Page 37 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

ESPs work in deep reservoirs, but are 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
A 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 in the wellhead if the
specific gravity is 800
2
kg/m . (0.8 times water).
By injecting gas into this
oil, the specific gravity is
lowered and the well will
start to flow. Typically gas
injected between the
casing and tubing, and a
release valve on a gas lift
mandrel is inserted into
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 startup. 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.

3.6.4 Plunger lift
The Plunger lift is normally used on low pressure gas wells with some
condensate, oil or water, or high gas ratio oil wells. In this case the well flow
conditions can be such that liquid starts to collect downhole and eventually
blocks gas so that the well production stops. In this case a plunger with an

35