Magnetic sensing apparatus having a helmholtz coil

Patent metadata

Field	Value
Publication number	US-9720126-B2
Application number	US-201214370518-A
Country	US
Kind code	B2
Filing date	Jan 19, 2012
Priority date	Jan 19, 2012
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

In some embodiments, an apparatus and a system, as well as a method and an article, may operate to acquire a first signal from a first magnetometer at least partially disposed within a Helmholtz coil, to acquire a second signal from a second magnetometer having a sensitivity at least one thousand times less than the first magnetometer, to process the second signal to determine a drive signal, to drive the Helmholtz coil using the drive signal so as to null an ambient Earth magnetic field surrounding the first magnetometer, and to process the first signal as one of a down hole location signal or a down hole telemetry signal, the location signal to determine a range to a sub-surface object, and the telemetry signal to provide data from down hole drilling operations. Additional apparatus, systems, and methods are disclosed.

First claim

What is claimed is:

1. A processor-implemented method, comprising:
acquiring a first signal from a first magnetometer at least partially disposed within a Helmholtz coil;
acquiring a second signal from a second magnetometer having a sensitivity at least one thousand times less than the first magnetometer;
processing the second signal to determine a drive signal;
driving the Helmholtz coil using the drive signal so as to substantially null an ambient Earth magnetic field surrounding the first magnetometer; and
processing the first signal as one of a down hole location signal or a down hole telemetry signal, the location signal to determine a range to a sub-surface object, and the telemetry signal to provide data from down hole drilling operations.

2. The method of claim 1 , further comprising:
determining the drive signal by repeatedly varying a current to the Helmholtz coil so as to establish upper and lower values of the current that provide a usable value of the first signal.

3. The method of claim 1 , further comprising:
detecting a drift in the Earth magnetic field by monitoring a low-pass filtered version of the first signal.

4. The method of claim 3 , further comprising:
upon detecting the drift has exceeded a predetermined amount, adjusting the drive signal by a scaling factor times the drift.

5. The method of claim 1 , wherein the first magnetometer is substantially surrounded by a first wellbore, further comprising:
determining the range to the sub-surface object as approximately the range from the first magnetometer to a well casing installed in a second wellbore that is different from the first wellbore.

6. The method of claim 1 , further comprising:
receiving the first signal from a down hole telemetry transmitter during the down hole drilling operations.

7. The method of claim 1 , further comprising:
circulating current associated with the first signal around the first magnetometer.

8. The method of claim 1 , further comprising:
concentrating current associated with the first signal in a path by providing the path as one of increased conductivity relative to a ferrous housing surrounding the first magnetometer.

9. The method of claim 1 , further comprising:
shielding the first magnetometer with a magnetic shielding material in substantially all directions that are not aligned with a sense axis of the first magnetometer.

10. The method of claim 1 , wherein acquiring the first signal further comprises:
acquiring the first signal from the first magnetometer when the first magnetometer is disposed within a drill collar.

11. An apparatus, comprising:
a first magnetometer at least partially disposed within a Helmholtz coil;
a second magnetometer having a sensitivity at least one thousand times less than the first magnetometer; and
a signal processor configured to drive the Helmholtz coil according to a signal provided by the second magnetometer so as to substantially null an ambient Earth magnetic field surrounding the first magnetometer, and to receive a down hole location signal or a down hole telemetry signal from the first magnetometer.

12. The apparatus of claim 11 , wherein the first magnetometer comprises:
at least one of a Rb magnetometer or a diamond magnetometer.

13. The apparatus of claim 11 , wherein the second magnetometer comprises:
a flux gate magnetometer.

14. The apparatus of claim 11 , wherein the Helmholtz coil and the second magnetometer comprise:
three-axis units substantially aligned along the three axes.

15. The apparatus of claim 11 , wherein the Helmholtz coil and the first magnetometer comprise:
single-axis units substantially aligned along the single axis.

16. The apparatus of claim 11 , further comprising:
a low pass filter coupled to an output of the first magnetometer, the low pass filter to provide a drift monitoring output associated with the Earth magnetic field.

17. The apparatus of claim 11 , further comprising:
a magnetically-permeable shield substantially surrounding the first magnetometer, with an opening substantially aligned with a sense axis of the first magnetometer.

18. A system, comprising:
a down hole tool housing; and
an apparatus attached to the housing, the apparatus comprising a first magnetometer at least partially disposed within a Helmholtz coil, a second magnetometer having a sensitivity at least one thousand times less than the first magnetometer, and a signal processor configured to drive the Helmholtz coil according to a signal provided by the second magnetometer so as to substantially null an ambient Earth magnetic field surrounding the first magnetometer, and to receive a down hole location signal or a down hole telemetry signal from the first magnetometer.

19. The system of claim 18 , wherein the housing comprises:
one of a wireline tool body, a measurement while drilling down hole tool, or a logging while drilling down hole tool.

20. The system of claim 18 , wherein the down hole tool housing has a plurality of longitudinal channels around an outer perimeter, and wherein the first magnetometer is disposed within a covered one of the channels, along with a copper bar attached to the down hole tool housing.

21. The system of claim 18 , further comprising:
an insulating gap in a drill collar of the down hole tool housing, the insulating gap proximate to the first or the second magnetometer.

Assignees

• Rodney Paul F
• Halliburton Energy Services Inc

Inventors

• Rodney Paul F

Classifications

• G01V3/40 Primary

  specially adapted for measuring magnetic field characteristics of the earth · CPC title

• G01V3/28 Primary

  using induction coils · CPC title

• E21B47/12

  Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling · CPC title

• G01V3/34

  Transmitting data to recording or processing apparatus; Recording data · CPC title