Patent ID: 6348796
Filing Date: 2002-02-19
Classification: G01V

Abstract:
An apparatus conveyed in a borehole for obtaining a resistivity image of an earth formation penetrated by the borehole, the apparatus comprising:(a) a plurality of measure electrodes in electrical contact with the formation, each of the plurality of measure electrodes connected to a source of electrical current for conveying a beam of measure current corresponding to each measure electrode into the formation, said plurality of measure electrodes at a first electrical potential; (b) at least one guard electrode at a second potential substantially encircling each of said plurality of measure electrodes for conveying a current for defocusing the measure currents for a first distance into the formation, said second potential having a magnitude less than a magnitude of the first potential; and (c) a pad at a third electrical potential connected to a source of electrical current for conveying a current into the formation for refocusing the measure current at a second distance into the formation, said third potential greater having a magnitude greater than a magnitude of the first potential and said second distance being greater than the first distance.