NEW CONCEPTS OF THE OPTIMUM MICROEMULSION PHASE TYPE AND THE OPTIMUM SALINITY PROFILE IN SURFACTANT/POLYMER FLOODING

According to the conventional concepts in surfactant/polymer flooding (SP), 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. Many measured data suggest these concepts cannot be universally valid. 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. Over 200 simulation cases covering a variety of flow conditions have been made. The simulation results clearly demonstrate that the two conventional concepts cannot be universally valid. In surfactant‑polymer 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 the type III. 2. The optimum salinity must be used in the surfactant slug. 3. Two cushion slugs (polymer or water) with the same optimum salinity are placed immediately before and after the surfactant slug. But the optimum salinity in the cushion 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 are used to design an optimized field SP program.