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Geophysical Constraints

In this case, by far the most important constraint was that the maximum minimum offset not be greater than the depth of the target reflector. The rays were split into three groups according to the depth of their reflecting point in the target reflector: from 300 to 400 m, from 400 to 700 m and deeper than 700 m. These ranges were chosen such that the densest acquisition is only used in the part of the surface that contributes the most to the image of the shallow part of the target horizon, and the coarser geometry be used in the part of the surface area that corresponds to the deeper parts of the target horizon with a transition zone in between. The different zones themselves were chosen according to the emergence coordinates of the normal rays. Figure [*] shows the three zones in map view superimposed on the topography. The dark shaded zone in the middle corresponds to the shallow part of the target horizon, the annular zone to the 400-700 meter depths and the darkest zone to the deeper parts of the target horizon. The important point is that this area is a small part of the total survey area. In fact, if we circumscribe a rectangle on this zone we find that its area is only about 3.5 km2. Similarly, the area of zone 2 is about 7.5 km2 which leaves zone 3 with an area of 89 km2.

 
zones1
Figure 8
Survey area divided into three zones according to the depth of the target horizon. The dark shaded zone in the middle corresponds to the shallow part of the target horizon. The important point is that this area is a small part of the total survey area.
zones1
view

Another constraint was the aspect ratio of the recording patch. This is intended to maintain a range of short offsets where the reflector is shallow and longer offsets where the reflector is deeper. Also, this has the effect of avoiding abnormally high folds due to the contribution of long offsets that are not required where the reflector is shallow. Total fold was also considered a constraint to make sure that the minimum fold requirement is honored and to penalize geometries with much higher folds.


next up previous print clean
Next: Logistic Constraints Up: The Proposed Approach Previous: Preprocessing
Stanford Exploration Project
7/8/2003