Seismic image of the top of Jurassic structure under Polish Outer Carpathians in the zone Southeast of Krakow

The modeling is a method well supporting seismic research during projecting, processing and interpretation of seismic data. In the presented paper, the multivariate seismic modelling was used for evaluation of influence of changing structure of Carpathian flysch on the seismic image of Upper Jurassic (Malm) rocks. This research investigated Podgrodzie structure in the marginal part of the Outer Carpathian fold-and-thrust-belt. The gas deposits in this area are localized on tectonic uplifts, bounded by thrust dislocations.The complex structure and tectonics of the Carpathian flysch makes the interpretation of seismic image of the reservoir Upper Jurassic carbonates somewhat difficult. The poor recognition of velocities of flysch sequences makes this interpretation even more difficult. The multivariate seismic modelling is necessary in this situation. It allows evaluation of influence of selected model elements of the originating wavefield. It is possible finding the model correctly approximating investigated orogen by matching registered and theoretical field. The Outrider (Divestco Inc.) and Omega (WesternGeco) system were used for offset and zero-offset modelings. The performed modelling shows that influence of changing velocity and geometry of reflecting boundaries on underlying stratigraphic stages is insignificant. This influence is only significant in the zones of steep dipping flysch layers where large horizontal contrast of velocity significantly influences the seismic image of Jurassic rocks. Outside these zones the seismic image of the top of Jurassic reliably restores the real boundary. The obtained results show that the multivariate seismic modeling is a method, which can be used with good results, under the complex seismogeological conditions. The modelling could be also helpful evaluating the reliability of register seismic data.