Home › Tools › Critical Velocity Calculator
Free Engineering Tool · No Signup, No Email Gate

Critical Velocity Calculator — Turner / Coleman / Lea

Enter your tubing ID, flowing wellhead conditions, gas specific gravity, and liquid type. The calculator returns critical velocity (ft/s) and critical rate (Mcfd) from all three correlations side-by-side. Use it to gauge whether a gas well is at risk of liquid loading at its current operating point — and to compare what each correlation tells you for the same conditions.

Inputs

Results

Turner1969 · most conservative
—
ft/s
—
Mcfd
Coleman1991 · low-pressure wells
—
ft/s
—
Mcfd
Leamodern · k=1.4
—
ft/s
—
Mcfd
Recommended correlation for your inputs

—

Computed gas density at depth

—

v_T (Turner) = 1.92 × [σ × (ρL − ρg)]0.25 / ρg0.5 σ in lbf/ft, ρ in lb/ft³, output in ft/s. Padded 20% over the basic spherical-droplet drag derivation.
v_C (Coleman) = 1.59 × [σ × (ρL − ρg)]0.25 / ρg0.5 Removes Turner's 20% padding. Better fit for low-pressure (FTP < 500 psi) mature wells.
v_L (Lea) = 1.40 × [σ × (ρL − ρg)]0.25 / ρg0.5 Modern reference, k chosen at 1.4 for typical fluid load. Used for vertical and near-vertical gas wells.

Critical rate (Mcfd) = 3056 × p × vc × A / (T × Z), with A = tubing cross-section in ft², p in psia, T in °R, vc in ft/s. The constant carries the conversion from actual to standard conditions and from ft³/s to Mcfd.

How to use these numbers

Turner is the field default — and tends to over-predict on low-pressure mature wells. If your well is a mature shale gas or unconventional with FTP under ~500 psi and you trust it's still flowing dry, run Coleman alongside Turner and use the lower number as the alarm threshold.

Lea is the modern reference for vertical wells when σ and ρL are known with confidence. For deviated / horizontal completions past ~30° inclination, none of the three correlations applies cleanly — use them as a planning estimate, then validate against the well's own loading history.

This calculator is a planning estimate, not a directive. Fluid properties default to typical values; your actual σ, ρL, and Z at depth differ. For production-decision use, compare against your well's documented loading rate and PVT.

Background reading: 7 Early-Warning Signs of Liquid Loading (with formula derivations and a 24-hour decision tree).

Want this calc run automatically every morning, on every well?

WellRX charter partners get critical-velocity, no-arrival rate, DP-MCF divergence, and 40+ other diagnostics computed daily for every active well — with deviations surfaced in a ranked queue before 6:30 AM CT. 20–200 well operators. Setup waived, 50% off three months.

Apply to Charter Beta → Build a quote