Geoscience Reference
In-Depth Information
1. Reformat
2. Designature
3. Resample from 2 to 4 ms
4. Low cut filter (5/12 minimum phase filter)
5. Remove bad traces
6. Merge navigation with seismic headers
7. Spatial resampling from 12.5 to 25 m groups. Normal moveout (NMO) correction, K-filter,
trace drop, inverse NMO
8. Spherical divergence gain corrections
9. Deconvolution before stack
10. Shot interpolation to double fold in CMP gathers
11. Radon demultiple on interpolated gathers
12. High-frequency noise removal
13. Drop of interpolated traces
14. Flex binning increasing from 37.5 m on near to 50 m on far offsets
15. Sort to common offset
16. Dip moveout (including approximate NMO) halving the number of offset planes on output
17. Pre-stack time migration using constant velocity 1600 m/s
18. Inverse NMO
19. Re-pick velocities (0.5 km grid)
20. NMO
Processing hereafter continuing on three volumes:
21. Stack to generate three volumes: near offset stack, far offset stack and full offset stack
22. 3-D constant velocity inverse time migration
23. Bulk static (gun and cable correction)
24. K-notch filter to remove pattern caused by the acquisition
25. FXY deconvolution
26. FXY interpolation to 12.5 m
×
12.5 m bin grid
27. Pre-migration data conditioning (e.g. amplitude balance, edge tapers, etc.)
28. One pass steep dip 3-D time migration (using time and spatially varying velocity field)
29. Zero-phase conversion by matching to wells
30. Spectral equalisation
31. Bandpass filter
32. Residual scaling
Fig. 2.21
Typical 3-D processing sequence.
that was created by the source and converts it to a more compact form. For instance,
air guns output a signal with a main peak, followed by a smaller secondary peak due
to the re-expansion of the air bubble. Such a source signal is undesirable since every
reflection would be followed by a smaller repetition of itself. Designature removes
the second peak, giving the input wavelet a more compact form. A decision needs to be
made at this point whether the output should be zero- or minimum-phase. A zero-phase
wavelet is one that is symmetrical about its centre, while a minimum-phase wavelet is
one that starts at time zero and has as much energy near the start as physically possible
(fig. 2.22)
. There are arguments on both sides. It is certainly desirable to use zero-phase
