| 摘要 |
A steerable rotary drilling system for drilling or coring holes in subsurface formations comprises a bottom hole assembly 11 including a drill bit 13 carrying a plurality of cutting structures 16, and a mud hammer 14 which applies repeated axial impulses to the bit at a frequency greater than its frequency of rotation. Operation of the mud hammer 14 may be modulated in synchronism with rotation of the drill bit 13 and in controllable phase relation thereto. The drill bit is asymmetrically arranged, for example by an asymmetric distribution of the cutters 16, so that by appropriate selection of the phase relation the bit may be steered in a desired direction. <IMAGE> |
