Research on the Degradation Law and Influencing Factors of Guar Gum Fracturing Fluid by Biological Enzyme System

In response to the problems of reservoir contamination and pipeline corrosion caused by chemical gel dissolution in hydraulic fracturing of offshore oil fields, a biological enzyme degradation technology for guanidine gel fracturing fluid was proposed. This technology has advantages such as efficient degradation and low-carbon cleanliness. However, the degradation performance of a single biological enzyme is low. Therefore, a biological enzyme composite degradation system was constructed. The degradation laws of the system under the influence of multiple factors on guanidine gel fracturing fluid were analyzed, and its compatibility at different concentrations was characterized. Through microscopic flow simulation experiments, a microfluidic chip reflecting the characteristics of the fracture-sandstone system was designed to evaluate the degradation effect and migration characteristics of the biological enzyme system in heterogeneous formations. The research results show that the biological enzyme system after the combination of EE-1 enzyme and TD-1 enzyme exhibits excellent degradation performance. With the increase of system concentration, the decrease of temperature and the decrease of salinity, the average relative molecular weight of guar gum decreases, and the degradation rate of the biological enzyme system increases. At the microscopic scale, the degradation effect of the biological enzyme system varies in different permeability regions of the fracture-matrix. After degradation, the guar gum fracturing fluid is retained more seriously at the model inlet end and the low-permeability zone. The degradation rates of the biological enzyme system after 1 h and 6 h are 34.17% and 42.8%, respectively, and the displacement pressure difference is 1.19–1.65 MPa. This indicates that the degraded guar gum residue has achieved effective migration, the effective flow volume of the pore throat has increased, and the reservoir damage has been reduced. This biological enzyme composite degradation system can provide technical support for the hydraulic fracturing operations in offshore oil fields.