Synthesis And Evaluation Of Low-damage And High-temperature Resistant Clean Fracturing Fluid

Clean fracturing fluid has advantages in sand-carrying and gel-breaking without leaving residues;however,its practical applications are limited due to its poor temperature resistance and poor shear strength.These limitations make the application of clean fracturing fluid in high temperature reservoirs undesirable.Therefore,the development of VES fracturing fluid requires the improvement of the temperature resistance and the shear strength.In this study,this was achieved through enhancing the intermolecular force.We further investigate the effect of molecular microstructure on the thermal stability of the assembly from the perspectives of viscoelastic surfactant molecular structure design,synthesis route and synthesis scheme.Three new hightemperature resistant quaternary ammonium salt cationic viscoelastic surfactants are developed to improve the performance of clean fracturing fluid under high temperature conditions.Quaternary ammonium salt systems HCF-1?HCF-2 are thus developed to extend the application of clean fracturing fluid in the formations under 150 ?.We conduct experiments to evaluate the performances of those clean fracturing fluid systems.Our results show:(1)Good heat resistance: apparent viscosity of HCF-1 system is 31 mPa·s,apparent viscosity of HCF-2 system is 43 mPa·s at 150?.Excellent shear strength: viscosities of HCF-1 and HCF-2 system remain stable after 60 minutes of continuous shearing at 120? or 130?.(2)Good sand-carrying capability: settling rate of HCF-1 and HCF-2 are 1/3 and 1/14 of common gum fracturing fluid settling rate separately at 90?.(3)Able to break gel without leaving gel residues at room temperature after mixing with kerosene.(4)Minimal damage to core permeability: average damage rate of core permeability of HCF-1 and HCF-2 are 15.2% and 6.6% separately,hence better at protecting reservoir formation.