Adsorption analysis of natural anionic surfactant for enhanced oil recovery: The role of mineralogy, salinity, alkalinity and nanoparticles

Anionic surfactants are widely used as an effective chemical for enhanced oil recovery because of their unique characteristics of reducing interfacial tension (IFT) between the trapped crude oil and water, and alteration of wettability of reservoir rock from oil-wet to water-wet. However, the loss of surfactant by adsorption onto the solid rock surface is a major concern that reduces the efficiency of the surfactant flooding process and must be considered while designing the process. Present study highlights the equilibrium adsorption and kinetics of an anionic surfactant synthesized from soap-nut fruit on sandstone, carbonate and bentonite clay as representative of reservoir rocks. The mineralogy and morphology of the rocks were investigated by FE-SEM, XRD and BET surface area analysis. UV-Visible spectroscopy was used to measure the amount of surfactant adsorbed on solid rock/clay surface in batch experiments. The experimental equilibrium adsorption data were analyzed by using Langmuir, Freundlich, Temkin and Redlich-Peterson isotherm models and adsorption parameters were calculated. Adsorption kinetics of the surfactant system were studied and pseudo second order kinetic model was best fitted for the surfactant/rock/clay systems. Presence of salt was found to increase surfactant adsorption on rock/clay marginally. However, presence of alkali and nanoparticles was found to reduce the loss of surfactant by adsorption and shows synergistic effects on IFT reduction, which is beneficial for application of the surfactant in oil recovery. The findings of the study are quite helpful in proper designing of the surfactant flooding for enhanced oil recovery.