Adsorption of nonionic surfactants in sandstones

Adsorption of surfactants from aqueous solutions in porous media is very important in enhanced oil recovery (EOR) of oil reservoirs because surfactant loss due to adsorption on the reservoir rocks impairs the effectiveness of the chemical slurry injected to reduce the oil–water interfacial tension (IFT) and renders the process economically unfeasible. In this paper, two nonionic surfactants with different ethoxylation degrees were studied, ENP95 with ethoxylation degree 9.5 and ENP150 with ethoxylation degree 15. The experiments were carried out in a surfactant flooding apparatus, with a pressure gradient of 30 psi. The concentration of the injected solutions were 30% above the critical micelle concentration, to assure micelle formation. The results from the flow experiments of surfactant solutions in porous media showed that the adsorption extent was higher for ENP95 than for ENP150 because the previous surfactant has a smaller ethoxylation degree, that is, a smaller polar part.