Abstract: A new copolymer solution was developed and its indoor performance evaluation and field application were conducted.Deep shale gas development often saw technical challenges such as poor sand-carrying capacity,low width generation capasity,and complex variable viscosity processes of conventional fracturing fluids.To address these challenges,new mononers S1 and T1 were developed based on the characteristics of deep shale reservoirs in the Dingshan Block of southern Sichuan and according to the requirements of construction.A certain amount of acrylamide,sodium 2-acrylamido-14-alkyl sulfonate,and monomers S1 and T1 were copolymerized to form new copolymer solution.The copolymer solution underwent indoor performance evaluation and field application.The results show that the copolymer solution has a strong viscosifying effect;at a low mass fraction(0.005%),the molecules exhibit monodispersity and low viscosity,while at a high mass fraction(0.500%),the molecules form a spatial network structure through intermolecular forces,demonstrating strong elasticity.The copolymer solution with medium and high mass fractions exhibits good sand-carrying capacity,with a sedimentation velosity of 0.17 cm/min in a 1.500% mineralized water solution at 60 ℃;additionally,it also has good gel-breaking ability and salt resistance.Field applications show that the new real-time variable viscosity copolymer fracturing fluid can effectively switch between low,medium,and high viscosity in real-time,enhancing fracturing and sand-carrying capabilities.This research provides theoretical guidance and technical support for improving deep shale gas fracturing effects.

Key words: deep shale gas, real-time variable viscosity fracturing fluid, copolymer, sand-carrying capacity, gel-breaking ability, salt resistance