Effect of Main Factors on Oil Recovery of Surfactant-Polymer Flooding

Alkali-free surfactant-polymer combination flooding (SP flooding) can avoid side-effects encountered in alkali-surfactantpolymer (ASP) combination flooding, such as scaling and corrosion damaged the lifting system, strong emulsification resulted in produced liquid treatment problems and high cost of water handing. It can reduce the operation cost and be applied in oilfield easily. However, the oil displacement mechanism of SP flooding is not fully understood. In this paper, the main factors on enhancing oil recovery of SP flooding such as viscoelasticity, interfacial tension, emulsification and wettability of rocks surface were studied based on the Berea core oil displacement tests. The results of SP flooding physical simulation tests showed that: (1) High viscoelasticity of SP flooding was an important factor contributing higher oil recovery. When the ratio of viscosity of the displacement fluid to that of oil was more than 2, the higher oil recovery could be obtained by SP flooding. (2) The lower the interfacial tension, the higher the incremental oil recovery. When the interfacial tension of oil and water decreased to 5×10-3mN/m level, almost the highest incremental oil recovery of SP flooding could be obtained. Compared with the SP flooding system of solely high viscosity, more than 7-15% incremental oil recovery could be obtained by that of both lower interfacial tension and high viscosity (3) When emulsification intensity increased, the incremental oil recovery of SP flooding increased accordingly. Compard to the weak emulsification SP system, more than 6-11% incremental oil recovery could be obtained by means of enhancing emulsification ability. (4) Oil recovery of SP flooding at water-wet core condition was higher than that at intermediate-wet or oil-wet one. Studies on main factors for oil displacement efficiency of SP flooding are very important for the formula optimization of SP system, and they will provide foundation for scenario design of field tests and applications of SP flooding.