American Oil and Gas Reporter - September 2019 - 59

SpecialReport: Horizontal Wellbore Architecture

Method Characterizes Offset Pressure
DENVER-Pressure communication
between wells is common in horizontal
resource plays, especially with development activity concentrating on drilling
and completing infill child wells. During
hydraulic fracturing, child wells often
observe altered stress states related to
depletion effects in offset parent wells.
This stress alteration allows the child
well fracture to interact with multistress
zones, which ultimately affects the growth
rate and final geometry of the fracture.
The result is a nonuniform growth
profile of the child well's fracture. During
hydraulic fracturing, tip energy usually
is diverted toward the parent well because
of its lower localized stresses caused by
production, which may lead to a direct
communication event (i.e., frac hit).
Technological advancements have significantly reduced the cost of deploying
high-resolution surface and downhole
pressure gauges, which provides an opportunity to monitor and analyze parentchild well interactions with a level of
detail that has never been possible. However, for the industry to fully capitalize
on this potential breakthrough to characterize offset pressure, a cost-effective,
scalable, timely and standardized analysis
method is required to guarantee the integrity of recorded pressure data and minimize interpretation bias.
One approach to achieving standardization for offset pressure characterization
uses measurable values to quantify key
factors in interwell communication and
classify the nature of the pressure response
by analyzing transient pressure behavior
before, during and after the completion
of a stage. This repeatable and auditable
algorithmic implementation relates the
magnitudes and derivatives of the measured
pressure in the offset parent well(s) to the
treatment pressures and volumes pumped
in the child well during stimulation.
Pressure Response Categories
There are many root causes of pressure
responses observed in nearby parent wells
during hydraulic fracturing operations on
a child well, but the maximum pressure
gradients can be binned into one of four
categories:
· Poroelastic (fracture shadowing),

whereby the offset wells observe pressure
inflections from the increased effective
stress exerted by the fluid pressure within
the child well during fracturing. The fluid
pressure within the fracture compresses
the formation, and the compressive stress
field grows linearly with respect to the
dominant hydraulic fracture within a
given cluster.
· Fluid migration, which is common
and often mistakenly classified as a direct
communication event. In this situation, fluid
escapes from the fracture network surrounding the child well and migrates into
the parent well fracture network. It is characterized by a gradual pressure increase in
the parent well after stimulating the child
well with no immediate relaxation of pressure, as is typical of poroelastic events.
· Direct communication (frac hit),
which is indicated by an instantaneous
pressure increase and a significantly different buildup trend than poroelastic response. It is important to note that both
poroelastic and direct communication responses have similar inflection points at
the end of stimulation. The difference is
the pressure source: compressional force
for poroelastic stress shadowing and hydraulic pressure for frac hits.
· No observable pressure responses.
To date, this method has been used to
analyze more than 70 wells in U.S. and
Canadian basins. Classifying the type of
each pressure signal indicates direct fluid
communication, fluid migration, or
undrained poroelastic behavior governing

the observed pressure responses. In doing
so, the process reveals direct information
on zonal isolation, short- and long-term
well communication, and effective fluidic
pathways created by fracture networks.
This information, in turn, provides insights
into the effective distance between child
and parent wells, stress effects and barriers,
possible mitigation techniques to perform
on child wells, and suitable protective
techniques for the parent wells.
In addition, novel data visualization
and interaction play a central role in delivering insights, including the integration
of seismic attributes and well logs, to
support decision making regarding well
spacing, diverter deployment, tailored
volumes offsetting depleted heels, and
increased nonperforation zones (NPZs)
around faults.
Using pressure gauges on the parent
well provides the ability to conduct near
real-time analyses of communication with
the child well during treatment. Various
measurement techniques can be used to
analyze parent/child pressure communication, distinguish pressure response types
and diagnose the severity of communication,
including surface gauges with or without
a preloaded parent well and bottom-hole
gauges with or without isolation.
Each method has advantages and disadvantages, but high-resolution surface
monitoring is generally the optimal selection
given its measurement accuracy and lower
cost compared with downhole gauges.
However, parent well preloading is im-

FIGURE 1
Downhole (Red) and Surface (Blue) Pressures versus Time
Surface
Downhole

3,500

3,000
3,000

2,500
2,500
Gauge Pressure (psi)

By Justin Mayorga
and Erica Coenen

2,000
2,000

1,500
1,500

1,000
1,000

Nov 05

Nov 12

Nov 19

Nov 26

Dec 03

Dec 10

Dec 17
2018

SEPTEMBER 2019 59
American Oil and Gas Reporter - September 2019

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