1. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Locating Trapped Miners Using Time Reversal Mirrors Sherif M. Hanafy Weiping CaoKim McCarter Gerard T. Schuster February 7 th 2008

2. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Introduction Method Covered by Weiping Numerical Example Covered by Weiping Field Examples – University of Utah Test Finding Trapped Miners Time Shift Test Super-stack Results – Tucson, Arizona Test Finding Trapped Miners Time Shift Test Super-stack Results – Super-resolution Results Summary and Conclusions Outline

3. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Motivation Propose a seismic approach to find trapped miners in collapsed mines

4. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Find Trapped Miners [Step # 1] G1G2G3 ……………....... Gn Receiver Line Ground Surface Subsurface Mine Introduction Geophones are planted on the ground surface above the mine. Select some communication points inside the mine Introduction

5. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Find Trapped Miners (Step # 2) Gx Receiver Line Ground Surface Subsurface Mine Introduction From each communication point (Gx) we will record the earth’s natural band-limited Green’s function Direct Waves Introduction

6. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Now, we have n different CSG recorded from n different communication points Introduction G1G1 G2G2 G3G3 ……….GnGn G1G2G3Gn ………. Keep Them Safe, We Will Need Them Later Ground Surface Introduction

7. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Find Trapped Miners (Step # 3) Receiver Line Ground Surface Subsurface Mine After a collapse occurs, G1G2G3 trapped miners should go to the nearest communication point and hit the mine wall at this point This (SOS) call will be recorded by the geophones on the ground surface Introduction

8. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Does the recorded SOS looks like one of our previously recorded band-limited calibration Green’s functions? G1G1 G2G2 G3G3 ……….GnGn Recorded SOS NO Maybe NO The location of the trapped miners is the location of the calibration Green’s functions that best match the recorded SOS We can use a pattern matching approach between the recorded SOS and the calibration Green’s function gathers Introduction

9. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Mathematically, good match is crosscorrelation Crosscorrelation results Recorded SOS call Band-limited Green’s function Actually, we use a gather-to-gather no-shift crosscorrelation Introduction

10. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Corr. ……....... ………....... ………… Subsurface Mine Corr. Find Trapped Miners (Step # 4) Location of trapped miners Introduction

11. UofU TestTime ShiftSuper-stackTucson TestSuper-resolution Introduction Method Covered by Weiping Numerical Example Covered by Weiping Field Examples – University of Utah Test Finding Trapped Miners Time Shift Test Super-stack Results – Tucson, Arizona Test Finding Trapped Miners Time Shift Test Super-stack Results – Super-resolution Results Summary and Conclusions Outline

12. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Steam-Tunnel Test INSCC Building Study Area Football Stadium Guest House U of U Test Layout Overview

13. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Tunnel projection Receiver Line INSCC Building U of U Test Layout Overview Steam-Tunnel Test

14. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Number of receivers = 120 Receiver interval = 1 m Number of communication points = 25 Comm. point interval; Points 1- 6 & 20 – 25 = 4 m Points 6 – 20 = 0.5 m Distance from receiver line to tunnel = 35 m U of U Test Layout Overview Steam-Tunnel Test

15. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Putting the receivers on ground surface U of U Test Steam-Tunnel Test

16. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Entering the steam-tunnel U of U Test Steam-Tunnel Test

17. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Generating both Green’s function and SOS call U of U Test Steam-Tunnel Test

18. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Generating both Green’s function and SOS call U of U Test Steam-Tunnel Test

19. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Team Work U of U Test Steam-Tunnel Test

20. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Samples of the collected Data We made 20 stacks/communication point U of U Test Steam-Tunnel Test Time (ms)

21. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Samples of the collected Data We made one stack/communication point U of U Test Steam-Tunnel Test Time (ms)

22. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Trapped Miners Approach For each SOS call, a gather-to-gather no-shift crosscorrelation of that SOS shot gather with the calibration Green’s functions show that the peak of the correlated record coincides with the locations of the miners. U of U Test Steam-Tunnel Test

23. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Results of Trapped Miners Location of trapped miners U of U Test Steam-Tunnel Test Normalized m(x,0) X (m)

24. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Location of trapped miners U of U Test Steam-Tunnel Test Results of Trapped Miners Normalized m(x,0) X (m)

25. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Location of trapped miners U of U Test Steam-Tunnel Test Results of Trapped Miners Normalized m(x,0) X (m)

26. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Problems Facing Trapped Miners Approach SOS excitation time is unknown SOS Signal/Noise ratio is expected to be very low Solutions U of U Test

27. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Amplitude Time Shift Unknown SOS Excitation Time We use a simple time shift test Excitation Time Time Shift

28. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution The same procedure is repeated for all calibration Green’s functions with the same SOS call, the results in a 3D view will show both SOS excitation time and location of trapped miners. Unknown SOS Excitation Time Time shift test Time Shift

29. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Unknown SOS Excitation Time Results of time shift test Excitation Time Location of Trapped Miner -0.25 0.25 0 45 1 X (m) Time Shift (ms) Normalized Amplitude Time Shift

30. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Low S/N ratio of the SOS call We generated a random noise CSG This random-noise CSG is added to the recorded SOS The results are then used in our calculations += Super-stack

31. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Results with Random Noise Example 1 Results without adding noise Results with adding noise New S/N = 1:1738 Super-stack Normalized m(x,0) X (m) Normalized m(x,0) X (m)

32. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Results with Random Noise Example 2 Results without adding noise Results with adding noise New S/N = 1:1519 Super-stack Normalized m(x,0) X (m) Normalized m(x,0) X (m)

33. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Introduction Method Covered by Weiping Numerical Example Covered by Weiping Field Examples – University of Utah Test Finding Trapped Miners Time Shift Test Super-stack Results – Tucson, Arizona Test Finding Trapped Miners Time Shift Test Super-stack Results – Super-resolution Results Summary and Conclusions Outline

34. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Tucson, Arizona Test Number of receivers = 120 Receiver Interval = 0.5 m Number of communication points = 25 Comm. point interval; Tunnel 2 = 0.5 m Tunnel 3 = 0.75 m Distance from receiver-line to tunnel Tunnel 2 = 30 m. Tunnel 3 = 45 m. 60 m Tucson Test Trapped Miners Approach

35. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Receivers are planted on the ground surface Tucson Test Tucson, Arizona Test

36. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Inside the mine Tucson Test Tucson, Arizona Test

37. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Generating both Green’s function and SOS call Tucson Test Tucson, Arizona Test

38. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Generating both Green’s function and SOS call Tucson Test Tucson, Arizona Test

39. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Generating both Green’s function and SOS call Tucson Test Tucson, Arizona Test

40. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Team Work Tucson Test Tucson, Arizona Test

41. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution SOS CallG F from Tunnel 2G F from Tunnel 3 Tucson Test Tucson, Arizona Test

42. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Tucson Test Trapped Miners Approach Tucson, Arizona Test For each SOS call, a gather-to-gather no-shift crosscorrelation of that SOS shot gather with the calibration Green’s functions show that the peak of the correlated record coincides with the locations of the miners.

43. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Tucson Test Examples of the Results Tucson, Arizona Test Tunnel 2Tunnel 3 Normalized m(x,0) X (m) Normalized m(x,0) X (m)

44. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Excitation Time Location of Trapped Miner -0.25 0.25 0 1 X (m) Time Shift (ms) Normalized Amplitude 45 Tucson Test Tucson, Arizona Test Result of Time Shift Test

45. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Results without adding noise Results with adding noise New S/N = 1:1609 Tucson Test Super-Stack Results, Sample #1 Tucson, Arizona Test Normalized m(x,0) X (m) Normalized m(x,0) X (m)

46. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Results without adding noise Results with adding noise New S/N = 1:2670 Tucson Test Super-Stack Results, Sample #2 Tucson, Arizona Test Normalized m(x,0) X (m) Normalized m(x,0) X (m)

47. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Summary We have successfully introduced a TRM method to locate trapped miners in a collapsed mine Two field tests are made to validate the proposed TRM method Results from both field tests show that TRM can successfully locate trapped miners at both sites, even with signal-to-noise ratio as low as 0.0005

48. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Introduction Method Covered by Weiping Numerical Example Covered by Weiping Field Examples – University of Utah Test Finding Trapped Miners Time Shift Test Super-stack Results – Tucson, Arizona Test Finding Trapped Miners Time Shift Test Super-stack Results – Super-resolution Results Summary and Conclusions Outline

49. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Rayleigh Spatial Resolution Spatial resolution is defined by Sheriff (1991) as the ability to separate two features that are very close together, i.e., the minimum separation of two bodies before their individual identities are lost. Ground Surface 2L Z Super-resol.

50. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Expected Spatial Resolution Steam- Tunnel Test Tucson Test Tunnel # 2Tunnel # 3 10 m Z35 m30 m45 m L60 m30 m xx Rayleigh resolution 3 m5 m7.5 m Super-resol.

51. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Can Scatterers Beat the Resolution Limit? Recorded shot gathers (SOS & G) are divided into: - Shot gathers with direct arrivals only - Shot gathers with scattered arrivals only Super-resol.

52. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Super-Resolution The processing is made on the separated CSG by using: Super-resol. Full aperture width (120 channels) Half aperture width (60 channels)

53. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Super-Resolution Results using traces with only - Direct waves, full aperture width - Direct waves, half aperture width - Scattered waves, full aperture width - Scattered waves, half aperture width 1.Spatial resolution of correlating traces with scatterer-only events is much higher. 2.Spatial resolution of correlating traces with direct-only events depends on the aperture width. X (m) Super-resol.

54. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Super-Resolution Direct-Wave Half Aperture Direct-Wave Full Aperture Scattered-Wave Half /full Aperture Steam Tunnel Test Super-resol.

55. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Super-Resolution Tucson Test Super-resol. Direct-Wave Half Aperture Direct-Wave Full Aperture Scattered-Wave Half /full Aperture

56. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Expected Spatial Resolution Steam- Tunnel Test Tucson Test Tunnel # 2Tunnel # 3 10 m Z35 m30 m45 m L60 m30 m xx 3 m5 m7.5 m Rayleigh resolution 1 m1 m1 m Scatterers resolution Our approach shows a resolution 3 – 7 times better than the expected Rayleigh resolution limit. Super-resol.

57. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Introduction Method Covered by Weiping Numerical Example Covered by Weiping Field Examples – University of Utah Test Finding Trapped Miners Time Shift Test Super-stack Results – Tucson, Arizona Test Finding Trapped Miners Time Shift Test Super-stack Results – Super-resolution Results Summary and Conclusions Outline

58. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Summary and Conclusions Trapped Miners Approach – A clean (noise free) Green’s Function is required – Receiver-line should be fixed – Low Signal/Noise ratio is not a problem, thanks to Super- Stack – Excitation time of SOS call is not an issue, thanks to time shift test

59. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Summary and Conclusions Super Resolution – Using traces with scatterer only improve data resolution. In our results, traces with direct waves only give a 3-7 m resolution, while scatterer only give a 1 m resolution – Aperture width does not change the scatterer only results, while direct only waves is highly affected by the aperture width

60. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Super-resol. To the best of our knowledge, this is the first time super-stack and super-resolution properties are validated with a real seismic data. Summary and Conclusions For the first time in EM waves, Lerosey et al. (2007) succeeded to get a resolution of /30

61. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Implication Hydro-Frac Monitoring – Time reversal mirrors (TRM) approach has super stack property – No velocity model is required – Small aperture width gives good results If we have the exact velocity model – Reverse time migration (RTM) has both super-stack and super-resolution properties. Increasing the RTM resolution by 3-7 times deserves the effort of finding the exact velocity model.

62. IntroductionUofU TestTime ShiftSuper-stackTucson TestSuper-resolution Thank You