Title: Rheological Characterization of Hydraulic
Fracturing Fluids Using a Large, High Pressure Slot Flow
Apparatus.
Author(s): N. Goel, B.N. Rao, R. Subramanian and S.N.
Shah, The University of Oklahoma and D.L.Lord, Halliburton
Energy Services
Presentation: Society of Rheology Annual Meeting
Location: Galveston, Texas USA
Date: February 19, 1997
Abstract: Accurate rheological characterization of
fluids commonly encountered in hydraulic fracturing
treatments is achieved through a large, high pressure slot
flow apparatus. The apparatus is installed at the FFCF,
University of Oklahoma, and its construction and operation
are jointly supported by the Gas Research Institute (GRI)
and the U.S Department of Energy (DOE). The apparatus
consists of a vertical, variable width (0-1.25 in.),
parallel-flow cell that simulates the fracture geometry and
is capable of operating at elevated temperatures (up to 250
degrees F) and pressures (up to 1200 psi). The internal
dimensions of the slot are 7 ft. (2.13m) high and 9.3 ft.
(2.84m) long and the fluid enters and exits the slot through
perforation manifolds representative of a wellbore. The
fluid mixing and pumping equipment is chosen such that the
field conditions are represented as closely as possible.
Both thermal and shear conditioning of the fluid are
achieved through a combination of a low shear heat exchanger
and high shear coiled tubing (1.18 in. ID; up to 5000 ft.).
The shear and temperature effects on the fluid are estimated
by a series of pressure transducers and thermocouple leads
placed at strategic locations in he flow path. In addition,
differential pressure transducers along the length of the
slot are utilized for the rheological characterization of
the fracturing fluids. The fluids investigated include both
linear polymer solutions and crosslinked gels such as Guar
and Hydroxypropyl Guar (HPG) as well as sand slurries. The
results on rheology of the linear polymer solutions and
borate-crosslinked Guar gel analyzed on different days show
excellent agreement confirming the repeatability of the slot
rheology data. Further, the variable gap width capability of
the slot was used to observe the wall slip characteristics
of borate-crosslinked Guar gels. The experiments performed
using a testing procedure developed at FFCF to study this
phenomena show that the slot viscosities overlap at
different gap widths. The effects of pH, temperature, and
shear history are also studied in the present investigation
and a pH value is found to exist at different temperatures
for which the fluid is shear history independent. Finally,
the comparison of the slot measured viscosities with
conventional rheometer measurements show poor agreement in
the viscosities.
