Importance

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Abstract

Methods for determining the distance from a borehole to a nearby, substantially parallel target well for use in guiding the drilling of the borehole, including positioning a magnetic field sensor in the borehole at a known depth and providing a magnetic field source in the target well. The wells may be vertical or horizontal, and the source preferably is a solenoid movable in the target to a location at approximately the same depth as that of the sensor. The distance between the borehole and the solenoid is determined, in one embodiment, by moving the solenoid to depths above and below the depth of the sensor, and detecting maximum field vectors. The distance the solenoid moves between the maxima is the distance between the wells. In another embodiment, the ratio of solenoid magnetic field vectors is used to determine the ratio of the difference in depth z between the solenoid and the sensor to the lateral distance R between the wells. This ratio z/r is then used to determine the separation of the wells.

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First Claim