Magnetic sensor correction for field generated from nearby current

A method of calibrating a downhole tool for use in directional drilling operations with a drill string incorporating the downhole tool, comprising:

• stimulating a current through a power circuit provided in the downhole tool, the power circuit extending between and electrically coupling a power source and a load, wherein the power source and the load are each coupled to a body of the downhole tool,
• wherein the current generates a conductor magnetic field at a magnetic sensor coupled to the body separately from the power source and the load and configured to obtain sample measurements;
• measuring a magnitude of the conductor magnetic field to obtain a measured value for the conductor magnetic field;
• determining a relationship between the current and the measured value;
• calculating a correction factor for the sample measurements based on the relationship;
• and
• storing the correction factor in the downhole tool for downhole use in obtaining, with the magnetic sensor, a measurement of Earth's magnetic field for control of a directional drilling tool in the directional drilling operations.

A method, comprising:

• introducing a downhole tool into a wellbore during drilling operations with a drill string incorporating the downhole tool, the downhole tool having a body, a power source coupled to the body, and a load coupled to the body;
• flowing an operational current through a power circuit to operate the load, the power circuit extending between and electrically coupling the power source and the load, whereby an operational conductor magnetic field is generated based on an intensity of the operational current during the drilling operations;
• obtaining sample measurements of a magnetic field, during the drilling operations, with a magnetic sensor coupled to the body, wherein the magnetic sensor is positioned on the body separately from the power circuit, the power source, and the load such that the operational conductor magnetic field affects operation of the magnetic sensor;
• measuring, during the drilling operations, the intensity of the operational current with a current sensor communicably coupled to the power circuit during a time period in which the magnetic sensor obtains the sample measurements;
• receiving, during the drilling operations, a signal indicative of the intensity of the operational current with computing equipment in the downhole tool and communicably coupled to the magnetic sensor and the current sensor;
• receiving, with the computing equipment during the drilling operations, the sample measurements;
• obtaining, with the computing equipment during the drilling operations, a correction factor stored by the downhole tool;
• determining, with the computing equipment during the drilling operations and based on the correction factor and the signal indicative of the intensity of the operational current, a portion of the operational conductor magnetic field that is induced at the magnetic sensor by the operational current;
• removing, during the drilling operations, the portion of the operational conductor magnetic field from the sample measurements to obtain a measurement of the Earth's magnetic field with the computing equipment;
• and
• providing the measurement of the Earth's magnetic field for control of a directional drilling tool during the drilling operations.