Oil & Gas Terms in Category D

Deviation survey

An operation made to determine the angle from which a bit has deviated from the vertical during drilling.

There are two basic deviation-survey, or drift-survey, instruments: one reveals the drift angle; the other indicates both the angle and the direction of deviation.


Pertaining to packers and other tools left in the wellbore to be broken up later by the drill bit.

Drillable equipment is made of cast iron, aluminum, plastic, or other soft, brittle material.


A centrifugal device for removing sand from drilling fluid to prevent abrasion of the pumps.

It may be operated mechanically or by a fast-moving stream of fluid inside a special cone-shaped vessel.

Compare desilter.

Drillable squeeze packer

A permanent packer, drillable in nature, capable of withstanding extreme working pressures, for remedial work.

It has a positive flow-control valve built in.


A change in the angle of a wellbore.

In directional drilling, it is measured in degrees from the vertical


A centrifugal device for removing very fine particles, or silt, from drilling fluids to keep the amount of solids in the fluid at the lowest possible point.

Usually, the lower the solids content of mud, the faster is the rate of penetration.

The desilter work on the same principle as a desander.

Compare desander.


Abbr. downhole safety valve


See directional driller.

Directional driller

An individual trained in the science and art of intentionally drilling a well along a predetermined path in three-dimensional space, usually involving deviating the well from vertical and directing it in a specific compass direction or heading.

The directional driller considers such parameters as rotary speed, weight on bit, control drilling and when to stop drilling and take surveys of the wellpath, and works closely with the toolpusher.


Drill stem test

Dummy valve

A blanking valve placed in a gas lift mandrel to block off annular communication to the tubing.

Dry hole

An exploratory or development well found to be incapable of producing either oil or gas in sufficient quantities to justify completion as an oil or gas well.

Drill pipe pressure

The amount of pressure exerted inside the drill pipe as a result of circulating pressure, entry of formation pressure into the well, or both.


Trade name for a downhole motor driven by drilling fluid that imparts rotary motion to a drilling bit connected to the tool, thus eliminating the need to turn the entire drill stem to make hole.

Used in straight and directional drilling.

Drill pipe pressure gauge

An indicator, mounted in the mud circulating system, that measures and indicates the amount of pressure in the drill stem.

See drill stem.