5) Description

A drill collar is a device used in the drilling of oil wells for weighting the drill bit, enabling it to drill through rock. It is a bar made of solid steel, either plain carbon steel or a non-magnetic steel alloy, drilled lengthwise to permit the passage of drilling fluids. A drill collar forms the lowest element of a drill string, which encompasses all the elements of a down-hole process from the surface to the rock bit.

6) Structure

These devices are typically 31 feet (about 9.45 m) long and threaded at both ends, male at one end and female at the other, to allow multiple drill collars to be joined above the bit assembly.

The number of drill collars attached to a drill string will depend upon the material composition of the strata at the drill site and the likely depth of the well. A relatively shallow well with less dense geologic structure through which the bit must pass will require fewer drill collars than a deep shaft through dense material.

Typically, drill collars will be consistent in length but may vary in diameter, and their outside configuration may be slick or spiral. The outside diameter may vary from about 3-1/2 inches (8.89 cm) to 11 inches (27.9 cm) and greater. The reference to slick or spiral outer configuration refers to the machining of the outside surface of the collar.

7) Parameter

8) Mechanical Property