HIGH RESOLUTION VOLTAGE SENSING ARRAY

An apparatus and method for performing high transverse resolution voltage measurements in downhole logging tools utilized to determine the resistivity of an adjacent portion of a borehole wall. Two current electrodes 508 and 509 are energized by an excitation source to create an oscillatory electric field in a borehole wall The voltage drop from each voltage electrode in a row of laterally spaced voltage electrodes 604 is measured relative to a shared voltage electrode 606 longitudinally spaced from the row of electrodes The differential voltage is used in combination with a measured current flow to determine a resistivity value for the borehole. A second row of laterally spaced voltage electrodes 608 having electrodes laterally offset from the electrodes of the first row is included to provide high transverse resolution. A common mode voltage at the shared voltage electrodes is measured and utilized to minimize the resistivity measurement error.