Optimum phase type and optimum salinity profile in surfactant flooding

According to the conventional concepts in surfactant flooding, a type III microemulsion phase environment would give higher oil recovery than either a type II(-) or a type II(+) environment, and a negative salinity gradient is a preferred gradient which provides the highest oil recovery factor. However, principles and some measured data suggest that these concepts should not be valid universally.In this paper we investigate the effects of microemulsion phase type and salinity profile on oil recovery quantitatively by using a chemical flood simulator, UTCHEM (2000). Over 200 simulation cases covering a variety of flow conditions have been run. The simulation results clearly demonstrate that the two conventional concepts cannot be valid universally. We discuss the salinity gradient effect based on the principles of multiphase flow. In surfactant flooding, many parameters can affect oil recovery, especially multiphase flow parameters.In this paper we propose two new concepts. One is the optimum microemulsion phase type which is not necessarily type III. Another one is the optimum salinity profile which has the following characteristics:. 1. The optimum salinity is within the optimum phase type which corresponds to the highest oil recovery, not necessarily within type III. 2. The optimum salinity must be used in the surfactant slug. 3. Two guard slugs with the same optimum salinity are placed immediately before and after the surfactant slug. But the optimum salinity in the guard slug before the surfactant-polymer slug is preferred but not mandatory. 4. The salinity in the post-flush must be below the lower salinity bound of type III.Our simulation results show that the optimum salinity profile can always lead to the highest recovery, especially higher than that from the corresponding negative salinity gradient. Extensive literature information and laboratory data are used to support these new concepts. These concepts can be used to design an optimized field surfactant flooding program.