PRODUCTION OPTIMIZATION; CONVENTIONAL PLUNGER LIFTS
During the course of my career, I have been responsible for over a thousand plunger lifts all across Alberta. Following is a step by step procedure on how to determine settings for a simple conventional plunger lift:
1. Calculate your minimum close time required to get the plunger to the bottomhole spring. When a plunger is free falling in the tubing string, with no liquids holding it up, it will travel a little over 50 m/min. (ie. for a well that's 2000 m deep you want to give it at least 40 min.)
2. Ensure your well is in an unloaded state to begin. Either swab the well dry, or cycle the plunger a few times with no flow time in between to clean up any near wellbore liquids.
3. Drop the plunger to bottom and just before opening the plunger lift control valve, record your casing, tubing and line pressures.
4. Open the plunger control valve and start flowing the well. Monitor the pressures as the plunger comes up.
- The line pressure indicates how the pipeline infrastructure handles the extra gas. Sometimes the line pressure will remain consistent, while other times it will spike considerably.
- The casing pressure will tell you if the plunger is rising (unless you have a packer in your tubing string, which nullifies this point). As long as the casing pressure is falling, the plunger should be coming up. If the casing pressure quits falling, the plunger has stalled out.
Caution: listen for the plunger rising as it is hitting tubing connections on the way up. If it is coming too fast, pinch back the flowline valve to slow it down and prevent lubricator damage and/or failure.
5. Once the plunger reaches surface, engage the plunger catcher on the lubricator to hold the plunger there.
6. Shut in the flowline valves and record the tubing and casing pressures. The pressure differential tells you how much liquid is in the tubing. If you are close to equalized, open the flowline and continue flowing. Keep repeating this step periodically until you start to see a differential pressure.
7. Disengage the plunger catcher on the lubricator and shut in the well to drop the plunger.
8. Once your minimum close time is up, compare the casing pressure to the last cycle. If the casing pressure hasn’t built up to the same it was last cycle, you might lose some pressure each cycle until there is not enough to drive the plunger to surface. If this is the case, you will need to extend the minimum close time to compensate.
9. Open the plunger control valve to start the next cycle. Monitor the arrival time, and aim to have your plunger travelling at approximately 200 m/min. If it starts coming up faster than 350 m/min, the impact will cause permanent damage to the lubricator spring. This will in turn result in lubricator spring failure and could also result in lubricator failure.
10. Adjust settings accordingly to maintain this arrival time.
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This is only a basic method of determining plunger lift settings. Once you have your plunger running consistently, there are many different approaches you can take to optimize the settings further. In order to determine how to best optimize your plunger, the following factors need to be taken into consideration:
Economics / commodity pricing
Well performance / recovery
Gathering infrastructure
Offset wells
Liquid properties
Tanking vs recombining fluids (trucking expenses)
If you would like some help optimizing your plunger lift, please contact us for assistance!
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