Annular Velocity for Hole Cleaning
Cuttings only leave the hole if mud in the annulus moves fast enough to carry them, and annular velocity is the first check.
The equation
AV = 24.5 Q / (Dh² – Dp²)
- AV is annular velocity in feet per minute
- Q is flow rate in gallons per minute
- Dh and Dp are hole and pipe diameters in inches
Worked example
Pumping 600 gallons per minute in an 8.5 inch hole around 5 inch pipe gives 24.5 × 600 / (72.25 – 25) = 311 feet per minute, comfortable for a vertical section with a typical mud.
When to use it
Rules of thumb want roughly 100 to 200 feet per minute or more depending on hole angle and mud rheology. High angle wells clean poorly regardless of velocity without pipe rotation and low viscosity sweeps.
Related Calculators and Reference
- Mud Weight and Pressure Gradient Calculator: convert between ppg, SG, and psi per foot.
- Probabilistic STOIIP Calculator: volumes with uncertainty ranges.
- PetroWiki by SPE: the industry reference for petroleum engineering.