Water makes equipment and pipe lines corrode faster. In order to avoid operational difficulties, the gas is usually dehydrated; i.e. the water is removed.

Depletion control

A method of limitations that can be used depending on the speed in which an oil or gas reservoirs may be extracted.

Derrick

The pyramid-shaped construction above the wellbore.

Derrick floor

The floor below the derrick with the rotating table. It is also called drilling floor or drilling rig.

Desalting

Removing brine compounds from crude.

Desilters

See hydroclones

Development well

A well in a profitable field where a drilling to a strategically depth, which is thought to be productive, is made.
A well drilled in a proven field in order to complete the desired spacing pattern. Also see spacing

Dog collar

A safety device that is used when running or retrieving equipment or drill collars with a flush external surface. A dog collar is temporarily fitted to the assembly between the tool joint and the slips. In case the slips cannot hold the tool assembly, the dog collar will keep the entire assembly from dropping and thereby avoiding it to be lost down hole.

Dog leg

A specially crooked place in the wellbore where the trajectory of the wellbore changes rapidly. This can be created intentionally, but usually the term refers to a place in the hole, where direction is changed quicker than expected or desired.

Down hole

A term describing the tools and equipments used in a well.
The term is also used to describe the circumstances and techniques applied in a well.

Downstream

The common meaning is any step further along the process.
It can also refer to the refining and marketing areas of the oil/gas industry. Also see upstream

Drift

A process where a tool is run through the casing in order to ensure that no junk, rocks, dried cement or other kinds of debris are left inside the casing collar.

Drill collar

Extra heavy steel pipes that are placed right above the drill bit to apply extra pressure on the teeth and to hold the drill string away.

Drill cuttings

The small pieces of rocks that are generated when the drill bit drills its way through the formations of the underground structure. Is also referred to as simply “cuttings”.

Drilling floor

See derrick floor

Drilling mud

A mixture of clay, water and chemicals that is pumped through the drill string during drilling and circulates in the wellbore. This is done to cool the bit, lubricate the moveable parts of the drill bit, rinse the teeth and to create a sufficient back pressure in the wellbore in order to prevent fluids or gas pockets from flowing out.