IMPROVING FRACKING POWER & EFFICIENCY
Field trials demonstrate
e-frac efficiencies
STEPHEN WHITFIELD, ASSOCIATE EDITOR
Last year, NOV conducted an eight-month field trial of its
Ideal electric fracturing (e-frac) technology across several
reservoirs in Texas and New Mexico. The tests, completed
in collaboration with NexTier Oilfield Solutions, focused on
measuring the efficiency gains that can be generated by
using an e-frac system. The tests also aimed to demonstrate
that the Ideal technology can help operators maintain high-
horsepower operations without putting excessive strain on
the frac motor.
“What we wanted to focus on was, how do we harness
the electrical capability in the e-frac system to drive better
fracturing performance, lower NPT and improve efficiency
on location?” said Travis Bolt, Product Development Manager
and Head of R&D for Pressure Pumping Equipment at NOV.
“The cost of fracturing continues to be high. We’re seeing an
increase in complexity around frac operations. We’re all con-
verging on that question of, what’s the next step for fracturing
equipment?” At the 2022 SPE Hydraulic Fracturing Technology
Conference in The Woodlands, Texas, on 3 February, Mr Bolt
discussed both the general efficiencies that can be realized
from an e-frac system, which uses a natural gas reciprocating
engine as its primary power source, as well as more specific
field testing results for the Ideal system.
Control of equipment to improve reliability was a major
focus of the field testing. This primarily involved examining
the turndown ratios of the motors, or the ratio of a motor’s
speed relative to the base speed at which it can be operated
safely at 100% torque without suffering thermal damage. An
e-frac system typically has a 100:1 turndown ratio, meaning
that it can operate safely at 100% torque while running at 1% of
its base speed. As an example, Mr Bolt noted that for an e-frac
system nominally rated to run at 1,800 rev/min, a 100:1 turn-
down ratio means that the engine can operate safely at 100%
torque while running at 18 rev/min.
This ability to generate torque at low motor speeds means
that operators can more easily apply torque in a controlled
Continued on page 35
At the 2022 SPE Hydraulic
Fracturing Technical Con-
ference on 3 February,
NOV’s Travis Bolt discussed
the efficiency gains that
were seen during field trials
conducted last year of the
company’s e-frac system.
34 we have much more visibility to steer these efficiencies even
further.” Electric frac pumps
Later this year, Liberty expects to commercially launch a new
electric pump system featuring a multimotor design. The compa-
ny says the digiFrac system will have twice as much horsepower
per unit than conventional pressure-pumping technologies.
The system’s power frame is flanked on either side by a pod
housing five individual electric motors, each of which can generate
up to 400 hp continuously or 550 hp at peak. This design eliminates
the transmission, drive shaft and pinion found in conventional
diesel frac systems and replaces it with a planetary gear system.
The planetary system utilizes a center gear – known as a sun
gear – that serves as the driver of the system. Three exterior gears
– referred to as planets – rotate around the sun gear. Because
the planet gears are evenly distributed around the sun gear, the
system provides higher torque compared with the standard trans-
mission used in a diesel frac system.
Removing the transmission from digiFrac is an example of
improving efficiency at the margins, said Ron Gusek, President
of Liberty. Shifting gears under load using a standard transmis-
sion introduces stress at potential failure points in a conventional
frac pump, increasing the need for maintenance and decreasing
runtime. “If you’ve ever driven a car with a manual transmission,
shifting gears can be a little clunky. Every time you have to shift
gears, there’s a little shock to the system, and that vibration can
be hard on components,” Mr Gusek said. “When we’re changing
gears on a frac pump, it’s no different. With an electric pump, we
have a smooth system where it’s quite literally turning a dial to
ramp up the speed of the pump.”
With the 10 motors working in unison, each pump will pro-
duce up to 4,000 hp continuously, or 5,500 hp intermittently. This
allows operators to remove up to 50% of their pumping trailers per
application. Combining this level of output with tight packaging, which
is enabled by removing the transmission, provides substantial
power density on the well pad. The result is high horsepower
delivered within a small physical footprint.
“If you look at a traditional frac pump, you would see the
radiator system at the front of the trailer, then a 12-cylinder diesel
engine, then the transmission, and then the pump at the very
back. That entire assembly is around 45 feet long,” Mr Gusek
explained. “If you look at digiFrac, all you have are a pump and
the electric motors attached to the sides of that pump. The foot-
print for that 5,500-horsepower pump takes up a space of 8 by 13
feet.” The footprint to deliver double the horsepower is effectively
halved, he added.
Additionally, with 10 motors operating individually at a lower
horsepower, the digiFrac system is better suited to maintain con-
tinuous high horsepower throughout a run, even in the event of
an equipment failure.
