LAUSR

Abstract Chemical flooding, one of the Enhanced Oil Recovery (EOR) techniques used to increase oil production, consists in the injection in the well of an aqueous formulation containing various chemical additives such as surfactants. However, its performance can be significantly altered by the loss of surfactants in reservoir rocks. More precisely, surfactant loss due to adsorption on the reservoir rock may have a non-negligible impact on the efficiency of the injected formulation. In this article, we considered the adsorption of a mixture of two anionic surfactants having an important industrial relevance for EOR applications. Adsorption was studied on silica, representative of reservoir rocks such as sandstone, by combining Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and neutron reflectivity experiments. A preliminary characterization of the surfactant mixture solution demonstrated the formation of unilamellar vesicles in the bulk. Whereas an adsorbed layer was measured with the single AOT vesicles, but not with the SDBS micelles, we observed that mixing both anionic surfactants change the adsorption phenomenon. Indeed, non-negligible adsorption was measured for the mixture even at concentrations where only slight adsorption had been observed with the individual surfactants. This suggests that the structure of the aggregates formed in the bulk has a non-negligible impact on the adsorption. We note that the addition of salt tends to enhance the adsorption by screening the repulsive interactions between both negatively charged surfactants and silica at neutral pH. The present work provides new insights into the description of the adsorption of a mixture of surfactants of same nature in unfavorable conditions.