Optimization of alkaline- surfactant- polymer flooding system of Jing 11 block in Bieguzhuang oil field

Jing 11 block in Bieguzhuang oil field has the characteristics such as high clay content(29%), low crude oil viscosity(11 mPa·s), low acid value(0. 28 mgKOH/g crude oil), low reservoir temperature(54 ℃), high water flooding recovery(> 50%). An alkaline- surfactant- polymer flooding system which contains 12 000 mg/L of sodium carbonate, 3 000 mg/L of ES surfactant and1500mg/L of J4 polymer was optimized base on those characteristics. The thermal stability, low inter-facial tension as well as anti-adsorption ability of the system were explicitly investigated. The results showed that the system exhibited good thermal stability (viscosity retention rate was 50. 6 %) and the interfacial tension was still in ultra low levels after 90 days of ageing and three times of adsorption on the oil sands. The flooding experiments of the unaged and aged alkaline/surfactant/polymer system (ASP) were performed on heterogeneous double-tube sand pack models respectively. The experimental data showed that with a 90-percent cut in water, 31. 1% additional oil was produced by injecting 0. 3 porevolume of the unaged flooding system. Under the same operational condition, 22. 2 % additional oil was recovered when the aged system was injected. The 8. 9% fall in the oil recovery indicated that the ageing affected the results of the oil recovery. It was found that a decrease in the viscosity and an increase in the inter-facial tension of the ASP system were the causes of the reduction in oil recovery, which could play a guiding role in optimizing the flooding system. That is to say, both the viscosity and the inter-facial tension of the unaged flooding system and that of the aged system have to be measured. The optimum ASP system could be screened based on the higher visicosity retention and lower inter-facial tension after ageing.