“If you have one large motor running and something happens
to that motor, you’re out an entire piece of equipment,” Mr Gusek
said. “But if we have 10 small motors and something happens to
one motor? No problem. We still have nine more motors. That’s
M A R C H/A P R I L 202 2 • D R I L L I N G C O N T R AC T O R
IMPROVING FRACKING POWER & EFFICIENCY
part of our whole design philosophy: What can we do to maximize
our equipment hours as much as possible with as minimum an
amount of maintenance as possible?”
To improve system durability, the power frame was designed
with an internal geometry that improves its resistance to flex and
wear. Instead of creating a bore that is full of straight lines, Liberty
designed it with curves from top to bottom and front to back
to make the flow laminar and reduce the chance of cavitation.
Cavitation occurs when small, liquid-free bubbles form within
the liquid in low-pressure areas. When the pressure increases, the
bubbles collapse and generate shock waves that gradually wear
out the pump.
The digiFrac system will utilize Rolls Royce’s MTU 2.6-MWe
gas generator sets as its primary power source, effectively creat-
ing a hybrid system. This will allow for emissions reductions
– an estimated 25% in CO2 emissions compared with other off-
grid power sources – due to the gensets’ high thermal efficiency,
which helps reduce fuel usage.
“Rolls-Royce has done a lot of work with us to understand how
much fuel we were going to be consuming and how that would
affect the performance of the engine,” Mr Gusek said. “If we’re going
to deliver an electric frac fleet to a location for our customer, we
have to be confident that we’re going to dramatically reduce the
emissions footprint over the best available technology. Gas turbines
are great at delivering a huge amount of power into a small pack-
age, but the natural gas engine offers that opportunity of delivering
an efficient footprint that is better than the best available.”
Through a comprehensive testing program that included dura-
bility testing and four field trials completed in Q2-Q3 2021, the
system registered approximately 1,500 hours of operation in the
yard and on four pads – two in the Permian Basin and two in the
Denver-Julesburg Basin. While Liberty has not released details
from those field tests, it said results “affirmed confidence for com-
mercial production.”
In its Q3 2021 earnings call, Liberty had announced multi-year
agreements to commercially deploy the digiFrac technology in
2022 with two of its field-trial partners. Then, in the most recent
earnings call on 9 February, the company said it plans to start
deploying digiFrac pump systems into its frac fleets in early Q2
this year. DC
Click here to watch a video interview
with Turner Hall about GD Energy
Products’ Thunder 5000 HP pump.
Continued from page 34
manner, progressively increasing it over a period of time
instead of applying maximum torque all at once, which could
place unnecessary stress on the motor and pump. It also
allows users to increase pressure from the frac pump without
overstressing the system.
The ability to apply torque in a controlled manner, com-
bined with an electric motor’s ability to generate torque values
greater than 100% for short periods of time, can help minimize
the need for manual intervention on downhole issues. To dem-
onstrate this capability with the Ideal system, one of the tests
during the field trials focused on stuck augers. A 12-in. auger
was run on a 45° angle with both the e-frac and a conventional
frac system. Support testing prior to the field test showed that
the motor required between 225% and 275% torque to break the
auger free without manual intervention.
Testers applied torque progressively to the e-frac system,
reaching 260% torque in 3s. As a conventional diesel frac sys-
tem is unable to attain that level of torque, manual intervention
is typically required when the auger becomes stuck.
By providing the ability to address a downhole issue without
stopping operations, “we’ve prevented a person from having
to go out into the field and manually interact with a piece of
equipment,” Mr Bolt said.
Another focus area of the testing was the process of con-
verting raw fuel into energy applied at the wellhead, and its
impact on horsepower and engine efficiency, defined as the
ratio of work performed to the heat provided by an engine.
Electricity is subject to the Joule effect and magnetic losses
as it’s transported within a conventional system. These losses
can account for up to a 2.5% loss in overhead line transmission.
Another loss in the electrical system is the inefficiency of the
step-up and step-down transformer, which typically ranges
from 1% to 2%.
An e-frac system can mitigate the losses typically seen in
a conventional system, primarily because it consumes the
same amount of power as it generates, Mr Bolt said. NOV and
NexTier found that an e-frac system powered by natural gas
internal combustion generators can achieve a 4% increase in
efficiency over conventional systems.
“With mechanical systems, we have to worry about the ini-
tial energy conversion process of diesel fuel into mechanical
energy through a transmission, or through a pump,” Mr Bolt
said. “Typically, you have inefficiency at the generator source.
You lose energy at the transmission due to magnetic losses,
and then you have more inefficiency when you drop down in
torque. But when we looked at the data from our tests, what we
found was that, due to the initial efficiency gains that you have
with natural gas-powered systems, we’re seeing an increase
in efficiency versus a conventional system. In the world of
efficiencies, a 3-4% increase is a big deal.”
NOV and NexTier have said they expect to deploy the Ideal
fleet in the first half of 2022. DC
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