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Depletion

The removal of a non-renewable resource from a known deposit that may be sold.

Derrick

A tapered mast of open steel framework used in drilling to support the drill string and other equipment.

Development Well

A well drilled in a productive reservoir underlying a geographical area of known oil or gas accumulation and within a definable trap. A development well is a well that is drilled after an exploration well has confirmed the presence of petroleum in the formation. Usually, it takes several development wells to efficiently produce hydrocarbons from a formation.

Deviated Hole

A well bore which is off the vertical either by design or accident.

Dip

The inclination or slope of the rocks, expressed as degrees from the horizontal.

Discovery Well

An exploration test well that encounters a new and previously untapped oil or gas reservoir.

Drill Collar

A heavy wall component of the drill string placed between the bit and the drilling pipe to maintain vertical penetration of the bit and supply the weight necessary for drilling.

Drilling Contractor

A person or company whose business is drilling test wells on a contract basis for oil and gas companies.

Drilling Mud

A mixture of clay, water and chemicals pumped downhole through the drill pipe and drill bit.

Drill Pipe

High strength pipe, usually in 30 foot lengths, with threaded connections on each end.

Drill Stem

The entire drilling assembly from the seivel to the bit; composed of the kelly, drill pipe, and drill collars, used to rotate the bit and to carry the mud or circulating fluid to the bit.

Drill Stem Test

A method of obtaining a sample of fluid from a formation via a formation-tester tool attached to the drillstem. If the pressure is sufficient, fluid flows into the tester and up the drillpipe to the surface.

Dry Gas

A mixture of methane, ethane and LPG and up to three percent of carbon dioxide.

Dry Hole

An unsuccessful well that has been drilled to a certain depth without finding oil or gas. The well may flow water, gas or even oil but not in sufficient quantities for production; a duster.

Dual Completion

The completion of a well in two separate reservoirs which are producing at the same time.

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