Study of Fracturing Fluid on Gel Breaking Performance and Damage to fracture conductivity

Abstract As a thickening agent commonly used in hydraulic fracturing, guar gum has the advantage of low price and excellent performance. However, the gel breaking mechanism of fracturing fluid under high temperature and high pressure environment and the damage mechanism to the reservoir needs further study. The current criteria for judging gel breaking is based on the viscosity of the solution being less than 5 mPa s, however it's not always true that the gel breaks even if the viscosity of the fluid is low. To solve this problem, it's recommended in this paper to analyze the gel breaking performance of fracturing fluid by measuring the median molecular particle size and the residue content together with the viscosity of fracturing fluid. Moreover, the effects of the gel breaker on the crushing and formation embedding of the proppant, the adsorption and retention mechanism of the residue in the induced fracture and their influence on the conductivity are investigated. Studies show that the gel breaking performance of guar gum fracturing fluid is affected by the amount of gel breaker and temperature. Adding extra amount of gel breaker and imposing high temperatures do not effectively reduce the median molecular particle size of the fracturing fluid. The detrimental effect of the gel breaker and it's residue to the fracture conductivity is mainly reflected in three aspects: increased crush rate of the proppant due to soaking in the gel breaker, exacerbated embedding of the proppant into formation due to interaction of the fluid and the formation and the reduced pore diameter of the formation due to residue of the fracturing fluid. It's observed that the detrimental effect of the gel breaker on the conductivity of the fracture is mostly in the area with a high closing pressure of 50 MPa or above. This study provides a reference of tight sandstone reservoirs hydraulic stimulation and fracturing fluid formation damage for high temperature and high pressure oilfields like Tarim oilfield.