| 摘要 |
The drill bit assembly comprises: a drill bit (10), suited to be fixed to the distal end of a drill string (20); a casing shoe (12), for being mounted at the distal end of a casing column (14); and a ring bit (16), supported in its rotation by the casing shoe (12). The drill bot (10) and the ring bot (16) mutually axially slide inside one another, so that the drill bit (10) is configured to take on a cooperating condition and an independent condition. In the cooperating condition, the ring bit (16) surrounds the drill bit (10) and is integral in rotation to the drill bit (10); the ring bit (16) is operated in rotation, when the drill bit (10) is rotated. In the independent condition, the drill bit (10) axially exceeds the ring bit (16) and the ring bit (16) is independent, in its rotation, of the drill bit (10); the drill bit (10) is capable of rotating independently of the ring bit (16). |
