability alteration was investigated by measuring contact angles. Hexamine GS reduced contact angles by approximately 81% within a few minutes, accompanied by an efficient transition from an oil-wet to a water-wet state. Overall, the findings provide model-supported insight into spacer-length-dependent adsorption behaviour and highlight the potential of these bio-derived Gemini surfactants to minimise surfactant loss and improve wettability control in chemical EOR applications.