Directional drilling using variable bit speed, thrust, and actve deflection

摘要

A downhole assembly for directionally drilling a borehole has a motor, a transmission, and a steering mechanism. The motor has a rotor driven in a stator by flow of drilling fluid therebetween. The transmission operatively couples the rotor to a drill bit for drilling the borehole. A flow control controls the flow of drilling fluid through an internal passage of the rotor. The flow control can thereby vary the drive of the rotor in a bit speed effect that preferentially cuts the wall of the borehole to achieve directional drilling. The flow control can also thereby create a differential pressure displacing the rotor along a longitudinal axis of the motor in a thrust effect. The steering mechanism responds to the displacement of the rotor and deviates a direction of the drill bit from the longitudinal axis of the motor to further achieve directional drilling. The bit speed effect, the rotor displacement, and the deviation are preferentially coordinated to coincide or at least operate together.