| 摘要 |
An electrical logging system for determining the electrical resistivity of a substrate formation from a cased borehole comprises voltage and current supply means, voltage and current control means, electrode support means, and voltage and current processing means. In particular the system comprises a first pair of current electrodes (A, B), adapted to be electrically connected at different heights to the casing within said borehole nearby one of the ends of the borehole for supplying an electrical current to said casing and providing a casing current between said electrodes through the intermediate casing part thus defined, and a second pair of voltage electrodes (M, N), for detecting voltages provided by leakage currents leaking form the casing into the formation. Said second pair of electrodes is adapted to be arranged above or below said first pair of electrodes between said intermediate casing part and the other end of the borehole.
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