American Oil and Gas Reporter - April 2020 - 44

pages 44-49_Layout 1 4/6/2020 1:50 PM Page 44

SpecialReport: Industry Breakthroughs
Closed System
The technology has been validated
with low-frequency distributed acoustic
sensing (DAS) strain monitoring, microseismic monitoring, video-based downhole
perforation imaging, and production logging data in multiple plays and basins.
SWPM necessitates using a well that
acts as a closed system. In other words,
it cannot be connected by perforations
to the formation being stimulated in the
offset well. The casing must be sealed,
but uncompleted or existing wells can
be used for monitoring as long as the
shallowest perforations are isolated from
the targeted formation. For an existing
producing well, a plug is set above the
shallowest perforations to create a closed
system from the top of the plug to the
surface where pressure measurements
are recorded.
The wellbore is filled with low-compressibility fluid (e.g., completion brine)
to amplify the pressure response created
during monitoring. Fractures intersecting
the sealed wellbore cause local deformations, resulting in a small reduction in
the fluid volume inside the casing which,
in turn, generates a discernable and distinct
pressure response. Multiple sealed wellbores can be used to monitor a single
treatment well to allow for a more detailed

understanding of fracture growth. The
entire sealed wellbore acts equally for
pressure monitoring and is not biased by
large fluctuations in pressure magnitudes.
Pressure magnitudes generated in a sealed
wellbore range from less than 1 psi to
more than 10 psi (but normally less than
100 psi).
The field execution of SWPM is simple
and does not require any tools to enter
the wellbore. A surface pressure gauge
(or downhole gauge) provides the necessary data needed to evaluate fracture interactions with the monitor wellbore.
There is no need to alter zipper operations
as long as there are available sealed wellbores to use as monitor wells. SWPM's
main restriction to operations is the necessity to leave new wellbores sealed by
not opening toe sleeves or shooting perforations for any stage until monitoring
of offset treatment wells is completed.
Figure 1 shows an example of two sequential stages of a fracturing treatment
monitored with SWPM and DAS crosswell strain. The SWPM and cross-well
strain data were recorded on the same
monitor well. Each stage was completed
using five perforation clusters, which are
noted by the triangles on the left side of
the figure (colored by stage). The y-axis
on the strain rate plot is measured depth

FIGURE 1
DAS Cross-Well Strain, Treatment Data and SWPM Responses

44 THE AMERICAN OIL & GAS REPORTER

(increasing from top to bottom) of the
fiber optic cable along the lateral of the
offsetting monitor well. The treatment
well and monitor well were separated by
approximately 600 feet laterally and 100
feet vertically.
Time spans four hours and increases
from left to right on the plot. The colors
represent the condition of the fiber optic
cable at various depths over a portion of
the offset well's completion. Green represents a neutral strain state, red is an increasing strain rate (or decrease in cable
diameter, representing an area of tension),
and blue is a decreasing strain rate (or
increase in fiber optic cable diameter,
representing an area of compression).
Treatment data from the treatment
well and SWPM responses recorded in
the monitor well are shown in the three
tracks below the strain data. The top
track includes treatment pressure and
pump rate. The second track is the measured pressure (blue) from the sealed wellbore offsetting the treatment well. The
third track is the sealed wellbore pressure
derivative (brown) with respect to time.
VFR Measurement
The first stage is shown on the lower
left of Figure 1. The first fracture arrival
occurred early in the stage. It is identified
on the strain-rate plot by a tensile region
(red) located between two compressive
regions (blue). At the same time the strain
recorded a fracture intersection, the SWPM
data shows a pressure inflection amplified
on the derivative plot. The timing of the
"volume to first response" (VFR) for
each stage is noted by dashed gold lines
for both stages. Simply stated, VFR is
the volume of fluid pumped into the treatment well when the fracture intersection
occurs at the monitor well. It is a qualitative
measure of cluster efficiency, or fluid
distribution uniformity within a stage.
As shown in Figure 1, as Stage 1 progressed, a second fracture intersected the
monitor well at a shallower measured
depth (heelward). The strain response
shows a tensile region between two compressive regions and sealed wellbore pressure shows a second pressure inflection.

American Oil and Gas Reporter - April 2020

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