The permeability of proppant-packs may be significantly damaged by the gelling agents used in hydraulic fracturing fluids. Several recent fracture conductivity studies have sought to quantify the damage caused by common fracturing fluids over a wide range of downhole conditions. However, viable approaches to reducing the proppant-pack permeability damage caused by these fluids have rarely been discussed.
Oxidative breakers have been well documented as being useful for degrading the viscosity of hydraulic fracturing fluids. Degrading the fluid to a non-viscous state was long thought to provide sufficient polymer degradation to minimize the proppant-pack permeability damage. Recent studies have illustrated that the permeability is significantly impaired by the concentrated polymer residue even though sufficient breaker concentrations have been added to effectively reduce the fluid viscosity.
This study is concerned with the determination of the concentrations of an oxidative breaker which are required to significantly reduce the proppant-pack permeability damage caused by concentrated aqueous hydraulic fracturing fluids. Long-term proppant-pack permeability testing was performed using a modified API-type fracture conductivity cell which permitted fluid loss through two low-permeability cores. The fluids which were evaluated were linear and crosslinked gels of natural guar and hydroxypropyl guar (HPG). The effective polymer concentrations were varied from 100 to 440 Ib/Mgal to account for concentration due to fluid-loss.
Test results indicate that elevated breaker concentrations can very effectively reduce proppant-pack permeability damage. The breaker concentrations required to show significant reduction in permeability damage were found to be strongly dependent upon the polymer concentration and the presence of crosslinker. An understanding of the relationships of these parameters and the resultant retained proppant-pack permeability can be very useful in the design of fracturing treatments or the prediction of well performance.