Transcript Wavelet Extraction using Interferometry

Source Wavelet
Extraction using
Seismic Interferometry
C. Boonyasiriwat and S. Dong
February 5, 2008
1
Outline



Goal and Motivation
Theory
Numerical Results





SSP (Surface Seismic Profile) Synthetic Data
SSP North Sea Data
VSP (Vertical Seismic Profile) Synthetic Data
Summary
Future Work
2
Goal

To estimate a seismic source signature.
Original Shot Gather
Virtual Shot Gather
0
0
0.2
0.2
True Source Signature versus Extracted Source Signature
1
0.4
0.4
0.6
Extracted Source
0.8
True Source
0.6
0.6
0.4
0.8
1
1.2
0.2
Amplitude
Time (s)
Time (s)
0.8
1
1.2
0
-0.2
-0.4
-0.6
1.4
1.4
1.6
1.6
-0.8
-1
0
0.1
0.2
0.3
0.4
0.5
Time (s)
1.8
2
1.8
0
1000
Offset (m)
2000
2
0
500 1000 1500 2000 2500
Offset (m)
3
Motivation

seismic migration/interpretation
4
Outline



Goal and Motivation
Theory
Numerical Results





SSP (Surface Seismic Profile) Synthetic Data
SSP North Sea Data
VSP (Vertical Seismic Profile) Synthetic Data
Conclusion
Future Work
5
Theory

Behura (SEG 2007) presented the “Virtual Real
Source” method to extract the source wavelet
from SSP synthetic data.

This method is based on Seismic Interferometry
using the reciprocity equation of correlation type.

Assumptions: no attenuation and source
signature is the same for all shots.
6
Theory
Virtual
SSPMultiple:
Primary:
|W()|2G(B|A)
SSP Primary:
SSP
W()G(A|s)
W()G(B|s)
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Theory

| W ( ) |2
Virtual CSG Pvirt ( A | B) 
G ( A | B)  G * ( A | B)
2ik

Real CSG

Extracted Wavelet


Pobs ( A | B)  W ( )G( A | B)
 Causal[ Pvirt ( A | B)]P ( A | B) 
W ( )  2ik

*
Pobs ( A | B) Pobs ( A | B)   

*
obs
*
8
Outline



Goal and Motivation
Theory
Numerical Results





SSP (Surface Seismic Profile) Synthetic Data
SSP North Sea Data
VSP (Vertical Seismic Profile) Synthetic Data
Conclusion
Future Work
9
10-Layer Model
11
Original CSG vs Virtual CSG
Virtual Shot Gather
0
0
0.2
0.2
0.4
0.4
0.6
0.6
0.8
0.8
Time (s)
Time (s)
Original Shot Gather
1
1.2
1
1.2
1.4
1.4
1.6
1.6
1.8
1.8
2
2
0
1000
Offset (m)
2000
0
500 1000 1500 2000 2500
Offset (m)
12
True Source vs Extracted Source
True Source Signature versus Extracted Source Signature
1
Extracted Source
0.8
True Source
0.6
0.4
Amplitude
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.1
0.2
0.3
Time (s)
0.4
0.5
13
Mapleton Model
14
Original CSG vs Virtual CSG
Virtual Shot Gather
0
0
0.05
0.05
0.1
0.1
Time (s)
Time (s)
Original Shot Gather
0.15
0.15
0.2
0.2
0.25
0.25
0
10
20
30
Offset (m)
40
0
10
20
30
Offset (m)
40
15
True Source vs. Extracted Source
Mapleton Model: Source Extraction Result
1
Extracted Source
0.8
True Source
0.6
0.4
Amplitude
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
0.01
0.02
0.03
0.04
Time (s)
0.05
0.06
0.07
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North Sea Data
120 Hydrophones
1001 Shots
b) Original CSG 1
a) Virtu
0
0
0.5
0.5
1.5
dt = 4 ms
Tmax = 6 s
1
Time (s)
1
25 m
1.5
2
2
2.5
2.5
19
Original CSG vs. Virtual CSG
a) Virtual CSG 1
0
0
0.5
0.5
1
1
Time (s)
Time (s)
b) Original CSG 1
1.5
1.5
2
2
2.5
2.5
3
1
1.5
2
Offset (km)
2.5
3
1
1.5
2
Offset (km)
2.5
20
North Sea Extracted Source Wavelet
Window Length = 5 Source Wavelet Period
1
Direct arrival
0.8
0.6
0.4
Amplitude
0.2
0
-0.2
-0.4
Bubble pulses
-0.6
Surface reflection (ghost)
-0.8
-1
0
0.1
0.2
0.3
0.4
0.5
0.6
Time (s)
Recorded Air-gun signature (Dragoset, The Leading Edge, 2000)
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Motivation for VSP Case

Why extract a VSP source wavelet?

It’s because we also need an accurate
source wavelet for VSP data processing:
deconvolution, migration, improving
spatial resolution.
24
Simple VSP Model
VSP
SWP
VSP
25
Original VSP CSG vs Virtual VSP
CSG
b) Virtual CSG 125
0
0
0.5
0.5
1
1
1.5
1.5
Time (s)
Time (s)
a) Original CSG 125
2
2.5
2
2.5
3
3
3.5
3.5
4
4
0
1000
2000
Z (m)
3000
0
1000
2000
Z (m)
3000
26
True Source vs. Extracted Source
VSP Model: Source Extraction Result
Extracted Source
1
True Source
Amplitude
0.5
0
-0.5
-1
0
0.05
0.1
Time (s)
0.15
0.2
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Outline



Goal and Motivation
Theory
Numerical Results





SSP (Surface Seismic Profile) Synthetic Data
SSP North Sea Data
VSP (Vertical Seismic Profile) Synthetic Data
Summary
Future Work
28
Summary




Seismic interferometry can provide a good
estimate of a source wavelet from seismic data
without subsurface information.
The source signature is assumed to be the same
for every shot and there is no attenuation.
The minimum phase assumption is not required.
The accuracy of the wavelet estimate degrades
with decreasing source aperture.
29
Future Work



Test on the variation of source wavelets, e.g.,
varying amplitude and phase spectra.
Apply this method to VSP field data.
Estimate a source radiation pattern.
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