American Oil and Gas Reporter - March 2019 - 49

SpecialReport: Unconventional Resource Science

Study Assesses 'Generational Effects'
By Kimberly Ayers,
Henry Jacot
and Alivia Ayers
PITTSBURGH-In the Appalachian
Basin and other horizontal resource plays,
the generational effects of parent and
child wells are becoming a primary concern to operators as they increasingly
shift focus to full-field development using
multiwell pads. The issues surrounding
generational effects include child well
spacing and stimulation designs, protecting
parent wells from frac hits, parent well
recompletion/refracturing, depletion of
stimulated reservoir volumes, and re-orientation of stress profiles.
To examine the relationship between
parent and child wells, a study was conducted on a 10-well pad in Southwestern
Pennsylvania to analyze detailed pressure
and temperature data recorded by a bottom-hole memory gauge in a parent Marcellus Shale well during hydraulic fracturing operations of offset child wells
completed in both the Marcellus and Burket shales. The analysis also included
hydraulic fracture modeling to mitigate
communication between parent and child
wells and rate transient analysis (RTA)
to understand the depletion of the producing zones.
In this case, the parent well had been
producing only for a short time prior to
being shut in to complete the child wells.
Once child well stimulation operations
were completed, the bottom-hole gauge
data from the parent well were examined
to identify the general magnitude and
timing of frac hits in relation to the rock
matrix, completion design parameters
and completion sequence. Logistic regression testing also was performed on
individual parameters to determine key
influencers of frac hits.
The results of the study concluded
that more than 75 percent of the frac
stages in the Marcellus child wells had
communicated with the parent well, with
the most frac hits attributed to the nearest
child well.
The operator drilled 10 horizontal
wells on the pad with approximately
8,000-foot lateral lengths in the same azimuth: five wells in the Marcellus Shale
and five in the Burket Shale overlying
the Marcellus (in this area, the distance
between the Burket and Marcellus is 250

feet). The wells were drilled in a stacked
pattern with 600-foot spacing. All 10
wells were drilled under similar parameters
with similar lateral lengths and identical
casing programs.
Because of a variety of factors, the
operator chose to complete and produce
only one well-the center Marcellus well,
the P3-M-in the initial phase of development and temporarily leave the remaining
nine wells drilled but uncompleted. After
nine months on line, during which it produced 600 million cubic feet of gas and
8,200 barrels of condensate, the P3-M
was shut in for a second phase of completion operations.
Phase Two Operations
The first step in phase two was conducting flowing material balance, linear
flow analysis and reservoir simulation
on the parent well to understand pressure
depletion related to its brief production
history. A calculated sand face pressure
match was achieved and the resulting
simulation showed minimal reservoir
pressure depletion, given its short time
on production and nanodarcy permeability.
The minimal reduction in reservoir pressure was not expected to have a major
impact on fracture growth and communication.
Based on RTA results and other operational considerations, the operator chose
to complete five additional wells during
phase two: three of the Marcellus (C1M, C4-M and C5-M) and two of the
Burket (C11-B and C15-B) DUCs. Figure
1 shows the P-3M parent well in red, the
five child wells completed in phase two
in green, and the four wells left as DUCs
in grey.
The two Burket wells are located farthest away from the parent, and the C4M Marcellus well is closest to the parent.

Because of its proximity to P3-M's slightly
pressure-depleted area, it was determined
that the C4-M would have a smaller stimulation design with reduced fluid and
proppant volumes to lessen the potential
impact on the nearby parent well.
The operator removed the tubing,
loaded the P3-M parent wellbore with
produced water and installed the bottomhole pressure gauge beneath a retrievable
bridge plug. The bottom-hole gauge
recorded pressure data at a one-second
interval. The P3-M was shut in for 21
days prior to starting the first frac stage
on the first of the five child well completions. As expected, pressure buildup was
recorded on the parent well during the
shut-in period.
Three-dimensional hydraulic fracture
modeling was performed to estimate the
fracture dimensions for the P3-M. The
parent well was completed with an "engineered" design where perforations were
selected based on cased hole log data acquired with the XMAC™ acoustic tool
from Baker Hughes, a GE Company.
Stage 11 was modeled and consisted of
approximately 8,000 barrels of slickwater
and 474,000 pounds of sand. The stage
length was 236 feet with five clusters per
stage. The designed injection rate was
90 barrels a minute.
To more accurately model the fracture
growth, "stress shadowing" was included
in the model from Stage 10. The modeling
results show unequal fracture growth because of stress shadowing and interference
between fractures in the same stage. The
cluster closest to the toe took the least
amount of fluid, while the cluster closest
to the heel took the most fluid.
Given the 3-D hydraulic fracture modeling results, the completion design team
focused on the distance from the parent
well and the target formation as primary

FIGURE 1
Cross-Sectional View of Wellbores with Parent Well (Red),
Child Wells (Green) and DUCs (Gray)
C11-B

600'

12-B

13-B

250'

C1-M

600'

2-M

P3-M

14-B

C15-B

Burket

5'

1,22

C4-M

600'

C5-M

Marcellus

1,200'

MARCH 2019 49



American Oil and Gas Reporter - March 2019

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

Contents
American Oil and Gas Reporter - March 2019 - Intro
American Oil and Gas Reporter - March 2019 - 1
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