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flow gas-lift system. However, there are special schemes available
for such wells.
 Gas lift is relatively inefficient, often resulting in large
capital investments and high energy-operating costs. Compressors
are relatively expensive and often require long delivery times. The
compressor takes up space and weight when used on offshore
platforms. Also, the cost of the distribution systems onshore may
be significant. Increased gas use also may increase the size of
necessary flowline and separators.
 Adequate gas supply is needed throughout life of project. If
the field runs out of gas, or if gas becomes too expensive, it may
be necessary to switch to another artificial lift method. In addition,
there must be enough gas for easy startups.
 Operation and maintenance of compressors can be
expensive. Skilled operators and good compressor mechanics are
required for reliable operation. Compressor downtime should be
minimal (< 3%).
 There is increased difficulty when lifting low gravity (less
than 15°API) crude because of greater friction, gas fingering, and
liquid fallback. The cooling effect of gas expansion may further
aggravate this problem. Also, the cooling effect will compound
any paraffin problem.
 Good data are required to make a good design. If not
available, operations may have to continue with an inefficient
design that does not produce the well to capacity.
Potential gas-lift operational problems that must be resolved
include:
 Freezing and hydrate problems in injection gas lines
 Corrosive injection gas
 Severe paraffin problems
 Fluctuating suction and discharge pressures
 Wireline problems
Other problems that must be resolved are:
 Changing well conditions
 Especially declines in BHP and productivity index (PI)
 Deep high-volume lift
 Valve interference (multipointing)

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