| 摘要 |
<p>The present invention provides a method of drilling a borehole in a formation (i.e. open-hole drilling). The method uses a drill bit that has at least one blade (14) that is movable between an extended configuration and a retracted configuration. The blade is movable by increased fluid pressure applied to the drill bit. The invention also provides a drill bit that is provided with at least one blade that can be moved between an extended configuration and a retracted configuration. The drill bit is provided with a locking means that prevents the blade from partially or fully extending until required.</p> |
