AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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The Ordovician-Silurian unconventional petroleum system in the Baltic Basin (SE Poland)

Abstract

The Baltic Basin is located in the western margin of the East-European Craton. The most promising complexes for the unconventional deposits in the investigation area are claystones of Caradoc and bituminous claystones of the Llandovery. The thickness of these horizons, usually of 20-30m and 50-60 m, respectively point them as possible source of unconventional hydrocarbons. Previous studies has confirmed the presence of shale gas in the northern part of the Baltic Basin (Darżlubie area), and little weaker potential in the central part (Gdańsk–Malbork–Prabuty area). The eastern part of the study area is very poorly recognized, but the preliminary geochemical results indicate that the Palaeozoic source formations also have some a hydrocarbon potential. The presence of numerous conventional hydrocarbon fields in the Kaliningrad District and in the western border of Lithuania confirms these assumptions. The Llandovery and Caradoc claystones and siltstones generally reveal fair to good oil-source rock potential. Locally it is very good to excellent, but a significant part of the results shows weak potential. The measured organic carbon content (TOC) reached 12 wt% and 80 mg hydrocarbons/g of rock. In the analyzed strata oil-prone Type-II kerogen is present, deposited in anoxic and sub-oxic conditions. The maturity of the organic matter shown that the organic matter reveals wide range of thermal maturity, from initial phase of the “oil window” up to the late mature phase. Generally, the maturity increases in south-west direction. According to geochemical recognize the timing of hydrocarbon generation were modelled for Lower Palaeozoic source rock complexes. The 1D modelling (BasinMod™ software) was carried out in profiles of wells throughout the study area. The modelling indicated that the onset of petroleum generation from the Lower Palaeozoic source rocks occurred from the early Devonian through the early Carboniferous period. The peak of hydrocarbon generation took place from the late Devonian to the Tournaisian time. The 3D static modelling of reservoir properties (Petrel software) and simulation of the development, diversity and evolution of organic facies (OF-Mod 3-D software) was performed too. Based on sparse hard data and well logs were defined basic components of lithology and reservoir variability: shale volume, quartz and carbonate content, porosity, TOC, and Brittleness Index.

The small amount of input data available at the stage of the paper preparation allows only initial, but positive assessment of the productivity of the Ordovician-Silurian unconventional system in the analysed part of the Baltic Basin.

The studies were financed by the National Science Centre, Poland (Project No. UMO-2016/21/B/ST10/02079) and AGH-University of Science and Technology (Project no. 11.11.140.626).