Rheology and delayed micellar formation process of novel tetrameric cationic surfactant fracturing fluid

To enrich the clean fracturing fluid system with high temperature resistance, a novel tetrameric cationic surfactant (TET) was developed and used as a thickener and mixed with different concentrations of sodium salicylate (NaSal) to obtain a new clean fracturing fluid. The flow curves, thixotropy, viscoelasticity, temperature resistance property, and proppant-suspending capacity were further investigated. The rheological study showed that the Casson model could be used to accurately describe the flow curve of TET/NaSal micelle solutions and the addition of NaSal improved the thixotropy and viscoelasticity of surfactant solution. The optimal mass ratio of TET/NaSal solution was 5/1.5 wt%, and it had good proppant-suspending capacity. What is more, the retained viscosity of TET/NaSal (5/1.5 wt%) solution was 52.27 mPa·s after shearing at 140°C and 100.0 s⁻¹ for 65 min, which met industry requirements (viscosity > 20 mPa·s) of viscoelastic surfactant fracturing fluids. Moreover, the combination of 10 wt% TET aqueous solution with pH value of 8.51 and 2.6 wt% salicylic acid (HSal) suspension of the same mass significantly delayed micellar formation. The four-parameter rheo-kinetics model can be used to fit the viscosity curves of micellar formation, which provided the rheological basis for the study of delayed viscoelastic micellar formation.