Performance evaluation of oil-displacement viscoelastic zwitterionic surfactant fracturing fluid

Viscoelastic surfactant (VES) fracturing fluid has advantages in sand-carrying and micelle-breaking without residues, while its practical applications are always limited due to the poor temperature and shearing resistance. Accordingly, a kind of stearicamide propyl hydroxylsulfobetaine (SPHB) was self-synthesized by using stearic acid, N, N-dimethyl-1,3-propane diamine, and sodium 3-shloro-2-hydroxypropane sulfonate as raw materials, and a novel VES fracturing fluid (HCF) was prepared by optimizing the ratio of SPHB and counterion. The composition of the novel fracturing fluid system was determined according to the viscosity varies with temperature. Moreover, the temperature and shearing resistance, viscoelastic, sand-carrying, drag reduction, micelle-breaking, and oil displacement properties of the system were systematically studied. The results showed that the optimum molar ratio of SPHB to salicylate counterion in the fracturing fluid system was 1:1. Surface tension test showed the critical micelle concentration (CMC) of SPHB surfactant solution is 6.27 × 10-4 mol /L and the surface tension γcmc is 40 mN/m. The apparent viscosity of the novel fluid was kept above 50 mPa·s after continuous sheared for 60 min under the condition of 170 s−1 at 130 ℃. Besides, it has good viscoelastic property and sand-carrying performance, and the experimental results showed that the drag reduction rate of the novel fluid reaches more than 60% at different temperatures. The micelle-breaking performance of the novel system was perfect. There is basically no solid residue in the micelle-breaking solution, and the permeability damage rate of the micelle-breaking liquid to the natural core was only 9.41%, which showed the novel fluid has the characteristics of low damage. Finally, low-permeability natural cores were used to carry out micelle-breaking fluid oil displacement experiments, including single core flooding and double-tube parallel core flooding, and the mechanism of micelle-breaking fluid improving oil recovery was revealed.