American Oil and Gas Reporter - December 2019 - 52

SpecialReport: Stimulation & Completion Technology
terial to be transported to the fracture tip
and along the entire height of the fracture
at its intersection with depleted rock.

FIGURE 2
Fracture Widths and Proppant Sizes
10,000

Sieve Size (um)

Proppant Size Distribution

1,000

100

150
200
U.S. Mesh Size

of the decreasing principal stresses.
Because of the high fluid efficiency in
the ultra-low permeability rock, the fracture
reaches the height constraint shortly into
the fracture treatment. At the time of
interest, the fracture width at the intersection
between the infill well fracture with the
depleted reservoir ranges from 0.10 to 0.75
millimeters. The proppant size comparison
with the simulated width is shown in Figure
2. Assuming the optimum particle bridging
ratio (i.e., the ratio of slot width to the
particle diameter), 100-mesh sand best
meets the requirements for bridging at the
intersection with pressure-depleted rock.
Optimizing Particulate Blends
Laboratory testing was performed to
optimize different particulate blends and
evaluate the effects of particle concentration,
particle size distribution and fluid viscosity.
The simulations indicated that particles in
the range of 0.04-0.30 millimeters (50- to
170-mesh) are appropriate to use as base
diverting agents. The effective pore diameter
range of 100-mesh sand packs is 0.00700.1633 mm. The analysis shows that the
silica flour is a reasonable bridging material
for 100-mesh sand packing. The lodged
particles from either 100-mesh sand or
silica flour would block flow pathways
and reduce conductivity.
It should be noted that 100-, 40/70and 30/50-mesh sands all have a broad
52 THE AMERICAN OIL & GAS REPORTER

250

300

350

enough size range to be able to effectively
bridge off at the fracture extremities as
the base diverting material, with 325-mesh
silica flour able to lodge at the pore structures of the base diverting agent to reduce
the flow capability of the diverter packing.
However, field practices show that it is
extremely challenging to transport 30/50mesh sand to the desired fracture extremities
even with a 30 pound/1,000 gallon guar
borate gel system because of high formation
temperatures. The laboratory studies, therefore, focused on evaluating 100-mesh sand
as the base diverting agent.
In early field trials, it was found that
fluid viscosity played a critical role in
particulate sealing effectiveness. Specifically, significant viscosity of the fracturing fluid was needed to get sand out
to the extremities of the fracture to
bridge narrow fractures that could grow
into the influence of the parent well.
This suggested that bridging efficiencies
would be improved with a viscous carrying fluid such as the guar-borate delayed cross-linked gel system.
It was not necessarily that inefficient
transport of 100-mesh sand would interfere
with its ability to bridge, but that less
material would be available to bridge
along the height of the fracture near the
tip because of settling. The higher-viscosity
fracturing fluid allows more effective farfield bridging by enabling diverting ma-

A wide range of 100-mesh sand products are available. To evaluate the effect
of size distribution on particulate bridging
ability, experiments were run using three
types of 100-mesh sand slurries in both
0.010- and 0.016-inch wide slots. Most
of the particles were larger than 150 microns for all three types of nominal 100mesh sand. In all tests, the concentration
of both 100-mesh sand and silica flour
was fixed at 50 pounds each per 1,000
gallons of clean fluid.
All three sands sealed the 0.010-inch
slot. However, in the 0.016-inch slot
test, only Type I 100-mesh sand sealed
with the given volume of fluid and solids
loading. This result is consistent with
the expectation that the mixture with
the broadest particle size distribution
will be the least permeable and bridge
more effectively.
Consequently, the effects of various
ratios of Type I 100-mesh sand and 325mesh silica flour were investigated while
holding total silica particle concentration
constant at 100 ppt. All silica mixtures
quickly sealed the 0.010-inch slot, but
sealing was not as efficient for the 0.016inch slot tests. Average fluid loss was 70
mL, a fivefold increase compared with
the narrower slot. In these tests, there
was no clear advantage to adding silica
flour in any percentage, because Type I
100 sand covered a wide range of particle
sizes, including the size range of the
silica flour. Higher concentrations of Type
I 100-mesh sand are able to bridge wider
slots. In fact, Type I 100-mesh sand alone
can seal slot widths up to 0.020 in. at
500 ppt and 1,000 ppt concentrations.
Larger size particulates such as 40/70or 30/50 sand need to be considered for
bridging wider fractures, but as noted,
transporting larger proppant to the fracture
extremities without some degree of settling
can be difficult, even when using crosslinked fluid.
In the fracture conductivity tests, pack
permeability of 40/70-mesh sand was
compared with packs containing mixtures

American Oil and Gas Reporter - December 2019

Table of Contents for the Digital Edition of American Oil and Gas Reporter - December 2019