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Geometry with the Proposed Methodology

As mentioned above, I subdivided the rays (and the survey area) into three groups. For each group I computed the optimum geometry using the corresponding subset of rays and the corresponding constraints as summarized in Table 5. The maximum minimum offset, the total fold of coverage, the maximum offset and the aspect ratio were chosen differently for each zone. The source and receiver interval, however, were kept constant, meaning that the surface bins are the same, and were not included in the table. I did not apply any constraint to the offset or azimuth distribution in those bins, although I will implement that in the future.
 
Table 5: Constraints applied in each zone: c1 is for maximum minimum offset, c2 is for available channels, c3 is for aspect ratio, and c4 is for fold.
Zone c1 c2 c3 c4
1 300-400 2000,3000,5000 1-3 24-36
2 500-600 2000,3000,5000 1-3 24-36
3 800-900 2000,3000,5000 1-2 24-32

I tried a total of 4608 geometries for each zone with parameter values as summarized on Table 6. Note that except for the receiver and group interval, the parameters are different in each zone. Also different are the constraints as shown in Table 5.
 
Table 6: Parameters for trial geometries in each zone. Units are in meters.
Zone drl dsl nrl
1 180,200,220,240,260,280,300,320 180,200,220,240,260,280,300,320 6,8,10,12
2 360,380,400,420,460,500,540,580 360,380,400,420,460,500,540,580 4,6,8,10
3 540,560,580,600,640,680,720,760 540,560,580,600,640,680,720,760 4,6,8,10


 
Table 7: Parameters for the optimum geometry in each zone. Units are meters.
Zone dr ds drl dsl nrl
1 20 20 180 320 12
2 20 20 360 440 10
3 20 20 720 720 10

The parameters of the resulting geometry for the three zones are summarized in Table 7. The parameters are significantly different, especially between zone 1, corresponding to the shallow part of the target horizon and zone 3 corresponding to the deep part of the same horizon. Notice that having these different parameters does not in itself compromise the logistics, since the distance between the receiver lines in zones 1 and 2 is half that in zone 3. In fact, for zone 3 the inversion gave me a handful of geometries that satisfied the objectives and the constraints equally and I chose the one that had this property. Logistically, all that would be required is to add an additional receiver line between two adjacent receiver lines in zones 1 and 2 assuming that we have enough equipment (and we do, since that was a constraint to the inversion). The different separation of the source lines is even less of a problem since we can in principle drill the shot-holes along any line we want.

 
next up previous print clean
Next: The bottom line Up: Alvarez: 3-D survey design Previous: The Optimization
Stanford Exploration Project
7/8/2003