Title: New Empirical Correlation to Predict
Apparent Viscosity of Borate-Crosslinked Guar Gel in
Hydraulic Fractures
Author(s): Naval Goel and S.N. Shah, The University
of Oklahoma and M. Asadi, Stim-Lab
Presentation: Permian Basin Oil and Gas Recovery
Conference
Location: Midland, Texas USA
Date: March 23-27, 1998
Abstract: 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 Guar 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 are performed under representative field
conditions. Because of these complexities, there is no
reliable correlation available in the literature to relate
the borate-crosslinked Guar gel viscosity with its dependent
properties. Therefore in the present study, the
borate-crosslinked Guar gel rheology measurements, obtained
under field scale form a High Pressure Simulator, are used
to develop a model. The model was developed using the
multiple linear regression analysis of the experimentally
gathered data. The model related the apparent viscosity of
the borate-crosslinked Guar gel with three independent fluid
variables: time of wellbore pre-shear, temperature, and
fracture shear rate. The time of shear pre-conditioning was
varied by pumping the fluid through different lengths of an
1.188 inch ID coiled tubing. The temperature was changed by
heating the fluid in a formation thermal simulator slot.
Using different coefficients of the independent variable,
the model is correlated for the borate-crosslinked Guar gel
of pH 9, 10, and 11. The developed model is presented in a
very simple form. Furthermore, its form is based on field
experimental results and it is supported with theoretical
observations make on the borate-crosslinked fracturing fluid
systems form the literature. The correlation will be very
helpful for comparison of model calculated values with the
laboratory measured viscosities, as the laboratory values
are not supported with the field scale fluid
characterization capability. This comparison will, then,
benefit industry in improving fluid viscosity estimation and
help in the success of stimulation treatments.