| 摘要 |
A method (and apparatus) for causing deviation of a borehole being drilled by rotary drilling using a bit (24) having at least one nozzle (38,40,42) through which a drilling fluid is caused to flow such that in use the flow of drilling fluid through the nozzle allows one sector of the bit (24) to cut more effectively than the remainder of the bit, the method comprising modulating the flow of the drilling fluid through the nozzle such that as the bit rotates the cutting action of the one sector is optimised when in the desired direction of deviation and reduced at other locations in the borehole, the apparatus comprising a rotary drill bit (24) with at least one nozzle (38,40,42) and modulator means to modulate the flow of drilling fluid through the nozzle.
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