Page 15 - Artificial Lift Methods

Hydraulic Lift

Petroleum Extension-The University of Texas at Austin
Velocity Strings

and Foam Lift

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In this chapter:
• Typical applications of foam-lift technology
• Operating principles and the role of critical velocity
• Using surfactants to lower surface tension

• How system components work to extend well life

n a flowing gas well, liquids entrain in the gas and accumulate at the
Ibottom of the well. This increases the bottomhole pressure (BHP) Foam lift is primarily a
in the well and inhibits gas inflow. Also, accumulated liquids displace dewatering technology,
gas in the near-wellbore formation, reducing gas permeability and although effective surfactants
have been developed for
hindering gas migration to the wellbore. If flow velocities are suffi- hydrocarbons.
ciently high, the flowing gas will continuously blow liquids out of the
well to keep the well unloaded, or clear of liquids. However, at lower
gas velocities liquids accumulate in the wellbore, slowing gas inflow.
Eventually the entrained and accumulating liquids can increase BHP
to the point that gas production ceases.
The term liquid loading refers to the accumulation of liquids
in a wellbore that inhibits gas inflow. One way to prevent or relieve
liquid loading is to enhance gas velocities; another way is to cause
the liquid to foam so that it can be more easily displaced.
Flow velocities can be increased by reducing the cross-sectional
flow area of the gas stream. This can be accomplished by flowing
the well fluids through reduced diameter tubing (velocity string) or
through the annulus around an inserted dead string of tubing. Gas
flow velocities can also be increased by injecting gas to comingle
with produced gas.

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