The plungers upstroke movement creates a sealing between gas and liquid phases. A surfacing plunger deliquify the well with each cycle.
Higher shut-in times are used for the intermittent gas lift and conventional plunger lift cases to build-up a pressure in the casing to lift accumulated liquid and plunger.
Little to no shut-in time is required for continuous flow plunger lift. The plunger and liquid slug are lifted with drag force generated by gas and liquid flow.
Understanding the mechanics of the continuous flow plunger (CFP) lift upstroke stage is important to
Continuous flow plunger upstroke relies on drag force generated by the flow. The drag lifts the plunger and the liquid slug on top of it. Using force balance equation, a dimensionless parameter drag coefficient is retrieved. The drag coefficient is denoted as CDhigh for the merged two-piece plunger and closed bypass plunger.
Instantaneous upstroke is shown in the slow-motion video on the left. Initially, the ball sitting on BHA, and the sleeve is falling. As ball and sleeve merge, they upstroke without any delay.
The two-piece plungers that started the upstroke were observed to be surfacing without stalling in the experiments.
If the flow rate was insufficient, no upstroke movement was made. Two-piece plunger sitting on BHA do not build-up pressure at the casing. Increase gas flow rate or shut-in well for Pcasing buildup would be required to send two-piece plunger up.
Starts upstroke with liquid slug
Liquid fallback is an important consideration
Catches liquid along the way
Stationary or falling liquid film
Removal of hydrostatic backpressure before liquid loading conditions
Increased slug weight slows down the plunger
The gas expansion increases the drag force hence vplunger
Continuous flow plunger lift upstroke model methodology provides plunger velocity calculation iteratively with the consideration of CDhigh, hL, vL for each segment of the well. The liquid slug growth calculated for each segment starting from the BHA to the surface.
Key outputs
Kinetic energy at impact
Hydrostatic pressure
Heavier plungers surface slower due to higher weight. The models are capable to consider this effect for upstroke velocity estimations
