| 摘要 |
A method and apparatus for drilling a borehole under an obstacle including placing a solenoid on the surface of the earth at the far side of the obstacle, near a preselected borehole exit location. A drilling assembly at an entry location on the near side of the obstacle is driven to produce a borehole which is directed under the obstacle toward the exit location. Initially, guidance of the drilling assembly is by conventional survey techniques, but when the borehole moves to within about 100 meters of the solenoid, the solenoid magnetic field is used to guide the drilling operation.
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