| 摘要 |
Provided is a bore hole underreamer in a terrestrial formation, intended in particular for oil drilling. The underreamer has a hollow body and at least two cylindrical bores. The bores are provided through an external wall of the body and have axes that are transverse to a longitudinal axis of the body. The bores are distributed over the circumference of the hollow body and each bore contains a cylindrical widening arm. Each arm has a bladed cutting end disposed on the outside of the body that slides between active and inactive positions. Another end of each arm is disposed inside the body and receives fluid pressure for pushing the arm into the active position. The underreamer includes a locking member for locking the arms in their inactive position when the locking member is immobilised in the body in a releasable fashion in a locking position. When released, the locking member leaves the locking position under a thrust from at least one of the arms subjected to the pressure capable of pushing the arm into its active position.
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