| 摘要 |
<p>A weighted drilling head has a motor to drive two rotary drilling tools. The axial drilling pressure is provided by the weight of the head. The head pref. includes a motor to drive each tool, and may be formed by an assembly of identical modules. The drive motors are pref. electric motors powered by batteries forming part of the weight of the head. The latter is pref. suspended by a cable, the tools turning in the same or opposite sense.</p> |
