Impact of Spacer Structure on Organic Acids Desorption Efficiency Induced by Gemini Surfactants

Organic acids, together with other polar molecules, constitute the oil-wetting components in crude oil. A commonly adopted understanding is that the adsorption of organic acids leads to the further adsorption of organic materials on the hydrophobic tail groups of the adsorbed organic acid molecules, making the rock surface oil-wet. Although the impact of organic acids in oil-wetting of the rock surface has been unfolded for many different conditions, there are still some questions around the oil-wetting reactions induced by organic acids. A group of in-house synthesized cationic gemini surfactants have been shown effective in altering rock wettability from oil-wet to water-wet conditions. To study the impact of spacer structure on organic acids desorption, experiments were taken to show the impact of the water film in the oil-wetting process of rock by organic acids, and the effectiveness of different cationic gemini surfactants in wettability alteration. SEM and zeta potential experiments were conducted to show the adsorption and desorption of organic acids. Static contact angle measurements were conducted to show the wettability change. Difference in the wettability alteration performance was closely related with the spacer structure. Results showed that polarity of the spacer group is not the only factor that impacts the surfactant's potential in changing rock wettability.