Alkali - surfactant - polymer (ASP) combination flooding technique is one of the effective enhanced oil recovery ways for mature oilfields. However, alkali can lead to difficulty of the scaling and emulsification problems in lifting and produced liquid treatment. So alkali-free surfactant - polymer (SP) combination flooding is a green technology can solve these problems caused by alkali. The key technology of SP flooding is development low cost and high efficiency surfactants. In this paper, the novel betaine surfactant was synthesized with cheap raw material of fatty acid, which had intellectual property and excellent properties. Experimental results showed that the surfactant had wide adaptability and could achieve ultra-low interfacial tension (IFT, less than 1.0×10−2mN/m) in different reservoir conditions, not only for low temperature and low salinity oilfield (45°C, 5,100 mg/L), but also for high temperature and high salinity oilfield (90°C, 100,000 mg/L). The dynamic adsorptions of this betaine were less than 1.0 mg/g rock, and it could maintain ultra-low IFT for 9 times adsorption with the natural sand. The alkali-free SP formulations with the betaine had long term stability, and could maintain ultra-low IFT within 180 days, and the viscosity retention rates were greater than 90%. The systems of the novel betaine surfactant had good emulsifying capacity and stripping film capacity. The alkali-free SP formulations with the betaine had high oil-displacement efficiency. After water flooding, it could increase oil recovery 21.5% (OOIP, Original Oil In Place) in Daqing sandstone oilfield, 23.4% (OOIP) in high temperature and high salinity carbonate reservoir rock, 15.5% (OOIP) in Changqing low permeability oilfield. Excellent properties of this novel betaine surfactant indicate that it is a promising surfactant for alkali-free SP combination flooding applied in different reservoirs.

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