Definition - What does Drill String/Stem mean?
A drill string or drill stem, commonly written as "drill string/stem" for short, is a drill pipe consisting of tool joints, a swivel, a bit, a drill string, drill collars, drives, subs, a top drive, shock absorbers, reamers and other equipment used during the drilling process.
The drill string transmits and supports axial load, torsional load and transmits drilling fluid. The drill string is the main part of the drilling rig in directional drilling and is fitted with tracking and steering capabilities. The directional control in drilling the pilot hole is achieved by a non rotating drill string that has an assymetrical edge.
Trenchlesspedia explains Drill String/Stem
In Horizontal Directional Drilling (HDD) and other directional drilling methods, it is the drill string that bores the pilot bore hole measuring a few inches in diameter. This hole is subsequently enlarged during the reaming process to attain the diameter required for the pipe to be installed. The directional bias like a mud motor or slant face in the drill head near the leading drill rod, helps in controlling the direction of the drill. The change in direction is achieved by orienting the drill head in the desired direction and pushing the drill string forward. The pilot bore hole and the reaming process can be done by fluid jet cutting and by using the cutting torque produced by the rotation of the drill string.