Moveout errors

From the initial migration I chose thirteen reflectors to perform tomography with (Figure 7). To constrain the upper portion of the model I chose the sea bottom reflection and the chalk boundary reflection. I chose the salt top and bottom reflection along with four reflectors to the left and five to the right of the salt body. The volume of data made accurate picking of the reflectors difficult especially under the salt edge. As a result, I concentrated more on the area right of the salt where reflector coherency was good in the initial migration.

 

elf3d.reflectors.vel0
Figure 7 The thirteen reflectors used in tomography superimposed on the initial migration image.

I performed moveout analysis using equation () and extracted the moveout along the thirteen reflectors. Figure 8 shows slices through the bottom 12 reflector semblance cubes. Generally the chalk reflector (top-left) showed little to no moveout errors. The remaining eleven showed varying degree of residual moveout. I then created smooth semblance error maps using fitting goals similar to (), replacing the 1-D differential operator with the Laplacian. Figure 9 shows the resulting semblance maps for the same 12 reflectors as Figure 8.

 

sem-ref.3d
Figure 8 Initial moveout semblance along the lower 12 reflectors used in tomography.

 

smooth.3d
Figure 9 Initial moveout semblance along the lower 12 reflectors used in tomography.