production · tubing performance
Liquid Velocity (Tubing)
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Inputs
STB/d
in
Description
Computes superficial liquid velocity in production tubing from surface liquid rate and tubing internal diameter. Unlike gas, liquid is only mildly compressible — this calculator treats surface (stock-tank) rate as approximately equal to downhole rate, the same simplifying convention already used throughout this discipline's existing lift-batch calculators (e.g., ESP Horsepower's flow-rate input), rather than requiring a formation volume factor correction.
Variables
| Symbol | Unit | Description |
|---|---|---|
| v | ft/s | Liquid Velocity |
| q | STB/d | Liquid (oil, water, or total liquid) production rate at surface (stock-tank) conditions. |
| d | in | Tubing internal diameter at the point where velocity is being evaluated. |
Assumptions
- Surface (stock-tank) liquid rate is treated as approximately equal to downhole rate — a reasonable simplification for liquids given their low compressibility, unlike gas where the same approximation would be badly wrong (see Gas Velocity's own Bg correction)
- Single-phase liquid flow — no significant free gas volume fraction in the tubing at the point of evaluation
- The tubing ID is the actual current internal diameter, not nominal/new-pipe specification
Limitations
- Does not apply a liquid formation volume factor (Bo) correction — for a well with substantial solution gas breaking out of the liquid at low flowing pressure, actual downhole liquid volume can differ meaningfully from the surface rate used here
- Assumes single-phase liquid; a well producing significant free gas alongside liquid needs a multiphase treatment (out of scope — see the deferred Multiphase Gradient work), not this single-phase velocity alone
- Does not itself flag erosional velocity limits against a specific API RP 14E constant — the result note includes a generic 15 ft/s screening flag, not a rigorous erosional-velocity calculation
Use Cases
- → Erosional velocity screening: Check liquid velocity in the tubing against erosional velocity guidelines.
- → Multiphase gradient correlation input: Superficial liquid velocity is a required building-block input for multiphase pressure-gradient correlations (e.g., Beggs-Brill), which combine it with superficial gas velocity to characterize the flow regime.
- → Friction pressure loss input: Feeds directly into the Reynolds Number and Friction Factor calculators, and into Flowing Bottomhole Pressure (Tubing Traverse)'s own internal friction term.
Related Calculations
Region Notes
Global
For a well producing meaningful free gas alongside liquid, this single-phase velocity understates the true mixture velocity — treat it as the liquid-only component, not the full flowing velocity.
References
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