A robust viscoelastic surfactant tolerating 20% HCl up to 150 ℃ for oil well stimulation

Viscoelastic surfactants (VES) are often used as viscous diverters in acidizing stimulation to prolong the acid consumption time and maximize zonal coverage of the acid for improving well productivity. However, the ceiling temperature of commercial VES cannot exceed 120 ℃ in practical use because of the poor thermal stability and fragile molecular structure, hindering their implementation in high-temperature oil reservoirs, i.e., ≥150 ℃. Here we synthesized a novel C₂₂-tailed diamine, N-erucaminopropyl-N,N-dimethylamine (EDPA), and examined comparatively its rheological behavior, assemblies morphology and molecular stability in 20 wt% HCl with a commercial VES, erucyl dimethyl amidopropyl betaine (EDAB). The feasibility of EDPA for acidizing stimulation was assessed by acid etching of carbonate rock with its HCl solution at 150 ℃. Rheological results showed that the 2.5 wt% EDPA–20 wt% HCl solution maintains stable viscosity of 90 mPa s at 150 ℃ for 60 min, while that of 2.0 wt% EDAB HCl solution is just 1 mPa s under identical conditions. ¹H NMR spectra and cryo-TEM observations revealed that the chemical structure and self-assembled architectures of EDPA remained intact in such context, but the EDAB suffered from degradation due to the hydrolysis of the amide group, accounting for the poor heat-resistance and acid-tolerance. The reaction rate of 2.5 wt% EDPA HCl solution with carbonate rock was one order of magnitude lower than that of 20 wt% HCl solution at 150 ℃, underpinning the potential of EDPA to be used in the high-temperature reservoirs acidizing. This work improved the thermal tolerance of VES in highly concentrated HCl solution, paving a feasible way for the acidization of high-temperature reservoir environments (~150 ℃).