| 摘要 |
PCT No. PCT/GB91/02031 Sec. 371 Date May 21, 1993 Sec. 102(e) Date May 21, 1993 PCT Filed Nov. 18, 1991 PCT Pub. No. WO92/09783 PCT Pub. Date Jun. 11, 1992.A downhole steering tool comprises a hollow mandrel (11), an independently rotatable sleeve (12) extending over a portion of the mandrel (11), steering plungers (26) carried by the sleeve (12) and extendable and retractable laterally to and from pressure contact with the hole wall (28) for steering a drill below the tool when in use, releasable locking means (14) for locking the sleeve (12) to the mandrel (11) rotationally, and fluid control means (15) operable to direct to the locking means (14) and the steering plungers (26) a portion from fluid circulation through the mandrel (11) to release the locking means (14) and to extend the steering plungers (26) by means of pressure of the fluid.
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