American Oil and Gas Reporter - July 2015 - 91

SpecialReport: New Products/Technology
engineered wells (Figure 3).
Perforation efficiencies ranged from
75 to 89 percent, with an average of 82
percent. This represented an 18 percent
average increase over traditional geometric
completions, including a full 50 percent
reduction in nonperforming clusters. Net
present value calculations based on production results showed an increase of
40,000 barrels-worth $1.5 million at the
time-in the first year of production alone.
This yielded a 15-to-1 return on investment
for acquiring the comprehensive log data
required to properly engineer completions.

Through-The-Bit Tool
Since the Eagle Ford consortium study
was completed, a through-the-bit dipole
service has been commercialized that applies the latest acoustic technology to
acquire borehole-compensated monopole,
cross-dipole, and low-frequency Stoneley
wave measurements. It is capable of
measuring both fast- and slow-shear slownesses, as well as compressional slowness
and low-frequency Stoneley waves, in a
single small-diameter sonic tool.
As a result, operators may place engineered completions with greater confidence, based both on accurate fracture
detection and direct anisotropic stress
measurements at every point along the
lateral. What is more, they can eliminate
the risks, rig time and costs associated
with additional logging runs to acquire
standard dipole sonic logs.
Extensive field trials of through-thebit dipole sonic technology in both vertical
and horizontal wells determined that the
measurement quality of the slim tool
varied only 1-2 percent from that of
leading standard-size dipole sonic tools.
More than 50 logging jobs-most in unconventional plays across North America-have employed the new service.
An operator in the Wolfcamp Shale
of West Texas was one of the early
adopters of the small-diameter dipole
sonic tool, despite having already achieved
considerable success using monopole and
synthetic shear data to plan engineered
completions.
Not only is the Wolfcamp reservoir
deep and highly pressured, but it consists
of laminated, clay-rich layers under variable stress. Historically, therefore, the
company found it challenging to produce
the field efficiently. Among other problems, its geometrically spaced perforation
clusters often suffered screen-outs in parts

of the wellbore that happened to land in
rocks of higher stress. Costs to mitigate
screen-outs exceeded $300,000 per incident.
By incorporating a full suite of throughthe-bit logging tools, measuring petrophysical and mechanical rock properties
along the lateral, and optimizing perforation intervals based on computed stresses
(Figure 4), the operator was able to boost
90-day cumulative oil production by 39
percent in his first horizontal well with
engineered completions.
Compared with three geometrically completed wells in the same area, three subsequent horizontal wells using through-thebit logs and engineered completions delivered, on average, a 103 percent increase in
90-day cumulative production. In addition,
eliminating screen-outs saved hundreds of
thousands of dollars in operating expenses.
Since then, the operator has used the
same logs and engineered workflow for
every new well in the field. However,
petrophysicists never have been able to
directly measure all the reservoir's acoustic
properties or fully quantify stress
anisotropy. Field testing of the new
through-the-bit dipole sonic tool enabled
them to reliably measure up to 30 percent
anisotropy in one Wolfcamp well for the

first time (Figure 5). This allows the operator to further refine engineered completions, and gives completion engineers
substantially greater confidence in the
accuracy and reliability of their designs.
Another operator, who was targeting
the Buda Limestone in South Texas, now
is using Stoneley wave measurements
from through-the-bit dipole technology
for independent fracture detection, especially in the absence of borehole imaging.
In this case, it is vital to position hydraulic
fracture stages on either side of natural
fractures to prevent proppant from being
lost, which can have a significant impact
on costs.
Not only do Stoneley measurements
confirm the presence and location of fractures, but increases in Stoneley slowness
indicate probable gas entry points in the
lateral (Figure 6). After initial throughthe-bit dipole sonic logging, the operator
confirmed these results by logging the
interval again, using standard-size sonic
and formation microimaging tools.
Conclusion
One of industry's greatest challenges
in unconventional plays-especially at today's oil prices-lies in designing completions that increase production signifi-

FIGURE 5

New, through-the-bit dipole sonic measurements enabled the operator to reliably measure
up to 30 percent slowness-based anisotropy in one Wolfcamp well.

JULY 2015 91

American Oil and Gas Reporter - July 2015

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