To design a successful hydraulic fracturing treatment employing borate crosslinked gels, accurate measurements of rheological properties of such fluids are required. Rheological characterization of borate crosslinked gels has been difficult with the rotational type viscometer. In this paper, we present the rheological properties of various borate crosslinked fluids employing a new procedure which simulates field pumping conditions, i.e. crosslinking the fluid on the fly, and fluid flow down tubing or casing and in the fracture.

The effects of fluid pH, gelling agent concentration, type of gelling agent, and temperature on the rheological properties of fluids have been measured. It was found that these parameters have significant effect on the final viscosity of gel in the fracture.

From the laboratory test data, correlations to estimate friction pressures in field size tubulars have been developed. It is also shown that in conjunction with field calibrations, these correlations can aid in accurate prediction of friction pressure of borate crosslinked fluids.

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