# US 2023/0056853 A1 · Null point depth calibration

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- Number: US 2023/0056853 A1
- Document ID: US20230056853A1
- Status: Published application
- Kind: A1
- Application number: 17/881,804
- Filed: 2022-08-05
- Published: 2023-02-23
- Earliest claimed: 2021-08-09
- Assignees: The Charles Machine Works, Inc.
- Applicants: The Charles Machine Works, Inc.
- Inventors: Scott B. Cole
- Web page: https://patentgrep.com/patent/US20230056853A1

## CPC

- E21B 47/092: by detecting magnetic anomalies
- E21B 7/046: {horizontal drilling (drilling with mechanical conveying means E21B7/003)}
- G01V 3/08: operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices (with electromagnetic waves G01V3/12)
- G01V 3/081: {the magnetic field is produced by the objects or geological structures (characterised by the method of magnetic field measurement G01R33/00)}
- G01V 3/38: Processing data, e.g. for analysis, for interpretation, for correction
- G01V 3/15: specially adapted for use during transport, e.g. by a person, vehicle or boat
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)

## Abstract

A calibration method for calibrating an underground beacon and tracker system for use with horizontal directional drilling. The beacon emits a magnetic field, which is received at an above-ground receiving antenna. The antenna is used to locate front and rear null points in the emitted field. The vertical and horizontal offset between the null points is determined to locate the beacon. Then, the magnetic field strength is determined at one of the null points. This value may be used to calculate or update a calibration constant. The calibration constant is then used in subsequent locating step while the characteristics of the underground environment surrounding the beacon remain similar.

## Claims

### Claim 1

A method, comprising:
advancing a drill string carrying a beacon to a first underground location;
emitting an electromagnetic signal from the beacon;
performing a calibration procedure comprising:
at an above ground location, detecting a first null point and a second null point with a receiving antenna;
determining a distance between the first null point and the second null point and storing the distance in a memory;
receiving a signal indicative of a pitch of the beacon;
determining a signal strength at the selected one of the first null point and the second null point;
using the pitch and the signal strength to determine a calibration constant; and
storing the calibration constant in a memory.

### Claim 2 (depends on 1)

The method of claim 1 further comprising:
using the distance between the null points to determine a depth of the beacon below a selected one of the first null point and the second null point and storing the depth in the memory;
from the distance and the depth, determining a radial distance between the beacon and the selected one of the first null point and the second null point; and
using the radial distance to determine the calibration constant.

### Claim 3 (depends on 2)

The method of claim 2 further comprising:
thereafter, advancing the drill string; and
using the calibration constant determined with the beacon at the first underground location, determining a location of the beacon after the drill string has been advanced.

### Claim 4 (depends on 2)

The method of claim 2 further comprising:
advancing the drill string such that the beacon is at a second underground location, in which the second underground location has differing soil conditions from the first underground location; and
performing the calibration procedure at the second underground location.

### Claim 5 (depends on 4)

The method of claim 4 further comprising:
thereafter, advancing the drill string; and
using the calibration constant determined with the beacon at the second underground location, determining a location of the beacon after the drill string has been advanced.

### Claim 6 (depends on 4)

The method of claim 4 further comprising:
thereafter, advancing the drill string; and
using the calibration constant determined with the beacon at the first underground location, determining a location of the beacon after the drill string has been advanced.

### Claim 7 (depends on 4)

The method of claim 4 in which the calibration constant determined by the calibration procedure with the beacon at the first underground location is characterized as a first calibration constant and the calibration constant determined by the calibration procedure with the beacon at the second underground location is characterized as a second calibration constant; and
in which:
each of the first calibration constant and second calibration constant are stored in the memory; and
one of the first calibration constant and second calibration constant is selected for use when the beacon is at a third underground location.

### Claim 8 (depends on 1)

The method of claim 1 in which the selected one of the first null point and the second null point is located above the drill string.

### Claim 9 (depends on 1)

The method of claim 1 in which the selected one of the first null point and the second null point is located in front of a projected path of the drill string.

### Claim 10 (depends on 2)

The method of claim 2 in which the distance is determined by a method comprising the steps of:
locating the first nul point;
marking a location of the first null point;
locating the second null point;
marking a location of the second null point; and
measuring the distance between the marked locations of the first and second null points.

### Claim 11 (depends on 10)

The method of claim 10 in which the location of the first null point and the second null point are physically marked; and
manually measuring the distance between the physical marks.

### Claim 12 (depends on 10)

The method of claim 10 in which the steps of marking a location of a first null point and marking a location of a second null point comprise digitally marking GPS coordinates.

### Claim 13 (depends on 12)

The method of claim 12 in which a processor calculates the difference between the first null point and the second null point from the GPS coordinates.

### Claim 14 (depends on 1)

The method of claim 1 further comprising determining a vertical distance between the first null point and the second null point.

### Claim 15 (depends on 14)

The method of claim 14 wherein the step of determining the vertical distance comprises using an altimeter.

### Claim 16 (depends on 14)

The method of claim 14 wherein the step of determining the vertical distance comprises using a laser level.

### Claim 17

A method comprising:
emitting an electromagnetic field from a beacon at a below ground location;
detecting the electromagnetic field at a tracking antenna at an above ground area;
determining a first null field location on a surface of the ground;
determining a second null field location on the surface of the ground;
at a selected one of the first null field location and the second null field location, detecting a strength of the electromagnetic field; and
from the first null field location, the second null field location, and the strength of the electromagnetic field, determining a calibration constant with the beacon at the below ground location.

### Claim 18 (depends on 17)

The method of claim 17 in which the first null field location and the second null field location are determined by the tracking antenna.

### Claim 19 (depends on 17)

The method of claim 17 further comprising
determining a distance between the first null field location and the second null field location; and
determining a depth of the beacon relative to a selected one of the first null field location and the second null field location.

### Claim 20 (depends on 17)

The method of claim 17 further comprising:
with a drill string connected to a horizontal directional drilling system, advancing the beacon to the below ground location;
after the step of determining the calibration constant at the below ground location, advancing the beacon to a new below ground location;
thereafter, determining a depth of the beacon at the new below ground location using the calibration constant.

### Claim 21 (depends on 17)

The method of claim 17, wherein the below ground location is characterized as a first below ground location and further comprising:
advancing the beacon to a second below ground location; and
changing the calibration constant based upon the first null location, the second null location, and the strength of the electromagnetic field with the beacon at the second below ground location.