American Oil and Gas Reporter - December 2019 - 50

SpecialReport: Stimulation & Completion Technology
Based on the area-specific type curves,
pumping far-field diverters increased the
P50 estimated ultimate recovery by 6%.
For all wells impacted by far-field diverters, the infill wells saw larger benefits
(increase of 7% in P50 EUR) compared
with parent wells.
The fracture system created in multistage
fracturing of parent wells leaves unconventional reservoirs with pressure depletion
of varying magnitudes, depending on the
scale of the initially stimulated reservoir
volume and duration of parent well production. Significant challenges are encountered while fracturing offset infill
wells, which are typically hundreds of
feet away from the depleted parent wells.
Because of the low fluid leak-off rate,
high pump rate and large job size, hydraulic
fracture wings can propagate into rock depleted by parent well production. Therefore,
the fracturing treatments often are handicapped by asymmetrical fracture growth,
as longer fractures can develop in the direction of the parent well. This is attributable
to the reduced rock stress associated with
pore pressure depletion. This parent-infill
well fracture interaction can hurt both
parent and child well production.
Various parent well protection methods
have been implemented in the field to
mitigate the fracture-to-fracture interference, including shutting in the parent
well, pumping into the parent well directly
or indirectly through infill well fractures,
refracturing the parent well, and using
far-field diverting agents in infill well
treatments. All of these methods protect
the parent wells and increase infill well
fracturing efficiency by building up stress
in the depleted area and restoring energy
in the depleted area to resist influx from

infill well fracturing. Pumping a far-field
diverting agent fills the gap when refracturing or injecting into parent wells cannot
be financially or operationally justified.
Far Field Diverters
Historically, particulates have been
used as diverting agents in both nearwellbore and far-field regions. The mixture of large and small particulates in
near-wellbore diverters is designed to
bridge in the near-wellbore area to redistribute the treatment toward other
perforation clusters in a multi-cluster
fracturing treatment. The far-field diverter mixture's small particle size facilitates transport farther in the fracture
for bridging at the fracture tips, restricting fracture length growth and increasing net fracture pressure.
This study used two far-field diverter
systems: 100-mesh sand blended with 325mesh silica flour, and 100-mesh sand blended with dissolvable particulates comparable
in size to the silica flour. Both diverting
systems demonstrated superior frac hit and
productivity metrics compared with base
case wells that used no far-field diverters.
The silica flour and 100-mesh sand mixture
performed on par with the significantly
more expensive blend of dissolvable fine
particulate and 100-mesh sand.
The idea is to transport the mixture
deep into the fractures and form a mechanical baffle in a sufficiently narrow
part of the connected fracture that mitigates
the potential for the high-velocity fracturing fluid to sweep proppant into the
parent wellbore. In the ideal situation,
100-mesh sand bridges off at the fracture
tip, and 325-mesh silica flour lodges in
the pore throats of the 100-mesh sand
pack.. The working mechanism is illus-

FIGURE 1
Far-Field Diverters Bridging between Parent
And Infill Child Well Fractures

Per Cluster
Fracture

Parent Well

Height

Infill Well

Length

(High Pressure)

(Low Pressure)

Diverter Bridges
at the Tip

50 THE AMERICAN OIL & GAS REPORTER

Existing Cluster
Proppant Pack

trated in Figure 1. Since wellbore fluid is
displaced ahead of the diverter mixture,
the parent well still should observe some
pressure increase.
To model the fracture width profile in
the parent-infill well scenario, a 3-D stress
field is required to account for reservoir
depletion. The study used an explicitly
two-way coupled flow and geomechanics
simulator to compute the stress tensors at
the time of infill well completion. Fracture
widths at the infill well fracture tips were
calculated under the depleted stress environment using a fracture simulator based
on the boundary element method.
General Workflow
The study's general workflow consisted of:
· Modeling fracture propagation to
characterize the width profile at fracture
extremities in a depleted-stress environment;
· Using a slotted-disk device to evaluate and optimize particulate blends for
bridging slots representative of width
near the fracture tip;
· Measuring the permeability of the
proppant pack with and without the diverting materials to evaluate its fracture
conductivity damage potential;
· Conducting rheological tests replicating the downhole environment to formulate a system for transporting the diverting materials;
· Performing statistical analysis of 511
fracture hits at 30 parent wells with key
treatment indicators categorized by the diverter type and parent well condition; and
· Comparing production trends of the
influenced wells with area-specific type
curves and offset wells without diverter
trials.
Modeling fracture tip widths at the
depleted stress field showed that the insitu stress field was altered because of
depletion by parent well production, with
infill well fractures growing preferentially
toward the parent well side. As the fractures
approach the depleted area, fracture height
is reduced because of the decreasing net
pressure and the elliptical shape of the
depleted rock volume. The skewed fracture
half wing gains larger fracture height as
it grows within the depleted area because
American Oil and Gas Reporter - December 2019

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