Successful design and completion of the hydraulic fracturing treatments depend on accurate estimation of fracturing fluid viscosity under in-situ conditions. However, the viscosity of the widely used borate-crosslinked gual gel is extremely difficult to measure due to its dependence on temperature, wellbore shear pre-conditioning, fracture shear rate, and pH. Furthermore, these properties require that the fluid mixing, pumping, and characterization to be performed under representative field conditions. Because of these complexities, there is no reliable correlation available in the literature to relate borate-crosslinked guar gel viscosity with its dependent properties. Therefore, in the present study, borate-crosslinked guar gel rheology measurements, obtained with a field scale High Pressure Simulator (HPS), are used to develop a correlation. The empirical correlation is developed on the basis of method of reduced variables, whereby shear stress-shear rate data at different temperatures are combined into one curve at a reference temperature T_o. Present study extends this method to include the effect of shear history on the rheology of guar polymer crosslinked with borate ions. In the paper, this technique is used to generate master curves of reduced apparent viscosity-shear rate for borate-crosslinked guar at each pH. Furthermore, the developed empirical equations relate apparent viscosity of crosslinked guar to fluid temperature, shear history and shear rate. The developed correlation is presented in a simple form. The correlation will be helpful for comparison of model calculated values with the laboratory measured viscosities, as the laboratory values are not supported by a field scale fluid characterization equipment.
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