Operators using delayed crosslinkers in fracturing fluids often specify an exact "crosslink time" to avoid the detrimental effects of shear. However, the field methods currently used for determining "crosslink time" do not simulate mixing and pumping conditions. To measure viscosity development under simulated field conditions, laboratory tests were performed with four common crosslinked fracturing fluids using a capillary rheometer to control temperature and shear. The results of this study indicate 1) the on-site "crosslink time" tests do not accurately represent viscosity development under actual treating conditions and 2) accurate control of the "crosslink time" is not necessary to insure optimum fluid performance. Also, the use of specific composition dual crosslinker systems (which combine fast and slow crossl inkers) appeared to be the best way to obtain good performance both at the perforations and in the fracture.

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