PASSIVE REFLECTIVE IMAGING FOR VISUALIZING SUBSURFACE STRUCTURES IN EARTH AND WATER

• US 20090059721A1
• Filed: 07/21/2008
• Published: 03/05/2009
• Est. Priority Date: 07/20/2007
• Status: Active Grant

• Current Assignee: Wayne Simon
• Original Assignee: Wayne Simon
• Inventors: Simon, Wayne
• Granted Patent: US 7,724,608 B2
• Time in Patent Office: Days
• US Class Current: 367/38
• CPC Class Codes: G01V 1/28 Processing seismic data, e.g. for interpretation or for event detection G01V1/48 takes precedence
• CPC Class Codes: G01V 2210/55 Array focusing; Phased arrays

Abstract

A system and method is provided that uses signals from a plurality of seismic sensors to define an acoustic lens for subsurface imaging. More specifically signals provided by an array of sensors/geophones may be utilized to form an acoustic lens that can be focused on a subterranean point by properly adjusting the signals recorded at each sensor prior to summation of those signals. To form such an acoustic lens, each of the seismic sensors is moved onto a hypothetical acoustic lens surface (e.g., spherical surface) having a focal point located on the subterranean point of interest in order to calculate a time delay for each signal. Once the signals for each sensor is time-delayed, information in the time-delayed signals, which is received from the point of interest, may be temporally aligned. Accordingly, the time delayed signals may be combined to generate reflection information for the point of interest.

Claims

1. A method for use in connection with seismic exploration, comprising:

obtaining a plurality of seismic signals associated with seismic information, wherein said seismic signal are obtained from an array of seismic receivers;

selecting a subterranean point of interest;

adjusting each of said signals to focus on data associated with said point of interest, wherein adjusting produces a plurality of adjusted seismic signals; and

summing said adjusted seismic signals, wherein a sum of said adjusted seismic signals is indicative of a reflection value for said subterranean point of interest.

2. The method of claim 1, wherein adjusting each of said signals comprises:

time delaying at least a portion of said signals such that ray paths between corresponding ones of the seismic receivers and said point of interest are substantially equal.

3. The method of claim 2, wherein time delaying comprises:

calculating distances between said receivers along their respective ray path and a position on a hypothetical spherical surface, wherein said point of interest is a center of said spherical surface and wherein said time delay for each said signal is based on said distances.

4. The method of claim 3, wherein said time delay is calculated by dividing said distance with a propagation velocity associated with seismic energy recorded by said seismic receiver.

5. The method of claim 1, further comprising:

repeating the selecting adjusting and summing steps for a plurality of subterranean points of interest.

6. The method of claim 5, wherein said plurality of subterranean points of interest have a common depth.

7. The method of claim 5, wherein said plurality of subterranean points of interest lie along a common line and refraction values of said plurality of subterranean points of interest along said common line define a two-dimensional profile.

8. The method of claim 7, wherein said plurality of subterranean points of interest lie along a plurality of common lines and reflection values of said plurality of subterranean points of interest along said common lines define two-dimensional profiles.

9. The method of claim 8, further comprising:

using two or more of said two-dimensional profiles to generate a three-dimensional profile of a subterranean area of interest.

10. The method of claim 1 wherein obtaining said seismic signals comprises:

recording data associated with passive vibration sources.

11. The method of claim 1, wherein at least a portion of said seismic receivers are surface based receivers.

12. The method of claim 1, wherein adjusting each said signal further comprises:

adjusting the phase of each seismic signal such that said seismic signals add constructively.

13. The method of claim 12, further comprising:

transforming said seismic signals into frequency domain signals.

14. The method of claim 12, further comprising:

adjusting signal velocity for said seismic signals.

15. A method for use in connection with seismic exploration, comprising:

obtaining a plurality of seismic signals associated with passive seismic vibrations, wherein said seismic signal are obtained from an array of seismic receivers;

selecting a subterranean point of interest;

time delaying each said signal such that ray paths between the seismic receivers generating the signals and said point of interest are substantially equal;

identifying a reflection value for said point of interest utilizing said seismic signals from said seismic receivers.

16. The method of claim 15, wherein time delaying comprises:

calculating distances between said receivers along their respective ray path and a position on a hypothetical spherical surface, wherein said point of interest is a center of said spherical surface and wherein said time delay for each said signal is based on said distances.

17. The method of claim 16, wherein said time delay is calculated by dividing said distance with a propagation velocity associated with seismic energy recorded by said seismic receiver.

18. The method of claim 15, wherein identifying comprises iteratively solving said reflection value using said seismic signals.

19. The method of claim 15, wherein identifying further comprises:

adjusting each of said seismic signals based on a phase value of each of said seismic signals.

20. The method of claim 19, further comprises:

transforming said seismic signals into frequency domain signals.

21. The method of claim 19, further comprising:

summing said seismic signals.

22. The method of claim 15, further comprising:

repeating the selecting and identifying steps for a plurality of subterranean points of interest.

23. The method of claim 22, wherein said plurality of subterranean points of interest have a common depth.

24. The method of claim 22, wherein said plurality of subterranean points of interest lie along a common line and reflection values of said plurality of subterranean points of interest along said common line define a two-dimensional profile.

25. The method of claim 23, wherein said plurality of subterranean points of interest lie along a plurality of common lines and reflection values of said plurality of subterranean points of interest along said common lines define two-dimensional profiles.

26. The method of claim 25, further comprising:

using two or more of said two-dimensional profiles to generate a three-dimensional profile of a subterranean area of interest.

27. A method for use in connection with seismic exploration, comprising:

obtaining a plurality of seismic signals from an array of seismic receivers;

selecting a subterranean point of interest;

for each receiver;

determining a first distance of a ray between said receiver and said point of interest;

determining a second distance along said ray between said receiver and a spherical surface, wherein said point of interest is at a center of said spherical surface;

time delaying the seismic signal of said receiver based on said first and second distances to produce a time delayed signals; and

identifying a reflection value for said point of interest using a plurality of said time delayed signals.

28. The method of claim 27, further comprising:

adjusting the phase of said time adjusted signals.

29. The method of claim 27, further comprising:

cross-correlating said time delayed signals.

30. The method of claim 27, wherein time delaying each said signal comprises:

dividing the difference between said first and second distances with an assumed propagation velocity associated with seismic energy recorded by said seismic receiver.

31. The method of claim 30, further comprising:

iteratively adjusting said propagation velocity to reduce a lag time associated with said signal.

32. A system for use in connection with seismic exploration, comprising:

a plurality of seismic receivers for recording seismic information and generating seismic signals, wherein said receivers are disposed in an array; and

a processor operative to obtain said seismic signals originating from said seismic receivers, said processor further operative to;

determining a first distance of a ray between a physical location of each said receiver and a subterranean point of interest;

determining a second distance along said ray between said receiver and a spherical surface, wherein said point of interest is at a center of said spherical surface;

time delaying the seismic signal of said receiver based on said first and second distances to produce a time delayed signals; and

identifying a reflection value for said point of interest using a plurality of said time delayed signals.