Study on gel breaking mechanism of guar gum fracturing fluid by biological enzyme and ammonium persulfate

To solve the problem that the residue produced after the gum fracturing fluid is broken will cause damage to the formation. In this paper, the molecular weight, molecular size and the relative content of oligosaccharides in guar gum fracturing fluid under different breaking methods were studied, and the molecular composition and content of residue were studied. The results show that compared with ammonium persulfate breaker, biological enzyme , ammonium persulfate and composite breaker can effectively reduce the molecular weight and molecular size of gel breaker; The oligosaccharide in the gel breaking solution is mainly disaccharide pentasaccharide; The analysis of gel breaker residue showed that the content ratio of mannose / galactose in residue molecule was 0.38, and the low ratio resulted in poor molecular water solubility. The use of acid action mode can effectively degrade the residue and improve the conductivity of proppant.