36
LNG
INDUSTRY
SEPTEMBER
2014
that has historically been underserved. Antero has converted
over 80% of its drilling fleet from diesel to 100% natural gas
fuelling.
Taking action
Leveraging its knowledge in developing unconventional
reserves based on previous experience in the Barnett,
Woodford and Piceance Shale Plays, several years ago Antero
made a decision to commit 100% of its resources to build and
develop a leading production position in the Appalachian Shale
Basin (Marcellus and Utica Shale Plays).
When an exploration play is rapidly developed into
producing assets, environmental issues can challenge
objectives and schedules. Antero’s strategy to develop its
Marcellus/Utica reserves was partly based on the transition of
its drilling and completions operations from diesel fuel to a
100% natural gas platform.
The company planned to maximise use of very low cost
wellhead gas as much as possible, but knew that its raw
wellhead gas contained significant amounts of NGL
hydrocarbons. Antero also needed a gas supply solution when
drilling in new, undeveloped areas so that it could utilise its
drilling rigs 100% of the time. It required a consistent, reliable
and repeatable solution, and while recognising that natural gas
use for fuelling its rigs and frac fleets could significantly
improve its bottom-line, the company was also committed to
the issues of safety and the environment. As such, the
company executed the following strategies throughout its
drilling operations:
Working with two large contract drilling companies
(Patterson-UTI and Precision Drilling), Antero decided to
implement 100% gas drilling over the long-term using
GE-Waukesha’s ‘rich-burn’ gas engine technology.
It began converting its regional vehicles to natural gas
combustion (NGV).
It commenced construction of a central frac ‘flowback’
water treatment facility that will allow the company to
recycle over 90% of its water consumption requirement in
frac operations.
Gas drilling solution
In 2012, Antero set out to find strategic partners to address
its challenges for designing a 100% gas-fuelled drilling
platform with a primary goal of utilising wellhead gas as much
as possible, and also providing a reliable fuel supply when
wellhead gas was not available.
The company worked with its primary drilling contractors
to explore gas engine technology that would be able to
efficiently utilise wellhead gas over a wide range of gas quality.
It also wanted these rigs to operate with extreme reliability
and, most importantly, be readily accepted by the drill rig
operators. GE-Waukesha, working closely with Patterson-UTI,
provided just such a solution. Patterson-UTI chose the
Waukesha rich-burn gas engines for the following reasons:
The Waukesha spark-ignited gas engines are able to
operate without a load bank, meaning that the drilling
technician experiences diesel-like performance from a
natural gas engine. As a result, the transition to rich-burn
gas engines was relatively easy from an operator’s
perspective.
The Waukesha engines, both the 1.0 MW (L5794) and
1.2 MW (F7044) models, could handle very hot (high BTU)
field gases, which enabled the gas engine powered drill
rig to operate on field gas in almost any shale formation.
This fuel tolerance is highlighted in Figure 1, which shows
that the engine power output can handle rich gases up
1650 Btu/ft
3
without ‘knocking’ (power vs. Waukesha
Knock Index).
The Waukesha engines could achieve US Environmental
Protection Agency (EPA) mobile certification on field gas.
In addition to the performance aspects, the Patterson-UTI
team also considered the emissions profiles of various drilling
engines available on the market. These data are provided in
Table 1.
Figure 1.
Waukesha engines power output operating on
various fuel compositions (LHV). (Source: GE-Waukesha.)
Table 1.
Engine emissions (Source: GE-Waukesha)
Power
NO
x
CO
NHMC PM Methane slip CO
2
Model
Three-way
catalyst
Fuel
Load (%) bhp kW g/bhp-hr g/bhp-hr g/bhp-hr g/bhp-hr g/bhp-hr
g/bhp-hr
7044GSI
Y
Commercial
quality natural
gas
100% 1680 1253 0.28
1.3
0.03
0.001
1.23
542
3512C N
Diesel
100% 1476 1101 6.20
0.19
-
.03
-
465.7
5794GSI
Y
Commercial
quality natural
gas
100% 1380 1029 0.32
1.8
0.02
0.001
1.06
524
