Adsorption II. Nonequilibrium adsorption of surfactants onto three reservoir cores from the Norwegian Continental Shelf. The effects of clay minerals

Austad, T., Bjorkum, P.A. and Rolfsvag, T.A., 1991. Adsorption II. Nonequilibrium adsorption of surfactants onto three reservoir cores from the Norwegian Continental Shelf. The effect of clay minerals. J. Pet. Sci. Eng., 6: 125-135. Three sandstone cores from different petroleum reservoirs on the Norwegian Continental Shelf have been circulated with a surfactant mixture consisting of ethoxylated sulfonate and the corresponding alcohol for several weeks at 80 degrees C. A fast and a longtime, diffusion-controlled adsorption process has been detected. This process is related to the clay minerals. The kinetics of the diffusion-controlled adsorption process is simulated by a simple first-order rate equation in the available adsorption area. The value of the rate constants are discussed in relation to the mineralogical properties of the kaolinite present in the cores. A diffusion-controlled adsorption mechanism is proposed, suggesting that only surfactant monomers are diffusing through the pore throats of the micropores. Chemical analysis of the surfactant mixture shows that the concentration ratio between the anionic sulfonate and the nonionic alcohol changes during the whole adsorption process. The variation in the concentration ratio can be related to the different core minerals being covered with surfactants at different times.