The geological and geophysical interpretation of the sub-Carpathian autochthonous gas-bearing Devonian structures of Lachowice-Stryszawa

Abstract

The problem of searching for oil and gas in Devonian carbonate reservoirs under autochthonous Miocene molasse and Carpathian flysch fold-thrust cover has been presented on the example of Lachowice-Stryszawa structure (western segment of Polish Carpathians). The structure of Carpathian autochthonous substratum as interpreted from vertical Lachowice 7 well and directional Stryszawa 1K well profiles showed the occurrence of inversional strike-slip fault separating blocks of different tectonic development. The misleading seismic wave diffraction effect generated by narrow fault-framed trough closing up Stryszawa gas-productive anticline has been proved with theoretical modelling of the wave-field using 1D and 2D seismogeological models. The seismic lines as interpreted with the use of LANDMARK workstation and software allowed to establish the reflection boundaries not only from Carpathian overthrust and autochthonous Miocene but also from Devonian substratum and deeper basement. As a result, the time-structure map of the top of autochthonous Palaeozoic substratum has been presented. This suggests the occurrence of mostly longitudinal pairs of strike-slip faults and fault-related structures of the substratum. The faults originally developed under tensional regime were rejuvenated into compressional ones due to Carpathian fold-thrust movements.