As the alkali in alkaline-surfactant-polymer (ASP) flooding often causes the difficult problems of scaling and emulsification, surfactant-polymer (SP) flooding was proposed for enhancing heavy oil recovery in China. However, it is difficult to reduce the interfacial tension (IFT) to an ultra-low value without alkali for the traditional chemical system. This paper presents a type of betaine surfactant which has an excellent ability to reduce oil/water IFT at low concentration without alkali, and alkali lignin with low-price was compounded as a sacrificial agent to reduce the adsorption. Finally, sandpack flooding tests were conducted to examine the effectiveness of enhanced oil recovery by compound chemical system containing polymer, betaine and alkali lignin.
The results showed that the IFT reduced to 0.001 mN/m or less at a betaine concentration range of 0.01wt% to 0.1wt% without alkali, meeting the requirements of SP flooding; the dynamic adsorption test showed that of the adsorption amount reduced approximately 40% when the mass-ratio of alkali lignin and betaine was 1 to 7.5; moreover, the polymer added into compound surfactant system accelerated the reduction of the oil/water IFT. Sandpack flooding tests indicated that the injected chemical system containing polymer, betaine and alkali lignin after water flooding could enhance oil recovery by 13%~20%, which was significantly higher than that of polymer flooding under the same conditions.