American Oil and Gas Reporter - August 2022 - 83

SpecialReport: Hydraulic Fracturing Tech
can be brought on line or shut off as
needs change. "
The smaller generators run off reciprocating
natural gas engines rather than
turbines. According to Beach, emissions
from these engines are lower than a turbine.
However, turbines can burn a much
wider B range of gas.
" To combine turbines' more complete
fuel combustion with the advantages of
smaller equipment, some industry players
are moving toward placing small turbines
from the aircraft industry on trailers to
drive pumps directly, " Beach relates.
" This approach, called turbine direct
drive, lets each turbine run at or near
maximum horsepower to improve fuel efficiency
and cut emissions. "
Shrinking On-Site Footprints
As they build natural-gas-powered
fleets, hydraulic fracturing companies are
simplifying operations and maintenance
by packing more horsepower into each
pump, observes Jason C. Williams, vice
president and director of engineering at
ShalePumps LLC. " We have developed
natural-gas-powered pump trailers that
can deliver 7,000 horsepower in a footprint
comparable to a conventional 2,500
horsepower quintuplex trailer, " he says.
High rod load capability is a must for
pumps to endure the forces created at
such high horsepower, Williams describes.
" Where a typical 2,500 horsepower
pump may have a max rod load
capacity between 200,000 and 220,000
pounds, the high-horsepower pumps can
withstand 395,000 lbs, " he says. " That
capability comes from thicker, heavier
materials. "
While high-horsepower pumps can be
powered electrically, Williams predicts
that most will be driven mechanically.
" Using aeroderivative natural gas-powered
turbines to drive the pumps eliminates
the need for an electric motor or
variable frequency drives, " he explains.
" Instead, the turbines on each trailer
transfer power to the pump through a
multispeed transmission. "
The simpler design translates into
lower costs, Williams reports. " We can
field a fleet of 7,000 horsepower units
powered by mechanical drives for almost
the same price as a fleet of new conventional
Tier IV 2,500 horsepower units, "
New hydraulic fracturing fleets often use higher-horsepower pumps to streamline maintenance,
shrink site footprints and ease operations, ShalePumps LLC observes. To
minimize fuel costs and emissions, many of these pumps are powered by aeroderivative
turbines that run on natural gas.
he clarifies. " The high-horsepower, direct-drive
fleets can shave as much as $10
million or $15 million off the cost to
build natural gas-powered fleet. "
Horsepower density is key, Williams
says. " With 5,000 horsepower pumps
driven by turbines, the cost for each
horsepower may be 15%-20% higher
than for a conventional 2,500 horsepower
Tier IV fleet, " he contrasts. " As the
pumps' horsepower goes up, the cost per
horsepower falls into line with that of
conventional fleets. These savings are
why we see high-horsepower pumps connected
to aeroderivative turbines as the
most likely path forward. "
Turbines' Virtues
According to Williams, direct-drive
fleets' virtues have been validated independently
by a study presented at the
2021 DUG East conference. During the
study, the emissions testing firm Air Hygiene
International Inc. and West Virginia
University's Center for Alternative Fuels,
Engines and Emissions quantified the
emissions associated with several fleet
types. " Ultimately, the study concluded
that direct-drive turbines were the most
efficient way to power fleets from both an
emission and cost perspective, " Williams
summarizes.
The aeroderivative turbines are extremely
reliable, he assures. " Conservative
estimates put their lives between
60,000 and 70,000 hours, about three
times the life expectancy of a typical piston-drive
diesel engine, " he reports. " The
turbines are new to the oil and gas industry,
so no one has run them that long yet.
However, some of the aircraft engines on
which they are based have logged more
than 100,000 hours. "
Like all mechanical drives, the turbines'
output will vary based on environmental
conditions, Williams says. For
turbines, one of the biggest factors is the
amount of oxygen in the intake air,
which declines at higher elevations and
temperatures. " During summer in West
Texas, a hot area that is well above sea
level, the twin turbines on each trailer
may top out at 7,200 or 7,300 horsepower, "
he calculates. " During winter,
when the air is cold and dense, the turbines'
output can jump to 8,600 or 8,800
horsepower, which should allow pumps
to achieve higher rates. "
To limit fuel consumption and emissions,
the aeroderivative turbines can be
turned off as needed, Williams says.
" There is no need to conduct a lock out
and tag out inspection when they are shut
off or turned on. In fact, the turbine can
turn back on 20 seconds after shutdown
and hit full power within a minute. " ❒
AUGUST 2022 83

American Oil and Gas Reporter - August 2022

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