--> Shale gas potential of the north-central onshore area of the Baltic Basin

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Shale gas potential of the north-central onshore area of the Baltic Basin


The main aim of basin modeling in the Baltic Basin was to simulate source rock properties of upper Cambrian, Ordovician and lower Silurian rock formations using an alternative scenario-testing approach of the erosional and heat flow history. An additional important point of the modeling was the determination of the conventional and/or unconventional hydrocarbon resources, which might give reliable numbers related to any hydrocarbon potential assigned to the lower Paleozoic strata. Integrated basin modeling was applied in the onshore area of the Baltic Basin in the northern part of Poland. The presented study brings relatively fresh observations on the burial history of several rock units in these Paleozoic strata and several improvements in the heat flow scenario. The geological profile begins with the crystalline basement represented by igneous and metamorphic rocks. The basement surface is confirmed from several deep boreholes and interpreted from seismic profiles. The sedimentary profile begins with Ediacaran sandstones. The thickness of the overlaying Paleozoic sequences fluctuates over a wide range of values from 1,800 meters in the Gdansk borehole up to 3,000 meters in the Koscierzyna borehole. The thickness of the Mesozoic strata also significantly varies from one location to another in the range of 460-1,400 meters. The petrophysical parameters of the Paleozoic cover, typical for conventional play, can be found only in the middle Cambrian sandstones. Potential unconventional play is exclusively related to source rocks beds. Rock-Eval pyrolysis and vitrinite reflectance measurements were performed in order to determine the thermal maturity of the studied sediments. In total, a few hundred samples from five boreholes were analyzed for this study. The present-day borehole temperature, vitrinite reflectance and maximum pyrolysis temperature were used for verification of reliability and 1-D calibration of the model. Input parameters for modeling were interpreted from the original descriptions of the boreholes and a few seismic profiles. The application of thermal modeling suggests a maximum paleo-temperature of about 150-160°C for the top of the crystalline basement. The varied distribution of vitrinite reflectance with depth is interpreted as being a result of variable heat flow over Paleozoic era and a few erosion events. The amount of uplift and denudation strongly depends on location and fluctuates between 1,000 meters to the north-east (Zarnowiec and Darzlubie boreholes) to 2,000 meters to the south-west (Koscierzyna borehole).