Method and apparatus for the study of resistivity of a geological formation surrounding a borehole of a well equipped with a metal coating. The invention relates to a method and a device for the study of the resistivity of a geological formation surrounding a borehole of a well equipped with a metal coating.An electric current is applied to the coating to cause a current leakage to the interior of the training in a certain level, and said current is derived by a feedback circuit in contact with the coating on both sides of the level of measurement.The said circuit being organised so as to ensure that the current that flows along the coating at this level has a low value in comparison with the current derived and determined the difference between the voltage drops in the sections located adjacent to the coating On both sides of the level of measurement, and then deducted from the current (Ifor) to escape.
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