Measurements of Surfactant Adsorption on Sandstone in the Presence of Deep Eutectic Solvents

How to reduce surfactant adsorption on a rock surface is a challenging task because surfactant adsorption would negatively affect the performance of surfactants in enhanced oil recovery. This study thoroughly investigates the effects of various deep eutectic solvent (DES) samples on surfactant adsorption. The surfactant adsorption amounts are quantitatively determined by measuring the variations in the surface tensions of surfactant solutions before and after the adsorption experiments. First, the surface tensions of various pure DES solution samples at different concentrations are measured. The results suggest that the prepared DES samples cannot alter the surface tension of water. Then, the surface tensions of various pure surfactant solutions with different concentrations are measured to build the relationship between surface tension and surfactant concentrations. Afterward, the adsorption experiments are conducted by mixing the crushed Berea sandstone samples with the pure surfactant solutions and the composite DES-surfactant solutions. Next, the surface tensions of the supernatants separated from the mixtures are measured. Correspondingly, the surfactant adsorption amounts are back-calculated from the built relationship between the surface tension and surfactant concentration. The results demonstrate that the DES samples prepared in this study can inhibit the adsorption of the three surfactants on the rock surface. Among all the tested DES samples, the DES sample of choline chloride (ChCl)/urea (1:2) has the most promising performance in inhibiting the adsorption of the surfactant of petroleum sulfonate on the rock surface. Finally, two dynamic adsorption experiments further prove that surfactant adsorption on sandstone particles can be inhibited by adding DES samples.