| 摘要 |
The present invention provides a directional drilling apparatus for use i n the directional drilling of bore holes. In one embodiment the apparatus co mprises a plurality of cutting elements (16) movably mounted with respect to a rotatable body member (12), wherein the cutting elements are movable betw een first, radially retracted, positions and radially extended, positions fo r cutting. A rotary valve (42) is provided for synchronising the movement of the cutting elements between their respective extended and retracted positi ons in accordance with the rotational position of the body member in the bor e hole being drilled. Control of the directional drilling system is effected by synchronised movement of the cutting elements from an inner to an outer radial position in accordance with the angular position of the drill bit. Fo r example, by deploying the dynamic cutters over a 240- period, an elongate arcuate channel parallel to the longitudinal axis of the BHA will be produce d. As drilling progresses a near bit stabiliser (20) contacts with the porti on of the well bore which was not removed with the dynamic cutters and this contact exerts a force onto the drill bit. The force causes the drill bit to cut sideways and hence deviation of the drill bit is achieved.
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