American Oil and Gas Reporter - January 2022 - 66

opening steps had four unique choke settings
starting at 100% open (the normal
operating choke size setting at this point
in the well life cycle), dropping to 80%,
then 60%, and finishing at 120%. At each
opening, the well produced long enough
to ensure a sufficiently stable flowing
regime to perform production analysis,
and in this case, four hours sufficed.
Figure 1 displays produced gas and
water flow rates at surface. The choke
setting is marked above each flowing period.
The production data is crucial for
calibrating the thermal DTS model. The
period selected for calibration was the
100% open choke setting (the normal
operating choke size). During all periods,
the water flow was captured downstream
of a dump-valve, causing " spikes " in
water flow that are not representative of
the actual flow rate. Also, the well was
slugging as noted later in the DAS and
downhole pressure data. To account for
this, a stable flow period the week prior
at the 100% open choke setting is examined.
A very stable water flow rate of
2,000 bbl/d was found and this value
was used in the DTS model.
The goal of the test monitoring program
is twofold and examines production at
the wellbore, stage and cluster levels to
determine two-phase production allocation,
and stage and cluster design effectiveness.
Two methodologies were employed
to quantify inflow performance:
· DAS-based acoustic noise logging
to allow for a near-cluster level inflow
performance assessment; and
FIGURE 1
Gas and Water Flow Rates Measured at Surface
6,000
5,000
4,000
3,000
2,000
1,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
Gas Flow Rate (Mcf/d)
Water Flow Rate (bbl/d)
100%
80%
60%
· Thermal modeling to allow for
stage-by-stage multiphase allocation.
The data processing workflow for multiphase
allocation typically combines
DAS derivates such as acoustics spectral
noise logging, sound speed analysis and
thermal plumes analysis to constrain an
enthalpy balance based thermal model.
The sound speed analysis did not reveal
any propagation throughout the horizontal
section and therefore could not be used
for fluid composition trending and as an
input to the thermal model. The very high
number of closely spaced perforations
were likely to be the reason for the strong
attenuation of the tube waves.
Thermal Modeling
The thermal model considers essential
well information, including a well diagram,
fluid properties, deviation survey,
surface rates and other reservoir information
that can help reduce the uncertainty
of the model.
Building and running a thermal model
in an unconventional horizontal well with
hundreds of fractures represents a challenge,
since even after one month of production,
the well still exhibits particular
temperature features that resemble the
temperature changes induced by the stimulation
and fracturing process. This means
there can be specific depths in the DTS
trace that could resemble a Joules-Thomson
cooling effect, yet they are temperature
cooling remnants induced by stimulation
fluids. These lingering stimulation features
can affect the spatial derivative calculation
in the thermal model and allocate a larger
amount of production to a zone that is
not necessarily a high production contributor.
This is where DAS derivatives
play an essential role in constraining and
tuning the thermal model.
The model then was further constrained
for multiphase allocation using DAS derivatives
transient thermal plumes from
shut-in to flow, slow-strain root-meansquared
(RMS) waterfalls during stable
flow, and acoustic spectral activities.
Dual-speed thermal plumes were utilized
for two-phase fluid entry point identification
and the slow strain waterfalls to
identify the main flow regimes. The main
water entry points identified were then
included in the water profile for the
thermal model.
Due to limitations in the simulation
running time for the thermal model to
reach convergence and the very high
amount of stages and clusters, the thermal
model was built to perform a stage allocation
from stages 7-69 and to perform a
cluster level allocation toward the heel
from stages 70-99.
Analysis And Results
The thermal plumes created during the
initial well opening (100% normal operating
choke setting) and for seven hours
following are displayed in the expanded
slow-strain DAS RMS amplitude waterfall
plot in Figure 2. Immediately upon opening,
thermal plumes were spotted as hotter
reservoir fluid entered the wellbore and
caused a thermal strain on the DAS fiber.
120%
66 THE AMERICAN OIL & GAS REPORTER
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Flowrate_MCFD
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American Oil and Gas Reporter - January 2022

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