production · lift
Rod Pump Displacement (PD)
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Inputs
in
in
spm
Description
Computes the theoretical (idealized, 100%-fillage) daily displacement of a sucker rod (beam) pump from its plunger diameter, effective downhole stroke length, and pumping speed. This is the reference figure Rod Pump Efficiency compares an actual measured production rate against.
Variables
| Symbol | Unit | Description |
|---|---|---|
| PD | STB/d | Theoretical Pump Displacement (PD) |
| D | in | Nominal pump plunger (piston) diameter, from the pump's API sizing designation. |
| S | in | Actual downhole plunger stroke length, already corrected for rod stretch and overtravel from the surface polished-rod stroke — not the raw surface stroke itself. Supply the already-corrected downhole figure; this calculator does not perform that conversion. |
| N | spm | Pumping unit speed, in strokes per minute. |
Assumptions
- The pump barrel fills completely with liquid on every stroke (100% theoretical fillage) — this is exactly what makes the result "theoretical"; actual production is always somewhat lower, which is what Rod Pump Efficiency quantifies
- S is the effective downhole plunger stroke, already corrected for rod stretch and overtravel from the surface polished-rod stroke — a required user input, not derived internally
Limitations
- Does not model gas interference, fluid pound, worn barrel/plunger clearance slippage, or standing/traveling valve leakage — all of these reduce actual delivered volume below this theoretical figure; use Rod Pump Efficiency against a measured rate to quantify the real-world shortfall
- The surface-polished-rod-stroke-to-downhole-plunger-stroke conversion (rod stretch correction) is out of scope for this calculator — S must already be the corrected downhole value
Use Cases
- → Theoretical capacity check: Establish the maximum theoretical daily fluid volume a given pump size, stroke, and speed can displace, before any real-world efficiency losses.
- → Efficiency-calculation input: Feed PD directly into Rod Pump Efficiency alongside a measured actual production rate to see how much of theoretical capacity is actually being realized.
Related Calculations
Region Notes
Permian Basin
Common Wolfcamp/Bone Spring sucker rod installations run 1.75-2.25 in plunger diameters at 6-12 spm with 86-144 in surface strokes, sizing to roughly 150-450 bbl/d theoretical displacement before efficiency losses.
References
Primary source
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