Directional drilling

The technique of drilling at an angle from the vertical by deflecting the drill bit. Directional wells are drilled to develop an offshore lease from one drilling platform; to reach a pay zone where drilling cannot be done, such as beneath a shipping lane.

Discovery

A find of significant quantities of gas or oil.

Dome

A roughly symmetrical upfold of the layers of rock in which the beds dip in all directions more or less equally from a common point; any deformation characterized by local uplift and approximately circular in outline; e.g. the salt domes of Louisiana and Texas.

Drill cuttings

Chips and small fragments of drilled rock that are brought to the surface by the flow of the drilling mud as it is circulated.

Drill pipe

Heavy, thick walled, hollow steel pipe used in rotary drilling to turn the drill bit and to provide a conduit for the drilling mud.

Drilling contractor

A person or company whose business is drilling wells. Wells are drilled on several contract specifications: per foot, day rate, or turnkey (that is, upon completion). Most major oil companies do not own drilling rigs. Exploration and development drilling is contracted. Personnel manning the rigs work for the contractor.

Drilling mud

A special mixture of clay, water, or refined oil, and chemical additives pumped down hole through the drill pipe and drill bit. The mud cools the rapidly rotating bit; lubricates the drill pipe as it turns in the well bore; carries rock cuttings to the surface; serves as a plaster to prevent the wall of the borehole from crumbling or collapsing; and provides the weight or hydrostatic head to prevent extraneous fluids from entering the well bore and to control down hole pressures that may be encountered.

Dry hole

A well drilled to a certain depth without finding commercially exploitable hydrocarbons.

Dry gas

Natural gas from the well that is free of liquid hydrocarbons; gas that has been treated to remove all liquids; pipeline gas.

E

Economically Recoverable Resource Estimate

An assessment of hydrocarbon potential that takes into account (1) physical and technological constraints on production and (2) the influence of exploration and development costs and market price on industry investment in OCS exploration and production.