Influence of salinity and hardness on the static adsorption of an extended surfactant for an oil recovery purpose

Injection of surfactants solutions is the most promise in chemical oil recovery method for the reduction of the remaining oil in a reservoir at the end of its exploitation. Surfactant adsorption in a porous media is one of the main issues because an important amount of surfactant tends to adsorb on the surface of the grains of sand and clay, and this can limit its capacity of reducing the interfacial tension. In this work, the effect of the concentration of monovalent and divalent ions on adsorption was investigated, since most reservoirs connate waters exhibit different degrees of salinity and hardness. For this systematic study, experimental adsorption assessments were performed using aqueous solutions of an alcohol propoxy sulfate surfactant. The results show that by changing the surfactant concentration, salinity, or hardness of the water, the adsorption behavior was not monotonic, as suggested by the Langmuir or Freundlich adsorption isotherms models. This behavior demonstrates that the adsorption phenomenon is affected by many parameters of a reservoir that are not considered deeply in traditional kinetics models and must be studied more carefully, especially the effect of electrolytes.