Retention Of Foam-Forming Surfactants At Elevated Temperatures

Abstract

Abstract There is considerable interest in the use of foam-forming surfactants for mobility control in steamfloods. To provide effective mobility control, the injected surfactant must propagate from the injection well toward the production well. One of the important parameters affecting foam propagation through the reservoir is the retention of surfactant due to its adsorption on reservoir rock. Because the foam encounters a range of temperatures and salinities between the injection and production wells, it is necessary to evaluate the temperature and salinity dependence of surfactant adsorption. This paper reports on the results of adsorption measurements an elevated temperatures for two typical commercially available surfactants currently in use for such applications an alpha olefin sulphonate and a synthetic alkyl toluene sulphonate. Adsorprion experiments were performed in unconsolidated sand cores of temperatures ranging from 50 °C to 150 °C The role of clays in surfactant adsorption was investigated by comparing the results obtained in clean sand with those obtained in cores containing known amounts of clays. Surfactant adsorption was de/ermined from surfactant concentration profiles at the core outlet. This analysis can be used for evaluating the whole adsorption isotherm provided a specific adsorption model (for example, the Langmuir isotherm) is assumed. Automatic history matching procedures for that purpose were tested and their efficiency evaluated. The results show that adsorption of both surfactants in clean sand is relatively low and decreases with increasing temperature. The alkyl toluene sulphonate was found to adsorb more than the alpha olefin sulphonate, and its adsorption was more strongly affected by salinity. The presence of clays in the core resulted in increased surfactant adsorption. Introduction The injection of foam-forming surface active agents in steamflooding applications has the potential for improving the performance of this enhanced oil recovery (EOR) process by two mechanisms. It can improve conformance by reducing steam mobility in the steam zone, and it can increase the oil displacement efficiency in the swept zone. Irrespective of which mechanism is dominant, for economic reasons it is desirable to inject the lowest surfactant concentration which is still effective in improving oil recovery. The rate of propagation of dilute surfactant solutions through the reservoir may be strongly affected by adsorption of the injected surfactant on reservoir rock surfaces. Thus the evaluation of surfactant adsorption should always be included when assessing the effectiveness of the surfactant in improving steamflood performance. As the injection of steam may result in large temperature and salinity gradients in the reservoir, a complete evaluation of surfactant adsorption requires its measurement over a wide range of temperatures and salinities. This paper describes the results of adsorption measurements for two types of commercially available foam-forming surfactants, an alpha olefin sulphonate and a synthetic alkyl toluene sulphonate. Adsorption of these two surfactants in unconsolidated cores saturated with either distilled water or a lowsalinity synthetic brine was evaluated at three temperatures. The solid used in the study was either a clean silica sand or a mixture of the sand and one of two types of pure clays montmorillonite and kaolinite.