The annulus of an

oil well An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas m ...

water well A well is an excavation or structure created on the earth by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. The ...

is any void between any piping, tubing or casing and the piping, tubing, or casing immediately surrounding it.Schlumberge
Oilfield Glossary: Term 'annulus'
, retrieved 18 February 2010. It is named after the corresponding geometric concept. 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 A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petr ...

. For a new well in the process of being drilled, this would be the void between the

drill string A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid (via the mud pumps) and torque (via the kelly drive or top drive) to the Well drilling#Drill bits in mechanical drilling, drill bit. The term ...

and the formation being drilled. 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. All of the water in between the straw and the sides of the glass would be the annulus (yellow area in diagram), with the straw itself representing the

and the sides of the glass representing the formation. While drilling,

drilling fluid In geotechnical engineering, drilling fluid, also known as drilling mud, is used to aid the drilling of boreholes into the earth. Used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also use ...

is pumped down the inside of the drill string and pushes the drill cuttings up the annulus to the surface, where the cuttings are removed from the

(

drilling mud In geotechnical engineering, drilling fluid, also known as drilling mud, is used to aid the drilling of boreholes into the earth. Used while drilling oil well, oil and natural gas wells and on exploration drilling rigs, drilling fluids are a ...

) by the shale shakers. In a completed well, there may be many annuli. The 'A' annulus is the void between the production tubing and the smallest

casing string In drilling technology, casing string is a long section of connected oilfield pipes that is lowered into an wellbore and cemented in place. The purpose of the casing pipe is to: * Prevent the borehole from collapsing. * Prevent formation fluids ...

. The 'A' annulus can serve a number of crucial tasks, including

gas lift A gas lift or bubble pump is a type of pump that can raise fluid between elevations by introducing gas bubbles into a vertical outlet tube; as the bubbles rise within the tube they cause a drop in the hydrostatic pressure behind them, causing t ...

and

well kill A well kill is the operation of placing a column of special fluids of the required density into a well bore in order to prevent the flow of reservoir fluids without the need for pressure control equipment at the surface. It works on the principle ...

s. A normal well will also have a 'B' and frequently a 'C' annulus, between the different casing strings. 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. There is said to be "communication" between these connected annuli. During

coiled tubing In the oil and gas industry, coiled tubing refers to a long metal pipe, normally in diameter which is supplied spooled on a large reel. It is used for Well intervention, interventions in oil well, oil and gas wells and sometimes as production ...

interventions, the void between the coil and the production tubing can also be considered an annulus and be used for circulation.

References

{{DEFAULTSORT:Annulus well Petroleum technology Water wells

See also

References