| 摘要 |
The invention relates to a directional casing drilling system comprising a casing string, a drilling rig and a retrievable Bottom Hole Assembly (BHA). The drilling rig comprises a casing drive for rotating the casing string in the borehole, a control system for controlling the casing drive, and a mud pump for pumping a continuous flow of drilling mud into the casing string. The BHA comprises a torque transfer section, with which it is secured in the casing string, and a drill bit section held in a drilling position in the torque transfer section. lt further comprises a mud drive that rotates the drilling position of the drill bit section about the longitudinal axis of the torque transfer section, and a communicating device for communicating the orientation of the drill bit to the control system. The BHA is steered by adjusting the rotational speed of the casing string. |
