| 摘要 |
A rotating, transversely magnetized, magnet on a drill collar induces magnetization in a casing of a preexisting well. A coil rotating synchronously with the magnet produces a current at twice the frequency of rotation and having an amplitude that depends upon the distance from the magnet to the preexisting well. Alternatively, a variable magnetic field is produced in the casing using a switchable magnet. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
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