Electromagnetic formation evaluation tool apparatus and method

An electromagnetic formation evaluation tool apparatus comprising:

• a conductive housing;
• a plurality of exciter electrodes, each electrode located around the periphery of the conductive housing, the plurality of exciter electrodes including a positive exciter electrode configured to transmit a formation current into a geological formation and a plurality of negative exciter electrodes configured to receive the formation current from the geological formation;
• a plurality of monitor electrodes, each electrode located around the periphery of the conductive housing, pairs of the monitor electrodes located between each pair of positive and negative exciter electrodes, the plurality of monitor electrodes insulated from the conductive apparatus housing;
• a receiver circuit coupled to each pair of monitor electrodes and configured to measure a voltage differential between each pair of monitor electrodes;
• and
• a power amplifier circuit coupled to the positive exciter electrode and to the conductive apparatus housing in a region of the positive exciter electrode, the power amplifier circuit configured to generate the formation current such that the formation current returns to the power amplifier circuit through the conductive apparatus housing.

A method for determining geologic formation properties, the method comprising:

• applying a voltage signal to an exciter electrode;
• transmitting a formation current through the geological formation;
• generating a magnetic field outside of a conductive housing of a formation tool apparatus in response to using the conductive housing as a return path for the formation current;
• measuring a voltage differential based on the formation current and the magnetic field;
• and
• calculating apparent resistivity of the geological formation based on the voltage differential.