production · lift
Plunger Lift Minimum Casing Pressure (Pcmin)
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Inputs
lbf
in
—
ft
psi
psi
Description
Computes the minimum surface casing pressure required to lift a plunger and its accumulated liquid slug to the point they just reach surface, from the plunger's weight, the tubing size it travels in, the slug's size and gravity, and the friction and minimum line-pressure the plunger must overcome. The plunger-lift analog to Gas Lift Valve Pressure's force balance.
Variables
| Symbol | Unit | Description |
|---|---|---|
| Pcmin | psi | Minimum Casing Pressure (Pcmin) |
| Wp | lbf | Weight of the plunger, from its manufacturer specification. |
| ID | in | Actual current internal diameter of the production tubing the plunger travels in — not the nominal/new-pipe ID if wear or scale is significant. |
| SG | — | Specific gravity of the liquid slug the plunger carries to surface (water = 1.0). |
| Ls | ft | Length of the accumulated liquid slug riding above the plunger, from the well's shut-in buildup time and estimated liquid accumulation rate. |
| Pfric | psi | Pressure allowance for friction as the slug moves up the tubing at the plunger's operating velocity — not computed internally by this calculator; supply an estimate from a plunger-lift design chart or prior well performance (see limitations). |
| Ptmin | psi | Minimum surface tubing (sales line) pressure the plunger and slug must discharge against. |
Assumptions
- The plunger and liquid slug behave as a single rigid mass at the moment they just reach surface — Foss & Gaul's (1965) original simplifying assumption
- No allowance is made for the weight of the gas column in the tubing above the slug
- The tubing ID used for At is the actual current internal diameter, not the nominal/new-pipe ID — wear or scale buildup reduces effective ID over a well's life
Limitations
- Friction pressure (Pfric) is a required user input, not computed internally — this calculator does not model the friction factor or plunger velocity that would be needed to derive it, so an inaccurate estimate propagates directly into Pcmin
- This is (Pc)min only — the casing pressure required at the moment the plunger/slug just reach surface — not (Pc)max, the higher pressure required to start the plunger cycle at the bottom of the well (which requires a gas-expansion adjustment this calculator does not model)
- Does not account for liquid slug fallback or leakage past the plunger during its ascent, which reduces the effective slug size delivered to surface below the input Ls
Use Cases
- → Plunger lift feasibility screen: Check whether a well's available shut-in casing pressure is sufficient to lift a candidate plunger and expected slug size to surface before committing to an installation.
- → Cycle pressure troubleshooting: Diagnose an underperforming plunger lift well by checking whether its actual operating casing pressure is close to, or well below, the computed minimum.
Related Calculations
Region Notes
Permian Basin
Plunger lift is common on late-life Permian gas and gas-condensate wells transitioning off other lift methods as liquid loading becomes the dominant production constraint; 2-3/8 in and 2-7/8 in tubing (ID roughly 1.9-2.4 in) are the most common sizes in these installations.
References
Primary source
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