| 摘要 |
<p>A drilling assembly for connection to a drill string, for use in drilling holes in subsurface formations, comprises a drill bit (15) carrying cutters located and orientated to perform cutting action on the formation as the drill bit rotates anti-clockwise relative thereto. A drive unit (13), such as an hydraulically driven positive displacement motor or turbine, or an electric motor, is operatively coupled to the drill bit (15) to rotate the drill bit anti-clockwise relative to the drive unit, and a hole opener (14) is coupled to the drive unit for rotation therewith. There may be provided two drive units in series, comprising a first drive unit (20) operatively coupled to the drill bit to rotate the drill bit in one direction relative to the first drive unit, and a second drive unit (23) operatively coupled to the first drive unit to rotate the first drive unit in the opposite direction relative to the second drive unit. A hole opener is coupled to at least one of the drive units for rotation therewith. <IMAGE></p> |
