Patent ID: 8633702
Filing Date: 2014-01-21
Classification: G01V

Abstract:
1. An apparatus for making a resistivity measurement of an underground formation surrounding a borehole, comprising: a conductive tool body; at least one current injector electrode positioned between the tool body and a wall of the bore hole; at least one current return electrode positioned between the tool body and the wall of the bore hole, the current injector electrode and the current return electrode being electrically isolated from each other; an electrical measurement device configured to monitor a voltage or a current signal indicative of an impedance imbalance; a regulator connected to the electrical measurement device, the regulator configured to receive the voltage or the current signal indicative of the impedance imbalance and configured to generate an adjustment signal based on the voltage or the current signal indicative of the impedance imbalance; an adjustable electrical device connected to the regulator, the adjustable electrical device configured to receive the adjustment signal from the regulator and based on the adjustment signal configured to (a) improve a balancing condition and thereby supress the impedance imbalance such that the potential difference between the tool body and the formation is about 25% or less than the potential difference between the current injector electrode and the current return electrode, or (b) reduce the effects of non-optimal balancing, such that the potential difference between the tool body and the formation is about 25% or less than the potential difference between the current injector electrode and the current return electrode.