| 摘要 |
A rotary drill bit assembly (1) suitable for directionally drilling a subsurface borehole the assembly (1) comprising a bit body (3) extending along a central longitudinal bit-body axis (8), and having a bit-body face (10) at its front end, wherein an annular portion of the bit-body face is provided with chip-making elements (12); a pilot bit (20) extending along a central longitudinal pilot-bit axis (32), the pilot bit (20) being partly arranged within the bit body (3) and projecting out of the central portion (14) of the bit-body face (10), a joint means (30) arranged to pivotably connect the pilot bit (20) to the bit body (3) so that the bit-body axis (8) and the pilot-bit axis (32) can form a variable diversion angle; and a steering means (40, 42, 45, 47, 55, 62) arranged to pivot the pilot bit (20) in order to steer.
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