Application of 2-D forward seismic modelling for impro- ved imaging of sub-salt Rotliegend strata in Polish Basin

Abstract

Forward seismic modelling can aid seismic studies of the pre-Zechstein strata in areas of developed salt tectonics, such as the Obrzycko–Szamotuły region, NW Polish Basin. The results not only can be used for seismic interpretation, but also can support the planning of survey methodology and the workflow of seismic data proce- ssing. This paper presents the results of modelling that was carried out, before the acquisition of the regional-scale, seismic line Obrzycko-1–Zabartowo-1–Zabartowo-2 (Górecki, 2010). An interpreted, seismic transect was used to build a basic, seismic-geological model. The modelling was based on seismic ray theory. The zero-offset mo- delling (theoretical wave field) for different geometries of salt structures showed that an increase in salt thickness resulted in a pull-up of reflection events, related to the sub-salt horizons. The incorporation of faults and salt overhangs into a model significantly complicated the seismic wave field. The results of offset modelling, pre- sented in this paper as seismic ray tracing and common-shot gathers, proved that (1) the seismic response of the Rotliegend (Permian) formations can be recorded, despite the presence of the overlying salt pillows and diapirs, if offsets several kilometres long are used, and (2) the complex configuration of seismic reflectors (diapirs with salt overhangs, faults) gives rise to complicated, seismic ray paths that may cause difficulties in common-depth-point stacking and therefore decrease the quality of the seismic records.