Blowout preventer

A special assembly of heavy-duty valves, commonly called the BOP stack, installed on top of a well which can be closed to prevent high-pressure oil or gas from escaping (a blowout) from the well hole during drilling operations.

Bonus

The cash consideration paid to the United States by the successful bidder for a mineral lease. The payment is made in addition to the rent and royalty obligations specified in the lease.

Borehole

The hole in the earth made by the drill; the uncased drill hole from the surface to the bottom of the well.

Casing

Steel pipe used in oil wells to seal off fluids in the rocks from the bore hole and to prevent the walls of the hole from caving.

Casinghead

The top of the casing set in a well; the part of the casing that protrudes above the surface and to which the control valves and flow pipes are attached.

Casinghead gas

Gas produced from an oil well as distinguished from gas from a gas well. The casinghead gas is taken off at the top of the well or at the separator.

Choke

A type of orifice installed at the surface on the tubing string to adjust and control the amount of oil or gas flowing from a well. It is customary to refer to the production of a well as so many barrels or thousands of cubic feet through a 1/4-inch or 1/2-inch choke, or whatever the size of the opening. The flowing pressure exerted by the well's production give an indication of the strength of the well, and is helpful in determining whether a well is commercial.

Commercial well

A well of sufficient net production that it could be expected to pay out in a reasonable time and yield a profit from the operation. A shallow 50-barrel-a-day well in a readily accessible location onshore could be a commercial well. Such a well in virtually any offshore area where enormously expensive producing facilities and pipe lines would have to be constructed would not be considered commercial.

Completed well

A well that has been mechanically completed for production or service use. There may be more than one completed zone in the well. (See Active well.)

Concession

Usually used in foreign operations and refers to a large block of acreage granted to the operator by the host government for a certain time and under certain government conditions which allows the operator to conduct exploratory and/or development operations. The Concession Agreement assures the holder of certain rights under the law.