Reducing adsorption of anionic surfactant for enhanced oil recovery: Part I. Competitive adsorption mechanism

•Competitive adsorption of sodium polyacrylate and anionic surfactant is studied.•As Mw of polyacrylate increases, adsorption of surfactant decreases.•Above Mw of 4500Da, no decrease in adsorption of surfactant is observed.•Data are interpreted by low desorption and high surface coverage of polyacrylate. Although injection of surfactants in oil reservoirs often can lead to production of more oil, loss of surfactant due to adsorption on porous media can make this process economically unfeasible. In this work, we examine the adsorption of an anionic surfactant blend and sodium polyacrylate on dolomite and demonstrate that, under certain conditions, the sodium polyacrylate adsorbs preferentially and inhibits the adsorption of surfactant. The addition of sodium polyacrylate significantly reduces the amount of surfactant adsorption above a critical polyacrylate molecular weight. On the other hand, presence of anionic surfactant has no significant effect on the adsorption of polyacrylate. We also demonstrate high concentrations of anhydrite acts against preferential adsorption of sodium polyacrylate. This study demonstrates that polyacrylate molecular weight and concentration as well as polyacrylate-to-anhydrite molar ratio are key variables governing the competitive adsorption of anionic surfactant and polyacrylate, which are interpreted by negligible desorption and high surface coverage of polyacrylate.