| 摘要 |
The specification discloses a method and system for determining the position of a drill bit in the earth without interrupting the drilling operations. In operation, rotation of the drill bit against the formation being drilled generates coherent acoustical signals which are recorded at the surface of the earth by a plurality of spaced detectors. The signals recorded at each of the different detectors are time shifted relative to each other. These time shifts correspond to possible locations of the drill bit within the earth and are controlled to some degree by the length of drill pipe in the borehole. After the acoustic signals are shifted in time their coherency is determined. This procedure is repeated for a number of assumed locations of the drill bit. The drill bit position is determined to be at the location having the highest coherency value. In this manner the surface detectors are focused on precise positions within the earth avoiding interference from acoustical signals generated at the surface or from the drill pipe.
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