Patent attributes
A rotary steerable tool (2) for use in a downhole drilling apparatus for adjusting the direction of drilling is disclosed. The tool comprises a tubular outer housing (20) and a row of steering pushers (24) slidably mounted to the housing for movement between an extended position, in which the steering pusher engages a wall of a borehole formed by the drilling apparatus, and a withdrawn position, in which the steering pushers do not engage the wall of the borehole. A tubular sleeve (4) is mounted inside the housing (20) to transmit rotary drive to a drilling bit. A pressure chamber (22) defined between the sleeve (4) and the housing (20) communicates with the steering pushers (24) to move the steering pushers (24) to the extended position. A piston (56) is slidably mounted in the sleeve (4) and is moved by means of changes in drilling fluid pressure between a first axial position, in which the interior of the sleeve (4) communicates directly with the pressure chamber (22) for directional drilling, and a second axial position, in which the interior of the sleeve (4) does not communicate directly with the pressure chamber (22) for straight drilling.
