Electrode array for measurement of borehole resistivity

摘要

An array of electrodes is presented for accurate and improved measurement of borehole resistivity. The electrode array comprises five electrodes mounted on a relatively short insulated segment of a drill string. Current flows from the first electrode to the second electrode and is sensed by third and fourth electrodes. Any leakage current from the first electrode is collected by a fifth electrode and is kept isolated from the current flowing between the first and second electrodes thus insuring accurate determination of apparent formation resistivity. A current source, preferably a constant current source is used to determine the current in the circuit of the first and fifth electrodes.