Method and system for deghosting

Details Method and system for deghosting Method and system for deghosting

2000-12-01

2002-11-05

McElheny, Jr., Donald E. (Department: 2862)

Data processing: measuring, calibrating, or testing

Measurement system in a specific environment

Earth science

C367S021000

Reexamination Certificate

active

06477470

ABSTRACT:

BACKGROUND OF THE INVENTION
Currently in the art of geophysical marine seismic prospecting, a vessel tows very long streamers which have many seismic receivers attached. Often these streamers are miles long. These receivers receive a portion of a scattered acoustic wavefield originated from the sounding of a seismic source. The acoustic wavefield generated by the seismic source is scattered by reflections and refractions in the earth. Because these streamers are very long, have many receivers, and are towed behind a moving vessel, the coverage in the sailer in-line direction-is very large. However, only a few streamers can be towed behind the vessel at any one time. Therefore, there is relatively very little coverage of the streamers in the cross-line direction. While there are various conventional methods to increase the number of streamers a vessel can tow in the cross-line direction, this coverage is still much less than in the in-line direction.
Because this coverage is very small, very little cross-line processing has been developed. Instead, development has concentrated on in-line processing. Furthermnore, conventional in-line processing simply is not suitable for cross-line data. Currently, various passes with the vessel are made. During each of these passes, limited cross-line information is gathered. The processors then recreate the information in the cross-line direction by patching the data together. This is both inaccurate and expensive.
Furthermore, because this data must be then processed onshore much later, conventional methods have not been able to determine the quality of the in-line or cross-line data received while the vessel is still near the acquisition site. This results in a wasted opportunity to accurately collect data.
Turning now to streamer configurations, further conventional methods teach using various levels of streamers towed at different depths—usually two. These conventional methods teach to tow these cables directly above one another. This is difficult to do. Ocean currents tend to thrust the miles and miles of cables. Despite this fact, conventional methods continue to design processing algorithms for streamers towed directly above one another.
As a result, there is a long felt need for a method and system for deghosting seismic data in both the in-line direction and the cross-line direction, an improved quality control method for data acquisition, and an improved streamer configuration for vertically separated cables.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, a method for processing a scattered acoustic wavefield is provided. The scattered acoustic wavefield,(
230
) is received by at least two receivers (
201
). These receivers (
201
) are offset (
250
) and located at approximately the same depth (
205
). The method comprises transforming (
101
) the scattered acoustic wavefield (
230
) to the frequency domain (
101
). The method also comprises transforming (
105
) the scattered acoustic wavefield (
230
) from the frequency domain to the spectral domain. The method also comprises deghosting (
110
) the scattered acoustic wavefield (
230
) in the spectral domain. The method further comprises transforming (
115
) the substantially deghosted transformed acoustic wavefield to the space-time domain.
In an even further embodiment of the present invention, a method for processing a scattered acoustic wavefield (
230
) received by at least a first set (
501
) of two receivers (
201
) and at least a second set (
502
) of two receivers (
201
) is provided. The first set (
501
) of two receivers (
201
) is offset (
250
) at substantially a first depth (
515
) which is vertically offset (
520
) from at least a second set (
502
) of two receivers (
201
) offset (
250
) at substantially a second depth (
505
). The method comprises transforming (
401
) the scattered acoustic wavefield (
230
) received at the first depth (
515
) to the frequency domain. The method further comprises transforming (
405
) the scattered acoustic wavefield (
230
) received at the second depth (
505
) to the frequency domain (
405
). The method further comprises transforming (
410
) the scattered acoustic wavefield (
230
) received at the first depth (
515
) from the frequency domain to the spectral domain. The method further comprises transforming (
415
) the scattered acoustic wavefield (
230
) received at the second depth (
505
) from the frequency domain to the spectral domain. The method also comprises generating (
420
) a substantially deghosted scattered acoustic wavefield in the spectral domain. The method further comprises transforming (
425
) the substantially deghosted scattered acoustic wavefield to the space-time domain.
In an even further embodiment, a method for receiving an acoustic wavefield beneath the surface of the water is also provided. In one embodiment, the method comprises receiving at least a portion of an acoustic wavefield (
230
) at a first position (
701
). The method also comprises receiving at least a portion of an acoustic wavefield (
230
) at a second position (
702
) and receiving at least a portion of an acoustic wavefield (
230
) at a third position (
703
). The first position (
701
), the second position (
702
), and the third position (
703
) are triangularly positioned (
720
) relative to one another.
In another embodiment of the present invention, a method of controlling the quality of seismic data acquisition substantially near the acquisition site is provided. The method comprises generating (
901
) a scattered acoustic wavefield (
230
). The method further comprises receiving (
905
) at least a portion of the scattered acoustic wavefield (
230
). The method further comprises substantially deghosting (
910
) the scattered acoustic wavefield (
230
) relatively near the acquisition site. The method further comprises evaluating (
915
) the quality of the substantially deghosted scattered acoustic wavefield.
In a further embodiment, a system for processing a scattered acoustic wavefield (
230
) received by at least two receivers (
201
) offset (
250
) at substantially the same depth (
205
) is provided. The system comprises means for transforming (
1101
) the scattered acoustic wavefield (
230
) to the frequency domain. The system further comprises means for transforming (
1101
) the scattered acoustic wavefield (
230
) from the frequency domain to the spectral domain. The system further comprises means for deghosting (
1115
) the scattered acoustic wavefield in the spectral domain. The system further comprises means for transforming (
1120
) the substantially deghosted transformed acoustic wavefield (
230
) to the space-time domain.
In an even further embodiment, the system comprises a means for transforming (
1201
) the scattered acoustic wavefield (
230
) received at the first depth (
515
) to the frequency domain. The system further comprises means for transforming (
1205
) the scattered acoustic wavefield (
230
) received at the second depth (
505
) to the frequency domain. The system further comprises means for transforming (
1210
) the scattered acoustic wavefield (
230
) received at the first depth (
515
) from the frequency domain to the spectral domain. The system further comprises a means for transforming (
1215
) the scattered acoustic wavefield (
230
) received at the second depth (
505
) from the frequency domain to the spectral domain. The system further comprises means for generating (
1220
) a substantially deghosted scattered acoustic wavefield in the spectral domain. The system further comprises means for transforming (
1225
) the substantially deghosted scattered acoustic wavefield to the space-time domain.
In still another embodiment of the present invention, a system for receiving an acoustic wavefield beneath the surface of the water is provided. The system comprises means for receiving at least a portion of an acoustic wavefield at a first position (
1305
). The system further comprises means for receiving at least a portion of an acoustic wavefield at a second position (
1310
). The syste

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