Fracture Conductivity Damage Due to Crosslinked Gel Residue and Closure Stress on Propped 20/40 Mesh Sand

Abstract

ABSTRACT The commonly used cross-linked fracturing fluids, called gels, were broken in a 20/40 mesh sandpack. The san dpa ck simulated a 2.0 lbm/ft2 propped fracture and was used to test the effects of gel residue and closure stress on fracture con ductivity. The gel residues that were evaluated in this test were derived from the gels made with hydroxypropyl guar (HPG), guar, and carboxymethyl hydroxyethyl cellulose (CWEC) polymers. The relative gel residue volumes for these polymers were determined. Reduction in sand permeability due to these residue volumes was compared between polymers at given closure stress levels. A linear-flow proppant conductivity test cell was used to measure the permeability of the sand under closure stresses up to 10000 psi. For the HPG polymer, both cross-linked and linear fluids were evaluated. Among the three polymers evaluated, the CMHEC gel cross-linked with trivalent aluminum caused the least reduction in sand permeability. The borate cross-linked guar gel resulted in the greatest reduction. However, the difference in permeability reduction caused by the borate cross-linked guar and titanate cross-linked HPG gels was small. Test results for the HPG polymer indicated that the reduction in permeability both due to the cross-linked and linear fluids was nearly the same. Sand permeability was continuously reduced with increasing closure stress. However, the permeability reduction above 4500 psi closure stress was inconsistent. An increase of polymer concentration further reduced sand permeability, but the amount of reduction was not directly proportional to the increase of polymer concentration.