Discussion

The results shown in the previous section demonstrate that with the 3D Radon transform it is possible to attenuate, although not completely remove, the diffracted multiples. It should be noted, however, that in this seismic section it is very difficult to find a legitimate primary reflection below the salt and in particular below the edge of the salt, where the contamination by the diffracted multiples is stronger. It is somewhat disappointing that the attenuation of the diffracted multiples didn't help in uncovering any meaningful primary reflections in this case. We expect the situation to be different with other datasets.

We mentioned before that working in image space (ADCIGs in this case) is convenient because the migration takes care of the complexity of the wavefield propagation, but attenuating the multiples after migration does not come without a price. The estimation of the migration velocities may be more difficult and less accurate because of the presence of the multiples. There is therefore an inherent trade-off when choosing to work in image space. Good migration velocities for weak subsalt primaries may be particularly difficult to estimate in the presence of the multiples. On the other hand, the parabolic or hyperbolic assumption for the moveout of the multiples in data space may not be appropriate at all in complex media. An alternative could be to do a standard Radon demultiple before prestack migration to facilitate the choice of the migration velocities and 3D Radon demultiple on the ADCIGs to attenuate residual multiples, in particular diffracted multiples.

We should also emphasize that adding the extra dimension to deal with the diffracted multiples does not in itself resolve the usual problem that non-flat primaries may map to the multiple region and therefore we have to trade primary preservation for multiple attenuation. We saw this limitation in this case, which forced us to let some residual multiple energy leak into the extracted primaries. Obviously, the flatter the primaries in the ADCIGs, the better our chances to reduce the residual multiple energy.