American Oil and Gas Reporter - July 2018 - 50

SpecialReport: Horizontal Wellbore Construction
parent and child wells.
Parent well stimulation designs should
be modified so that the spatial extent of
depletion is reduced away from the well.
The child well stimulation design also
should be modified to create child well
fractures in the reservoir's undepleted
parts. For a defined well spacing, increasing the number of clusters per stage
can create more and shorter fractures
along the well to help accomplish this
objective without increasing treatment
cost.
One known problem of having multiple
clusters in a stage is that all clusters may
not contribute to production. This can be
improved by using limited-entry techniques during perforation. Another option
to activate multiple clusters is using farfield diverters to prevent the creation of
a single dominant fracture in a stage.
If the parent well already has been
stimulated and has been on production
for some time, the operator can try to
modify reservoir conditions to increase
stresses near the parent well to prevent
attracting fractures from the child well
to the depleted reservoir region. As noted,
one way to accomplish that is refracturing
the parent well, which increases stresses
in the vicinity of the parent well fracture
because of stress shadow induced by the
extended fracture.

Figure 4 shows the impact of refracturing on the pressures and stresses between parent and child wells. The top
figure (A) is before refracturing and
demonstrates the effect of only the parent
well depletion, while the bottom figure
(B) is after refracturing. The top left part
of each figure shows the reservoir pressure
profile, while the bottom left shows the
difference between the stress in the direction along the fracture and in the direction perpendicular to the fracture. The
bottom right shows the stresses and pressures along the dashed line in the bottom
left figure and the top right shows the
stresses and pressure along the parent
well's location.
During refracturing, injected fluid
leaks off and increases pressure in the
region around the parent well fracture.
Fracture opening and propagation also
increases the stresses around the fracture.
Note Syy-Sxx indicates the stress contrast
between horizontal principal directions.
In blue regions of Syy-Sxx, the maximum
horizontal stress direction reoriented toward the direction perpendicular to the
fracture face. The total stress magnitudes
along the dotted line are the magnitudes
along the thin solid lines in the left-side
figures. This reverses the principal horizontal stress components in the region

around the parent well fracture. The relative increase in the stresses and pressures
along the specified axes also suggests
that fracture opening and propagation reverses horizontal stresses in the region
near the fractures.
This increase in stresses and pressures
also is observed in the region between
parent and child wells, suggesting that
the fracture that propagates from the child
may be restricted in growth toward the
parent well because of altered stress magnitudes and principal directions.
The study results indicate that possible
mitigation strategies to prevent child well
underperformance include:
* Modifying the completion and treatment design of parent well fractures to
reduce the spatial extent of depletion
away from the parent well;
* Modifying child wells' frac design
to prevent the propagation of child well
fractures in the depleted region of the
reservoir; and
* Refracturing the parent well to increase stresses in the reservoir.
Based on these findings, operators can
better understand reservoir-scale stress
changes during depletion from existing
wells, and appropriate strategies for parent-child wells can be designed to maximize the effectiveness of infill stimulations.
r

RIPUDAMAN MANCHANDA is a research associate at the University of
Texas at Austin. His focus is on developing reservoir-scale hydraulic fracturing models to predict field observations related to the geomechanics of
unconventional reservoirs. He has provided consulting support to several oil
and gas companies for developing completion strategies for unconventional
assets, including optimizing well placement, well spacing, fracture spacing,
fracture sequencing, refracturing, fluid
diversion, parent-child interference
analysis, infill well fracturing, and fracture design. Manchanda has a B.S. in
chemical engineering from the Indian
Institute of Technology, and an M.S.
and a Ph.D. in petroleum engineering
from the University of Texas at Austin.

research engineering scientist at the
Center for Petroleum and Geosystems
Engineering at The University of Texas
at Austin. His interests include reservoir
simulation, geomechanics, injection well
performance and hydraulic fracturing.
Bhardwaj holds a B.S. in petroleum engineering from the Indian School of
Mines and an M.S. in petroleum engineering from The University of Texas at
Austin.

University and M.S. and Ph.D. degrees in
petroleum engineering from the University
of Texas at Austin.

PRATEEK BHARDWAJ is a reservoir
engineer with ExxonMobil, based in India. Previously, Bhardwaj worked as a
50 THE AMERICAN OIL & GAS REPORTER

JONGSOO HWANG is a post-doctoral
fellow in the Center for Petroleum and
Geosystems Engineering at The University
of Texas at Austin. He has worked as a
reservoir engineer at ConocoPhillips, and
as a production engineer at Korea National
Oil Corporation. Hwang's research interests
include reservoir geomechanics, fracturing,
waterflooding design, formation damage
analysis, gas condensate reservoirs and
numerical simulations. He holds a B.S. in
chemical engineering from Seoul National

MUKUL M. SHARMA holds the Tex
Moncrief Chair in the Department of
Petroleum and Geosystems Engineering
at the University of Texas at Austin. His
research interests include hydraulic fracturing, water management, formation
damage and improved oil recovery. He
is a member of the U.S. National Academy
of Engineering and a former SPE distinguished lecturer. Sharma has been the
recipient of the John Franklin Carll
Award, the Lucas Gold Medal, the SPE
Faculty Distinguished Achievement Award,
the Lester C. Uren Award and the SPE
Formation Evaluation Award. He holds
a bachelor's in chemical engineering
from the Indian Institute of Technology
and an M.S. and Ph.D. in chemical and
petroleum engineering from the University
of Southern California.

American Oil and Gas Reporter - July 2018

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