American Oil and Gas Reporter - January 2022 - 64

Stress shadow interference also can
cause runaway dominate fractures. One
potential design change to battle against
dominate fractures is to decrease the perforation
density per cluster, creating some
level of " limited entry " as well as diverters.
Doing so increases the pressure across
the perfs, which may help ensure even
flow into each cluster during treatment.
Finding the right balance of stage and
cluster spacing has a lot of potential if
optimized for the well, reservoir and current
economic environment.
However, quickly finding the ideal
lateral length and perf cluster design for
the economic conditions requires a diagnostic
tool that can tie those design
changes back to production in near real
time. One such solution is fiber optic
sensing, which simultaneously can measure
all events happening along the entire
wellbore with little interference to the
true production flow regime during inflow,
while also maintaining high spatial resolution
down to the cluster level.
To take its lateral length and perf
cluster designs to the next level, Rockliff
used wireline-deployed fiber optic cable
to monitor the production of a hydraulically
fractured horizontal well so that
the insights could be applied to the 40+
horizontal wells it completes annually
within its large East Texas acreage position.
In this area, the Haynesville is located at
approximately 11,000 feet true vertical
depth, making it a high-temperature (300+
degrees Fahrenheit), predominantly dry
gas-producing reservoir.
The well was producing for one month
before intervention to install the distributed
acoustic sensing (DAS) and distributed
temperature sensing (DTS) wireline-deployed
fiber optic cable. The temporary
fiber optic line was conveyed down hole
using a tractor and left in the wellbore
over two and a half days.
Production Uplift
The focus of the test was to optimize
the completion design by varying the
amount and distance between clusters of
perforations along a section of the wellbore
in an effort to discern their effect on production.
Production allocation then was
quantified for both individual stages and
perforation clusters. Results show that
64 THE AMERICAN OIL & GAS REPORTER
the stages with an increased amount of
clusters exhibited greater uniformity and
produced 140%-175% more, depending
on the choke setting. Additional data and
time are needed from full wellbore tests
to confirm if incremental production uplift
accelerates production or adds to the estimated
ultimate recovery.
With fiber optics, simultaneous measurements
of acoustic fields (DAS), strain
(distributed strain sensing, or DSS), and
temperature (DTS) along the horizontal
distance of the fiber can be made instantaneously
at the speed of light. Fiber traditionally
has been placed in the well
permanently by clamping and cementing
a tubing-encased fiber in place on the
outside of the casing. " Engineered " fiber
is now able to be placed inside a wireline
cable that can be deployed inside the
casing to acquire data, and then subsequently
retrieved for use on additional
wells. Temporary deployment gives an
operator more flexibility to diagnose other
wells of interest rather than only a few
with permanent fiber.
Moreover, improvements in the surface
interrogator hardware and enhanced engineered
fiber design boost the signalto-noise
level by 20 decibels (100 times)
compared with standard single-mode
fibers.
Fiber data is a distributed measurement,
meaning at every meter along the optical
fiber acoustic, strain and temperature data
can be acquired. The fiber optic system,
which includes the surface fiber optic
sensing interrogator unit (laser) and the
actual fiber itself, measures those physical
properties at multiple sampling locations
along the fiber.
For this Haynesville project, the plan
was to record at a gauge length (or measuring
length of the fiber covering multiple
sampling locations) of 10 meters and 2
meters using two single-mode engineered
DAS fibers and a DTS fiber in the same
wireline cable. However, plans were
changed during the job because of equipment
availability, so that data was recorded
only on a 10-meter (32.8-foot) gauge
length DAS fiber with a spatial sampling
interval of 0.25 meters. The physical property
output (acoustic, strain, temperature)
is measured at the gauge-length level,
and not at the sampling location level.
Project Setup
A coiled tubing clean out operation
was performed before logging the well to
increase the chances of reaching the toe
without experiencing increased friction
caused by solid materials and well tortuosity
along the wellbore. A high-temperature
tractor was chosen to pull the wireline
fiber to the toe. The tractor was ultimately
able to pull the wireline fiber to a total
depth of 20,700 feet, allowing production
to be measured from all but the first six
stages of the 99-stage wellbore.
Although the wireline fiber cable with
the 2-meter engineered fiber was not available,
the 10-meter gauge length fiber provided
the benefit of measuring flow from
very low producing clusters but could not
fully isolate inflow to an individual cluster.
The engineered DAS fiber was sampled
at 5 kilohertz with a spatial sampling of
one meter and the DTS data was recorded
at one meter spatial sampling.
The well had been fracture stimulated
using a slickwater fluid system with diverters
designed for 10,000 barrels per
stage, 160,000 pounds of 100-mesh sand
per stage, and 194,000 pounds of 40-70
mesh sand per stage for all 99 stages.
The cluster design was identical across
stages 1-74, but a variable design was
implemented for stages 75-99. Stages 174
all contained six clusters at six shots
per foot, with an average cluster spacing
of 17 feet. The variable design of stages
75-99 included nine clusters per stage
(11-foot cluster spacing) with 33% fewer
shots per foot and a tapered perf design
to promote greater uniformity. Regardless
of design, entry-hole diameter and the
total amount of shots per stage (36) were
kept constant.
Stage 100 was left unfractured to later
be used as a baseline measurement for a
separate camera project. One of the
focuses of the production monitoring test
is to investigate if there was a noticeable
change in production at the location of
the stages with shorter cluster spacing
and shot reduction designs.
Production Monitoring Objectives
A total of 60 hours was allotted to produce
the well at variable rates. Four opening
and closing sequences were chosen to
capture any production changes. The four
American Oil and Gas Reporter - January 2022

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