GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 53 presence of reflectors having a similar seismic facies to that of the UU interpreted in the entire dataset. Furthermore, in some areas evidences of sub parallel reflectors beneath the MU at a time of 5.6-6 s TWT were interpreted as LU. Pre stack depth migration (psdm). PSDM processing was twice tested, on the same segment chosen for the reprocessing in time domain, to better image the complex structural conditions of the investigated media. Two velocity fields were separately applied to perform PSDM1 and PSDM2: the VELGEOD and the VELGEOD2, respectively. The first is described above. The latter was determined on semblance panels (generated by the GeoDepth software- Paradigm Inc., 2008) computed from different CDP gathers chosen so that the lateral velocity variations could be constrained by the vertical borders that define the transition from a small sedimentary basin to a salt structure. In this way, the software could perform the velocity model by smoothing velocity values within the same structure, that are assumed to have the similar velocity trend. Furthermore, VELGEOD2 was picked focusing only on few, deep and strong primary reflections. Their identification was primarly based on the seismic interpretation conducted, on the basis of new evidence, on the reprocessed section. Comparing PSDM1 and PSDM2, some differences can be pointed out. The wide salt diapir (around CDP 800), interpreted as connected to the mother layer, generates a suspected pull up Fig. 2 – A) Interpretation of a detail of C88M1 REPRO reprocessed in time domain and characterised by wide salt diapir generating pull up event. Results on the corresponding detail of pre stack depth migration outcomes: B) PSDM1 and C) PSDM2. (D) Schematized pull up event interpreted on C88M1 REPRO reprocessed in time domain. (E) Velocity Spectra on Semblances related to CDP800 of VELGEOD–PSDM1 and (F) CDP820 of VELGEOD2- PSDM2.