Annular velocity


Annular velocity is the speed of the drilling fluid's movement in a column called an annulus in oil wells. It is commonly measured in feet per minute or meters per minute. Annular velocity is often abbreviated as AV, though this is not exclusively so, as AV also refers to apparent viscosity which is calculated from rheometer readings from tests that the mud engineer performs.

Scope

For this article, annular velocity is described, as used in drilling fluid applications in the oil exploration industry. There may be other applications in other fields of study such as fluid mechanics or fluid dynamics.

Determination

The annular velocity can be calculated using one of the following formulas.
Or
Where:
  • AV = annular velocity in Ft/min
  • PObpm = pump output in bpm 1 barrel = 42 gallons
  • POgpm = pump output in gpm 1 gallon = 0.0238095238 barrels
  • ID2 = inside diameter of the wellbore or casing, squared
  • OD2 = outside diameter of the drill pipe or tubing, squared
  • 1029.4 = A conversion factor constant used to calculate the volume between the outside of a tube within the inside of another tube, using barrels.
  • 24.5 = A conversion factor constant used to calculate the volume between the outside of a tube within the inside of another tube, using gallons.
  • Pump Output = Refers to the measurement of the quantity of a fluid.

Application

The annular velocity is one of two major variables in the process of cleaning
solids from the wellbore. By maintaining the annular velocity at certain rates in conjunction with the rheological properties of the drilling fluid, the wellbore is kept clean of the drill cuttings to prevent them from settling back down to the bottom and causing drilling problems.
The other major variable is the rheology of the drilling fluid. Rheology is sometimes thought of as viscosity to the uninitiated, though improperly. Viscosity is a very basic measurement of the fluids resistance to change in movement or flow. The viscosity of a fluid can be measured with a Marsh Funnel. Rheology is the study of viscosity and requires more precise and complicated procedures and equipment for its determination. For drilling fluid applications a rheometer is used.