3-D PRESTACK WAVEPATH MIGRATION H. Sun Geology and Geophysics Department University of Utah

Outline Problems in 2-D WM Problems in 2-D WM Objectives of 3-D WM Objectives of 3-D WM Numerical Results Numerical Results Conclusions Conclusions

Lower CPU Efficiency Lower CPU Efficiency only 1/3 faster than KM only 1/3 faster than KM or even 2 times slower than KM or even 2 times slower than KM Moderate CPU Efficiency Moderate CPU Efficiency 4~11 times faster than KM 4~11 times faster than KM By Slant Stacking By Slant Stacking Problems in 2-D WM

2-D KM of a Single Trace RS N N 1 1 CPU Count = N 2A A B B C C

2-D WM of a Single Trace RS A B C CPU Count = 3 * ( Tracing + Searching + Migrating ) = 3 * ( N + 2N + 7N) = 30N = 3 * ( N + 2N + 7N) = 30N N N 1 1 A B C

Outline Problems in 2-D WM Problems in 2-D WM Objectives of 3-D WM Objectives of 3-D WM Numerical Results Numerical Results Conclusions Conclusions

To Achieve Higher CPU Efficiency To Achieve Higher CPU Efficiency Compared to 3-D KM Compared to 3-D KM To Generate Comparable or Better To Generate Comparable or Better Image Quality than 3-D KM Image Quality than 3-D KM Key Goals of 3-D WM

Outline Problems in 2-D WM Problems in 2-D WM Objectives of 3-D WM Objectives of 3-D WM Numerical Results Numerical Results 3-D Point Scatterer Data 3-D Point Scatterer Data 3-D SEG/EAGE Salt Data 3-D SEG/EAGE Salt Data 3-D West Texas Field Data 3-D West Texas Field Data Conclusions Conclusions

3-D Prestack KM Point Scatterer Response Reflectivity Y Offset (km) X Offset (km) Reflectivity Y Offset (km) X Offset (km) Reflectivity Y Offset (km) X Offset (km) Reflectivity Y Offset (km) X Offset (km) Z0 Z0-1 Z0-9 Z0+8

Reflectivity Y Offset (km) X Offset (km) Reflectivity Y Offset (km) X Offset (km) Reflectivity Y Offset (km) X Offset (km) Reflectivity Y Offset (km) X Offset (km) D Prestack WM Point Scatterer Response Z0 Z0-1 Z0-9 Z0+8

Outline Problems in 2-D WM Problems in 2-D WM Objectives of 3-D WM Objectives of 3-D WM Numerical Results Numerical Results 3-D Point Scatterer Data 3-D Point Scatterer Data 3-D SEG/EAGE Salt Data 3-D SEG/EAGE Salt Data 3-D West Texas Field Data 3-D West Texas Field Data Conclusions Conclusions

A Common Shot Gather Trace Number 1390 Time (sec) 0 5.0

Receiver Distribution Crossline (m) Inline (m)

Inline Velocity Model Offset (km) 09.2 Depth (km) SALT

Inline KM (CPU=1) Inline WM (CPU=1/33) Offset (km) Depth (km) Offset (km) 09.2

Receiver Distribution Crossline (m) Inline (m)

Inline KM (CPU=1) Inline WM (CPU=1/170) Offset (km) Depth (km) Offset (km) 09.2 (subsample)

Zoom Views of Inline Sections Offset: 3~6.5 km, Depth: 0.3~1.8 km WM Model KM SubWM

Offset: 1.8~4 km, Depth: 0.6~2.1 km WM Model KM SubWM Zoom Views of Crossline Sections

Inline: 1.8~7.2 km, Crossline: 0~4 km WM Model KM SubWM Horizontal Slices (Depth=1.4 km)

Outline Problems in 2-D WM Problems in 2-D WM Objectives of 3-D WM Objectives of 3-D WM Numerical Results Numerical Results 3-D Point Scatterer Data 3-D Point Scatterer Data 3-D SEG/EAGE Salt Data 3-D SEG/EAGE Salt Data 3-D West Texas Field Data 3-D West Texas Field Data Conclusions Conclusions

A Common Shot Gather Trace Number Time (sec) 0 3.4

Receiver Distribution Crossline (km) Inline (km)

Receiver Distribution Crossline (km) Inline (km)

Inline KM (CPU=1) Inline WM (CPU=1/14) Offset (km) Depth (km) Offset (km)

Inline KM (CPU=1) Inline WM (CPU=1/50) Offset (km) Depth (km) Offset (km) (subsample)

Crossline KM (CPU=1) Crossline WM (CPU=1/14) Offset (km) Depth (km) Offset (km)

Crossline KM (CPU=1) Crossline WM (CPU=1/50) (subsample) Offset (km) Depth (km) Offset (km)

Inline: 0~4.6 km, Crossline: 0~3.8 KM (CPU=1) Horizontal Slices (Depth=2.5 km) WM (CPU=1/14) WM (Sub, CPU=1/50)

Outline Problems in 2-D WM Problems in 2-D WM Objectives of 3-D WM Objectives of 3-D WM Numerical Results Numerical Results Conclusions Conclusions

Conclusions SEG/EAGE Salt Data SEG/EAGE Salt Data Fewer Migration Artifacts Fewer Migration Artifacts Better for Complex Salt Boundary Better for Complex Salt Boundary Higher Computational Efficiency Higher Computational Efficiency CPU CPU KM: 1 WM: 1/33 KM: 1 WM: 1/33 Subsampled WM: 1/170 Subsampled WM: 1/170

Conclusions West Texas Field Data West Texas Field Data Fewer Migration Artifacts Fewer Migration Artifacts Similar Image Quality Similar Image Quality Higher Computational Efficiency Higher Computational Efficiency CPU CPU KM: 1 WM: 1/14 KM: 1 WM: 1/14 Subsampled WM: 1/50 Subsampled WM: 1/50

Conclusions Trade-off: between Image Quality Trade-off: between Image Quality and CPU Costs and CPU Costs Caution: WM Angle Estimation Caution: WM Angle Estimation Sensitive to Recording Geometry Sensitive to Recording Geometry

More Robust Angle Calculation More Robust Angle Calculation Crossing-event Calculation Crossing-event Calculation 3-D Marine Field Data 3-D Marine Field Data 3-D Iterative Velocity Analysis 3-D Iterative Velocity Analysis Future Work Future Work

Real-time Velocity Updating for Target-oriented Migration Possible ? Question

Acknowledgements Acknowledgements I thank UTAM sponsors I thank UTAM sponsors for their financial support