Method and system for detection of a material within a region of the earth

• US 10,247,844 B2
• Filed: 12/04/2013
• Issued: 04/02/2019
• Est. Priority Date: 12/04/2013
• Status: Expired due to Fees

• Current Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Inventors: Fukushima, Eiichi, Altobelli, Stephen A., Thomann, Hans
• Primary Examiner(s): Nguyen, Tung X
• Assistant Examiner(s): Hawkins, Dominic E
• Application Number:
  US15/035,491
• Publication Number:
  US 20160291191A1
• Time in Patent Office: 1,945 Days
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/445 MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging
• CPC Class Codes: G01R 33/4616 using specific RF pulses or specific modulation schemes, e.g. stochastic excitation, adiabatic RF pulses, composite pulses, binomial pulses, Shinnar-le-Roux pulses, spectrally selective pulses not being used for spatial selection
• CPC Class Codes: G01R 33/4838 using spatially selective suppression or saturation of MR signals
• CPC Class Codes: G01V 3/14 operating with electron or nuclear magnetic resonance

Abstract

Methods and systems for detecting a material within a region of the Earth are provided. The region may be under a surface of earthen formation, ice, snow, or water. The method may be practiced in a variety of applications, for example in an arctic region to detect oil spills, leaks, or seepages. The methods and systems may include using at least one coil to transmit a radio frequency (RF) excitation signal into the region of the Earth; and receive any NMR response signals to determine the presence of the material of interest.

Claims

1. A method of detecting a first material in the presence of a second material within a region of interest in the Earth comprising:

transmitting a first inversion radio frequency (RF) excitation signal with at least one coil in the presence of a static magnetic field, the excitation signal sufficient to invert magnetization vectors of both the first and second material in an inversion region within the region of interest such that a plurality of magnetization vectors of the first and second material are substantially aligned with the negative (−

) z axis;

at a point in time when the longitudinal magnetization vector of the second material is substantially zero along the z-axis, transmitting a second RF excitation signal that is a read excitation signal with the at least one coil such that the NMR signal from the second material is selectively suppressed in a detection region a given distance remote from the at least one coil; and

receiving any NMR signal of the first material generated by the second RF excitation signal originating from the detection region.

2. The method of claim 1, further comprising applying a magnetic pre-polarization to increase the effective static magnetic field.

3. The method of claim 1, wherein the static magnetic field is the Earth'"'"'s magnetic field.

4. The method of claim 1, wherein the first inversion RF excitation signal is an adiabatic fast passage inversion sweep.

5. The method of claim 1, wherein the first inversion RF excitation signal is a hard inversion pulse.

6. The method of claim 1, wherein the second RF excitation signal is a hard read pulse.

7. The method of claim 1, wherein the second RF excitation signal is an adiabatic fast passage read sweep.

8. The method of claim 7, wherein the second RF excitation signal has a maximum amplitude value less than the first inversion RF excitation signal.

9. The method of claim 1, further comprising transmitting a third RF excitation signal to generate a spin echo which is detected by the at least one coil.

10. The method of claim 9, further comprising transmitting a plurality of RF excitation signals to generate an additional spin echoes which are detected by the at least one coil.

11. The method of claim 9, wherein the third RF excitation signal and/or the plurality of RF excitation signals are hard pulses.

12. The method of claim 1, wherein the sequence of first inversion RF excitation signal, second RF excitation signal and any additional excitation signals in the sequence is repeated at a repetition rate greater than the T1 relaxation rate of the first material and less than the T1 relaxation time of the second material.

13. The method of claim 1, wherein the detection region does not substantially exceed the inversion region.

14. The method of claim 1, wherein the at least one coil is a flat coil.

15. The method of claim 14, wherein the flat coil comprises a central coil array including a plurality of substantially parallel wire elements;

and a first wire return side and a second wire return side opposite the first wire return side, each return side having a varying radius of curvature.

16. The method of claim 5, wherein the at least one coil is operatively connected to a transmitter;

receiver; and

at least one switch and configured to provide a broadband signal response at a transmitting Q factor when transmitting the adiabatic fast passage sweep and to receive signal response in a narrow band at a greater Q factor compared to the transmitting Q factor.

17. The method of claim 1, further comprising applying at least a first depth profiling RF excitation signal and a second depth profiling RF excitation signal, wherein the first depth profiling RF excitation signal has a different amplitude from the second RF depth profiling RF excitation signal.

18. The method of claim 17, wherein the first depth profiling RF excitation signal and the second RF depth profiling RF excitation signal are hard pulses.

19. The method of claim 1, wherein the first material is an organic material and the second material is water.

20. The method of claim 18, wherein the organic material is an oil.

21. The method of claim 18, wherein the organic material originates from activities associated with an industrial process.

22. The method of claim 1, wherein the region is under a surface of Earthen formation, water, snow, or ice.

23. The method of claim 1, further comprising mapping a plurality of regions in an area of concern to determine the presence of the first material.

24. A method of detecting a first material in the presence of a second material within a region of the Earth comprising:

transmitting a first adiabatic fast passage inversion sweep with at least one coil in the presence of a static magnetic field, the sweep sufficient to invert magnetization vectors of both the first and second material in an inversion region such that the magnetization vectors of the first and second material are substantially aligned with the negative (−

) z axis;

at a point in time when the longitudinal magnetization vector of the second material is substantially zero along the z-axis, transmitting a second RF excitation signal that is a read excitation signal with the at least one coil such that the NMR signal from the second material is selectively suppressed in a detection region a given distance remote from the at least one coil; and

receiving any NMR signal of the first material generated by the second RF excitation signal originating from the detection region, wherein the static magnetic field is Earth'"'"'s magnetic field.

25. The method of claim 24, wherein the second RF excitation signal is an adiabatic fast passage read sweep which rotates the longitudinal magnetization to generate transverse magnetization.

26. The method of claim 24, wherein the first material is an organic material and the second material is water.

27. The method of claim 24, wherein the region is located under a surface of ice.

28. A system for detecting a material within a region of interest in the Earth comprising:

at least one coil positioned proximate to the region;

a transmitter operatively connected to the at least one coil;

a receiver operatively connected to the at least one coil; and

at least one switch configured to provide a broadband signal response in the at least one coil at a transmitting Q factor when transmitting an adiabatic fast passage excitation signal and to receive a NMR signal response in a narrow band at a greater Q factor compared to the transmitting Q factor.

29. The system of claim 28, further comprising a tuning capacitor operatively connected to the at least one coil.