The space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow.
pipe may consist of drill collars, drillpipe, casing or tubing.

An accessory employed above a packer, to permit annulus-to-tubing circulation or vice versa.

A downhole tool typically used with motors or assemblies that restrict the allowable fluid-circulation rates. when operated, the circulation sub allows a higher circulation rate to be established by opening a path to the annulus in the top section of the tool string. this is especially useful in applications such as drilling in slim-diameter wells, where a [...]

A heavy, flanged steel fitting connected to the first string of casing. it provides a housing for slips and packing assemblies, allows suspension of intermediate and production strings of casing, and supplies the means for the annulus to be sealed off. also called a spool.

A sleeve designed to shut off tubing-to-annulus flow should the sliding sleeve become inoperative.

The set of dense rubber, washer-shaped pieces encircling a packer, which are designed to expand against casing or formation face to seal off the annulus.

A measure of the resistance of a fluid to flow. resistance is brought about by the internal friction resulting from the combined effects of cohesion and adhesion. the viscosity of petroleum products is commonly expressed in terms of the time required for a specific volume of the liquid to flow through a capillary tube of [...]

A device to monitor rate of fluid from the annulus.

A preventer having a unit of packing material whose closure depends on well pressure coming from below. it is used primarily to strip pipe through the hole or allow pipe to be moved with pressure on the annulus.

An unloader; provides a means to equalize tubing and annulus pressure.

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 [...]

Fluid pressure in the annulus between tubing and casing or between two strings of casing.

The space surrounding one cylindrical object placed inside another, such as the space surrounding a tubular object placed in a wellbore. also known as annulus.

In drilling-fluid terminology, yield point means yield value (which see). of the two terms, yield point is more common.

Water put into an empty string of pipe in a wellbore to prevent the pipe from being crushed by pressure in the annulus.