Plunger fall velocities for various plungers have been measured in many different wells in the field and measured in a large scale well simulator. A new theoretical plunger fall velocity model has been developed. This model equates plunger fall velocity to be inversely proportional to a constant multiplied by the square root of the density of the gas the plunger falls through. The measured fall velocity at a specific pressure and temperature is used to calibrate the model, and then the model can be used to calculate fall velocity at other conditions for the same plunger or used to show how changing a feature like plunger weight can impact fall velocity. The model's predicted fall velocity for different types of plungers will be compared with measured fall velocities.
A large scale plunger lift well simulator was used to determine plunger fall behavior in clear PVC tubing through compressed air and through gas free water. The performance of 36 different types and metallurgies of plungers were measured. Both in the field and at the well simulator an acoustic instrument was effectively used to accurately measure plunger fall velocity.
All plungers have the same general trend of fall velocity; where the plunger fall velocity is fast at low pressure and slows at higher pressure. Construction features of plungers and well conditions impacting plunger fall velocities will be highlighted. Using published fall velocities to determine the shut-in time period for a particular plunger type but may not be accurate for a well, because well pressure significantly impacts plunger fall velocity. The knowledge of how various parameters impact plunger fall velocity allows the operator to determine if the plunger has reached the bottom of the tubing by the end of the shut-in period and then optimize the plunger lifted well using the shortest possible shut-in time to maximize liquid and gas production.