American Oil and Gas Reporter - August 2022 - 73

SpecialReport: Hydraulic Fracturing Tech
Microproppants Boost Frac Efficiency
By Carl T. Montgomery
and William E. Strobel
TULSA-It is commonly acknowledged
within the industry that the stress cage or
hoop stress left around a horizontal well
after it is drilled can cause severe complexity
in the geometry of hydraulic fractures
created during subsequent stimulation
operations. If the intent is to create a
transverse fracture, then the fracture will
reorient normal to the wellbore, which
will cause a chokepoint or kink to form
as the fracture reorients.
The severity of this " kink " is a function
of the delta between the two horizontal
stresses, and is called tortuosity. It can
cause severe placement problems associated
with excess treating pressures and
near wellbore premature screen-outs. In
addition, if the kink persists, it can limit
the production of the well because of low
near-wellbore fracture conductivity and a
convergent flow excess pressure drop.
The general paradigm for the design
of hydraulic fractures is to underflush
the treatment to ensure that proppant is
left in the near-wellbore fracture to
prevent the fracture from pinching off
and restricting flow. Many slot flow
studies have been completed that show
the forming of a " dune " when a low-viscosity
frac fluid is used to place proppant.
A dune has a large void area near the
wellbore, where the velocity of the fluid
exiting the perforation is high enough to
sweep the proppant away from the nearwellbore
region.
Recent downhole video photos show
that when fracturing treatments were
intentionally overflushed, the fractures
were wide open even though no proppant
was seen. The current theory is that the
strong force of proppant erosion during
the treatment etched enough rock material
from the fracture face to prevent
it from sealing back up after fracture
closure. The shale revolution has delivered
hundreds of thousands of wells
using the overflushing technique and
post-production data shows that overflushed
wells are linked to stronger well
performance.
Microproppant Case Study
A major operator recently completed
a test to determine whether a ceramic
microproppant would improve the completion
efficiency of the company's frac
treatments. The study consisted of a fourwell
study in which 18 of a total of 87
stages in two wells were treated with the
microproppant. One of the microproppant
wells used a 10 clusters-per-stage perforation
design, where each cluster received
three 0.42-inch entry hole diameter, 25gram
charges for a total of 30 perforations
and treated with 420,000 pounds of 100mesh
sand. In addition to the 100-mesh
sand, nine of the stages in this well included
10,604 pounds of microproppant
pumped at concentrations of 0.25 and
0.50 pounds/gallon in the pad.
The second microproppant well used
14-clusters per stage with the same perforation
design and was treated with
588,000 lbs of 100-mesh sand. The stages
that included the microproppant were
treated with 14,750 lbs of microproppant
pumped at concentrations of 0.25 and
0.5 lbs/gal in the pad. After cleanup, an
ultrasonic imaging tool was run to evaluate
which stages had a more consistent perforation
uniformity.
Figure 1 shows the results for two
adjacent stages (stages 12 and 13). The
vertical axis represents the eroded area
of the perforation. The initial perforation
size was 0.42 inch, which is the " 0 "
FIGURE 1
Stages 12 and 13 of the 10-Cluster Design
12
0.4
13
point on the vertical axis. The " 0.4 "
point on the vertical axis represents an
eroded area of 0.4 square inch above
the baseline of 0.42 inch. Stage 12 is a
microproppant stage and each vertical
blue line represents one perforation. This
stage was a 10-cluster design with three
perforations for each cluster, for a total
of 30 perforations. If one counts the
blue lines, 28 of the 30 perforations (or
98%) received proppant. On stage 13,
which was also perforated with 30 perforations,
17 of the 30 perforations (57%)
received proppant. Stages 13 also shows
that perforation No. 7 was a " runaway "
perforation that took a large portion of
the total treatment.
Figure 2 shows a statical analysis composite
of all the stages. The light blue
boxes represent the nonmicroproppant
baseline stages while the dark blue boxes
represent the microproppant stages. The
white line running through the boxes is
the median value for all of the tests. The
results indicate that the median value for
the number of perforations that received
proppant increased by 13.1% in the 10cluster
well and 16.1% in the 14-cluster
well. In general, the completion efficiency
of the stages treated with the ceramic microproppant
was increased by 15% to an
overall competition effectiveness of 54%.
Perforation Erosion
The expected impingement velocity of
proppant entering the fracture is in the
range of 50-90 mph. Using the 10-cluster
case and the pump rate shown in Figure 3
AUGUST 2022 73
American Oil and Gas Reporter - August 2022

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