From Regional Depositional Architecture to Reservoir-Scale Considerations, Lower Paleozoic Baltic Basin, N Poland

Abstract

The western edge of the East European Craton in Poland has recently been the focus of intense exploration efforts for unconventional hydrocarbons, led by Polish and foreign companies. Results of early exploration wells clearly demonstrate that there are still many unknowns regarding various aspects of the unconventional petroleum system, both regional (structure and depositional architecture of the Lower Paleozoic succession) and more local (variations of shale thickness, TOC, mechanical properties etc.). In order to shed light on some of these problems high-effort regional reflection seismic survey PolandSPAN has been acquired that covered entire Lower Paleozoic basin developed above the SW edge of the East European Craton. Following regional interpretation a feasibility study devoted to seismic reservoir characterization has been completed that allowed to assess applicability of seismic reflection data for reservoir-oriented studies of the Lower Paleozoic shales in Poland. The Lower Paleozoic basin in Poland is located above the southwest edge of the East European Craton, northwest from the Teisseyre – Tornquist Zone which is separating the cratonic plate from the West European Platform (Ziegler, 1992; Doornenbal & Stevenson, 2010). Later Late Paleozoic tectonic movements resulted in compartmentalization of the Lower Paleozoic basin into three sub-basins: Baltic Basin, Podlasie Basin and Lublin Basin (Fig. 1). During the Precambrian/Cambrian, the cratonic edge underwent extension and rifting of the Rodinia supercontinent, while Cambrian – Middle Ordovician subsidence was driven by a post-rift lithospheric thermal cooling (Poprawa et al., 1999; Poprawa, 2006a). In the Late Ordovician – Silurian, the cratonic edge was under the strong influence of the Caledonian thrust belt, and was incorporated into its flexural foredeep basin (Poprawa et al., 1999; Nawrocki & Poprawa, 2006). Deposition was dominated by fine-grained organic rich shales, generally derived from the eroded orogenic wedge and deposited in the distal foredeep basin (Poprawa et al., 1999; Poprawa, 2006b). The Silurian Caledonian foredeep basin encompassed vast areas stretching from the present-day Sweden across Estonia, Latvian, Lithuania, Russia (i.e. Kaliningrad District), Poland, Belarus, Ukraine and farther to the southeast (Poprawa et al., 1999; Skompski et al., 2008; Zdanaviciute and Lazauskiene, 2007). Presently available information regarding the Caledonian orogenic wedge is very limited and mostly indirect, based on e.g. provenance studies of the foredeep infill, as it was destroyed and deeply buried during the later tectonic phases (Poprawa, 2006b).