DUAL COIL FOR ELECTROMAGNETIC SOUNDING OF LAYERED EARTH

• US 20150048833A1
• Filed: 01/24/2014
• Published: 02/19/2015
• Est. Priority Date: 08/13/2013
• Status: Active Grant

• Current Assignee: Geonics Limited (Geonics SH Ltd.)
• Original Assignee: Geonics Limited (Geonics SH Ltd.)
• Inventors: Bosnar, Miroslav
• Granted Patent: US 9,477,004 B2
• Time in Patent Office: Days
• US Class Current: 324/334
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence

Abstract

Methods and systems for measuring subsurface electrical conductivity, using first and second sensor coils. The second sensor coil has a smaller effective area and a greater bandwidth than the first sensor coil. The first and second sensor coils are positioned with respect to each other to achieve zero or near zero mutual inductance.

Claims

1. A device for measuring subsurface electrical conductivity, the device comprising:

a first sensor coil having a first effective area and a first bandwidth; and

a second sensor coil having a second effective area smaller than the first effective area and a second bandwidth greater than the first bandwidth;

wherein the second sensor coil is coupled to the first sensor coil at a position having an amount of overlap with the first coil and at a position where mutual inductance between the first and second sensor coils is substantially zero.

2. The device of claim 1 wherein the second sensor coil is moveably coupled to the first sensor coil for adjusting the amount of overlap between the first and second sensor coils.

3. The device of claim 2 wherein the second sensor coil is moveable from a storage configuration of the device where the device has a reduced footprint and the mutual inductance between the first and second sensor coils is substantially non-zero, to an operating configuration of the device where the mutual inductance between the first and second sensor coils is substantially zero.

4. The device of claim 2 wherein the second sensor coil is flippable from the storage configuration of the device to the operating configuration of the device.

5. The device of claim 2 wherein the second sensor coil is slideably moveable relative to the first sensor coil.

6. The device of claim 5 wherein a common longitudinal axis is shared by the first and second sensor coils, the longitudinal axis passing through respective centers of the first and second sensor coils, and wherein the second sensor coil is moveable along the common longitudinal axis.

7. The device of claim 1 wherein each of the first and second sensor coils is a square coil.

8. The device of claim 1 further comprising a transmitter for communicating measurements of electrical conductivity from each of the first and second sensor coils.

9. The device of claim 1 further comprising a transmitter coil for generating a primary field, wherein the first sensor coil and the second sensor coil are configured to measure a resulting secondary field generated by a subsurface.

10. A method of measuring subsurface electrical conductivity of a target site, the method comprising:

positioning a first sensor coil to measure electrical conductivity of the target site, the first sensor coil having a first effective area and a first bandwidth;

positioning a second sensor coil to measure electrical conductivity of the target site, the second sensor coil having a second effective area smaller than the first effective area and a second bandwidth greater than the first bandwidth;

the first and second sensor coils being positioned with respect to each other to reduce mutual inductance between the first and second sensor coils to substantially zero; and

while keeping both the first and second sensor coils in position, obtaining measurements of electrical conductivity from the first and second sensor coils.

11. The method of claim 10 wherein the measurements of electrical conductivity are obtained simultaneously from both the first and second sensor coils.

12. The method of claim 10 wherein the first and second sensor coils are positioned to at least partially overlap.

13. The method of claim 10 wherein the first and second sensor coils are coupled to each other.

14. The method of claim 10 wherein the first and second sensor coils are positioned at the same time.

15. The method of claim 10 wherein the second sensor coil is positioned prior to positioning of the first sensor coil.

16. The method of claim 10 wherein one of the first and second sensor coils is firstly positioned and the other of the first and second sensor coils is secondly positioned, the secondly positioning comprising adjusting overlap between the first and second sensor coils to achieve substantially zero mutual inductance.

17. The method of claim 16 wherein the secondly positioning comprises positioning the other of the first and second sensor coils to share a common longitudinal axis with the one of the first and second sensor coils, the common longitudinal axis passing through respective centers of the first and second sensor coils, and wherein adjusting overlap comprises moving the other of the first and second sensor coils along the common longitudinal axis.

18. The method of claim 16 wherein the secondly positioning comprises:

applying an input signal to the one of the first and second sensor coils;

measuring an output signal from the other of the first and second sensor coils; and

adjusting overlap between the first and second sensor coils until there is substantially zero output signal from the other of the first and second sensor coils.

19. The method of claim 16 further comprising:

prior to the secondly positioning, measuring an initial inductance of one of the one and the other of the first and second sensor coils;

wherein the secondly positioning comprises adjusting overlap between the first and second sensor coils until measured inductance of the one of the one and the other of the first and second sensor coils substantially equals the initial inductance.

20. The method of claim 10 wherein the first and second coils are positioned to share a common longitudinal axis passing through respective centers of the first and second coils.