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back to the surface. It provides a piston-like interface between
liquids and gas in the wellbore and prevents liquid fallback — a
part of the liquid load that effectively is lost because it is left
behind. Because the plunger provides a “seal” between the liquid
and the gas, a well’s own energy can be used to lift liquids out of
the wellbore efficiently.
Plunger lift commonly is used to remove liquids from gas
wells or produce relatively low volume, high GOR oil wells.
Plunger lift is important and, in its most efficient form, will
operate with only the energy from the well. Fig. 5.9 shows a
schematic of a plunger lift installation. A free-traveling plunger
and produced liquid slug is cyclically brought to the surface of the
well from stored gas pressure in the casing tubing annulus and
from the formation. In the off cycle, the plunger falls and pressure
builds again in the well. A new two-piece plunger (cylinder with
ball underneath) can lift fluids when the components are together,
but both components are designed to fall when separate. Use of
this plunger allows a shut-in portion of the operational cycle that is
only a few seconds long, resulting in more production for many
wells.
There is a chamber pump that relies on gas pressure to
periodically empty the chamber and force the fluids to the surface,
which is essentially a gas-powered pump. There are variations of
gas lift and intermittent lift, such as chamber lift. Not all possible
variations of artificial lift can be discussed; however, the principles
presented apply to the selection of all methods that might be
considered.
The cycle starts with the plunger falling into the well with
its valve open. Gas, condensate and oil can pass though the
plunger until it reaches bottom. There the valve is closed, now
with a volume of oil, condensate or water on top. Gas pressure
starts to accumulate under the plunger and after some time pushes
the plunger upwards, with liquid on top, which eventually flows
out of the wellhead discharge [15].

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