Slippage occurs when a gas-liquid mixture flows up a tubing string, with the lighter gas phase rising faster than the heavier liquid phase due to differences in buoyancy and velocity. The slip velocity is defined as the difference in velocities between the gas and liquid phases. Slippage assists in lifting oil from the well when in the flow slug regime, but severe slippage can lead to segregated flow in the low velocity bubble flow regime.

1. TWO PHASE

2. Slippage
• When agas-liquid mixture flows up a tubing string, the effects of buoyancy on each of the
phases will not be equal. The lighter of the phases, primarily gas, will rise upwards at an
incrementally higher rate compared to the oil due to the effects of buoyancy and higher
velocity.
• The slip velocity, Vs, is defined as the difference in velocities of the two phases, ie, for a
gas-oil system.
Vs=Vg-Vo
• Particularly in the flow slug regime, the impact of slippage is to
assist in lifting the heavier phase (oil) from the well.
• However if slippage is severe it can promote segregated flow
particularly in the low velocity bubble flow regime