Adsorption VII. Dynamic adsorption of a dual surfactant system onto reservoir cores at seawater salinities

The adsorption of a dual surfactant system of the type nonylphenyl-6-ethoxy-sulfonate (6EOS) and dodecyl-benzene-sulfonate (DDBS) in the mole ratio of 1:1 has been studied by: (a) static adsorption onto kaolinite, (b) nonequilibrium long-term dynamic adsorption on a reservoir core, and (c) dynamic slug injection in a Berea core. The studies were conducted at 70 °C using artificial seawater. The corefloods were performed at residual oil saturation. The static adsorption of the mixture showed that DDBS adsorbed more strongly than 6EOS at surfactant concentration below the CMC. The plateau adsorption appeared to be quite similar, but significantly higher than for pure 6EOS. The long-term dynamic study was conducted by circulating the dual surfactant solution through the core for 16 weeks, and the slug injection was performed by injecting 0.5 PV of the surfactant mixture followed by a xanthan solution. In both cases it appeared to be a selective adsorption until the surfactant mixture, forming the most stable micelles, was obtained. Further adsorption at surfactant concentration above the CMC seems to be governed by a linear relationship between the two surfactants. Possible impacts on surfactant flooding, using dual surfactant mixtures of this type, are discussed.