American Oil and Gas Reporter - February 2017 - 27

TECHCONNECTIONS
Consistent Hole Size
For Horizontal Perforations
Improves Performance
Recently in Houston, I attended a Society of Petroleum Engineers Gulf Coast Section Westside Study Group luncheon.
The speaker, Dan Pratt, discussed the importance of consistently
sized perforations for unconventional reservoirs. Pratt is the
vice president of engineering and technology for Owen Oil
Tools, a division of Core Lab, and has been developing oil field
explosives for almost 40 years. Through the years, he has come
to specialize in developing oil field perforators and shaped
charges. In fact, Pratt holds numerous U.S. patents relating to
designs for shaped charges, charge liners and materials used in
propellant stimulation. In my opinion, he may have one of the
most interesting jobs in the oil field. Until hearing this presentation,
I always had thought in terms of "perf it, pump it and produce
it." As it turns out, the perf portion of this process is slightly
more important than I originally assumed.
At its core, the purpose of perforating always has been to
create effective communication between the wellbore and formation. According to Pratt, until recently, any change in charge
design revolved around increasing the depth of penetration into
the reservoir or enlarging the hole size. However, as horizontal
unconventional wells have become the norm for many operations,
it has become necessary to develop new, enhanced perforating
systems that are geared at hole size uniformity.
According to Pratt, an operator generally communicates the
desired hole size to the service provider. Typically, perf sizes
are selected to complement the fracturing treatment design and
optimize pumping effectiveness. A good service company should
have no problem creating the average desired hole size and
meeting the operator's design requirements on the surface.
However, a closer look at the data around each specific perf
often reveals a relatively large deviation between the actual
maximum and minimum hole size in a particular orientation.
Pratt warns that this inconsistency can increase perf friction and
tortuosity while reducing cluster efficiency in multi-stage wells.
There are two components to perforating, Pratt explains. The
first component creates a specifically-sized hole in the tubular
and cement sheath surrounding the well. The second component
creates hole length or a "perforating tunnel" into the formation.
When designing a treatment, operators or engineers must
consider hole size, information they can get from a variety of
sources. The American Petroleum Institute conducts testing in
actual well tubulars and has recommended practices for designing
these treatments. Quality control testing and simulations are
also available for consideration during design.
According to Pratt, the standard API hole size for 4.5-inch
casing is 0.39 inches, but when he showed testing data, the hole
size varied greatly. The actual sizes among four perforations he
cited were 0.37, 0.39, 0.31 and 0.26 inches. While hardly uncommon, Pratt says this hole size variability can impact overall
frac effectiveness and well performance.
Pratt went on to compare various treatments to show how the
selection of quality treatments can improve the standard deviation
among perforations. His first example showed actual data using

"A relatively large deviation between the actual
minimum and maximum hole size can increase
perf friction and tortuosity while reducing

"

cluster efficiency in multi-stage wells.

the conventional low-cost charge. The difference from minimum
to maximum was 0.25 of an inch or a standard deviation of 28.5
percent. The slightly costlier treatment design proved a little
better with a difference from minimum to maximum of 0.14
inches or 15.9 percent standard deviation. Finally, a perforator
specifically designed to create consistent-sized holes yielded a
range of 0.03 inches between minimum and maximum, or a 3.2
percent standard deviation.
According to Pratt, the most commonly phased perf gun in
today's completions offers 60 degree phasing and the clearance
between the gun's outside diameter and the casing's inside
diameter varies according to gun position. In a horizontal well,
the gun will be on the bottom of the wellbore, making the shots
at 6 o'clock closer than those at 12 o'clock. Using conventional
charges can reduce the perf hole size in the wellbore's 12
o'clock portion and ultimately diminish the frac's effectiveness
in these perfs.
Like most techniques used to optimize treatments and well
performance, getting it right takes a little more work and maybe
some more upfront cost, however the increased success over
time and among wells speaks for itself. As you design your next
treatment or work with your service company, take a closer
look at hole size among perforations and see if perf optimization
makes sense for your operation.
❒

JEREMY VISCOMI is the Mid-

continent Regional Lead for
the Petroleum Technology
Transfer Council. He has more
than a decade of experience
in developing and organizing
technical conferences and special events, primarily in the
oil and gas industry.
FEBRUARY 2017 27



American Oil and Gas Reporter - February 2017

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