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Downhole Gas Compression – A New Artificial Lift Technology for Gas Wells
Figure 1: Incremental Production with 250kW Downhole Gas
What Is the Corac Downhole Gas Compressor?
Compressor Installed
The Corac DGC (see Figure 2) consists of a high-speed permanent
magnet motor that enables the high power density required for
600
this application to be achieved. The motor rotor is supported on
gas bearings that operate with the well gas as the lubricant and
500
Lift curve
offer a very low-friction support system. The rotor runs at
Inflow curve
without DGC
45,000–60,000rpm.
400
The whole unit is cooled by the main gas flow around the outside of
300
the motor, and it is the temperature of this gas that limits the
200
Lift curve
performance of the system. Currently, the technology is capable of
with DGC
operating with an inlet gas temperature of 105ºC. However, this
Flowing BH pressure (psi)
100
Additional production
0
0 2 4 6 8 10 12 Corac has developed its
Gas rate (MMscf/d)
own bespoke software to
No DGC With DGC PI C-0.06 n-1
analyse the suitability of
BH = bottom-hole; DGC = downhole gas compressor; MMscf/d = million standard cubic feet per day.
downhole gas compression for a
Figure 2: The Corac Downhole Gas Compressor
range of conditions and
reservoir behaviours.
temperature limit covers a significant proportion of available gas
wells around the world, of which there are a conservatively
estimated 100,000 waiting for this technology to be applied.
The compressor system comprises two to six independent compressor
units arranged in series and mounted in a standard length of
production tubing. Because of the high speed of the motors, the
motor inverter drives themselves have to be positioned downhole,
again using the gas flow to cool the electronic components. The
electronics therefore present a unique design challenge: first, there is
a need to package a lot of electronics in a very small diameter, and
installed. Other wells can demonstrate between 30 and 50% second, there is a need to take any heat away successfully. This
increased production. technology therefore goes several stages beyond automotive
under-bonnet high-temperature electronics capability.
One operator has evaluated the value of DGC technology on one of
its fields. The complete installation of 21 units, auxiliary power, Product Range
subsea cables and workover costs offshore are recovered within two Figure 3 indicates the range of applications of DGC technology related
to the overall tubing diameter, well flow rate, maximum inlet gas
temperature and the resultant achievable pressure ratio necessary.
The compressor system
Ancillary Equipment
comprises two to six The DGC system cannot be inserted completely independently into the
independent compressor units
well. Depending on how the well is operated, the safety procedures
involved for that particular well and the requirements of the system
arranged in series and mounted
itself, an arrangement of completion jewellery will be necessary to
in a standard length of
complete the system. The DGC can be deployed via coiled tubing or
installed within the production tubing.
production tubing.
Summary
Corac has developed a compressor system capable of maintaining
years at a very conservative gas price of US$1.80/thousand standard production from a well at significantly lower reservoir pressures than
cubic feet. The incremental production would be in excess of 800 conventional approaches. It is ideally suited to wells that are
billion standard cubic feet over a 10-year programme. declining, where reservoir drawdown is low and the flow of gas is
EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 2
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