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Next: CONCLUSION Up: Bevc: Imaging complex structures Previous: LAYER-STRIPPING KIRCHHOFF MIGRATION

MARMOUSI EXAMPLE

Figure 7 is the result of an industry standard Kirchhoff migration of the Marmousi synthetic using eikonal traveltimes. The upper portion is well imaged; however, the anticlinal structure below 2200 m and the target zone at a lateral position of about 6500 m and depth of 2500 m is not imaged.

Figure 8 is generated by downward continuing the data to a depth of 1500 m in one datuming step. The downward continued data are then migrated and combined with the previous image of the upper 2000 m. The anticlinal structure and the target are now clearly imaged.

Continuing the data to 1500 m in three steps of 500 m each, results in an even crisper image of the anticline and the target (Figure 9). In both of these images, the events which unconformably define the top of the anticline, the anticline events themselves, and the target events, are clearly imaged.

mig0
mig0
Figure 7.
Standard Kirchhoff migration using eikonal traveltimes.
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mig1
mig1
Figure 8.
Migrated image using traveltimes calculated from the surface, and traveltimes calculated from a depth of 1500 m. The lower part of the image was obtained by migrating data which was redatumed to a depth of 1500 m in one step of downward continuation.
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mig2
mig2
Figure 9.
Migrated image using traveltimes calculated from the surface, and traveltimes calculated from a depth of 1500 m. The lower part of the image was obtained by migrating data which was redatumed to a depth of 1500 m in three steps of 500 m each.
[pdf] [png] [scons]

In Figure 10, I compare the images in the vicinity of the target zone to the velocity model and a filtered reflectivity model which represents the desired image. Both images compare favorably to the desired reflectivity. The image obtained by downward continuing the data in three steps of 500 m is superior since the events display better lateral continuity and the image is clearer. This is because the traveltimes calculated for each of the 500 m steps are simpler and better behaved than the traveltimes calculated for one step of 1500 m.

targref
targref
Figure 10.
Comparison of the velocity, the reflectivity, and the images in the target zone.
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next up previous [pdf]

Next: CONCLUSION Up: Bevc: Imaging complex structures Previous: LAYER-STRIPPING KIRCHHOFF MIGRATION

2013-03-03