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 may ...

water well A well is an excavation or structure created in the ground 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. Th ...

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 Drill cuttings are broken bits of solid material removed from a borehole drilled by rotary, percussion, or auger methods and brought to the surface in the drilling mud. Boreholes drilled in this way include oil or gas wells, water wells, a ...

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 petro ...

. 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 Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

. While drilling,

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

is pumped down the inside of the drill string and pushes the

up the annulus to the surface, where the cuttings are removed from the

(

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

) by the

shale shakers Shale shakers are components of drilling equipment used in many industries, such as coal cleaning, mining, oil and gas drilling.They are the first phase of a solids control system on a drilling rig, and are used to remove large solids ( cuttings ...

. In a completed well, there may be many annuli. The 'A' annulus is the void between the

production tubing Production tubing is a tube used in a wellbore through which production fluids are produced (travel). Background Production tubing is run into the drilled well after the casing is run and cemented in place. Production tubing protects wellbore cas ...

and the smallest

casing string In drilling technology, casing string is a long section of connected oilfield pipe that is lowered into a wellbore and cemented. The purpose of the casing pipe is as follows: * prevent the collapse of the borehole * prevent formation fluids from ...

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

gas lift Gas lift or bubble pumps use the artificial lift technique of raising a fluid such as water or oil by introducing bubbles of compressed air, water vapor or other vaporous bubbles into the outlet tube. This has the effect of reducing the hydrostati ...

and

well kill A well kill is the operation of placing a column of heavy fluid 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 that the hydrostatic head ...

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

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 industries, coiled tubing refers to a very long metal pipe, normally in diameter which is supplied spooled on a large reel. It is used for interventions in oil and gas wells and sometimes as production tubing in depleted g ...

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