1. The Relationship between Uncertainty and Quality in Seismic Data
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The Relationship between Uncertainty and Quality in Seismic Data
by Gregg Parkes and Chris Walker
PGS Research

2. The Relationship between Uncertainty and Quality in Seismic Data
Talk Outline
The Relationship between Uncertainty and Quality in Seismic Data
Introduction
Stacking velocity errors
Acquisition parameter uncertainty
Conclusions

3. What limits the quality of the seismic image?
Geology
Acquisition geometry parameter variations
Processing underlying processing model - errors - statics, stacking velocity, migration velocity, etc…..

4. Relating uncertainty to quality
Systematic approach :
Model acquisition and/or processing uncertainty and determine effect on image at the target

5. Possible measures of quality :
Measuring quality
Possible measures of quality :
S/N ratio
Wavelet coherency
Bandwidth
AVO attributes
Other appropriate signal characteristics
In general, selected quality measures will be target specific

6. The Relationship between Uncertainty and Quality in Seismic Data
Talk Outline
The Relationship between Uncertainty and Quality in Seismic Data
Introduction
Stacking velocity errors
Acquisition parameter uncertainty
Conclusions

7. Shallow data example

8. Deep data example

9. Statistical distribution of picks

10. Velocity picking errors for shallow dataset

11. Velocity picking errors for deep dataset

12. Velocity experiment summary
Error distribution is close to Gaussian
Depth dependence strong
Noise level dependence weak
Geology dependence strong
1.5% (s.d.) error is close to theoretical limit
Typical data ( < 5 seconds ) 2% - 4 % (s.d.) is representative
Deep dataset gave range from 0.5% (shallow) up to 10% -15% (deep/poor quality)

13. Mapping from velocity uncertainty to quality

14. The Relationship between Uncertainty and Quality in Seismic Data
Talk Outline
The Relationship between Uncertainty and Quality in Seismic Data
Introduction
Stacking velocity errors
Acquisition parameter uncertainty
Conclusions

15. How do these allowed variations impact image quality?
Typical acquisition specifications - source tolerances
Timing :  1 msec
Depth :  0.5 m
Drop-outs :  10% peak amplitude  10% Primary/Bubble ratio
How do these allowed variations impact image quality?

16. Mapping from timing uncertainty to quality

17. Timing, depth and drop-out comparison

18. Random and systematic depth comparisons

19. Velocity errors - 90% confidence bands

20. Absolute threshold from statistical analysis of uncertainty

21. The Relationship between Uncertainty and Quality in Seismic Data
Talk Outline
The Relationship between Uncertainty and Quality in Seismic Data
Introduction
Stacking velocity errors
Acquisition parameter uncertainty
Conclusions

22. The Relationship between Uncertainty and Quality in Seismic Data
Conclusions
The Relationship between Uncertainty and Quality in Seismic Data
Uncertainty in both acquisition and processing parameters produce changes in seismic quality
Quality effects can be balanced against each other to set equivalent tolerances
Analysis of uncertainty must be target specific, including choice of quality attributes