GNGTS 2013 - Atti del 32° Convegno Nazionale

for the purpose of validating the new procedure for the multiples migration, the implemented code still produces acceptable results. We first tested our migration procedure on a very simple synthetic dataset created ad-hoc for the experiment. The data were generated using a FD (Finite Difference) software. The model used for the simulation provides a single flat reflector in a constant velocity medium. Fig. 1 shows the migrated sections obtained with both the standard imaging procedure and the migration of multiples. Only a single CSG (Common Shot Gather) was processed. The acquisition geometry of the shot gather under analysis provides a split-spread arrangement of the receivers (from x=1000 m to x=5000 m) while the source is placed at x=3000 m. It is possible to notice that the multiples migration not only is able to reconstruct the subsurface discontinuity but it also provides a much wider illumination. We tested our new imaging algorithm also on the more realistic synthetic dataset Sigsbee2b. Fig. 2 shows the comparison between the conventional migration result and the migrated section obtained by migrating the multiples. The two images are very similar thus confirming the feasibility of the proposed procedure. Moreover there are areas where the multiples migration produces better results, especially in terms of vertical resolution. The yellow arrows superimposed onto the images point to some artifacts coming from the cross-talk terms that generate in the multiples imaging while the yellow box highlight the area where the main improvements occur. Fig. 3 show an example of two A-CIGs (Angle Common Image Gathers) extracted from both the migrated sections obtained with the migration of primaries and the multiples image. It is possible to notice the different illumination provided by the multiple reflections. Final remarks. A new migration technique able to correctly account for surface-related multiples was presented with examples on both a simple ad-hoc synthetic data and on Fig. 1 – Imaging results on a simple synthetic data. Left: Conventional migrated section of a single shot gather. Right: Migration of multiples of the same single shot gather of the left- hand-side picture. It is possible to notice the wider illumination provided by the new migration procedure. Fig. 2 – Imaging results on the Sigsbee2b dataset (close-up). Top: Image from conventional imaging of primaries. Bottom: Migration of multiples. The yellow arrows indicate the cross-talk noise. In the highlighted area in the yellow box it is possible to notice the better results produced by the migration of multiples in terms of spatial resolution with respect of the primaries image. 38 GNGTS 2013 S essione 3.1