Methods for acquiring and processing seismic data

• US 5,924,049 A
• Filed: 01/30/1998
• Issued: 07/13/1999
• Est. Priority Date: 04/18/1995
• Status: Expired due to Term

• Current Assignee: WesternGeco LLC (Schlumberger NV)
• Original Assignee: Western Atlas International Incorporated (Northrop Grumman Corporation)
• Inventors: Beasley, Craig J., Chambers, Ronald E.
• Primary Examiner(s): McElheny, Jr., Donald E.
• Application Number:
  US09/016,679
• Time in Patent Office: 529 Days
• Field of Search: 702/17, 702/16, 702/14, 367/23, 367/53, 367/56, 367/57, 367/50
• US Class Current: 702/17
• CPC Class Codes: G01V 1/003 Seismic data acquisition in general, e.g. survey design G01V1/3808, G01V1/42 take precedence
• CPC Class Codes: G01V 1/006 generating single signals by using more than one generator, e.g. beam steering or focusing arrays G01V1/13, G01V1/3861 take precedence
• CPC Class Codes: G01V 1/38 specially adapted for water-covered areas G01V1/28 takes precedence
• CPC Class Codes: G01V 1/3861 control of source arrays, e.g. for far field control

Abstract

A method for acquiring and processing seismic survey data from two or more seismic sources activated simultaneously or nearly simultaneously or for a single source moved to and fired at different locations. In one aspect such a method includes acquiring seismic survey trace data generated by the source or sources, attaching source geometry to the traces, soring the traces according to a common feature thereof, (e.g. to CMP order), interpolating data points for discontinuities on the traces, selecting two halves or two portions slightly more than half of the traces, filtering the trace data for each of the two portions to filter out data related to a second one of the two seismic sources, reducing the filtered trace data to two halves of the data and deleting interpolated data, and then merging the two halves to produce refined useful seismic data related to a first one of the seismic sources. In one aspect the method includes re-processing the data and filtering out the trace data for the second seismic source to produce refined useful seismic data related to the second seismic source. In one aspect the sources are fired temporally close together and, in one particular aspect, they are fired substantially simultaneously.

Claims

1. A seismic survey method comprising

firing at least once at least two seismic sources which are spaced-apart and including at least a first source and a second source, producing with each seismic source an acoustic wavefield directed to at least one earth layer apart from the seismic sources,

detecting with at least one seismic detector a portion of each resulting acoustic wavefield from the at least one earth layer,

converting the detected portions of each acoustic wavefield coming from the at least one earth layer to a first primary data set indicative of the earth layer,

separating the first primary data set into at least two intermediate data sets, including at least a first intermediate data set and a second intermediate data set, each intermediate data set containing data related to the firing of each seismic source,

filtering the first intermediate data set to eliminate all data except data related to firing of the first source, producing a refined first data set,

filtering the second intermediate data set to eliminate all data except data related to firing of the first source, producing a refined second data set, and

merging the refined first and second data sets, producing a first primary refined data set comprising useful seismic data related to firing of the first source.

2. The seismic survey method of claim 1 wherein the first intermediate data set and the second intermediate data set combined include at least all data in the first primary data set.

3. The seismic survey method of claim 1 wherein the first intermediate data set includes an amount of common data which is also included in the second intermediate data set.

4. The seismic survey method of claim 3 wherein the amount of common data includes at least 33% of the data in the first primary data set.

5. The seismic survey method of claim 3 wherein the amount of common data includes at least 2% of the data in the first primary data set.

6. The seismic survey method of claim 1 wherein the at least two seismic sources are two sources fired within 25 seconds of each other.

7. The seismic survey method of claim 1 wherein the at least two seismic sources are two sources fired within 15 seconds of each other.

8. The seismic survey method of claim 1 wherein the at least two seismic sources are two sources fired substantially simultaneously.

9. The seismic survey method of claim 1 wherein the first primary data set is a set of a plurality of seismic data traces and the method further comprising

attaching source geometry information for each of the at least two seismic sources to each of the plurality of seismic data traces.

10. The seismic survey method of claim 9 further comprising sorting the plurality of data traces according to a common feature shared by the traces.

11. The seismic survey method of claim 10 wherein the common feature is from the group consisting of common midpoint, common offset, common detector, and common source.

12. The method of claim 1 wherein the seismic data traces contain discontinuities and the method further comprising

trade interpolating each of the plurality of seismic data traces producing interpolated data points for the discontinuities.

13. The method of claim 12 further comprising after separating the first primary data set into at least two intermediate data sets,

deleting the interpolated data points.

14. The method of claim 1 wherein the filtering of each intermediate data set is done by a filtering method from the group consisting of multi-channel filtering, f-k filtering, and Radon transform filtering.

15. The method of claim 1 wherein the at least two seismic sources are located on land.

16. The method of claim 1 wherein the at least two seismic sources are located on or in water.

17. The method of claim 1 wherein the at least two seismic sources are a single source fired at a first location and then moved and fired at a second location spaced apart from the first location.

18. The method of claim 1 wherein the at least one seismic detector is a plurality of seismic detectors.

19. The method of claim 1 wherein the at least two seismic sources are fired a plurality of times, the method including the at least one seismic detector detecting with respect to each firing, and processing resulting data as in the converting and subsequent steps of claim 1.

20. The method of claim 3 wherein the amount of common data constitutes an overlap zone between the first and second intermediate data sets and the method further comprising, after the filtering steps,

eliminating the overlap zone.

