| 摘要 |
Methods and related systems are described for making electromagnetic measurements of a subterranean rock formation (100; 700) through a conductive casing (176; 704) of a borehole. A number of transmitters/receivers (122; 126;...; 708; 710;...) are deployed into single well having a conductive casing (176; 704). A magnetic field is induced through the conductive casing (176; 704) and into a surrounding subterranean rock formation (100; 700), and the magnetic field is detected by the receivers. The receivers have main windings, feedback winding and bucking windings. One of the receiver coils in the tool string is excited at a time, and induced voltages at all of the other receiver coils, either in straight mode, or in feedback mode, are measured.
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