Calibration of electromagnetic measurement tool

A method for calibrating an electromagnetic measurement tool, the method comprising:

• (a) providing (i) a deep reading electromagnetic measurement tool including a transmitter deployed on a transmitter sub and a receiver deployed on a receiver sub and (ii) a reference tool including a reference transmitter and a reference receiver;
• (b) deploying a test loop on the reference receiver and electromagnetically coupling the test loop and the reference receiver to obtain a calibration factor for the reference receiver;
• (c) deploying a test loop on the reference transmitter and electromagnetically coupling the test loop and the reference transmitter to obtain a calibration factor for the reference transmitter;
• (d) conducting an air hang test with the reference tool wherein the reference transmitter and the reference receiver are electromagnetically coupled in a known conductivity environment to obtain an air calibration coefficient;
• (e) measuring a first calibration factor to match the receiver on the electromagnetic measurement tool to the reference receiver on the reference tool by deploying a test loop on the receiver, electromagnetically coupling the test loop and the receiver, and combining a voltage on either the test loop or the receiver with the calibration factor obtained in (b);
• (f) measuring a second calibration factor to match the transmitter on the electromagnetic measurement tool to the reference transmitter on the reference tool by deploying a test loop on the transmitter, electromagnetically coupling the test loop and the transmitter, and combining a voltage on either the test loop or the transmitter with the calibration factor obtained in (c);
• (g) combining the air calibration coefficient obtained in (d), the first calibration factor measured in (e), and the second calibration factor measured in (f) to compute a calibration quantity for the electromagnetic measurement tool;
• and
• (h) deploying the electromagnetic measurement tool in a subterranean wellbore;
• (i) causing the electromagnetic measurement tool to make electromagnetic measurements while deployed in the subterranean wellbore;
• and
• (j) multiplying at least one of the electromagnetic measurements made in (i) by the calibration quantity computed in (g) to compute a gain calibrated electromagnetic measurement.

One or more non-transitory computer-readable storage media comprising computer-executable instructions which upon execution by a computing device perform a method to:

• determine calibration standards for a reference tool including a reference transmitter and a reference receiver;
• compute a first calibration factor to match a receiver on an electromagnetic measurement tool to the reference receiver on the reference tool;
• compute a second calibration factor to match a transmitter on the electromagnetic measurement tool to the reference transmitter on the reference tool;
• and
• receive electromagnetic measurements made by the electromagnetic measurement tool while deployed in a subterranean wellbore;
• and
• apply the first and second computed calibration factors and at least one of the determined calibration standards to at least one of the electromagnetic measurements to compute a gain calibrated electromagnetic measurement.