An oil and gas operator collaborated with a service company to use bi-fuel fracturing pumps powered by natural gas to lower emissions during hydraulic fracturing operations. The operator supplied natural gas from existing pipelines to power 14 bi-fuel pumps, saving over $475,000 in fuel costs compared to diesel. Using natural gas also reduced the environmental footprint and eliminated the need for 16 diesel deliveries. The collaboration helped the operator achieve one of the cleanest shale gas completions in North America while improving efficiency.
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March 2014 World Oil: Greener completions advance in the Marcellus
1. World Oil / MARCH 2014 99
GreenercompletionsadvanceintheMarcellus
REDUCED EMISSION COMPLETIONS
Fracing operation underway in the
Marcellus region of rural Pennsylvania. The
use of bi-fuel fracing pumps reduced the
environmental footprint. Photo courtesy of
Cabot Oil & Gas.
An operator and service
company collaborate to
lower emissions and boost
efficiencies during hydraulic
fracturing operations through
the use of bi-fuel fracing
pumps and greener frac
fluids.
ŝŝ JERAMIE MORSCHHAUSER, Cabot Oil &
Gas Corporation; SEAN PARKER and BRIDGET
TODD, Baker Hughes
In the ongoing push to maximize pro-
duction at minimal environmental impact
and expense, oil and gas companies are
searching for more efficient and cleaner
E&P technologies that help achieve these
goals. At North American wellsites, this
search has led to a growing interest in en-
gines for drilling rigs and frac pumps that
are powered, in part, by natural gas. Bi-
fuel or dual-fuel engines use a combina-
tion of diesel fuel and natural gas—which
is abundant, relatively inexpensive and
clean—to help operators lower their op-
erating expenses and the environmental
footprints.
Cabot Oil & Gas has successfully used
bi-fuel engines on drilling rigs in its Mar-
cellus shale assets, and realized economic
and environmental benefits in its drilling
operations. Cabot wanted to extend these
benefits to its hydraulic fracturing opera-
tions by utilizing bi-fuel-powered pumps.
BI-FUEL ENVIRONMENTAL
DRIVERS
Like many operators, Cabot views in-
creased implementation of bi-fuel engines
as a way to satisfy the industry’s need for
greener completions. The term refers
to methods that minimize the release of
greenhouse gases and volatile organic
compounds (VOCs) during the comple-
tion phase of a well, by limiting the expo-
sure of the produced gas to the environ-
ment by capturing and injecting it into the
sales line, rather than flaring.
Much of the drive for green comple-
tions comes from increased regulations at
both the federal and state levels. As part of
the Clean Air Act, the U.S. Environmen-
tal Protection Agency (EPA) has adopted
multiple tiers of air emission standards for
non-road diesel engines. Most recently,
EPA has introduced a national program
aimed at reducing engine emissions by
integrating engine and fuel controls, as
a system, to gain the greatest emission
reductions. These Tier 4 emission stan-
dards will require engine manufacturers
to decrease exhaust emissions by more
than 90%, by producing engines with
advanced emission control technologies
similar to those already in place for high-
way trucks and buses.
Regulatory authorities at the state level
also have their own sets of emissions regu-
lations. In states such as California, Colo-
rado and New York, many regulations go
further, and are more restrictive than fed-
eral rules.
Apart from regulations placed on
the industry, many companies are go-
ing above and beyond the requirements,
whenever possible. One such example is
Cabot’s ability to directly turn wells in-
line after the completions process, rather
than flaring. New EPA regulations will
make this the industry standard in 2015,
but Cabot is already adopting the process
in areas, where pipelines are available.
GREEN COLLABORATION
Cabot has worked closely with Baker
Hughes to develop and implement frac
services in the Marcellus region that aim
to reduce the operator’s environmental
footprint while sharing the economic in-
centives for green completions. On the bi-
fuel engine front, Baker Hughes, working
with its engine supplier, Cummins, has
Originally appeared in World Oil
®
MARCH 2014 issue, pgs 99-102. Posted with permission.
2. 100 MARCH 2014 / WorldOil.com
REDUCED EMISSION COMPLETIONS
converted its Rhino hydraulic fracturing
pumping units to run on natural gas-die-
sel fuel blends.
The Cummins diesel engines are ret-
rofitted with bi-fuel conversion kits. The
engine supplier has developed bi-fuel
engines, ranging from 800 to 3,500 hp,
for high-horsepower markets, such as
oil and gas well servicing applications.
While the first engines met Tier 2 EPA
emissions regulations, Cummins is now
developing bi-fuel engines that meet
Tier 4 Final standards.
The process of converting a diesel en-
gine to run on a natural gas-diesel mix
is minimally invasive and requires little
modification to the original engine. A
conversion kit consists of a program-
mable logic controller (PLC), ductwork
to transport natural gas to the engine,
and a series of regulators to reduce the
gas pressure prior to entering the engine’s
combustion chamber. The PLC signals a
throttle valve that controls the natural gas
volume entering the engine, as well as the
subsequent substitution rate of natural
gas for diesel.
While natural gas can make up the
majority of the fuel mixture, some diesel
is required to act as the ignition source.
However, once the diesel starts the en-
gine, the PLC slowly ramps up the natural
gas injection. The injection rate of natural
gas increases with the horsepower output
of the engine, up to a current maximum
substitution level of 70% natural gas to
30% diesel.
The bi-fuel system responds quickly
to changes in natural gas supply pressure,
engine knock and cylinder temperature,
by making systematic adjustments to
optimize the substitution rate and pro-
tect the engine. If the natural gas supply
is compromised, the PLC can react and
turn off natural gas flow in as little as 250
msec, while the engine continues run-
ning without interruption on 100% die-
sel, until the gas supply problem is cor-
rected. The well completion experiences
no negative consequences with respect
to engine performance, due to natural
gas delivery variations.
FIELD APPLICATION
Cabot planned a stimulation opera-
tion that called for the service company
to provide a fleet of 14 bi-fuel pumps, to
stimulate a 10-well Marcellus pad, with a
total of 170 frac stages. While the pumps
could operate on natural gas supplied
as CNG or LNG, the operator chose to
use its own field gas as the source, which
was abundant and readily available from
gathering lines in close proximity to the
frac site.
LNG and CNG provide smaller
carbon footprints compared to diesel,
and they satisfy the lower emissions re-
quirements for green completions in
the field. However, these sources still
require processing at remote facilities,
over-the-road transportation to the field,
and onsite storage, all of which adds cost
and increased environmental and safety
concerns.
Field gas was the lowest-cost, most-
sustainable option, as its close proxim-
ity to the wellsite generated a lower, total
carbon footprint, compared to any other
natural gas source. Furthermore, Cabot’s
exceptionally pure field gas is rich in
methane, which increased the engine ef-
ficiency, required minimal processing and
eased concerns about supply disruptions.
While it was not required in this ap-
plication, the service company deployed
a Joule-Thompson skid in other liquids-
rich fields to separate heavier compo-
nents, such as ethane, propane and bu-
tane. Rather than flare off these heavier
hydrocarbons, the separated compo-
nents can be recirculated into the op-
erator’s sales line, further lowering both
emissions and costs.
The field plan called for piping field
gas from some of the operator’s produc-
ing wells to a gas processing unit (GPU)
near the frac pumps. The GPU contained
a dryer to remove condensate, and a filter
to remove particulates from the field gas
Fig. 2. Overview of frac pump setup.
Fig. 1. Baker Hughes Rhino pumps are driven by Cummins bi-fuel engines.