pH- and KCl-induced formation of worm-like micelle viscoelastic fluids based on a simple tertiary amine surfactant

To explore the application of pH-responsive surfactant, a pH-responsive N,N-dimethyl-erucamide-propylamine (DEAPA) self-assembly system was prepared and characterized. The rheological property and structural transformation of DEAPA molecular aggregations were comprehensively discussed with decreasing pH or increasing of Cl− concentration using rheology, dynamic light scattering (DLS), ultraviolet-visible (UV) spectrophotometry, and cryo-transmission electron microscopy (cryo-TEM). The properties of the DEAPA-KCl viscoelastic fluid used as the fracturing fluid were discussed in terms of the viscoelasticity, temperature-tolerance, and shear-tolerance, proppant suspension, and core permeability damage at pH 1.5. Results revealed that the microstructure of the DEAPA micelle first transformed from vesicles to spherical micelles, and finally changed to worm-like micelles when HCl solution was added. In addition, on increasing the KCl concentration, the system transforms from spherical micelles to worm-like micelles. When the Cl− concentration was increased to 0.50 mol/L (pH = 1.5), the storage modulus (G′) of the DEAPA-KCl fluid became over 15 Pa and loss modulus (G″) was over 5 Pa, which suggests that elasticity is the predominant property of these worm-like micelles. Also, the viscosity of the DEAPA-KCl fracturing fluid was constant at about 110 mPa s at 80 °C and shear rate of 170 s−1. The settling velocity of the DEAPA-KCl fluid was lower than 0.004 mm/s at 60 °C, and the core permeability damage was 6.75%. Therefore, the DEAPA-KCl system is suitable for use as an acidic viscoelastic fracturing fluid.