关键词: 无碱三元驱油体系, E表面活性剂, 中相乳状液, 界面张力, 乳化行为

Abstract: Alkaline/surfactant/polymer (ASP) flooding is one of the important methods to further greatly improve oil recovery. Although this technique has put into industrial application, it still has problems such as scaling in injection and production system and high cost of production and maintenance. According to the strong alkali[sodium hydroxide (NaOH)], weak alkali[sodium carbonate (Na₂CO₃)] and alkali-free strategic plan made for ASP flooding in Daqing oilfield, alkali-free three-component system was developed by replacing sodium carbonate with sodium chloride. However, the emulsion performance of the system is weak, and oil recovery increment is 2% -3% OOIP lower than that of the weak alkali ASP flooding system. To improve the emulsion performance and enhance oil flooding effect, E-surfactant was compounded with petroleum sulfonate based on the alkali-free three-component system to develop the alkali-free three-component emulsification flooding system of Daqing oilfield. The system is free of alcohol and additives, and it can form Winsor type Ⅲ middle-phase micro-emulsion with Daqing crude oil when the surfactant mass fraction is low (0.3%). Further study shows that the thickening property, interfacial activity, viscosity, interfacial tension stability and anti-adsorption properties of the above system are basically the same as those of the weak alkali ASP flooding system. The core flooding experiment results show that the system is characterized by strong injectability, low degree of chromatographic separation, and good emulsion performance, which can improve oil recovery by 41.12% higher than water flooding and 11.25% higher than weak alkali ASP system. According to the results of laboratory study, the cost for chemical agent per ton of oil in this system was initially estimated to decrease by 42.9% compared with the weak alkali ASP flooding system. The alkali-free three-component system developed for Daqing oilfield not only achieves the alkali-free goal of three-component flooding, but makes a leap from ultra-low interfacial tension compound flooding to low-concentration middle-phase micro-emulsion flooding, which has reached the goal of largely improving oil recovery and decreasing cost and increasing efficiency. In fact, the system has a broad application prospect and can also provide technical reference for the efficient development of other old continental sandstone oilfields.

Key words: alkali-free three-component flooding system, E-surfactant, middle-phase microemulsion, interfacial tension, emulsification behavior