# US 10,481,296 B2 · Magnetic sensor correction for field generated from nearby current

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- Number: US 10,481,296 B2
- Document ID: US10481296B2
- Status: Granted
- Kind: B2
- Application number: 14/777,899
- Filed: 2014-10-22
- Published: 2016-10-13
- Granted: 2019-11-19
- Earliest claimed: 2014-10-22
- Assignees: Hallibunon Energy Services, Inc.
- Applicants: Halliburton Energy Services, Inc.
- Inventors: Jonathan Peter Zacharko; Robert Scott Fulford
- Web page: https://patentgrep.com/patent/US10481296B2

## CPC

- G01V 13/00: Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00
- E21B 7/04: Directional drilling
- E21B 41/0085: {Adaptations of electric power generating means for use in boreholes}
- E21B 47/024: of devices in the borehole (determining slope or direction of the borehole E21B47/022)
- E21B 47/092: by detecting magnetic anomalies
- E21B 49/00: Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
- G01V 3/26: operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device (with electromagnetic waves G01V3/30)
- G01V 3/38: Processing data, e.g. for analysis, for interpretation, for correction
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

An example method of calibrating a downhole tool includes stimulating a known current through a power circuit provided in the downhole tool, the power circuit extending between and communicably coupling a power source and a load. A conductor magnetic field is generated as the known current flows through the power circuit and the conductor magnetic field is detectable by a magnetic sensor included in the downhole tool to obtain sample measurements of Earth's magnetic field. A magnitude of the conductor magnetic field is then measured to obtain a measured value for the conductor magnetic field, and a relationship between the known current and the measured value is determined to calculate a correction factor for the sample measurements based on the relationship. A computer in the downhole tool is then programmed to apply the correction factor to the sample measurements in response to operational currents measured in the power circuit during operation.

## Claims

### Claim 1

A downhole tool, comprising:
a body;
a power source coupled to the body;
a load coupled to the body;
a power circuit extending between and electrically coupling the power source and the load to conduct current provided by the power source to and from the load, wherein, when current flows through the power circuit, a conductor magnetic field is generated;
a magnetic sensor coupled to the body to obtain sample measurements of a magnetic field, wherein the magnetic sensor is positioned on the body separately from the power circuit, the power source and the load, such that the conductor magnetic field affects operation of the magnetic sensor;
a current sensor communicably coupled to the power circuit to measure the current in the power circuit; and
a computer communicably coupled to the magnetic sensor and the current sensor, the computer configured to:
receive the sample measurements of the magnetic field from the magnetic sensor during drilling operations using a drill string that includes the downhole tool,
receive current measurements from the current sensor during the drilling operations,
obtain a stored correction factor during the drilling operations,
determine, based on the stored correction factor and the received current measurements, a portion of the conductor magnetic field that is induced at the magnetic sensor by the conducted current during the drilling operations,
remove the determined portion of the conductor magnetic field from the sample measurements of the magnetic field to obtain a measurement of Earth's magnetic field during the drilling operations, and
provide the measurement of Earth's magnetic field for control of a directional drilling tool during the drilling operations.

### Claim 2 (depends on 1)

The downhole tool of claim 1, wherein the downhole tool comprises a tool selected from the group consisting of the directional drilling tool, a measure-while-drilling tool, a logging-while-drilling tool, one or more wireline tools, and any combination thereof.

### Claim 3 (depends on 1)

The downhole tool of claim 1, wherein the power source is selected from the group consisting of one or more batteries, a generator, a fuel cell, a capacitive bank, or any combination thereof.

### Claim 4 (depends on 1)

The downhole tool of claim 1, wherein the load comprises an electricity-consuming device selected from the group consisting of a sensor, a motor, an actuator, a downhole electronic device, a telemetry module, and any combination thereof.

### Claim 5 (depends on 1)

The downhole tool of claim 1, wherein the power circuit comprises a positive conductor that conducts a supply current from the power source to the load and a negative conductor that conducts a return current from the load.

### Claim 6 (depends on 5)

The downhole tool of claim 5, wherein one or both of the positive and negative conductors comprise a self-shielding structure selected from the group consisting of a coaxial cable, a twisted pair of wires, a bus bar, and a strip line.

