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Document Sample
CROSSWELL IMAGING BY 2-D
PRESTACK WAVEPATH
MIGRATION
H. Sun
Geology and Geophysics Department
University of Utah
SEG 2-D Overthrust Data
KM Image Model WM Image
4 Offset (km) 10 4 Offset (km) 10 4 Offset (km) 10
0.5
Depth (km)
2.5
2-D Husky Field Data
KM Image (Zoom A) WM Image (Zoom A)
2.5 Offset (km) 5.5 2.5 Offset (km) 5.5
2.5 2.5
Depth (km)
Depth (km)
5.0 5.0
SEG 3-D Salt Data
KM WM
CPU: CPU:
1 1/33
Model Sub
WM
CPU:
1/170
Horizontal Slice (Depth=1.4 km)
2-D KM of a Single Trace
C
B
A
R S
A
B
C
2-D WM of a Single Trace
C
B
A
R S
A
B
C
Wavepath Migration
Traveltime + Ray Direction
True Small
Reflection point Migration Aperture
Fewer Less
Artifacts Expensive
Outline
• WM Crosswell Imaging
• Synthetic Crosswell Data
• McElroy Crosswell Data
• Synthetic Single Well Data
• Conclusions
KM Crosswell Imaging
Source Receiver
Well Well
Down-going
Interface 1
Interface 2
Up-going
KM Crosswell Imaging
Source Receiver
Well Well
Interface 1
Interface 2
Up-going
KM Crosswell Imaging
Source Receiver
Well Well
Down-going
Interface 1
Interface 2
KM Crosswell Imaging
Source Receiver
Well Well
Down-going
Interface 1
Interface 2
Up-going
Problems in KM Crosswell Imaging
• Insufficient Stacking Leads to Artifacts
• Complex Data Cause Difficulty in
Up-going and Down-going Separation
• Slow Computation
WM Crosswell Imaging
Source Receiver
Well Well
Down-going
Interface 1
Interface 2
Up-going
Advantages of WM Crosswell Imaging
• Avoid Artifacts by Migrating to the
Primary Reflection Point
• Handle Complex Data by Migrating
Up-going and Down-going together
• No Constraints Needed
• Fast Computation
Shortcomings of WM
• Weaker Events
• Worse Interface Continuity
Outline
• WM Crosswell Imaging
• Synthetic Crosswell Data
• McElroy Crosswell Data
• Synthetic Single Well Data
• Conclusions
Fault Model A Common Shot Gather
0 Offset (m) 90 0 Geophone Depth (m) 210
0 0
Depth (m)
Time (s)
210 0.2
Crosswell Imaging of Synthetic Fault Data
KM Model WM WM (no separation)
Better Image
Better Resolution
Offset: 0~90 m, Depth: 0~210 m
Outline
• WM Crosswell Imaging
• Synthetic Crosswell Data
• McElroy Crosswell Data
• Synthetic Single Well Data
• Conclusions
Traveltime Tomogram A Common Shot Gather
0 Offset (m) 56 811 Hydrophone Depth (m) 963
811 0
6.7
Depth (m)
Time (s)
(km /s)
4.7
963 0.05
Source Well KM Image Receiver Well
811
?
?
Up-going
Depth (m)
Separation
Down-going
963
Synthetic 0 Offset (m) 56 Synthetic
Source Well WM Image Receiver Well
811
Up-going
Depth (m)
Separation
Down-going
963
Synthetic 0 Offset (m) 56 Synthetic
Source Well WM Image Receiver Well
811
Up-going
Depth (m)
NO Separation
Down-going
963
Synthetic 0 Offset (m) 56 Synthetic
Source Well KM(CPU=2.5) WM(CPU=1) WM (up+down) Receiver Well
Synthetic Offset: 0~56 m, Depth: 811~963 m Synthetic
Outline
• WM Crosswell Imaging
• Synthetic Crosswell Data
• McElroy Crosswell Data
• Synthetic Single Well Data
• Conclusions
OYO Salt Model
0 Offset (km) 9
0
Well
Depth (km)
?
?
?
?
Salt
????
6
2.8 4.5
Velocity (km/s)
OYO Salt Model
KM image Velocity Model WM image
2
?
?
?
?
Depth (km)
Well
?????
5
2.5 Offset (km) 6.5 2.5 Offset (km) 6.5 2.5 Offset (km) 6.5
Conclusions
Crosswell Synthetic Data
• Fewer migration artifacts
• Slightly better image resolution
• Better for dipping fault boundary
• No up- and down-going separation
Conclusions
Crosswell McElroy Data
• Similar image quality
• No up- and down-going separation
• 2.5 times faster than KM
• Worse image continuity
• Structure details? Artificial events?
Conclusions
Single Well Synthetic Data
• Similar image quality
• Fewer migration artifacts
Acknowledgements
I thank UTAM sponsors
for their financial support
