American Oil and Gas Reporter - April 2020 - 51

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SpecialReport: Industry Breakthroughs

Another way of investigating a parent
well's impact using SWPM is measuring
asymmetry of infill fracture geometry induced by primary well depletion. Figure
4A presents a map view of four horizontal
wells. The 1H is a depleted primary well
that had a cumulative production of
~500,000 barrels of oil prior to infilling
with the 5H, 7H and 9H wells. No depletion mitigation technique was employed.
The wells are spaced 600 feet laterally,
and the toe sections of the wells are
located at the top of the image with the
heels at bottom. The 5H and 9H were
completed in a zipper fashion, alternating

stress) are elevated enough, fractures
will grow asymmetrically toward the depleted volume.
Figure 4B shows a map view of the
1H, 4H and 7H wells in an adjacent unit
(the same unit in the microseismic example
in Figure 2) to the wells in Figure 4A.
The 1H is a depleted parent well that had
cumulative production of ~180,000 bbl
prior to infilling with the 4H and 7H.
Depletion mitigation was employed in
this unit; the primary well was recharged
with water prior to the offset well completions to increase pressure in the depleted
area and reduce the asymmetry of fractures
generated from infill wells. It is believed
that a major driver for infill well underperformance is the asymmetry of generated
fractures and a reduction of fracture height
in the first-order offset well.
This case study represents the Devon
team's attempt to alter subsurface pressure
and stress to redirect first-order fracture

FIGURE 4B
Map View of VFRs for Well Offsetting
Primary Well with Depletion Mitigation
1H
Parent Well

7H
SWPM

Stage

Fracture Geometry

between wells for each stage.
The bar chart on the 5H and 9H represents the VFRs measured using SWPM
recorded in the 7H. Each bar represents
the volume pumped into the treatment
well when the 7H sealed wellbore recorded
a pressure response. Longer bars equate
with more fluid pumped into the treatment
well before the response was recorded
on the 7H. The key take-away from the
image is the 5H failed to generate fractures
that contacted the 7H for the first 60% of
the lateral, while the 9H generated a response for every stage completed.
We believe the lack of pressure responses in the first portion of the 5H
completion was attributable to asymmetric
fracture growth into 1H depletion. This
response has been observed extensively
in the field to varying degrees, while the
primary well indicated continued pressure
build during offset stimulations. Until
that region's pressure (and resulting

Pressure Maintenance Strategy

were the slowest in the unit. In these
wells, average diffusivity was 25 feet2/s
(Figure 3B4).
We have several theories for what the
fracture diffusivity data says about fracture
interaction, but it is important to clarify
that these early hypotheses need additional
testing. The fact that the microseismic
often showed lower diffusivity that agreed
with the diffusivity in the well being
stimulated in unfractured rock leads us
to believe lower diffusivities (less 50
feet2/s) represent new hydraulic fracture
generation instead of restimulations of
previously created hydraulic fractures.
For the infill well completed next to a recently completed well (Figure 3B3), the
fact that diffusivity was high, leading to
higher fracture propagation speeds, leads
us to believe most of these responses
were also short-circuits into adjacent infill
hydraulic fractures.
The final wells in the unit, located on
Pad 2, had the highest fracture gradients
and were bounded by the other two pads
(Figure 3C). These wells had the lowest
diffusivities, where either the active
clusters were not being diverted into previously created fractures, or those previously created fractures had high enough
pressure to prevent a rapid pressure response. Regardless of the mechanism,
the higher fracture gradient was likely
responsible for the lower diffusivities and
prevented the negative impact of a shortcircuit cluster on completion efficiency.

30
1,000
VFR (bbls)

2,000

APRIL 2020 51

American Oil and Gas Reporter - April 2020

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