| 摘要 |
PCT No. PCT/GB89/01318 Sec. 371 Date May 1, 1991 Sec. 102(e) Date May 1, 1991 PCT Filed Nov. 3, 1989 PCT Pub. No. WO90/05235 PCT Pub. Date May 17, 1990.A directional drilling apparatus and method in which the drill bit is coupled to the lower end of a drill string through a universsal joint which allows the bit to pivot relative to the string axis. The bit is contra-nutated in an orbit of fixed radius and at a rate equal to string rotation but in the opposite direction. This speed-controlled and phase-controlled bit nutation keeps the bit heading off-axis in a fixed direction. The invention enables directional drilling while the drill string rotates normally.
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