Seismic data acquisition system

• US 6,002,640 A
• Filed: 05/11/1998
• Issued: 12/14/1999
• Est. Priority Date: 05/15/1997
• Status: Expired due to Fees

• Current Assignee: Jerald L. Harmon
• Original Assignee: GeoSystems LLC
• Inventors: Harmon, Jerald L.
• Primary Examiner(s): Oda, Christine
• Assistant Examiner(s): JOLLY, ANTHONY S
• Application Number:
  US09/075,968
• Time in Patent Office: 582 Days
• Field of Search: 367/38, 367/41, 367/42, 367/57, 367/56, 367/49, 367/76, 367/79, 367/55
• US Class Current: 367/38
• CPC Class Codes: G01V 1/223 Radioseismic systems

Abstract

A seismic data acquisition system is featured that utilizes a series of nearly identical seismic shots (SISS) to synchronize and to communicate with novel data acquisition units (NDAU) located in the field. Each SISS seismic shot is carefully timed to provide synchronization to each NDAU, and to allow the NDAU to correct for the time drift of its internal clock. Further, each NDAU is programmed with a number of menus, which are used to interpret the seismic shots received from a seismic source. Thus, communication from a central or headquarter site to each NDAU is facilitated, allowing for a change in production schedule and other variables. In addition, the disclosed seismic data acquisition system features movable SISS source sites and overlapping production and SISS shots.

Claims

1. A method of field seismic data acquisition, comprising:

(a) providing a series of nearly identical seismic shots from a fixed site, said series having at least first and second seismic shots;

(b) receiving said first and second seismic shots signal trains at a seismic receiver remote from said fixed site; and

(c) measuring the difference in arrival times between signal trains from said first and second seismic shots.

2. The method of claim 1, wherein said step of measuring includes comparing the signal trains of said first and second seismic shots.

3. The method of claim 1, wherein said seismic receiver is coupled to a data acquisition unit having a clock, said clock having a maximum expected time drift and wherein said fixed site has an area dependent upon said maximum expected time drift.

4. The method of claim 1, further comprising:

(d) computing a clock drift period of a clock corresponding to said seismic receiver, said clock drift period being based on said measured difference in arrival times for signal trains from said first and second seismic shots and a predetermined difference in arrival times for said first and second seismic shot signal trains.

5. The method of claim 4, wherein said pre-determined difference is a preprogrammed interval in a data storage device associated with said seismic receiver.

6. The method of claim 1, wherein said first seismic shot is preceded by a quiescent time during which neither production shots nor SISS shots are generated.

7. The method of claim 1, further comprising:

(d) computing a value corresponding to said measured difference in arrival times for said first and second seismic shots signal trains, said value being based on the magnitude of said measured difference in comparison with a set of pre-determined differences in arrival times for said first and said second seismic shot signal trains.

8. The method of claim 7, wherein said set includes an ordinal count number of possible values.

9. The method of claim 7, further comprising:

(e) determining a clock drift period based both on said measured difference in arrival times for said first and second seismic shot signal trains, and on one predetermined difference in arrival times of said set of predetermined differences in arrival times.

10. The method of claim 9 wherein said first and said second seismic shots are spaced by a buffer time.

11. The method of claim 7 further comprising:

(e) providing a third seismic shot preceding said first and second seismic shots, wherein said third seismic shot transmits only synchronization data.

12. The method of claim 9 further comprising:

(f) providing a third seismic shot preceding said first and second seismic shots, wherein said third seismic shot transmits only synchronization data.

13. The method of claim 1, wherein said series of nearly identical shots is interspersed with production shots, and wherein each production shot is accompanied by a corresponding shot of said series of nearly identical shots.

14. The method of claim 13, wherein said production shots and said shots of said nearly identical series of shots are all produced by vibrating seismic sources, and wherein said production shots and said series shots overlap with said production shots being a multi-frequency sweep and said series shots being approximately at a mono-frequency.

