| 摘要 |
A drilling unit containing a combined pilot bit and reamer. The drilling unit includes a housing containing a mud motor and a pilot bit extending from its distal end. A reamer is mounted to the housing. The mud motor turns the pilot bit while the reamer is turned either by the mud motor or as the drill string is rotated from the surface. The well bore is drilled and reamed in one pass. By positioning the reamer between the pilot bit and the mud motor, the mud motor must only pass through the larger reamer bore rather than the smaller pilot hole. This will allow larger mud motors to be used than would otherwise be possible. In one embodiment, the pilot bit is offset relative to the center of the end of the drill housing, providing increased tangential speed at the point of impact between the pilot bit and formation.
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