Drill pipe, is hollow, thin-walled, steel piping that is used on drilling rigs and horizontal drilling to facilitate the drilling of a wellbore and comes in a variety of sizes, strengths, and weights but are typically 27 to 32 feet in length (Range 2). Longer lengths exist up to 45 feet (Range 3). They are hollow to allow drilling fluid to be pumped through them, down the hole, and back up the annulus.
Because it is designed to transfer drilling torque for combined lengths that often exceed 1 mile down into the Earth's crust, the tempered steel tubes are expensive, and owners spend considerable efforts to reuse them after finishing a well. Used drill stem is inspected on site, or off location. Modified instruments similar to the spherometer are used at inspection sites to identify defects in the metallurgy, in order to prevent fracture of the drill stem during future wellboring. New drill pipe is classed as new (N class), becoming premium (P-class) and finally down to C (C 1 to 3) as the body outside diameter is worn down by usage. Eventually the drill pipe will be graded a scrap and marked with a red band.
Drill pipe is a portion of the overall drill string. The drill string consists of both drill pipe and the bottom hole assembly (BHA) which is the tubular portion closest to the bit. The bottom hole assembly will be made of thicker walled heavy weight drill pipe (HWDP) and drill collars which have a larger diameter and smaller internal diameter and provide weight to the drill bit and stiffness to the drilling assembly. Other BHA components can include mud motor, measurement while drilling collar (MWD), stabilizers, and other speciality downhole tools. The drill stem includes the entire drill string and the kelly which provides rotation and torque to the drill pipe.
See Drilling rig (petroleum) for a diagram of a drilling rig.
Anderson, Robert O. (1984). Fundamentals of the Petroleum Industry. Norman, Oklahoma: University of Oklahoma Press. ISBN 0-585-19475-0. Recommended Practice for Drill Stem Design and Operating Limits. Norman, Oklahoma: American Petroleum Institute. 1998.
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