15. The method of claim 3, wherein said data acquisition unit has a power conservation mode, and wherein said data acquisition unit is not in said power conservation mode for at least a maximum clock drift period prior to the targeted arrival time for said second seismic shot.

16. The method of claim 7 wherein said seismic receiver is associated with a data acquisition unit, said data acquisition unit having a clock subject to a maximum clock drift, said set of predetermined differences in arrival times comprising a number of target shot times, with each target shot time being spaced from its neighbor at least twice said maximum clock drift.

17. The method of claim 16 wherein each target shot time is an integer multiple of a unit time step.

18. The method of claim 1 wherein said fixed site is movable.

19. The method of claim 1 wherein said first seismic shot is provided at a first time proximate to a first predetermined shot generation time and said second seismic shot is provided at a second time proximate to a second predetermined shot generation time, said seismic receiver being associated with a clock having a corresponding clock drift, said method further comprising:

(d) correcting said clock drift period based on a magnitude between said second time and said second predetermined shot generation time.

20. The method of claim 1 wherein each shot is generated by a fixed site source unit, said fixed site source unit relying on an associated high-accuracy clock to time the generation of each of said shots.

21. The method of claim 7, wherein said value corresponds to an instruction for a processor.

22. The method of claim 1, wherein said method of field seismic data acquisition is also a method of seismic exploration, and further wherein said seismic receiver attaches to a data acquisition unit, said data acquisition unit comprising:

a clock;

a processor associated with said clock.

23. The method of claim 1, wherein said providing step also includes the provision of a third seismic shot, said third seismic shot being a parity shot.

34. The method of claim 1, wherein said first seismic shot is a calibration shot, said second seismic shot being about a predetermined time delay after said calibration shot.

35. The method of claim 1, wherein at least one of said series of nearly identical seismic shots is provided by a seismic source, said seismic source not being connected physically to said seismic receiver.

36. The method of claim 13, wherein said production shots are provided during predetermined production period and further wherein said series of nearly identical seismic shots are provided during predetermined periods allocated to the series of nearly identical seismic shots.

37. The method of claim 3, wherein said series of nearly identical shots including a third seismic shot, said first, second, and third seismic shots each being used to identify said clock drift.

38. The method of claim 21, wherein said processor changes operation based on said instruction.

24. A seismic data acquisition system, comprising:

at least one seismic source suitable for generation of a plurality of nearly identical seismic shots, said plurality of seismic shots being spaced in time from one another;

a seismic receiver suitable for reception of said seismic shots and further suitable for electrical generation of waveforms corresponding to said seismic shots;

a processor programmable to compare said waveforms from said seismic receiver, said comparison by said processor establishing a magnitude of said time spacing between selected pairs of said seismic shots.

25. The system of claim 24, further comprising:

a clock attached to said processor, said processor resynchronizing said clock based upon said magnitude of said time spacing.

26. The system of claim 24, wherein said processor is located at a headquarter site.

27. The system of claim 26, wherein said processor improves said establishing of said magnitude by adjusting said magnitude in reliance upon known errors other than clock drift associated with said seismic shots.

28. The system of claim 24, wherein said processor is housed in a data acquisition unit, said data acquisition unit further comprising:

a clock providing temporal data, said clock attached to said processor, wherein said processor correlates said waveforms and said temporal data.

29. The system of claim 28, wherein said data acquisition unit further comprises:

memory suitable for storage of selected ones of said waveforms and further suitable for storage of a plurality of commands;

wherein said processor uses said temporal data associated with said waveforms to select and execute at least one of said plurality of commands.

30. The system of claim 29 wherein said plurality of commands are organized in a plurality of command Menus, one of said commands switching from a first of said menus to a second of said menus.

31. The system of claim 24, wherein said processor is a means for comparing seismic shot waveforms to establish a time difference between and among two or more of said seismic shot waveforms.

32. The means for comparing of claim 31, wherein said means for comparing executes commands based upon said time difference.

33. The system of claim 24, wherein said seismic receiver includes a micro-hydrogenerator suitable for placement in a dynamic aquatic environment.