In this paper, two kinds of long-chain amine oxide surfactants, erucamidopropyl dimethylamine oxide (EAOS) and oleamidopropyl dimethylamine oxide (OAOS) were synthesized and compounded with different mass ratios. The rheological tests show that there is a synergistic effect between EAOS and OAOS, and this effect reaches the strongest at the EAOS/OAOS solution with α = 0.7 (α is the mass fraction of EAOS in the mixed surfactant). Through the synergistic effect between EAOS and OAOS, the temperature resistance of amine oxide surfactant solutions can be effectively improved. EAOS/OAOS (α = 0.7) solutions with total surfactant mass fractions of 3, 4, and 5 wt% show good high-temperature resistance at 130, 140, and 150 C, respectively. After shearing for 60 min at 100 s À1 , 160 C, the remaining viscosity of the 5 wt% EAOS/OAOS (α = 0.7) with 1 wt% KCl solution is 30 mPa s, meeting the demand of viscoelastic surfactant fracturing fluids.

Development of low-cost, high-temperature-resistant and salt-resistant fracturing fluids is a hot and difficult issue in reservoir fluids modification. In this study, an organic zirconium crosslinker that was synthesized and crosslinked with partially hydrolyzed polyacrylamide (HPAM) was employed as a cost-effective polymer thickener to synthesize a high-temperature-resistant and salt-resistant fracturing fluid. The rheological properties of HPAM in tap water solutions and 2 × 104 mg/L salt solutions were analyzed. The results demonstrated that addition of salt reduced viscosity and viscoelasticity of HPAM solutions. Molecular dynamics (MD) simulation results indicated that, due to electrostatic interaction, the carboxylate ions of HPAM formed an ionic bridge with metal cations, curling the conformation, decreasing the radius of rotation and thus decreasing viscosity. However, optimizing fracturing fluids formulation can mitigate the detrimental effects of salt on HPAM. The rheological characteristics of the HPAM fracturing fluid crosslinking process were analyzed and a crosslinking rheological kinetic equation was established under small-amplitude oscillatory shear (SAOS) test. The results of a large-amplitude oscillation shear (LAOS) test indicate that the heating effect on crosslinking is stronger than the shear effect on crosslinking. High-temperature-resistant and shear-resistant experiments demonstrated good performance of fracturing fluids of tap water and salt solution at 200 °C and 180 °C.

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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.