Oil & Gas Terms in Category A

Appraisal well

Additional wells drilled after a discovery, to confirm the size of a hydrocarbon deposit.

Normally used to run buildup tests, drill stem tests, top and bottom of formation, gather core or fluid samples or other evaluations.



To cease efforts to produce oil or gas from a well, and to plug a depleted formation and salvage all material and equipment.


To cease producing oil and gas from a well when it becomes unprofitable.

A wildcat well may be abandoned after it has proven nonproductive.

Several steps are involved in abandoning a well; part of the casing may be removed and salvaged; one or more cement plugs are placed in the borehole to prevent migration of fluids between the different formations penetrated by the borehole; and the well is abandoned.

In many states, it is necessary to secure permission from official agencies before a well may be abandoned.


American bureau of shipping


Of or relating to the bottom waters of the ocean.

Absolute zero

A hypothetical temperature at which there is a total absence of heat.

Since heat is a result of energy caused by molecular motion, there is no motion of molecules with respect to each other at absolute zero.

Abnormal pressure


Pressure exceeding or falling below the normal pressure to be expected at a given depth.

Normal pressure increases approximately 0.465 psi per foot of depth (10.5kpa per meter of depth).

Thus, normal pressure at 10,000 feet is 4,650 psi; abnormal pressure at this depth would be higher or lower than 4,650 psi.

See pressure gradient.


A subsurface condition in which the pore pressure of a geologic formation exceeds or is less than the expected, or normal, formation pressure.

When impermeable rocks such as shales are compacted rapidly, their pore fluids cannot always escape and must then support the total overlying rock column, leading to abnormally high formation pressures.

Excess pressure, called overpressure or geopressure, can cause a well to blow out or become uncontrollable during drilling.

Severe underpressure can cause the drillpipe to stick to the underpressured formation.

Absorption gasoline

The gasoline extracted from natural gas by putting the gas into contact with oil in a vessel and subsequently distilling the gasoline from the heavier oil.


American association of petroleum geologists



Toward the stern of a ship or mobile offshore drilling rig


Farther than aft


A vertical, cylindrical vessel that recovers heavier hydrocarbons from a mixture of predominantly lighter hydrocarbons.

Also called absorption tower.

See absorb.


Also called absorption oil.

See absorption oil.

Absolute porosity

The percentage of the total bulk volume of a rock sample that is composed of pore spaces or voids.

See porosity.

Absorption plant

A plant that processes natural gas with absorption oil

Absorption tower

Also called absorber.

See absorber.

Absorption-refrigeration cycle

A mechanical refrigeration system in which the refrigerant is absorbed by a suitable liquid or solid.

The most commonly used refrigerant is ammonia; the most commonly used absorbing medium is water.