Breaker Concentrations Required To Improve the Permeability of Proppant Packs Damaged by Concentrated Linear and Borate-Crosslinked Fracturing Fluids

Abstract

Abstract 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 provide sufficient polymer degradation to minimize the proppant-pack permeability damage. Recent studies have illustrated that proppant-pack permeability damage. Recent studies have illustrated that the permeability is significantly impaired by the concentrated polymer residue even though sufficient breaker concentrations 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 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 lb/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. performance Introduction Engineers designing and evaluating hydraulic fracturing treatments have frequently predicted productivity increases much greater than those actually observed. The in-situ Proppant pack permeability is known to be a major factor effecting productivity of permeability is known to be a major factor effecting productivity of fractured wells and is therefore of importance to the design and evaluation of fracturing treatments. The Proppant-pack permeability data provided for use in the design of fracturing permeability data provided for use in the design of fracturing treatments have typically been short-term data collected under ambient temperatures conditions without fracturing fluid present. Many efforts have recently been focused on the evaluation of long-term proppant-pack conductivity. Proppant-pack permeabilities were found to be significantly reduced when permeabilities were found to be significantly reduced when exposed to long periods at temperature and stress. The long-term permeabilities of many of the proppants tested in these studies have been reported to be as much as 50% less than was indicated by the previously published short-term values. The permeability of proppant-packs may also be significantly impaired by the gelling agents commonly used in hydraulic fracturing fluids. Among the parameters known to affect the degree of damage are the type and concentrations of the gelling agent, crosslinker, and breaker, and the reservoir temperature. Many researchers have attempted to quantify the damaging effects of unconcentrated fracturing fluids on the permeability of proppant-packs. Cooke correlated the effects of permeability of proppant-packs. Cooke correlated the effects of the residue of various unconcentrated gelling agents to the permeability reduction observed in short-term stressed permeability reduction observed in short-term stressed proppant-packs. The study demonstrated that the permeability of the proppant-packs. The study demonstrated that the permeability of the proppant-pack decreased with increasing gelling agent residue proppant-pack decreased with increasing gelling agent residue concentration. P. 409