Patent ID: 9223047
Filing Date: 2015-12-29
Classification: E21B,G01V

Abstract:
1. An apparatus for estimating a property of an earth formation penetrated by a borehole, the apparatus comprising: a carrier configured to be conveyed through the borehole; a first transmitter electrode disposed at the carrier and configured to inject electrical current into the earth formation; a first measurement electrode disposed at the carrier and configured to receive electrical current from the formation for measurement due to the current injection in order to estimate the property of the earth formation; a first measurement sensor coupled to the first measurement electrode and configured to measure electrical current amplitude and phase of the electrical current received by the first measurement electrode; a controller coupled to the first measurement sensor and configured to determine a phase difference between injected electrical current and received electrical current and to estimate the property using measured electrical current that is in-phase with the injected electrical current; and a first bucker amplifier coupled to the first measurement electrode and configured to inject an electrical current into the first measurement electrode based on the determined phase difference to create zero phase difference between the electrical current injected at the first transmitter electrode and the electrical current received by the first measurement electrode in accordance with a control algorithm implemented by the controller, wherein the control algorithm determines if a phase difference exists between the measured current and the transmitted current and determines the magnitude and sign of the phase difference if the phase difference is non-zero.