| 摘要 |
<p>A downhole tool (10) for drilling, reaming or cutting a borehole (B) comprises a body (12)and a numberof bore-engaging members (14) which are moveable between a first, retracted, position relative to the body (12) and a second, extended, position relative to the body (12). A first piston member (56) is disposed in the body (12) and is operable to move the bore-engaging members (14) in a first direction relative to the body (12).A second piston member (58) which is coupled to the mandrel (22) is operable to move in a second direction relative to the body (12). In use, engagement between the bore-engaging members (14) and the mandrel (22)as a result of either or both of the movement of the first and second piston members urges the bore-engaging members (14)to the second, extended, position.</p> |
