Adsorption characteristics of surfactants on different petroleum reservoir materials

The loss of injected chemical(s) in the reservoir during injection due to the adsorption of the surfactant (and co-surfactants) unto the rock materials weighs heavily on the economics and environmental footprint of the process and remains a focus of research attention. It is necessary that the surfactant loss in the reservoir during injection is minimized to improve on the process economics and ensure its wider application. In this study the adsorption of cationic and anionic surfactants onto the common reservoir rock material and drilling mud weighing agent is investigated at various surfactant concentration and salinity. The effect of pH was also studied by formulating an alkaline-surfactant mixture using various concentration of NaOH. The indirect method of residual equilibrium surfactant concentration measurement was employed to obtain the adsorption isotherm of cetyltrimethyl-ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on kaolin, silica, alumina and ilmenite. Surfactant concentration was varied from 50-600 ppm and the conductivity of the equilibrated media at room temperature is measured at various brine concentration and pH. Both surfactants were found to adsorb strongly onto the rock materials while stabilization in the level of adsorption in the region above the CMC was observed as the monomer concentration falls due to micelles formation. At same level of salinity, it was found that cationic surfactant adsorbed more strongly on the rock materials that the anionic surfactant. The volume adsorbed was found to increase up to a maximum of 1.170 mg/g and 1.8249 mg/g for SDS and CTAB respectively on kaolin and ilmenite for instance, as the concentration was increased at constant salinity. The same trend was noted as the brine concentration was varied with adsorption increasing with salinity for anionic surfactant. As pH increases the volume adsorption for SDS decreases while the opposite was the case with the cationic surfactant, CTAB which increase with the alkalinity of the solution