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Petroleum system modeling in the Baltic Basin


The shale gas potential of the Baltic Basin is found in the lower Paleozoic strata, which in the north and central part of the basin are buried at a depth between 2,500 and 4,500 meters. Unconventional hydrocarbon potential seems to have the greatest significance in the broad area belt assigned to the distribution of boreholes from Gdansk IG1 through Hel IG1 to Darzlubie IG1 and finally to Zarnowiec IG1. The beds, which can be treated as a potential exploration and production goal for unconventional hydrocarbon, form a several-dozen-meters thick lithological interval composed of a number of dissimilar lithological and stratigraphic units. Wide-ranging stratigraphic and lithological types of these beds include upper Cambrian, Ordovician and lower Silurian shales, siltstones, limestones, marls and fine-grained sandstones, which means that their enrichment in organic matter varies over a wide range of values as well. The unconventional potential of these fine-grained clastic and carbonaceous intervals follows an alteration in organic matter enrichment and lithology. One uniform geochemical parameter typical for the strata forming unconventional resources is organic matter type, which reflects a gas-prone organic matter. The key parameters influencing the content of all main fractions of hydrocarbon are thickness of good and very good source rocks, kerogen quality, organic carbon content and its convertibility to hydrocarbon. Consequently, supposed unconventional resources might amount to about 1.7·1012 kg HC or 2.6·109 m3 or 4.7·1011 m3 of oil and gas equivalents, respectively. Probably, kerogen composition and especially its moderate convertibility to hydrocarbon were the most meaningful geochemical and constitutive parameters responsible for determining resources of any type in the studied region. The vast majority of lithological intervals are kerogen dominated rocks. However, at some depths in the range of lower Paleozoic fine-grained clastics, kerogen dominated rocks may coexist with rocks impregnated by bitumen as well. The amounts of resins and asphaltenes are usually minor, but in some cases they can probably form impermeable horizons which might be risky for exploitation and cost-effective flow.