| 摘要 |
Direction of drilling a borehole is controlled using appts. having a rotary drill bit with at least one nozzle (38,40,42) through which drilling fluid flows in such a manner that its flow over cutting structures (30,32,34) on the bit causes one section of the bit to have an improved cutting action with respect to the remainder of the bit. Modulator means modulates the flow of drilling fluid through the nozzle so as to modulate the cutting action of the section such that the improved cutting action occurs in a desired direction of deviation of the hole. Also claimed is a method for causing deviation of a borehole being drilled by rotary drilling using the appts. such that the cutting action of the chosen sector is optimised when drilling in the desired direction of deviation and is reduced at other locations in the borehole. The modulator means forms part of the bottom hole assembly and is a flow interrupter. Synchronising means synchronises the modulation of the flow of drilling fluid with the rotation of the drill string, the means including accelerometers and/or magnetometers detecting the rotary position of the drill string and also a detector for detecting signals from the surface. A transmitting device transmits signals to the surface indicative of the position of the bit, the signals being pressure pulses in the drilling fluid. The nozzle arrangement in the bit may be a single nozzle directing flow at one part of the bit or a number of nozzles, the flow from one nozzle being directed at the workface and the flow from the other nozzles being directed at the cutting structures on the bit to act as mud picks. The internal geometry of the bit is such that there is greater flow in one section of the bit than in the remainder. The modulation of the flow of drilling fluid is synchronised with the rotation of the bit in the borehole during drilling.
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