Petroleum geology of the Polish part of the Baltic region - an overview

Abstract

The Polish part of the Baltic region is located within the contact zone between two large geological units: the Precambrian platform and the Paleozoic platform. It comprises the Polish sector of the southern Baltic Sea and the adjacent onshore part of Northern Poland (Western and Eastern Pomerania). The fundamental geological pattern is defined by the Teisseyre-Tornquist Zone, separating the East European Craton from the Paleozoic platform. As a result of exploration activity in the onshore Pomerania region, four oil fields in Cambrian sandstones, seven gas fields in Carboniferous sandstones, six gas fields in Rotliegend sandstones, and eleven oil fields within the Zechstein Main Dolomite horizon have been discovered. The petroleum play of the southern Baltic Sea region and adjacent areas must be considered separately for Eastern and Western Pomerania. In the Peribaltic Syneclise we can only take into consideration organic matter appearing in lower Paleozoic rocks but their geothermal history refers to the period from the Vendian up to the recent. The present extent of the "oil window" in the Upper Cambrian rocks is mainly restricted to the offshore area. Reservoir properties of the "gas window" Cambrian rocks are rather low due to intensive diagenetic processes. Acquisition of gas should be possible by processes of hydraulic stimulation (tight gas). Lower Paleozoic rocks rich in organic matter (Ordovician and Silurian), especially in the border zone of the EEC (Ro > 1.3%), could be an area of unconventional gas fields (shale gas). The Western Pomerania petroleum play shows two separate source rocks units. The older one embraces Carboniferous deposits with organic matter of terrestrial origin and generated gases accumulated in the Rotliegend and Carboniferous traps. The second petroleum system is located within the carbonates of the Zechstein Main Dolomite (Ca2). This is a closed system, meaning that the source rocks are at the same time the reservoirs sealed by Zechstein evaporates. Hitherto discovered hydrocarbon deposits in the Polish part of the Baltic region have confirmed good perspectives regarding oil and gas hydrocarbon zones. New, conventional and unconventional discoveries remain possible.