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Accumulator

A device used in a hydraulic system to store gasses or fluids temporarily. It is used to dampen pressure fluctuations in some applications.

Acidisation

A technique used to increase oil or gas production from a well. A stimulation fluid containing a reactive acid is pumped into the well in order to clean it and break down the stones containing the oil or gas. The acid disintegrates for instance calcium and chalk so that the oil flows easier through the pores.

Adjustable choke

A valve that is normally used in well control operations to reduce the pressure of a fluid from high pressure in the closed wellbore to atmospheric pressure. It is possible to adjust the valve (open or closed position) in order to control the pressure drop carefully. Also see choke

(AHD) Along hole depth

The distance along the well path from measured depth to a point in the well. 
 

Annular BOP

Ring that prevents blow outs. A large valve that controls fluids in the well.

Annular space

A term describing the ring-shaped space between the sides of the wellbore and the casing collar. This spaced is filled with cement.
 

Annulus

The ring-shaped area wedged in between two pipes when a smaller pipe is inserted into a larger one, for instance the wellbore and the drill string.

Annulus

API (American Petroleum Institute)

Leading oil industry organisation when it comes to setting standards for equipment and products. 
 

API gravity

A standardised scale indicating the specified weight for crude oil. This is measured at 60º F.

Appraisal drilling

A drilling done to determine the amounts of oil or gas that is assumed to be located in a reservoir along with production rate (the amount of oil/gas produced a day). By appraisal drilling it is possible to determine whether it is rentable to put the well into production. 
 

Area classification

Classifying a platform into areas according to explosion risk. Areas are classified into red, yellow and green areas. 
 

Associated gas

The type of natural gas found with oil in the ground either dissolved into the oil or in a layer above it. 
 

ASME

American Society of Mechanical Engineers

An organisation for engineers that have established a series of quality norms and procedure demands, for instance for welding on offshore constructions. 
 

Attapulgite

A type of clay added to saltwater-based drilling mud. It is used to improve the ability of the mud to lift particles of stone out of the wellbore. Also called salt gel. 
 

Australian offset

A drilling performed miles away from where there is any possibility of finding oil.

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