ReducedTime Migration of Converted Waves

1
Reduced-Time Migration of Converted Waves
David Sheley and Gerard T. Schuster University of
Utah
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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Problem Dark Flanks
0
m(r) d(zg, tsr trg)
Depth
Source Well
Receiver Well
Z
Offset
0
X
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Solution PS Transmission Migration
0
m(r) d(zg, tsr trg)
Depth
Source Well
Receiver Well
Z
Offset
0
X
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Motivation

• Problems
• Dark Flanks

• Solutions
• PS Transmission Migration

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Motivation

• Problems
• Dark Flanks
• Velocity Errors (Vp, Vs)

• Solutions
• PS Transmission Migration

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Motivation

• Problems
• Dark Flanks
• Velocity Errors (Vp, Vs)

• Solutions
• PS Transmission Migration
• Reduced-Time Migration

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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Reduced-Time Migration

• 1. Data time shift

d(zg, t )
S
Depth (m)
PS
P
Time (ms)
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Reduced-Time Migration

• 1. Data time shift

d(zg, t )
Depth (m)
Time (ms)
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Reduced-Time Migration

• 1. Data time shift
• d(zg, t) d(zg, t )
• tsg Observed direct-P traveltime

obs
2. Modify the migration equation
m(r) d(zg, tsr trg )
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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Focusing-Time ErrorConventional vs. Reduced-Time
2
2
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Focusing-Time Error
0
500
Offset (m)
0
Conventional Trans. PS Migration
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Depth (m)
12
Imaging Error (ms)
250
0
8
Reduced- Time Migration
Depth (m)
4
250
0
0
500
Offset (m)
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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Crosswell Model
0
Vp /Vs 1.5
5500 m/s
Source 1500 Hz
ds 2 m
Depth (m)
dg 2 m
Well Separation 100 m
5000 m/s
114
114
0
Offset (m)
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Synthetic Data
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Conventional PS Transmission Migration
True Velocity
0
Depth (m)
114
Offset (m)
0
100
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Conventional PS Transmission Migration
True Velocity
10 Velocity
0
Depth (m)
114
Offset (m)
0
100
Offset (m)
0
100
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Reduced-Time PS Migration
True Velocity
0
Depth (m)
114
Offset (m)
0
100
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Reduced-Time PS Migration
True Velocity
10 Velocity
0
Depth (m)
114
Offset (m)
0
100
Offset (m)
0
100
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Comparison 10 Velocity
Conventional PS
Recuced-Time
0
Depth (m)
114
Offset (m)
0
100
Offset (m)
0
100
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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Kidd Creek Crosswell
0
Receiver
Source
Well
Well
20
Depth (m)
40
60
Offset (m)
0
50
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Data Problems

• Time Delay 3 ms ?
• Well Location
• Velocity Model

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Time Shifted CRG
0
20
Depth (m)
40
60
0
6
Time (ms)
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Conventional
0
20
Depth (m)
60
Offset (m)
0
50
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Conventional
0
20
Depth (m)
60
Offset (m)
0
50
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Outline

• Motivation
• Reduced-Time Migration Theory
• Error Analysis
• Results
• Synthetic Data
• Field Data
• Conclusions

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Conclusions

• Transmission PS migration can image structure
  invisible to reflection migration.

• Reduced-time migration decreases the migration
  error of an incorrect velocity model.

• PS reduced-time migration can successfully image
  a transmitting boundary.

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Acknowledgements

• I sincerely thank the 1999 sponsors of the
  UTAM consortium for their financial support.