21. The method of claim 1 further comprising producing a second primary data set of data indicative of the at least one earth layer, producing at least two intermediate data sets by separating the second primary data set into at least a third intermediate data set and a fourth intermediate data set, then producing a second primary refined data set comprising useful seismic data related to firing of the second source by filtering the third and fourth intermediate data sets to eliminate all data except data related to firing of the second source producing third and fourth refined data sets and by then merging the third and fourth refined data sets producing a second primary refined data set.

22. The method of claim 21 further comprising

merging the first and second primary data sets producing a final data set comprising useful seismic data related to the firing of both the first and second sources.

23. The method of claim 21 wherein the third intermediate data set includes an amount of common data which is also included in the fourth intermediate data set.

24. The method of claim 21 wherein the at least two seismic sources are two sources fired within 15 seconds of each other.

25. The method of claim 21 wherein the at least two seismic sources are two sources fired substantially simultaneously.

26. The method of claim 21 the second primary data set is a set of a plurality of seismic data traces and the method further comprising

attaching source geometry information for each of the at least two seismic sources to each of the plurality of seismic data traces.

27. The method of claim 26 further comprising sorting the plurality of data traces according to a common feature shared by the traces.

28. The method of claim 27 wherein the common feature is from the group consisting of common midpoint, common offset, common detector, and common source.

29. The method of claim 26 wherein the seismic data traces contain discontinuities and the method further comprising

trace interpolating each of the plurality of seismic data traces producing interpolated data points for the discontinuities.

30. The method of claim 21 further comprising after separating the second primary data set into at least two intermediate data sets,

deleting the interpolated data points.

31. The method of claim 21 wherein the filtering of each intermediate data set is done by a filtering method from the group consisting of multi-channel filtering, f-k filtering, and Radon transform filtering.

32. The method of claim 21 wherein the at least two seismic sources are located on land.

33. The method of claim 21 wherein the at least two seismic sources are located on or in water.

34. The method of claim 23 wherein the amount of common data constitutes an overlap zone between the third and fourth intermediate data sets and the method further comprising, after the filtering steps,

eliminating the overlap zone.

35. The method of claim 1 wherein acoustic wavefields produced by the at least two seismic sources are comprised of plain signals.

36. The method of claim 21 wherein acoustic wavefields produced by the at least two seismic sources are comprised of plain signals.

37. A method of seismic exploration, comprising

advancing a swath of parallel elongated seismic cables along a line of survey, each said cable including a plurality of longitudinally spaced-apart detectors for detecting acoustic wavefields,

launching a first acoustic wavefield from the leading end of said swath,

detecting and storing said first acoustic wavefield, following reflection thereof from subsurface earth formations, as a first reflected seismic signal recording,

launching a second acoustic wavefield from the trailing end of said swath, launching said second acoustic wavefield temporally substantially simultaneously with said launching of said first acoustic wavefield,

detecting and storing said second acoustic wavefield, following reflection thereof from said subsurface earth formations, as a second reflected seismic signal recording,

processing said first and said second reflected seismic signal recordings, and

forming a substantially shadow-zone-free structural model of dipping subsurface earth formations by merging the processed first and second reflected seismic signal recordings.

38. The method as defined by claim 37, comprising

continuously advancing said swath along said line of survey at a preselected velocity, and

repeatedly launching said first and said second acoustic wavefields at first timed intervals of predetermined length.

39. The method as defined by claim 38, wherein

length of each said timed interval corresponds to a spatial advance of a multiple of the detector spacing at a preselected velocity of advance of said swath.

40. A system for acoustically surveying subsurface earth formations, comprising

a swath of a plurality of elongated parallel seismic cables, each said cable including a plurality of longitudinally spaced-apart detectors for receiving and converting acoustic wavefields to data sets of electrical signals,

means for effectively advancing said swath along a line of survey,

at least a first discrete acoustic source located near the leading end of said swath,

at least a second discrete acoustic source located near the trailing end of said swath,

timer means for causing said first and second acoustic sources to insonify said earth formations at substantially the same time, thereby to provide first and second reflected acoustic wavefields for reception by said detectors and for conversion of said first and second reflected acoustic wavefields to first and second data sets of electrical signals, and

means, operatively coupled to said detectors, for processing and merging said first and second data sets of electrical signals to provide a uniformly-insonified model of said earth formations.

41. The system as defined by claim 40 comprising

a first plurality of discrete acoustic sources located near the leading end of said swath,

a second plurality of discrete acoustic sources located near the trailing end of said swath, and

means for causing selected sources taken from the first and second pluralities of discrete acoustic sources to insonify subsurface earth formations at timed intervals in a desired operational sequence.

42. A method of seismic exploration comprising

advancing a swath of parallel elongated seismic cables along a line of survey, each said cable including a plurality of spaced-apart seismic transducers,

simultaneously launching first and second acoustic wavefields from the leading and trailing ends respectively, of said swath, each said acoustic wavefield being uniquely encoded,

detecting and recording the combined first and second encoded acoustic wavefields, following reflection thereof from subsurface earth formations,

decoding the combined recorded reflected wavefields to separate the first and second reflected acoustic wavefields,

separately processing each of the decoded first and second recorded reflected wavefields, and

generating a substantially uniformly-insonified model of dipping subsurface earth formations by merging the first and second processed reflected wavefields.