Adsorption reduction of a gemini surfactant on carbonate rocks using formic acid: Static and dynamic conditions

Surfactant flooding improves oil recovery by lowering the interfacial tension and/or altering the reservoir rock's wettability. However, surfactant losses caused by adsorption on the surface of the rock weaken the efficiency of this chemical enhanced oil recovery process. This study focuses on reducing the adsorption of a cationic gemini surfactant on carbonate rocks using formic acid. High-performance liquid chromatography integrated with an evaporative light scattering detector was employed to quantify both static and dynamic surfactant adsorptions. The results showed that the surfactant's adsorption on carbonate rocks was reduced dramatically by adding 1% formic acid to the surfactant solution. Static adsorption was reduced from 2.44, 1.62, and 1.51 mg/g-rock to 0.16, 0.14, and 0.13 mg/g-rock on Guelph dolomite, Guff dolomite, and Indiana limestone, respectively. The dynamic adsorption of the surfactant on Indiana limestone was reduced from 0.269 to 0.041 mg/g-rock. It is believed that the carboxyl group released by the formic acid-rock reaction shields the surfactant from the rock surface resulting in lower adsorption. This is evidenced by the surfactant solution's pH dropping below the point of zero charge of the rock, causing the repulsion of the cationic surfactant molecules off the surface. This study provides a low-cost option that provides a remarkable reduction in cationic surfactant adsorption on carbonate rocks.