| 摘要 |
An induction logging instrument is disclosed which includes at least one induction transmitter arranged as an axial magnetic dipole and at least one differential axial magnetic dipole receiver disposed at a selected axial distance from the at least one induction transmitter. In one embodiment, the receiver includes a pair of coils, each wound on an axis substantially parallel to an axis of the instrument. Each of the coil axes is displaced from the instrument axis by a substantially equal lateral distance in opposite directions. Each of the pair of coils is disposed at substantially the same axial position along the instrument, and the coils are interconnected in inverse series. In another embodiment, the receiver includes two pairs of coils, each wound on an axis substantially parallel to the axis of the instrument. Each of the coil axes in each pair is displaced from the instrument axis by a substantially equal lateral distance an in opposed directions. The pairs are substantially orthogonal to each other. Each of the coils is disposed at substantially the same axial position along the instrument, and the coils in each pair are connected to circuits adapted to determine a difference between signals induced in each of the coils.
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