Slides for my talk at EAGE 2017 in Paris, France. We introduce a technique which identifies corrupted areas in the updates of full-waveform inversions. These areas are then corrected to mitigate cycle-skipping artifacts and thus inversion converges to a more realistic model of the subsurface.

1. O. Ovcharenko, V. Kazei, D. Peter, T. Alkhalifah
June 14, 2017
Variance-based salt body reconstruction

2. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction2
Outline
Motivation
BP2004 model results
Salt flooding technique

3. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction3
(Jones et al., 2014)
• Hydrocarbons below salt bodies
• Seismic imaging challenged by high-
velocity contrasts
• Complex geometries, steep flanks
• Multipulses
• Illumination issues
Motivation

4. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction4
(Zhang et al., 2009)
Motivation
“Top-to-bottom” manual approach
• Robust
• Interpreter-biased
• Time consuming

5. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction5
(Esser et al., 2016)
Constrained optimization
• Automatic
• A priori model assumptions
• Computationally expensive
Motivation

6. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction6
(Alkhalifah, 2016)
Motivation
Gradient conditioning
• Less iterations
• Limited domain of convergence

7. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction7
Motivation
Many challenges in salt body imaging using FWI
We don’t have:
• Accurate starting model
• Low-frequency data
• Long-offset data
• …
How to overcome these difficulties?

8. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction8
(Bunks, 1995)
Global-minimum
Multiscale
Low
High

9. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction9
(Bunks, 1995)
Global-minimum Local-minimum
Multiscale strategy needs low-frequency data to find global minimum
Misfit function at different frequencies
Multiscale
Low
High

10. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction10
Local minima at different frequencies

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The proposed idea
Use variance between inversion results at different
frequencies to build a better initial model for FWI

12. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction12
Outline
Motivation
BP2004 model results
Salt flooding technique

13. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction13
0. Updates from different
frequencies
1. Average updates
2. Variance map and mask
3. Variance-based flooding
4. *FWI starting from “flooded” model
Variance-based salt flooding - Workflow

14. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction14
0. Updates from different
frequencies
1. Average updates
2. Variance map and mask
3. Variance-based flooding
4. *FWI starting from “flooded” model
Variance-based salt flooding - Workflow

15. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction15
Model updates from different frequencies
1. Averaging
0. Modeling
2. Variance
3. Flooding
Receivers
Sources
Crop from BP 2004 (Billette and Brandsberg-Dahl, 2005)
Size: 61 x 220, dx = 50 m
Acoustic, isotropic
Frequency domain

16. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction16
Model updates from different frequencies
1. Averaging
0. Modeling
2. Variance
3. Flooding
f4
f3
f2
f1
High frequency
Low

17. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction17
Size of cycle-skipping artifacts is proportional to wavelength λ
Selection of frequencies
λ1
λ2
λ3
λ4
Low-frequency
artifacts
Intermediate-frequency
artifacts
High-frequency
artifacts
Wavelength
f1
f2
f3
f4
Frequency
Low
High
Artifacts

18. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction18
Average model
Weighted average using weights
1. Averaging
0. Modeling
2. Variance
3. Flooding

19. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction19
1. Averaging
0. Modeling
2. Variance
3. Flooding
Variance between updates

20. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction20
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance between updates

21. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction21
0. Modeling
2. Variance
3. Flooding
Variance between updates
1. Averaging

22. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction22
Weighted variance
0. Modeling
2. Variance
3. Flooding
Variance
using weights
1. Averaging

23. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction23
0. Modeling
2. Variance
3. Flooding
Variance mask
Floating variance threshold
Initial threshold
1. Averaging
Maximum variance
Average variance

24. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction24
0. Modeling
2. Variance
3. Flooding
Variance mask and model overlap
1. Averaging

25. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction25
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance mask and model overlap

26. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction26
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance mask and model overlap

27. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction27
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance mask and model overlap

28. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction28
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance mask and model overlap

29. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction29
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance mask and model overlap

30. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction30
0. Modeling
2. Variance
3. Flooding
1. Averaging
Variance mask and model overlap

31. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction31
Input

32. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction32
Input

33. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction33
Input

34. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction34
Input

35. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction35
Input

36. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction36
Input

37. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction37
Input

38. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction38
Input

39. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction39
“Flooded” model

40. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction40
Outline
Motivation
BP2004 model results
Salt flooding technique

41. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction41
Central part of BP 2004
frequency range 3 -11 Hz

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Initial

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FWI without flooding

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Flooding result

45. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction45
FWI with flooding

46. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction46
Left part of BP 2004
frequency range 4 -11 Hz

47. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction47
Initial
Size: 107 x 550, dx = 20 m

48. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction48
FWI without flooding

49. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction49
Flooding result

50. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction50
FWI with flooding

51. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction51
Conclusions
• Updates at different frequencies can be analyzed to improve FWI
• Variance-based salt flooding
Gives good initial model
Easy to embed into an existing FWI
Independent on forward solver
Low computational costs
• Limitations
Shifted artifacts
Initial variance threshold

52. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction52
Acknowledgements
• Seismic Modeling and Inversion Group
• Seismic Wave Analysis Group
• KAUST
• Tristan van Leeuwen (Utrecht University)
• Veronica Tremblay (KAUST)

53. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction53
Conclusions
• Updates at different frequencies can be analyzed to improve FWI
• Variance-based salt flooding
Gives good initial model
Easy to embed into an existing FWI
Independent on forward solver
Low computational costs
• Requirements
Shifted artifacts
Initial variance threshold

54. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction54
Bibliography
Jones, Ian F., and Ian Davison. "Seismic imaging in and around salt bodies." Interpretation 2.4 (2014): SL1-SL20.
Quincy Zhang, Itze Chang, and Li Li (2009) Salt interpretation for depth imaging - where geology is working in the
geophysical world. SEG Technical Program Expanded Abstracts 2009: pp. 3660-3664.
Esser, Ernie, et al. "Constrained waveform inversion for automatic salt flooding." The Leading Edge 35.3 (2016):
235-239.
Tariq Alkhalifah (2016). ”Full-model wavenumber inversion: An emphasis on the appropriate wavenumber
continuation.” GEOPHYSICS, 81(3), R89-R98.
Nick McArnie (2013), PES GB, London, Frequency Decomposition and colour blending of seismic data
- “More than an image to me”