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Making CMP’s

Making CMP’s. From chapter 16 “Elements of 3D Seismology” by Chris Liner. Outline. Normal Moveout Stacking. Normal Moveout. Hyperbola:. x. T. Normal Moveout. x. T. “Overcorrected”. Normal Moveout is too large. Chosen velocity for NMO is too (a) large (b) small. Normal Moveout.

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Making CMP’s

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  1. Making CMP’s From chapter 16 “Elements of 3D Seismology” by Chris Liner

  2. Outline • Normal Moveout • Stacking

  3. Normal Moveout Hyperbola: x T

  4. Normal Moveout x T “Overcorrected” Normal Moveout is too large Chosenvelocity for NMO is too (a) large (b) small

  5. Normal Moveout x T “Overcorrected” Normal Moveout is too large Chosenvelocity for NMO is too (a)large (b) small

  6. Normal Moveout x T “Under corrected” Normal Moveout is too small Chosenvelocity for NMO is (a) too large (b) too small

  7. Normal Moveout x T “Under corrected” Normal Moveout is too small Chosenvelocity for NMO is (a) too large (b) too small

  8. Vinterval from Vrms Dix, 1955

  9. Vrms V1 V2 Vrms < Vinterval V3

  10. Vinterval from Vrms

  11. Primary seismic events x T

  12. Primary seismic events x T

  13. Primary seismic events x T

  14. Primary seismic events x T

  15. Multiples and Primaries x M1 T M2

  16. Conventional NMO before stacking x M1 NMO correction V=V(depth) e.g., V=mz + B T M2 “Properly corrected” Normal Moveout is just right Chosenvelocity for NMO is correct

  17. Over-correction (e.g. 80% Vnmo) x x M1 M1 NMO correction V=V(depth) e.g., V=0.8(mz + B) T T M2 M2

  18. f-k filtering before stacking (Ryu) x x M1 NMO correction V=V(depth) e.g., V=0.8(mz + B) T T M2 M2

  19. Correct back to 100% NMO x x M1 M1 NMO correction V=V(depth) e.g., V=(mz + B) T T M2 M2

  20. Outline • Convolution and Deconvolution • Normal Moveout • Stacking

  21. NMO stretching T0 V1 V2 “NMO Stretching”

  22. NMO stretching V1 T0 V2 “NMO Stretching” V1<V2

  23. NMO stretching V1 V1<V2 NMO “stretch” = “linear strain” V2 Linear strain (%) = final length-original length original length X 100 (%)

  24. NMO stretching original length = final length = V1 V1<V2 V2 X 100 (%) NMO “stretch” = X 100 (%)

  25. stretching for T=2s,V1=V2=1500 m/s Green line assumes V1=V2 Blue line is for general case, where V1, V2 can be different and delT0=0.1s (this case: V1=V2) Matlab code X 100 (%)

  26. Stacking + + =

  27. Stacking improves S/N ratio + + =

  28. Semblance Analysis X + + = Twtt (s) “Semblance”

  29. Semblance Analysis X V + + = V1 V2 Twtt (s) V3 Peak energy

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