Downhole positioning system

• US 20050183887A1
• Filed: 02/23/2005
• Published: 08/25/2005
• Est. Priority Date: 02/23/2004
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Rodney, Paul F.
• Granted Patent: US 7,686,099 B2
• Time in Patent Office: Days
• US Class Current: 175/26
• CPC Class Codes: E21B 47/04 Measuring depth or liquid level

Abstract

Downhole positioning systems and associated methods are disclosed. In some embodiments, the system comprises a downhole source, an array of receivers, and a data hub. The downhole source transmits an electromagnetic positioning signal that is received by the array of receivers. The data hub collects amplitude and/or phase measurements of the electromagnetic positioning signal from receivers in the array and combines these measurements to determine the position of the downhole source. The position may be tracked over time to determine the source'"'"'s path. The position calculation may take various forms, including determination of a source-to-receiver distance for multiple receivers in the array, coupled with geometric analysis of the distances to determine source position. The electromagnetic positioning signal may be in the sub-hertz frequency range.

Claims

1. A downhole positioning method that comprises:

receiving at each of multiple receivers an electromagnetic positioning signal from a source in a borehole; and

combining positioning signal measurements from each of the receivers to determine a position of the source.

2. The method of claim 1, further comprising:

tracking the position of the source to identify a borehole trajectory.

3. The method of claim 1, wherein said combining comprises:

determining for each receiver a source-to-receiver distance; and

calculating the source'"'"'s position from the source-to-receiver distances.

4. The method of claim 1, further comprising:

comparing the positioning signal at each receiver to a reference signal to measure a phase difference.

5. The method of claim 4, further comprising:

transmitting a pilot signal to the source; and

deriving the reference signal from the pilot signal.

6. The method of claim 5, wherein the pilot signal is transmitted as an electromagnetic wave.

7. The method of claim 5, further comprising:

correcting the phase differences to compensate for pilot signal propagation times.

8. The method of claim 1, further comprising:

measuring an amplitude of the positioning signal at each receiver using a three-axis magnetometer.

9. The method of claim 1, wherein the electromagnetic positioning signal has a frequency less than about 1 hertz.

10. The method of claim 1, wherein the source comprises a magnetic dipole.

11. A downhole positioning system that comprises:

a downhole source that transmits an electromagnetic positioning signal;

an array of receivers that receives the electromagnetic positioning signal;

a data hub that collects amplitude or phase measurements of the electromagnetic positioning signal from receivers in the array, wherein the data hub combines said measurements to determine a position of the downhole source.

12. The system of claim 11, wherein the data hub is further configured to determine a path of the downhole source.

13. The system of claim 11, wherein as part of determining said position, the data hub is configured to determine a source-to-receiver distance for multiple receivers in the array, and is further configured to determine said position from said distances.

14. The system of claim 11, further comprising:

a reference transmitter that transmits a pilot signal to the downhole source, wherein the downhole source is configured to derive the electromagnetic positioning signal from the pilot signal.

15. The system of claim 14, wherein the pilot signal is transmitted as an electromagnetic wave having a frequency of less than about 1 hertz.

16. The system of claim 14, wherein the receivers are configured to receive the pilot signal and to derive from the pilot signal a reference signal for the phase measurements.

17. The system of claim 16, wherein the data hub is configured to correct phase measurements for pilot signal propagation times.

18. The system of claim 11, wherein the receivers comprise superconducting quantum interference devices (SQUIDS).

19. The system of claim 11, wherein the electromagnetic positioning signal has a frequency less than about 0.1 hertz.

20. An information storage medium that when placed in operable relation to a processing device provides downhole positioning software that configures the processing device to:

obtain amplitude measurements of an electromagnetic positioning signal made by multiple receivers; and

responsively determine a subsurface position of a source that generates the electromagnetic positioning signal.

21. The medium of claim 20, wherein the electromagnetic positioning signal has a frequency less than about 1 hertz.

22. The medium of claim 20, wherein the downhole positioning software further configures the processing device to combine multiple subsurface positions to determine a borehole trajectory.