Patent ID: 6731114
Filing Date: 2004-05-04
Classification: G01V

Abstract:
Apparatus with capacitive electrodes for electrical prospecting in a borehole, comprisingat least two injection electrodes; at least two measurement electrodes, distinct from said at least two injection electrodes; a current generator for applying an electrical current between two of said injection electrodes, said current generator delivering alternating current at a frequency lying in the range 5 kHz to 100 kHz and at a voltage of less than 1000 volts; at least one support cable provided with electrical conductors, at least one of the measurement or injection electrodes being suspended from said cable and placed in said borehole, said suspended electrode having an outer surface that is substantially cylindrical and electrically conductive and having a sufficient length and a diameter matching that of said borehole and capacitively coupled with ground surrounding said borehole; means for displacing said suspended electrode in the borehole by means of the cable; means for measuring a position of said suspended electrode in said borehole; means for measuring current flowing through said at least two injection electrodes; means for measuring a potential difference between the at least two measurement electrodes; and means for processing said current measurement and said potential difference measurement to deduce therefrom characteristics of subsoil in which the borehole is situated, for said measurement position.