Synthesis of Didodecylmethylcarboxyl Betaine and Its Application in Surfactant–Polymer Flooding

Enhanced crude oil recovery by chemical flooding has been a main measure for postponing the overall decline of crude oil output in China, and surfactant‐polymer (SP) flooding may replace alkali‐surfactant‐polymer flooding in the future for avoiding the undesired effects of using alkali. In this paper the synthesis of a surfactant with a large hydrophobe, didodecylmethylcarboxyl betaine (diC12B), and its adaptability in SP flooding were investigated. The results show that diC12B can be synthesized by reaction of didodecylmethyl amine, a product commercially available, with chloroacetic acid in the presence of NaOH, with a resulting yield as high as 80 wt% under appropriate conditions. With double dodecyl chain diC12B is highly surface active as displayed by its low CMC, 3.7 × 10−6 mol L−1, low γCMC, 27 mNm−1, as well as high adsorption and small cross section area (≤0.25 nm2) at both air/water and oil/water interfaces at 25 °C. By mixing with conventional hydrophilic surfactants diC12B can be well dissolved in Daqing connate water and reduce the Daqing crude oil/connate water interfacial tension to about 10−3 mN m−1 at 45 °C in a wide total surfactant concentration range, from 0.01 to 0.5 wt%. And a tertiary oil recovery, 18 ± 1.5 % OOIP, can been achieved by SP flooding using natural cores without adding any alkaline agent or neutral electrolyte. DiC12B seems thus to be a good surfactant for enhanced oil recovery by SP flooding.