Modeling of free-surface multiples - 2

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Modeling of free-surface multiples - 2

• Introduction
• Long offset Faroes data velocity analysis and
  demultiple
• Modeling of free-surface multiple diffractions,
  3D geometry
• Further work

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East of Faroe Islands (ten 2-D lines, 1700 km
total)
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Pre-stack time migration
Top basalt
Intra basalt
Base basalt
West
East
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Line 105 - 1999 data
Top basalt
Intra basalt
Base basalt
7.5 km
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Line 104 - 1998 data
7.5 km
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Improved results from 1999 data

• Better multiple attenuation and velocity analysis
• Facilitated by small shot spacing, single cable
• Pre-stack time migration
• Tested on small area
• Claytons migration-velocity analysis
• Depth migration (coherency analysis and
  Kirchhoff)
• Demultiple using Delfts SRME

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Claytons Migration-Velocity Analysis

• Slant stack
• Downward continuation of the wave field
• Convergence criterion
• Input Velocity Output image

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Depth-Velocity model
Top B
Intra-B
Base-B
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SRME in Shot Gather Domain
WB
TB
TBM
WBM
TBM
Input
Input-Predicted multiples
Predicted multiples
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D(?) P (?) D (?) ( r W(?) -1 )P (?)
Pi(?,s,g) D (?,s,g) - ( r W(?) -1 ) Sx D(?,
s,x)P i-1(?,x,g)
x1
x2
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Further work (from last weeks seminar)

• Effect of position errors (non-coincident sources
  and receivers) on synthetics
• Use source and receiver positions from the field
  data
• Specifications for maximum feathering during
  acquisition
• ..

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Modeling, diffracted multiples, 3-D

• Reference Taylor Johnston, Edinburgh Univ,
  SEG-99
• Fast 2-D synthetic seismograms for testing
  multiple removal

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Modeling, diffracted multiples, 3-D

• With free-surface multiples

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An su modeling program
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Test cases for the modeling program

• 1 diffractor, no free-surface
• 1 diffractor, free-surface
• 2 diffractors, no free-surface
• 2 diffractors, free-surface

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1 diffractor, no free-surface
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1 diffractor, free-surface
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2 diffractors, no free-surface
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2 diffractors, free-surface
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Further work

• Investigate effect of feathering on demultiple
  for the long offset Faroes data
• Corrections during computation of the multiple
  model
• Tolerance on feathering
• Look at interpolation of missing near offset
  traces using Radon transforms and SEPs
  optimization libraries