Drill string

The typical layout of the drill string

DRILL STRING (EN: drill pipe string, drill column; DE: Bohrsaule; FR: colonne de forage; ES: columna de sondeo; RU: бурильная колонна) is the stepped hollow shaft, which is connecting the rock-destructing tool (the drill bit) with the ground surface equipment during the drilling of the deep wells (for example, for petroleum or gas).

The drill string is used for the creation of the axial load, for the transmission of the rotation to the drill bit (see the "Rotary drilling" article), for the delivery of the electrical (see the "Electrical drill" article) or of the hydraulic (see the "Turbine drilling" article) energy, for the delivery of the drilling fluid for the cleaning of the bottomhole, and for the outflow of the sludge, for the measurement of the curvature of the drilled well, and so on.

The drill string comprises the transition pipe, the thin-walled steel drill pipes, and the heavy weight drill pipes, to the bottom part of which there is attached the drill bit. Depending on the conditions for the drilling, there are installed near the drill bit the centering, calibrating, stabilizing, and widening devices. The external pipe of the drill string is connected with the swivel, which, with the help of the hook, of the hoist block, and of the rope, is suspended on the crown-block, which is installed within the upper part of the drilling derrick (Figure).

During the drilling, there act onto the drill string the dynamic and static loads, the fluctuations of the pressures of up to 25 megapascals, the temperature of up to 200 degrees Celsius, the aggressive environments. The reliability of the drill string determines up to the significant degree the efficiency of the drilling (especially during the rotary drilling).