The Study On Technology Of Alkali Free Foam Flooding After Polymer Flooding

In this paper, alkali free foam flooding laboratory research is carried out after the polymer flooding technology, through experiment binary low-tension system and foam system for heterogeneous formation flooding are screeninged. While foam system plugging thief layer and expand swept volum, binary low-tension system flow into the medium and low permeability layer and improve oil displacement efficiency, which more greatly improve the oil recovery after polymer flooding.Firstly, the method of airflow is used to proceed with foaming performance experiments by nitrogen gas. Among twelve kinds of foaming agents, surfactant CYL is the best foaming agent, foaming performance is stronger. Surfactant CYL has good compatibility with alkali surfactant, heat resistance, which can be adapted to different water quality conditions. In a wide range of oil field conditions, surfactant CYL can be used as foaming agent.Secondly, the evaluation of the interfacial tension experiments are done. The results show that, the interfacial tension of binary system which consisted of HLX and HPAM is close to the 10^-3mN/m magnitude. It is seen that the binary system has good salt-resistant, Viscosity retention rate and stable interfacial tension, which is able to meet the site's performance requirements.Finally, the concentration of the foaming agent CYL is 0.3%, surfactant of binary low-tension system is HLX, these are selected to proceed experiment on enhanced oil recovery after polymer flooding experiments. When gas-liquid ratio is 1:1, the concentration of polymer composed foaming system is 1200mg/L, slug size of binary foam system is 0.6 pore volum, the value of enhanced oil recovery is 8.78%. Under the condition of the same viscosity, slug size of displacement fluid, different ways of injection has great effect on displacement characteristics. The injection pattern of profile control and displace oil simultaneously is better than displace oil after profile control, of which, the injection pattern of (0.05PV CYL system +0.05PV N2 +0.1PV HLX system) alternating three times is best, the displacement recovery is 14.08%. The results show that while reducing the interfacial tension, we must focus on expanding swept volume of displacement to achieve the desired displacement effect.