Method and apparatus for rotary drill guidance

摘要

A process for controlling the direction of advance of a generally horizontal borehole extended through a subterranean coal- bearing formation by a rotary drilling operation. As the drill string is rotated in the hole, the advance of the drill bit is guided along a designated path by repeatedly deflecting the drill string from its axis in a constant radial direction. The drill string may also be centralized and the deflection operation carried out either within or outside of the drill-pipe segment between the bit and the centralizer. A deflection unit includes a plurality of deflector pads disposed about the periphery of a segment of the drill pipe. The deflector pads are cyclicly actuated to sequentially place each pad in an extended position at a constant rotational position of the drill pipe segment.