Patent ID: 7382136
Filing Date: 2008-06-03
Classification: E21B,G01V

Abstract:
1. An apparatus for investigating the wall of a borehole in a geological formation, the apparatus comprising: a pad having an inside face and an outside face for pressing against the wall of the borehole; a set of measurement electrodes mounted on the outside face of the pad and means for measuring the potential difference between two measurement electrodes; a source electrode adapted to inject current into the formation and a return electrode, the set of measurement electrodes being situated between the source electrode and the return electrode; shielding means which are arranged between the source electrode and the measurement electrodes and between the measurement electrodes and the return electrode, and wherein said shielding means being located substantially flush with the outside face of the pad and extending along the length of the outside face of the pad so that the electric field generated by the current and return electrodes is substantially eliminated in the pad and in the vicinity of the measurement electrodes.