Oil & Gas Terms in Category A


The maximum rate that a well can produce at the lowest possible bottom hole pressure (usually figured with a gas gradient).

see absolute open flow.

Absolute temperature scale

A scale of temperature measurement in which zero degrees is absolute zero.

On the rankine absolute temperature scale, in which degrees correspond to degrees fahrenheit, water freezes at 273 degrees and boils at 373 degrees.

See absolute zero.

Air drilling

A drilling technique whereby gases (typically compressed air or nitrogen) are used to cool the drill bit and lift cuttings out of the wellbore, instead of the more conventional use of liquids.

The advantages of air drilling are that it is usually much faster than drilling with liquids and it may eliminate lost circulation problems.

The disadvantages are the inability to control the influx of formation fluids into the wellbore and the destabilization of the borehole wall in the absence of the wellbore pressure typically provided by liquids.

Absolute permeability

A measure of the ability of a single fluid (such as water, gas, or oil) to flow through a rock formation when the formation is totally filled (saturated) with a single fluid.

The permeability measure of a rock filled with a single fluid is different from the permeability measure of the same rock filled with two or more fluids.

See effective permeability.

Associated reservoir

Oil and gas reservoir with a gas cap.

Gas production from these reservoirs may be restricted in order to preserve the gas cap energy and ultimate recovery.

Acid fracture

To fracture stimulate a formation by injecting the acid over the parting pressure of the rock and using the acid to etch channels in the fracture face.


In well logging: pertaining to being focused in one direction.

An azimuthal, or azimuthally focused, measurement has one or more directions perpendicular to the surface of a logging tool from which it receives most of its signal.

Examples are the density, laterolog and microresistivity logs.

Recent applications include azimuthal density and gamma ray in lwd tools.

A nonazimuthal, or azimuthally symmetric measurement is one which measures equally in all directions around the tool.

Examples are the induction, propagation resistivity log and gamma ray.


The space between two concentric objects, such as between the wellbore and casing or between casing and tubing, where fluid can flow.

pipe may consist of drill collars, drillpipe, casing or tubing.

Annular velocity

The speed at which drilling fluid or cement moves in the annulus.

It is important to monitor annular velocity to ensure that the hole is being properly cleaned of cuttings, cavings and other debris while avoiding erosion of the borehole wall.

the annular velocity is commonly expressed in units of feet per minute or, less commonly, meters per minute.

The term is distinct from volumetric flow.

Annular pressure

Fluid pressure in the annulus between tubing and casing or between two strings of casing.

Annular space

The space surrounding one cylindrical object placed inside another, such as the space surrounding a tubular object placed in a wellbore.

Also known as annulus.

Absolute viscosity

The measure of a fluid’s ability to resist flow without regards to its density.

It is defined as a fluid’s kinematic viscosity multiplied by its density.

Absolute open flow potential

The theoretical maximum flow that a well could deliver with a zero backpressure at the middle of the perforations.


The phase of petroleum operations that immediately follows successful exploratory drilling.

During appraisal, delineation wells might be drilled to determine the size of the oil or gas field and how to develop it most efficiently.



Authorization for expenditure.