Earth boring tool with continuous rotation impulsed steering

摘要

A pump pumps a drive fluid through a drill string and drill head during drilling. A movable element is mounted in the drill head for effecting a lateral movement on the drill head when moved in response to the pressure of the drive fluid in the drill head. This is in the form of pistons that are extended outwardly sideways from the drill head against the side of the borehole or an asymmetrical drill bit that applies a lateral force when a longitudinal force is applied to it. Steering is achieved by applying the lateral force when the drill head is in a selected rotational position. An indication is provided at the out-of-ground end of the drill string of the orientation of the drill head during rotation. A manually or automatically operated apparatus applies an impulse of force to the drive fluid at the out-of-ground end of the drill string when the drill head is at the selected orientation. This produces an impulse of increased pressure to the element in the drill head while the drill string is rotating. The synchronized application of a series of time-spaced lateral impulses to the drill head produces a continuous curve in the drilled borehole.