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extended position, in which the steering pusher engages a wall of a borehole formed by the drilling apparatus, and a withdrawn position, in which the steering pushers do not engage the wall of the borehole.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