1. n. [Drilling]

The speed at which drilling fluid or cement moves in the annulus. It is important to monitor annular velocity to ensure that the hole is being properly cleaned of cuttings, cavings and other debris while avoiding erosion of the borehole wall. The annular velocity is commonly expressed in units of feet per minute or, less commonly, meters per minute. The term is distinct from volumetric flow.

Alternate Form: AV

2. n. [Well Completions]

The linear velocity of a fluid passing through an annular space. The term critical annular velocity is often used to describe the flow rate or velocity at which entrained solids will be efficiently transported by the annular fluid. If the fluid velocity falls below the critical rate, there will be a risk of particles settling, forming beds or bridges that may obstruct the wellbore.