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Dariusz Botor, AGH University of Science and Technology (Poland)
Bartosz Papiernik, AGH University of Science and Technology (Poland)
Wojciech Górecki, AGH University of Science and Technology (Poland)
Pawe³ Kosakowski, AGH University of Science and Technology (Poland)
Tomasz Maækowski, AGH University of Science and Technology (Poland)
Beata Reicher, AGH University of Science and Technology (Poland)
Grzegorz Machowski, AGH University of Science and Technology (Poland)
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In the Carboniferous source rocks of the Fore-Sudetic Monocline (FSM, SW Poland), present-day organic carbon content ranges from 0.46 to 1.71%. Dispersed organic matter is principally of humic (gas-prone) character. However, subordinate quantities of oil-prone and mixed II/III-type kerogen occur particularly in the Lower Carboniferous sediments. The organic matter predominantly consists of vitrinite group macerals, whereas the inertinite group and liptinite group macerals are subordinate. Maturity increases toward the axial part of the Mid-Polish Trough and toward SE part of FSM. Tmax values range from 440 to 520 oC and vitrinite reflectance from 1.0 to 5.0%. The transformation degree of Carboniferous deposits corresponds to the phase of thermogenic dry gas generation and minor phase of gas condensate generation.
Due to deep burial, and magmatism (of the Early Permian age) and hydrothermal procesess, SR are overmature on large areas. Several stages of development of the hydrocarbon generation and migration/accumulation processes should be distinguished. In zones of very fast subsidence, with increased heat flow values, significant advancement of the generation processes took place as early as in the Late Carboniferous and the kerogen transformation ratio reached approximately 100%. However, in zones where the hydrocarbon potential was not exhausted in the stage of the Carboniferous development, two principal episodes of the generation and migration happened: the first in the Triassic and/or Jurassic and possibly the second in the Late Cretaceous times. The range of the kerogen transformation is very wide in these Mesozoic stages (20 - >90%), which is confirmed by the high thermal maturity (up to 5.0% Ro). Gas accumulations are genetically connected with hydrocarbon sources occurring in the Carboniferous source rocks. It should be assumed that migration was completed principally in the Mesozoic, usually Jurassic, which was the main period (?) of hydrocarbon migration and filling of numerous reservoirs. Most of the hydrocarbon fields occur in zones where the top of the pre-Permian basement attained thermal maturity on the order of 1.0-2.0% in the vitrinite reflectance scale.
The presence of the effective source rocks is restricted to zones of their maturity exceeding 1.0% Ro. The most prominent reservoirs for the Carboniferous source rocks occur in topmost parts of Rotliegend eolian sandstones (porosity 5 - 21%, permeability 0.1 - >100mD). Fluvial sandstones are slightly worse reservoirs (porosity 1-16%, permeability 0-25 mD). Over the Wolsztyn High and in the southern part of FSM, an important reservoir is Zechstein Limestone deposited as reefs or in shallow-marine platform conditions. The regional seal of the system are Zachstein evaporites.
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