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Permian Basin as a main exploration target in Poland

A b s t r a c t . The Polish Permian Basin (PPB) is a part of the Southern Permian Basin in the Western and the Central Europe. Results of burial and thermal analyses as well as a configuration of the Moho surface of the Polish Basin suggest the asymmetrical basin model. History of the Polish Basin reveals that the Late Permian and the Early Triassic periods represent the main rifting phase and its later development resulted from thermal relaxation. During the Late Triassic and the Jurassic time some cooling of rift heat field took place, but the turning point in thermal evolution of the Polish Basin was at the Jurassic/Cretaceous boundary when the south-western part of the Polish Basin was uplifted and intensively eroded. The knowledge on the Permian Basin in Poland is chiefly connected with petroleum exploration. The gas fields are located mainly in the Rotliegend reservoirs. The Zechstein deposits, overlying the Rotliegend, are also in the area of economic interest: hydrocarbons occurring in carbonate deposits of the Werra (Zechstein Limestone — Ca1 ) and Stassfurt (Main Dolomite — Ca2) cyclothems. Several tens gas fields have been hitherto discovered within the Rotliegend sandstones and the Zechstein limestones. Reservoirs are the clastic, terrestrial deposits of the Lower Permian and calcareous, biogenic carbonates of the Zechstein. Evaporates, mainly salts of the Werra cyclothem, are the regional sealing for the mentioned reservoirs. Natural gas accumulated in the Rotliegend sandstones and the Zechstein limestones is of the same origin: it was generated from organic matter occurred in the Carboniferous rocks and it migrated to higher places where it became concentrated within favourable structural or lithofacies conditions. High nitrogen content in the natural gas from the Polish Permian Basin is explained that nitrogen is generated from an organic matter within a sedimentary basin at higher temperatures than methane. Location of high helium concentration corresponds to the area of highest heat flow during the Late Permian, Triassic and Jurassic times, evidencing the Late Permian-Early Mesozoic rifting process. Numerous oil gas fields discovered in the Main Dolomite (Ca2) unit constitute it as one of the most important exploration target in the Polish Basin. It composes the closed hydrodynamic system sealed from the top and the bottom by evaporates. Both the source rocks and reservoirs are characteristic for this unit. Influence of the burial and thermal history of the Polish Basin on a petroleum play generation within the Main Dolomite unit is clearly visible. The previous and the present petroleum discoveries in the Polish Permian Basin, comparing to the other petroleum provinces in Poland, indicate it as a main exploration target.