Transcript Prestack Elastic Reverse Time Migration

Adaptive Grid
Reverse-Time Migration
Yue Wang
Outline
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Motivation and Objective
Reverse Time Methodology
Salt Dome Model Test
Field Data Test
Conclusions
Problem
• Kirchhoff migration is not
optimal for complex velocity
model.
Marmousi Model
Depth (km)
0
Low-velocity wedge
3
0
Distance (km)
9
Problem
Kirchhoff migration
Using first arrival time
Difficulty in imaging
Problem
Reverse-Time Migration RTM)
Using multi-arrival time
Image Expensive
complex structure
Solution
Variable grid size
Variable time step
Fast RTM
Objective
• Develop fast reverse time migration for
land and marine multi-component data
Outline
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•
•
•
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Motivation and Objective
Reverse Time Methodology
Salt Dome Model Test
Field Data Test
Conclusions
Reverse Time Operator
A 2-4 staggered-grid FD solver
Elastic wave equation
Variable Grid Size
Depth
Low velocity
High velocity
Distance
Variable Grid Size
Fine grid (dx dz)
Coarse grid (3dx 3dz)
z
Variable Grid Size
Fine grid
Use wave equation to
propagate waves
Coarse grid
Variable Time Step
Depth
coarse grid, fine time step
coarse grid, coarse time step
Distance
Variable Time Step
t
dt
dt
3 dt
z
dt
Variable Time Step
t
Fine time step
Use wave equation to
propagate waves
z
Coarse time step
Variable Time Step
Falk et al. (1998, Geophys. Pros. ):
1. Non-staggered-grid FD
2. 2x time step change
Variable Time Step
The new method :
1. Staggered-grid FD
2. 3x time step change
Amplitude
Numerical Results
Time t1
Amplitude
Fine time step
Depth
Coarse time step
No artificial reflections
Depth
Time t2
Outline
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Motivation and Objective
Reverse Time Methodology
Salt Dome Model Test
Field Data Test
Conclusions
Salt Model
Depth (km)
0
2.7
0
Distance (km)
4.5
Velocity Profile
P
2.7
1.5 Velocity (km/s) 4
0
Depth (km)
Depth (km)
0
S
2.7
0 Velocity (km/s) 2
Velocity Profile
P
Depth (km)
0
2.7
1.5 Velocity (km/s) 4
S
Fine grid size
Fine time step
Coarse grid size
Coarse time step
0 Velocity (km/s) 2
Shot Gather
Vertical
Normal Stress
Time (s)
0
Horizontal
2
0.9 Distance (km) 3.6 0.9 Distance (km) 3.6 0.9 Distance (km) 3.6
Kirchhoff Migration
Depth (km)
0
2.5
0.45
Distance (km)
4.05
Kirchhoff Migration
Depth (km)
0
2.5
0.45
Distance (km)
4.05
Reverse Time Migration
Depth (km)
0
2.5
0.45
Distance (km)
4.05
Reverse Time Migration
Depth (km)
0
2.5
0.45
Distance (km)
4.05
Outline
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•
•
•
•
Motivation and Objective
Reverse Time Methodology
Salt Dome Model Test
Field Data Test
Conclusions
Processed CSG
Radial Component
Vertical Component
Time (s)
0
2.7
0
Trace Number
80 0
Trace Number
80
Common Offset Gather
(Vertical Component)
Depth (km)
0
Signal/Noise Ratio High
4
0
Distance (km)
27
Common Offset Gather
(Radial Component)
Depth (km)
0
Signal/Noise Ratio Low
4
0
Distance (km)
27
Kirchhoff Migration
(Vertical Component)
Depth (km)
0
4
0
Distance (km)
27
Kirchhoff Migration
(Radial Component)
Depth (km)
0
4
0
Distance (km)
27
RTM
Depth (km)
0
4
0
Distance (km)
27
Comparison
RTM
KM
Depth (km)
0
4
0
Distance (km)
27 0
Distance (km)
27
Outline
•
•
•
•
•
Motivation and Objective
Reverse Time Methodology
Salt Dome Model Test
Field Data Test
Conclusions and Future Work
Conclusions
• Variable RTM 10 times faster than standard RTM
• Migrates Land and marine multi-component data
• Use primary and multiple reflections for imaging
Acknowledgement
We are grateful to the 1999 sponsors
of the UTAM consortium for the
financial support
Raw CSG
Radial Component
Vertical Component
Time (s)
0
2.7
0
Trace Number
80 0
Trace Number
80
Main Processing Flow
Geometry assignment, datuming and so on
Trace editing
Surface wave attenuation, amplitude balancing
P-velocity analysis
S-velocity analysis
Relative gain compensation, surface velocity estimation
KM
RTM
Shallow Velocity
Depth (km)
0
0.4
0
Distance (km)
27
Future Work
• Apply the RTM scheme for data set with
more complex structures.