### Claim 7 (depends on 5)

The downhole tool of claim 5, wherein the positive and negative conductors are fixed relative to the magnetic sensor.

### Claim 8 (depends on 5)

The downhole tool of claim 5, wherein the body is cylindrical and the positive and negative conductors are angularly offset by 180 degrees from the magnetic sensor about a circumference of the body.

### Claim 9

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.

### Claim 10 (depends on 9)

The method of claim 9, wherein stimulating the current through the power circuit comprises stimulating a known current through the power circuit.

### Claim 11 (depends on 9)

The method of claim 9, wherein stimulating the current through the power circuit further comprises measuring an intensity of the current with a current sensor.

### Claim 12 (depends on 9)

The method of claim 9, wherein determining the relationship comprises comparing an intensity of the current with the magnitude of the conductor magnetic field.

### Claim 13 (depends on 9)

The method of claim 9, wherein measuring the magnitude of the conductor magnetic field comprises measuring the magnitude of the conductor magnetic field with the magnetic sensor.

### Claim 14 (depends on 9)

The method of claim 9, further comprising, during the directional drilling operations:
introducing the downhole tool into a wellbore and flowing an operational current through the power circuit to operate the load, whereby an operational conductor magnetic field is generated based on an operational current intensity;
obtaining sample measurements of a magnetic field with the magnetic sensor;
measuring the operational current intensity with a current sensor communicably coupled to the power circuit during a time period in which the magnetic sensor obtains the sample measurements;
receiving a signal indicative of the operational current intensity with a computer associated with the downhole tool and applying the correction factor to the sample measurements with the computer based on the operational current intensity, and thereby removing the operational conductor magnetic field from the sample measurements to obtain the measurement of the Earth's magnetic field; and
dynamically calibrating the downhole tool while the downhole tool is located within the wellbore.

### Claim 15 (depends on 14)

The method of claim 14, wherein dynamically calibrating the downhole tool comprises:
stimulating a known current in the power circuit while the downhole tool is located in the wellbore;
measuring an intensity of the known current with the current sensor;
comparing a measured value of the intensity of the known current to a static sample measurement obtained by the magnetic sensor;
determining a new relationship between the known current and the measured value of the intensity of the known current; and
calculating a new correction factor for the sample measurements based on the new relationship.

### Claim 16 (depends on 15)

The method of claim 15, further comprising applying the new correction factor to the sample measurements in response to operational currents measured in the power circuit during operation.

### Claim 17 (depends on 9)

The method of claim 9, wherein the power circuit comprises a positive conductor that conducts a supply current from the power source to the load and a negative conductor that conducts a return current from the load, the method further comprising self-shielding one or both of the positive conductor and the negative conductor to provide a self-shielding structure, wherein the self-shielding structure is selected from the group consisting of a coaxial cable, a twisted pair of wires, a bus bar, and a strip line.

### Claim 18 (depends on 9)

The method of claim 9, wherein the power circuit comprises a positive conductor that conducts a supply current from the power source to the load and a negative conductor that conducts a return current from the load, the method further comprising coupling the positive and negative conductors to the body such that movement of the positive and negative conductors relative to the magnetic sensor is prevented.

### Claim 19

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.

### Claim 20 (depends on 19)

The method of claim 19, wherein the correction factor is determined prior to introducing the downhole tool into the wellbore by:
stimulating at least one known current through the power circuit;
generating a conductor magnetic field as the at least one known current flows through the power circuit, wherein the conductor magnetic field is detectable by the magnetic sensor;
measuring a magnitude of the conductor magnetic field to obtain a measured value for the conductor magnetic field;
determining a relationship between the at least one known current and the measured value; and
calculating the correction factor based on the relationship; and
storing the correction factor in the downhole tool.

### Claim 21 (depends on 19)

The method of claim 19, wherein the power circuit comprises a positive conductor that conducts current from the power source to the load and a negative conductor that conducts a return current from the load, the method further comprising coupling the positive and negative conductors to the body such that movement of the positive and negative conductors relative to the magnetic sensor is prevented.