American Oil and Gas Reporter - August 2015 - 77

SpecialReport: Hydraulic Fracturing Technology

Advanced Tools Simplify Fracturing
By Colter Cookson

Watching a good movie a second or
even a third time can be extremely rewarding. Characters' motives become
clearer, missed details emerge out of the
background, and plot line subtleties take
on new meaning. Believe it or not, the
same can be said of hydraulic fracturing
in unconventional basins.
As operators review their ever-expanding libraries of hydraulic fracturing
data, they are discovering details that are
leading to new understandings of how to
optimize stimulation treatments and boost
productivities on a stage-by-stage basis.
The goal remains unchanged-creating
flow conduits that connect the lateral to
the reservoir-but the industry's experience
base in resource plays continues to redefine
both best practices and best-in-class technologies.
The focus is on deploying advanced
perforating systems, downhole completion tools, and proppants and other components to improve the efficiency, cost
and operational safety associated with
multistage completions without compromising wellbore integrity or treatment
effectiveness.
And even though the industry still is
transcending the learning curve in unconventional reservoirs, the sequels are
being scripted. Operators of all sizes are
seeking to deploy many of the essential
tools and techniques pioneered in tight
oil and shale gas development to a diverse
set of applications, including stimulating
ultradeepwater wells in the Gulf of Mexico
Lower Tertiary trend, fracturing/refracturing conventional shallow vertical wells
in mature onshore fields, and ultimately,
ushering in comprehensive refrac programs
in horizontal resource plays.
Engineered Completions
"Early on, the industry used the traditional approach of fracturing in regular
intervals of so many feet, because in a
conventional reservoir with moderately
high permeability, all those fractures
could be expected to produce," recalls
George King, a distinguished engineering
adviser with Apache Corp. "Today, many
operators are looking for engineered completions that target the rock with the
greatest potential for natural fractures,
and avoid rock with low potential or geo-

hazards.
"We are getting smarter about where
we place the fractures," King assesses.
"Next, we need to get better at propping
small natural fractures to create more
stable contact with the pore throats,
fissures and microcracks in the formation."
Toward that end, operators are identifying proppants that are more easily
carried by slickwater and dispersed
throughout the contacted area, King says.
He expresses confidence that completion designs will continue to improve,
citing the industry's past accomplishments.
"Since the 1990s, we have moved from
being able to recover 1-2 percent of the
total gas in place in an unconventional
reservoir to 20-40 percent, with the exact
amount depending on the permeability
of the shale and the effectiveness of the
completion," he reports.
In oil shales, the recovery rate has increased from 1.0-1.5 percent to 5.0-8.0
percent. King suggests further improvements can be achieved by researching
flow physics and deploying additives traditionally seen as secondary flow improvement solutions.
"These additives change the viscosity
of the oil, the interfacial surface tension
or the surface wetting thickness to improve
oil flow and create better flow pathways.
The pathways are no wider than they
were before, but they are cleaner, which
allows the oil to flow," King outlines.
"Understanding how to use these chemicals more effectively is an area we need
to focus our efforts."
Given enough time, such efforts may
unlock heavier oil. "In many wells, the
oil in the reservoir has an API gravity of
30-35, but what is being produced has a
gravity of 40-50, because the heavier liquids are staying inside the rock," King
says. "The well only produces the drive
fluids, methane gas, and solvents. I think
the solution to getting the rest of the oil
will be rooted in modifying the oil or the
flowing pathways."
Refracturing
As technology improves, King predicts
a growing number of wells will become
candidates for refracturing. "Refracturing
older wells that were completed initially
using foams and cross-linked gels with
slickwater or hybrid fracturing fluids has

given tremendous improvements in flow.
Often, wells that have been producing
three or more years flow at higher-thanever rates after refracturing," he says.
Today, many wells are being designed
with refracturing in mind. King says well
integrity is a big part of that effort. "As
we apply cyclic stresses on cemented-in
casing during refracturing operations, we
can create leak paths, so we need to use
good pipe joint technology and cements
that can withstand the cyclic application
of pressure," he says.
"Once an operator knows a well is
suitable for refracturing from a well integrity standpoint, he needs to look at
the reservoir itself to find places that
have not produced yet, but could with a
refrac," King continues. "Many laterals
are a mile or a mile-and-a-half in length,
so there often are areas that have not
been stimulated adequately."
Refracturing operations have yielded
mixed results, King allows. "For the industry to perfect refracturing, it needs to
move from a single-well approach to a
'campaign' approach. Instead of refracturing a single well, commit to five, 10
or 15 wells and learn from each," he advises.
Advanced Ballistics
Completing horizontal wells, particularly in shales, has become increasingly
complex, observes Patrick Keenan, chief
executive officer of Guardian Global
Technologies. "Both the length of the
borehole's lateral section and the number
of frac stages needed to adequately access
and drain the reservoir have contributed
to the difficulty of accurately placing
perforating guns. To place the guns ondepth, orient them in the right direction,
fire them safely, and pull them out of the
hole without getting stuck required a new
approach."
To address these challenges, Guardian
has introduced its integrated Ballistics
Delivery System (BDS™). Keenan says,
"The delivery system incorporates everything needed, from the cable head to the
detonator, to deploy gun systems. In particular, it includes an addressable release
tool that can part the string without an
explosive charge and leave a clean fishing
neck if the tools become stuck, and a
cable head tension tool to measure wireline
compression and tension. In addition, the
AUGUST 2015 77

American Oil and Gas Reporter - August 2015

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