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Variance-based salt body reconstruction

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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.

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Variance-based salt body reconstruction

  1. 1. O. Ovcharenko, V. Kazei, D. Peter, T. Alkhalifah June 14, 2017 Variance-based salt body reconstruction
  2. 2. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction2 Outline Motivation BP2004 model results Salt flooding technique
  3. 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. 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. 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. 6. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction6 (Alkhalifah, 2016) Motivation Gradient conditioning • Less iterations • Limited domain of convergence
  7. 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. 8. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction8 (Bunks, 1995) Global-minimum Multiscale Low High
  9. 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. 10. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction10 Local minima at different frequencies
  11. 11. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction11 The proposed idea Use variance between inversion results at different frequencies to build a better initial model for FWI
  12. 12. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction12 Outline Motivation BP2004 model results Salt flooding technique
  13. 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. 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. 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. 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. 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. 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. 19. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction19 1. Averaging 0. Modeling 2. Variance 3. Flooding Variance between updates
  20. 20. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction20 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance between updates
  21. 21. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction21 0. Modeling 2. Variance 3. Flooding Variance between updates 1. Averaging
  22. 22. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction22 Weighted variance 0. Modeling 2. Variance 3. Flooding Variance using weights 1. Averaging
  23. 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. 24. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction24 0. Modeling 2. Variance 3. Flooding Variance mask and model overlap 1. Averaging
  25. 25. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction25 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance mask and model overlap
  26. 26. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction26 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance mask and model overlap
  27. 27. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction27 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance mask and model overlap
  28. 28. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction28 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance mask and model overlap
  29. 29. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction29 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance mask and model overlap
  30. 30. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction30 0. Modeling 2. Variance 3. Flooding 1. Averaging Variance mask and model overlap
  31. 31. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction31 Input
  32. 32. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction32 Input
  33. 33. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction33 Input
  34. 34. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction34 Input
  35. 35. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction35 Input
  36. 36. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction36 Input
  37. 37. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction37 Input
  38. 38. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction38 Input
  39. 39. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction39 “Flooded” model
  40. 40. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction40 Outline Motivation BP2004 model results Salt flooding technique
  41. 41. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction41 Central part of BP 2004 frequency range 3 -11 Hz
  42. 42. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction42 Initial
  43. 43. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction43 FWI without flooding
  44. 44. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction44 Flooding result
  45. 45. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction45 FWI with flooding
  46. 46. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction46 Left part of BP 2004 frequency range 4 -11 Hz
  47. 47. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction47 Initial Size: 107 x 550, dx = 20 m
  48. 48. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction48 FWI without flooding
  49. 49. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction49 Flooding result
  50. 50. oleg.ovcharenko@kaust.edu.saVariance-based salt body reconstruction50 FWI with flooding
  51. 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. 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. 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. 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”

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