Understanding the Cation-Dependent Surfactant Adsorption on Clay Minerals in Oil Recovery

摘要

Surfactants have the ability to mobilize residual oil trapped in pore spaces of matrix rocks by lowering the oil water interfacial tension, resulting in a higher oil recovery. However, the loss of surfactants by adsorption onto the rock surface has become a major concern that reduces the efficiency of the surfactant flooding process. In this study, the adsorption behavior of an anionic surfactant to a clay mineral surface was investigated by quartz crystal microbalance with dissipation monitoring upon variations with different cation conditions. Through recording the change of frequency and dissipation of clay-modified sensors, it allows us to do a real-time quantitative analysis of the surfactant adsorption with nanogram sensitivity. The results revealed that the surfactant adsorption increased in a Ca2+-containing solution with increasing pH from 6 to 11, whereas from a Na+-containing solution, more adsorption occurred at acidic conditions. The adsorbed amount went through a maximum (similar to 200 mM) as a function of the Ca2+ concentration, and the Voigt model suggested that multilayer adsorption of surfactants could be as many as 4-6 monolayers. Using mixed cation (Ca2+ and Na+) solutions, the amount of adsorbed surfactant decreased linearly with decreasing fraction of CaCl2, but Na+ competed for about similar to 30% adsorption sites. The importance of the presence of CaCl2 for the surfactant adsorption was stressed in high-salinity and low-salinity solutions in the presence and absence of Ca2+. Furthermore, increasing the temperature from 23 to 65 degrees C shows first a small increase of surfactant adsorption followed by a reduction of about 20%. The obtained results contribute to a better understanding of surfactant adsorption on clay surfaces and a guide to optimal flooding conditions with reduced surfactant loss.