Oil and gas production handbook - Process Control and ...

Installations down to 3.7 km with power up to 750 kW have been installed. At these
depths and power ratings, Medium Voltage drives (up to 5kV) must be used.
ESPs works in deep reservoirs, but lifetime is sensitive to contaminants such as sand,
and efficiency is sensitive to GOR (Gas Oil Ratio) where gas over 10% dramatically
lowers efficiency.
3.6.3 Gas Lift
Gas Lift injects gas into the
well flow. The downhole
reservoir pressure falls off to
the wellhead due to the
counter pressure from weight
of the oil column in the
tubing. Thus a 150 MPa
reservoir pressure at 1600
meters will fall to zero
wellhead pressure if the
specific gravity is 800 kg/m 2 .
(0,8 times water). By
injecting gas into this oil, the
specific gravity is lowered
and the well will start to
flow. Typically gas in
injected between casing and
tubing, and a release valve on
a gas lift mandrel is inserted
in the tubing above the
packer. The valve will open at a set pressure to inject lift gas into the tubing. Several
mandrels with valves set at different pressure ranges can be used to improve lifting
and start up. Ill: Schlumberger oilfield glossary
Gas lift can be controlled for a single well to optimize production, and to reduce
slugging effects where the gas droplets collect to form large bubbles that can upset
production.
Gas lift can also be optimized over several wells to use available gas in the most
efficient way.
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