STANDOFF COMPENSATION FOR IMAGING IN OIL-BASED MUDS

摘要

Disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between two current electrodes. The two current electrodes are each shielded with conductive shields to prevent current leakage into the logging tool body. A common mode voltage is measured, and the phase and amplitude of the excitation source is controlled to reduce the difference between the common mode voltage and reference voltage of a voltage detector. The logging tool is further provided with electronics coupled to the voltage detector and the current electrodes to determine a differential voltage between the voltage electrodes and current flows from the current electrodes. From the differential voltage and multiple current flows, the computing facilities determine, and may display, the resistivity as a borehole wall image.