| 摘要 |
A method of determining an electric conductivity of an earth formation formed of different earth layers (3, 5, 7) which earth formation is penetrated by a wellbore (1) containing a wellbore fluid, is provided. The method comprises lowering an induction logging tool (9) into the wellbore (1) to a location surrounding by a selected one of the earth layers (3, 5, 7), the tool (9) comprising magnetic field transmitter means (18) for inducing magnetic fields of different frequencies in said earth formation, and magnetic field receiver means (19) for receiving response magnetic fields and for providing a signal representative of each response magnetic field, at least one of the transmitter means (18) and the receiver means (19) having a plurality of magnetic dipole moments (26, 28) in mutually orthogonal directions. At least two of said different frequencies are selected, and for each selected frequency, the transmitter means (18) is operated so as to induce a magnetic field in the earth formation and the receive means (19) is operated so as to provide a signal representing a response magnetic field, wherein said at least one of the transmitter (18) and receiver means (19) is operated in said mutually orthogonal directions. The signals are combined in a manner so as to create a combined signal having a reduced dependency on the electric conductivity in the wellbore region. The formation resistivity and the relative orientation of the logging tool with respect to the formation layering is determined from the combined signal.
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