| 摘要 |
A method of determining an electric conductivity of an earth formation formed of different earth layers, whereby a wellbore containing a wellbore fluid extends through said formation, is provided. The method comprises lowering a n induction logging tool into the wellbore to a location surrounded by a selected one of the earth layers, the tool comprising magnetic field transmitter mean s suitable to induce magnetic fields of different frequencies in said earth layers, and magnetic field receiver means suitable to receive response magnetic fiel ds at different spacings from the induction means and to provide a signal representative of each response magnetic field. At least two of said different frequencies and at least two of said different spacings are selected, and for different combinations of each selected frequency and each selected spacing, the transmitter means is operated so as to induce a magnetic field of the selected frequency in said earth layers, which magnetic field induces a corresponding response magnetic field near the tool. The receiver means is operated at the selected spacing from the transmitter means so as to provide a signal representing the response magnetic field. Th e 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 and t he electric conductivity of an earth layer adjacent the selected layer.
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