| 摘要 |
<p>A drill string (11) in a well bore (10) has a mandrel (13) extending longitudinally thereof adjacent the lower end (14) of the drill string with a drill bit (15) connected to the mandrel. Longitudinally extending helical groove means (20) are provided in the mandrel and roller means (21) are supported on the drill string and engaged with the helical groove means. Spring means (23) is supported by the drill string and abuts the mandrel to tend to urge the mandrel longitudinally out of the drill string whereby the bit is urged into substantially continuous contact with the well bore bottom (16) as the drill string is rotated during drilling operations. Valve means (30) are provided for selectively circulating fluids from the drill string to the well bore above the drill bit, and when desired jar means (8) may be incorporated in the drill string to impart an up or down jar thereto should the drill string become stuck or tend to become stuck during drilling operations.</p> |
