Oil & Gas Terms in Category O

Opening ratio

The ratio between the pressure required to open the preventer and the well pressure under the rams.


The person or company, either proprietor or lessee, actually operating an oilwell or lease.

Generally, the oil company by whom the drilling contractor is engaged.

Offset-well data

Information obtained from wells that are drilled in an area close to where another well is being drilled or worked over.

Such information can be very helpful in determining how a particular well will behave or react to certain treatments or techniques.

Off production

Said of a well when it is shut in or temporarily not able to produce.

Open-hole completion

A method of preparing a well for production in which no production casing or liner is set opposite the producing formation.

Reservoir fluids flow unrestricted into the open wellbore.

An open-hole completion has limited use in rather special situations.

Also called a barefoot completion.

Oil-emulsion water

The water contained in an emulsion of oil and water.

Also called milk emulsion.

On the horn

Someone talking on a two-way radio to another person.


A projecting member run out at an angle from the sides of a portable mast or a land crane to the ground to provide stability and to minimize the possibility of having the mast or the crane overturn.

Oil pool

The accumulation of oil in the pores of sedimentary rock that yields petroleum on drilling.

Not a pool or pond in the ordinary use of the term.


A circular seal common in the oilfield; requires deformation (squeeze) to energize and seal.

Offset well

Well drilled near another one.

Organic theory

An explanation of the origin of petroleum, which holds that the hydrogen and the carbon that make up petroleum come from plants and animals of land and sea.

Furthermore, the theory holds that more of this organic material comes from very tiny creatures of swamp and sea than comes from larger creatures of land.

Outer continental shelf

An offshore area in the united states that begins where state ownership of mineral rights ends and ends where international treaties dictate.



The sediment weight pressing down on the formation.


The strata of rock that overlie the stratum of interest in drilling.

Offshore drilling

Drilling for oil or gas in an ocean, gulf, or sea, usually on the outer continental shelf.

A drilling unit for offshore operations may be a mobile floating vessel with a ship or barge hull, a semisubmersible or submersible base, a self-propelled or towed structure with jacking legs (jackup drilling rig), or a permanent structure used as a production platform when drilling is completed.

In general, wildcat wells are drilled from mobile floating vessels or from jackups, while development wells are drilled from platforms or jackups.