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Petroleum Geological Exploration Technology - Innovation Strategies, Upper Rotliegend, Polish Permian Basin

Abstract

The Rotliegend series of clastic sediments in the area of the Polish Permian Basin have been very important gas-bearing formation for the last decades. Until now gas deposits in the Polish Rotliegend Basin have been discovered only in structural traps in the top parts of these sediments. Most often traps are sealed with Zechstein Sea evaporates (salt and anhydrite) and they were found in aeolian sandstones or less often in fluvial sandstones, which in most cases having good reservoir properties. In recent years, exploratory works and research north of Wolsztyn-Pogorzela Paleo-High (near Poznań) has shown repeatedly, that hydrocarbons accumulations in multilevel traps are probable. Geological data clearly indicate the presence of such traps in terms of new approaching and searching techniques of exploration areas which were considered as non-gas bearing. In fact, a lot of well-drilled geological data, gathered for the last decades is excellent quality material to prove an innovative concept aiming to discover the new type of gas deposits. The reservoir rocks of these intraformational lithological traps in the Rotliegend sediments are composed of porous aeolian or fluvial sandstones. The innovative idea is trying to specify the definition of sealing rock as alluvial conglomerates within Rotliegend strata. The main component of conglomerates is clasts of volcanic rocks having a diverse mineralogical composition and clasts of Carboniferous sedimentary rocks with diverse lithology. Especially noteworthy is the significant amount of clay minerals (varies from 30 to 50%) present in conglomerates, formed during diagenetic processes. Successful results of Drill Steam Tester carried out within perspective Rotliegend strata with the non-commercial flow of gas provides the clear evidence of huge potential of gas accumulations/saturation in these series. Further evidence is given by the significant mudlogging data noted gas manifestations in lower part of Rotliegend strata below conglomerate layers combined with well logging gas indicating interpretation. In the light of borehole data and in particular VSP it turns out that the top of intraformational traps in Rotliegend can be also tracked on seismic data (low amplitude gas traps), therefore it is possibly to determine spatial range of this kind of sandy bodies.