Receiver System For Determining The Location Of A Magnetic Field Source

• US 20110227575A1
• Filed: 05/27/2011
• Published: 09/22/2011
• Est. Priority Date: 09/28/2007
• Status: Active Grant

• Current Assignee: Charles Machine Works Incorporated The
• Original Assignee: Charles Machine Works Incorporated The
• Inventors: Cole, Scott Bryan
• Granted Patent: US 8,482,286 B2
• Time in Patent Office: Days
• US Class Current: 324/326
• CPC Class Codes: E21B 47/0232 at least one of the energy sources or one of the detectors being located on or above the ground surface
• CPC Class Codes: G01R 33/02 Measuring direction or magnitude of magnetic fields or magnetic flux G01R33/20 takes precedence
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat
• CPC Class Codes: G01V 3/30 operating with electromagnetic waves

Abstract

A method and receiver system for identifying a location of a magnetic field source using two horizontally displaced tri-axial antennas. In a preferred embodiment two tri-axial antennas are positioned at opposite ends of a receiver frame. Each antenna detects in three dimensions a magnetic field from a source or transmitter. The receiver is maintained in a horizontal plane and the receiver is moved in the horizontal plane until a flux angle measured at each of the two points is zero so that the receiver is in the vertical plane perpendicular to the axis of the source. The depth and location of the source in three dimensions relative to the receiver is determined using the detected field values. The receiver is moved in a direction defined by a line containing the two points of the receiver until a magnitude of the magnetic field detected at each of the two points is substantially the same so that the receiver is positioned above the source.

Claims

1. A method for guiding a downhole tool assembly, the method comprising:

setting a receiver assembly at a target point, the receiver assembly comprising two antenna assemblies disposed in a substantially horizontal plane, such that the two antenna assemblies each lie on a desired borepath; and

simultaneously detecting in three dimensions at each of the two antenna assemblies a magnetic field transmitted from the downhole tool assembly to determine a position of the downhole tool assembly.

2. The method of claim 1 further comprising calculating the position of the downhole tool assembly in a vertical plane containing the desired borepath using the fields detected by the two antenna assemblies.

3. The method of claim 1 wherein the position of the downhole tool assembly comprises a depth of the downhole tool assembly and a horizontal distance to the downhole tool assembly.

4. The method of claim 1 further comprising the step of using the fields detected by the two antenna assemblies to calculate whether the downhole tool assembly is left or right of the desired borepath.

5. The method of claim 1 further comprising the steps of:

detecting a pitch of the downhole tool assembly; and

using the fields detected by the two antenna assemblies and the pitch of the downhole tool assembly to calculate a predicted depth of the downhole tool assembly when the downhole tool assembly is at the target point.

7. The method of claim 1 wherein the target point is a point a predetermined distance below the receiving assembly.

8. The method of claim 1 wherein the target point comprises a below-ground point, wherein setting the receiver assembly at the target point comprises positioning the receiver assembly on the ground above the target point.

6. The method of claim I further comprising the step of using the fields detected by the two antenna assemblies to determine whether the downhole tool assembly is approaching or has passed the target point.

9. A method for tracking a downhole tool assembly having a transmitter to transmit a magnetic field, the method comprising:

maintaining two and only two tri-axial antennas of a receiver assembly in a substantially horizontal plane;

simultaneously detecting in three dimensions the magnetic field at each of the two and only two tri-axial antennas; and

moving the receiver assembly in a horizontal plane until a flux angle measured at each of the two antennas is zero.

10. The method of claim 9 further comprising the step of displaying a location of the downhole tool assembly relative to the receiver assembly.

11. The method of claim 9 further comprising:

selecting a desired borepath;

setting the receiver assembly at a target point along the desired borepath, such that both antennas lie on a desired borepath; and

calculating a position of the downhole tool assembly in a vertical plane containing the desired borepath using the fields detected by the two antennas.

12. The method of claim 11 further comprising the step of using the fields detected by the two antennas to determine whether the downhole tool assembly is approaching or has passed the target point.

13. The method of claim 9 further comprising the steps of:

placing the receiver assembly on the ground; and

calculating a distance between the downhole tool assembly and the receiver assembly, such that the distance comprises a depth of the downhole tool assembly.

14. The method of claim 9 further comprising the step of calculating an offset using the detected field values, the offset representing a horizontal distance between the downhole tool assembly and the receiver assembly.

15. A receiver assembly for tracking movement of a downhole tool assembly through the ground, the downhole tool assembly comprising a transmitter, the receiver assembly comprising:

a frame;

two and only two tri-axial antennas supported by the frame, wherein the two antennas detect a magnetic field from the transmitter; and

a processor to receive an antenna signal from each of the two antennas and determine a location of the downhole tool assembly relative to the frame using the antenna signals;

wherein the two antennas detect the magnetic field when the antennas are held in a substantially horizontal plane.

16. The receiver assembly of claim 15 further comprising:

an orientation sensor, wherein the orientation sensor senses an orientation of the frame; and

wherein the processor determines the location of the downhole tool assembly using the antenna signals and the orientation of the frame.

17. The receiver assembly of claim 16 wherein the orientation sensor is an accelerometer.

18. The receiver assembly of claim 16 wherein the processor determines the location of the downhole tool assembly using the orientation of the frame to adjust for an effect of pitch of frame on detection of the magnetic field.

19. The receiver assembly of claim 15 wherein the two antennas are positioned at opposite ends of the frame.

20. The receiver assembly of claim 19 wherein the two antennas are maintained in a substantially horizontal plane.

21. The receiver assembly of claim 19 wherein the two antennas are approximately 30 inches apart.

22. The receiver assembly of claim 15 wherein the frame comprises a handle.

23. The receiver assembly of claim 22 wherein the frame maintains the two antennas in a substantially horizontal plane when the frame is held by the handle.