A reduction in us taxes for owners of an economic interest in minerals in place to compensate for the exhaustion of an irreplaceable capital asset.

This economic interest includes mineral interest, working interest in a lease, royalty, overriding royalty, production payment interest, and net profits interest.

A high-compression, internal-combustion engine used extensively for powering drilling rigs.

In a diesel engine, air is drawn into the cylinders and compressed to very high pressures; ignition occurs as fuel is injected into the compressed and heated air.

Combustion takes place within the cylinder above the piston, and expansion of the combustion products imparts power to the piston.

The mass or weight of a substance per unit volume.

For instance, the density of a drilling mud may be 10 pounds per gallon (ppg), 74.8 pounds per cubic foot (lb/ft), or 1,198.2 kilograms per cubic meter (kg/m3).

Specific gravity, relative density, and api gravity are other units of density.

N: a collar or coupling of tool steel, threaded internally, that can be used to retrieve pipe from the well on fishing jobs; the female counterpart of a taper tap.

The die collar is made up on the drill pipe and lowered into the hole until it contacts the lost pipe.

If the lost pipe is stuck so that it cannot rotate, rotation of the die collar on top of the pipe cuts threads on the outside of the pipe, providing a firm attachment.

The pipe is then retrieved from the hole.

Compare taper tap.

It is not often used because it is difficult to release it from the fish should it become necessary.

The power supplied to a drilling rig by diesel engines driving electric generators; used widely.

1.

Decrease in value of an asset such as a plant or equipment due to normal wear or passing of time; real property (land) does not depreciate.

2.

An annual reduction of income reflecting the loss in useful value of capitalized investments by reason of wear and tear.

The concept of depreciation recognizes that the purchase of an asset other than land will benefit several accounting cycles (periods) and should be expensed periodically over its useful life.

A condition in which the drill stem becomes stuck against the wall of the wellbore because part of the drill stem (usually the drill collars) has become embedded in the filter cake.

Necessary conditions for differential-pressure sticking, or wall sticking, are a permeable formation and a pressure differential across a nearly impermeable filter cake and drill stem.

Also called wall sticking.

See differential pressure, filter cake.

See gunk plug

Departure of the wellbore from the vertical, measured by the horizontal distance from the rotary table to the target.

The amount of deviation is a function of the drift angle and hole depth.

The term is sometimes used to indicate the angle from which a bit has deviated from the vertical during drilling.

See drift angle.

One of the rig crew members who gets his name from the fact that he works on a platform attached to the derrick or mast, typically 85 ft [26 m] above the rig floor, during trips.

On small land drilling crews, the derrickman is second in rank to the driller.

Larger offshore crews may have an assistant driller between the derrickman and the driller.

In a typical trip out of the hole (toh), the derrickman wears a special safety harness that enables him to lean out from the work platform (called the monkeyboard) to reach the drillpipe in the center of the derrick or mast, throw a line around the pipe and pull it back into its storage location (the fingerboards) until it is time to run the pipe back into the well.

in terms of skill, physical exertion and perceived danger, a derrickman has one of the most demanding jobs on the rig crew.

Some modern drilling rigs have automated pipe-handling equipment such that the derrickman controls the machinery rather than physically handling the pipe.

In an emergency, the derrickman can quickly reach the ground by an escape line often called the geronimo line.

The difference between two fluid pressures; for example, the difference between the pressure in a reservoir and in a wellbore drilled in the reservoir, or between atmospheric pressure at sea level and at 10,000 feet.

A large load-bearing structure, usually of bolted construction.

In drilling, the standard derrick has four legs standing at the corners of the substructure and reaching to the crown block.

The substructure is an assembly of heavy beams used to elevate the derrick and provide space to install blowout preventers, casingheads, and so forth.

Because the standard derrick must be assembled piece by piece, it has largely been replaced by the mast, which can be lowered and raised without disassembly.

1.

The device used to remove unwanted gas from a liquid, especially from drilling fluid.

2.

A device that removes air or gases (methane, h2s, co2 and others) from drilling liquids.

There are two generic types that work by both expanding the size of the gas bubbles entrained in the mud (by pulling a vacuum on the mud) and by increasing the surface area available to the mud so that bubbles escape (through the use of various cascading baffle plates).

If the gas content in the mud is high, a mud gas separator or “poor boy degasser” is used, because it has a higher capacity than standard degassers and routes the evolved gases away from the rig to a flaring area complete with an ignition source.

A piece of wood or concrete, usually buried, to which a wire guy line is attached for bracing a mast or tower.

The dispersion of solids that have stuck together in drilling fluid, usually by means of chemical thinners.

See flocculation.