Abstract: Karamay field fracturing fluid system occurs in the problems of incomplete guar gum breaking and oil layer damage. The study showed that the high-temperature enzyme breaker had incompatibility with additives of the Karamay fracturing fluid system. The fracturing fluid viscosity can be reduced to 3.3 mPa·s within 2.5 h by adding 250 mg/L enzyme breaker, 250 mg/L protective agent and 0.01% ammonium persulfate, and the residue of 280 mg/L, which meet the national standards of an oilfield. The molecular weight of the fracturing fluid was measured by mass spectrometry, which was mainly concentrated in the range of 2 147~6 366 Da, indicating that the enzyme breaker can be used to decrease the viscosity of fracturing fluid and degrades gum to oligosaccharides.

Key words: Karamay field, enzyme breaker, high temperature, fracturing, protective agent, viscosity, residue