A Low Elastic-microsphere/surfactant/polymer Combined Displacing Method after Polymer Flooding

Abstract

Abstract Polymer flooding has been widely applied in China and can enhance oil recovery by more than 10%. However, there is about 50% remaining oil in reservoirs. Therefore, it is important to develop a new technology which based on the mechanism of both lowering interfacial tension to an ultra-low value (103 mN/m grade) and improving sweep efficiency of displacing fluid after polymer flooding in extremely heterogeneous reservoirs. A novel dispersed viscoelastic microsphere flooding system (DVMFS) by the combination of low elastic microspheres, surfactants and polymers is suggested. Firstly, the suspension stability of the DVMFS was studied using TSI value measured by stability analyzer. The influence of surfactant concentration, polymer concentration and reservoir temperature was conducted. Then, the ability to reduce interfacial tension was measured using interfacial tensionmeter. Furthermore, conformance control ability was evaluated by double tube parallel model. Oil displacement efficiency of the system was obtained through core flooding experiments under a given reservoir condition after polymer-flooding. The results show that the low elastic microspheres with 23.6 Pa used in this paper has great swelling capability at the reservoir condition of Gangxi Oilfield. The deformable microsphere passes throw the pore throat easily because of its low elasticity. The dispersed system has great suspension stability. The lower the temperature and the higher concentration of surfactant and polymer are, the smaller the TSI value and the better the suspension stability are. Besides, the system has an ultra-low oil-water interfacial tension. The results of double tube parallel model and oil displacement experiment indicate that the injection profile was significantly adjusted and the oil recovery efficiency was increased by 21.66% after polymer flooding. This conformance control is a dynamic one because of the combination of low elastic microsphere, surfactant and polymer, which is different from the common gel conformance control technology. The DVMFS displays a promising application to improve oil recovery after polymer flooding for extremely heterogeneous reservoirs.