Swave processing

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?S-wave processing

• Vladimir Grechka
• Shell International EP

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Reflected PS-wave
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Complications of PS-wave data

• moveout asymmetry
• polarity reversal
• conversion point dispersal
• no standard processing flow

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PP PS SS method
(Grechka and Tsvankin, 2001)
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PP PS SS method
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PP PS SS method
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PP PS SS method

• PP and PS event correspondence
• ? accurate velocity and anisotropy
• model not needed
• prestack traveltime picking

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PP PS SS method

• PP and PS event correspondence
• ? accurate velocity and anisotropy
• model not needed
• prestack traveltime picking

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PP PS SS method

• PP and PS event correspondence
• ? accurate velocity and anisotropy
• model not needed
• prestack traveltime picking
• convolution of PP and PS traces

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PP PS SS method

• PP and PS event correspondence
• ? accurate velocity and anisotropy
• model not needed
• prestack traveltime picking
• convolution of PP and PS traces
• ?S data suitable for
• S-wave velocity analysis

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?S-wave data
integration over all P-wave source and
receiver locations
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Synthetic example
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Input PP and PS data
PS moveout asymmetry
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Input PP and PS data (zoom)
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Input PP and PS data (zoom)
polarity reversal
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Input PP and PS data (zoom)
polarity reversal
different PP and PS wavelets
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Generated ?S data
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Generated ?S data
correct traveltimes of ?S arrivals
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Generated ?S data (zoom 1)
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Generated ?S data (zoom 1)
longer ?S wavelets
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Generated ?S data (zoom 1)
longer ?S wavelets no polarity reversal
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Generated ?S data (zoom 1)
longer ?S wavelets no polarity reversal
almost zero ?S trace at zero offset
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Generated ?S data (zoom 2)
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Generated ?S data (zoom 2)
?S-waves cannot be reconstructed at large
offsets
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Generated ?S data (zoom 2)
?S-waves cannot be reconstructed at large
offsets ? critical angle
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Critical offset for ?S-waves
S
P
P
R
critical ray
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Critical offset for ?S-waves
S
P
P
R
critical ray
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Critical offset for ?S-waves
S
P
P
R
critical ray
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Gulf of Mexico (PP-waves, shallow)
offset depth
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Gulf of Mexico (?S-waves, shallow)
offset depth
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Gulf of Mexico (PP-waves, deep)
offset depth
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Gulf of Mexico (?S-waves, deep)
offset depth
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PP- and ?S-wave gathers
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Evidence for effective anisotropy
in homogeneous VTI media
isotropy does not fit data
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Conclusions (I)

• complications of PS-wave data irrelevant
• ? moveout asymmetry
• ? polarity reversal
• ? conversion point dispersal

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Conclusions (II)

• ?S data ideal for S-wave velocity analysis
• accuracy of shear-wave stacking velocities
  governed by the ratio
• straightforward estimating of
  effective anisotropy

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Issues

• absence of P-wave data (gas chimneys)
• event correspondence

Further opportunities
post-critical ?S events diving P-waves
amplitudes migration of ?S data
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Acknowledgements

• Helmut Jakubowicz (Veritas)
• Joe Dellinger (BP)
• Chris Corcoran, Fons ten Kroode,
• Jon Sheiman, Allen Hillery, Jared Martin,
• Mark Zama, Paul Milcik, Barbara Yantis,
• Richard Cook (Shell)
• Pawan Dewangan (CSM)

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Appendix
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?S-wave data
integration over all P-wave source and
receiver locations
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Spectrum of ?S trace
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Spectrum of ?S trace (single event)
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Spectrum of ?S trace (single event)
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Stationary phase conditions
stationary phase conditions matching of
PP and PS reflection slopes
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Phase at stationary point
kinematics of pure-S primary
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Spectrum of ?S trace in 3-D
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