Annulus (well)

The presence of an annulus gives the ability to circulate fluid in the well, provided that excess drill cuttings have not accumulated in the annulus, preventing fluid movement and possibly sticking the pipe in the borehole.

An easy way to visualise this would be to stand a straw (purple in diagram) straight up in the center of a glass of water.

The 'A' annulus can serve a number of crucial tasks, including gas lift and well kills.

These annuli do not normally have any connection to well bore fluids, but maintaining pressure in them is important in order to ensure integrity of the casing strings.

Though all annuli in a completed well are expected to be isolated from the production tubing and each other, connections allowing the flow of fluids between them may sometimes occur, due to either intervention or wear and tear.