Definition - What does Annulus mean?
Annulus, also known as Annular Space, is the space between an object which is inserted into another circular object such as a pipe. The space can also be offset which means that object is not centralized. The Annulus between the conduit, pipe, periphery of opening and tubing depends upon the maximum diameter, type of firestop configuration and the object. It can also be referred to as the space between the flushed and undisturbed zone which contains a buildup of formation water. It is formed during the invasion caused by various mobilities of water and oil.
Petropedia explains Annulus
The Annulus or the offset penetrant can present a difficulty for letting a fire test pass. The metallic object and metallic sleeve conducts heat through a firestop. The insulation at the bottom of the floor systems and in the middle of the wall systems boost more heat that travels through the object and sleeve that put more force on the seal on the unexposed side. The person who constructs the well is required to make sure that all the spaces other than annular space that surrounds the well screen are sealed so that the movement of natural gas, water, contaminants and other materials between the ground surface and subsurface formations is prevented.