Data and migration results

Figure  shows the data after the far offsets have been removed. A multiple train caused by the fast middle layer has died down over the inner offsets at the time of the anomaly. Therefor, removing the far offsets, we were able to create a nearly multiple free data volume for imaging purposes. The middle half of the total offset range was kept. Figure  is the image produced by shot-profile migration using all the available data. Figure  shows the image for the step anomaly and the scallop anomaly. Identical images were created by stacking all of the shots and migrating with a planar horizontal source function, and source-receiver migration (not shown).

 

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Figure 1 Shot record and time slice of the inner offsets of modeled data. The time slice shows the anomaly.

 

alloffsmig Figure 2 Shot-profile migration using all available data. Interference from intrabed multiples from middle layer decreases image quality.

 

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Figure 3 Both data sets produce very clean images when only near offset traces are migrated. Image produced with shot-profile migration.

To understand the importance of multiple shots, two single shot data volumes were migrated with shot-profile migration. Figures  is the image from a shot located at the left edge of the model space. The bottom reflector is very poorly imaged, and their is no indication of the anomaly. If the shot were located directly over the anomaly, as in Figure , the anomaly is noticeable though the quality of the image is poor.

 

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Figure 4 Image from a single shot at the far left edge of the model.

 

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Figure 5 Image from a single shot directly over the anomaly.