INDEPENDENT MODIFICATION OF DRILL STRING PORTION ROTATIONAL SPEED

摘要

A method of operating a drill string comprises independently modifying a rotary speed of a downhole portion of the drill string relative to other downhole portions of the drill string, each of the portions comprising a plurality of drill pipe sections. The modified-speed portion of the drill string can comprise a downhole end portion of the drill string extending between a downhole drill string end and a curved portion of the borehole in which the drill string is located. The downhole end portion can be rotated at an increased speed relative to a portion of the drill string coincident with the curved portion of the borehole. Independent speed modification can be effected by incorporating one or more transmission modifier devices in the drill string, the transmission modifier device being switchable between a disengaged mode in which it transfers unmodified drill string torque and rotation, and an engaged mode in which it transmits torque and rotation along the drill string at a modified speed and torque. Selective switching of the transmission modifier devices, while downhole, maybe controlled from the surface.