Sources of natural gases in Middle Cambrian reservoirs in Polish and Lithuanian Baltic Basin as determined by stable isotopes and hydrous pyrolysis of Lower Palaeozoic source rocks

Molecular and isotopic compositions and origin of natural gases from Cambrian and Carboniferous-Lower Permian reservoirs of the onshore Polish Baltic region

“…4a, b, the vitrinite reflectance curves are fitted after mode of Faber (1996, 1997) based on average δ 13 C = −29.0 ‰ for Ordovician Type-II kerogen (Więcław et al 2010a). However, hydrous pyrolysis experiments of gas generation simulation and calibration of gas isotope models for Upper Cambrian-Tremadocian source rocks (Kotarba and Lewan 2013) reveal that isotope curves on both δ 13 C(C 2 H 6 ) versus δ 13 C(CH 4 ) ( Fig. 4a) and δ 13 C(C 3 H 8 ) (Fig.…”

“…The Llandovery (Silurian) strata reveal moderate and locally high hydrocarbon potential of source rocks, for which the present TOC content reaches locally 10 wt% (usually 1-2 wt%) (Więcław et al 2010a, b). Hydrous pyrolysis experiments (Kotarba and Lewan 2013) reveal that the Llandovery source rocks are not contributors to the natural gas accumulations in the Middle Cambrian reservoirs. However, Silurian organic-rich facies are potential rocks for shale gas and shale oil (e.g.…”

“…Moreover, the same type of organic matter occurs within the Visean (Mississippian) and Westphalian (Pennsylvanian) strata where the present TOC contents are up to 2.6 and 2.2 wt%, respectively. Kotarba (2010) and Kotarba and Lewan (2013) made the first attempts to explain the origin of natural gases accumulated in the Middle Cambrian reservoir in onshore and offshore areas of Eastern Pomerania based on hydrous pyrolysis experiments. On the basis of these results, Kotarba and Lewan (2013) concluded that hydrocarbon gases and carbon dioxide were generated within the oil window from Type-II kerogen.…”

“…Kotarba (2010) and Kotarba and Lewan (2013) made the first attempts to explain the origin of natural gases accumulated in the Middle Cambrian reservoir in onshore and offshore areas of Eastern Pomerania based on hydrous pyrolysis experiments. On the basis of these results, Kotarba and Lewan (2013) concluded that hydrocarbon gases and carbon dioxide were generated within the oil window from Type-II kerogen. No isotopic studies of noble gases in natural gases accumulated in the Middle Cambrian and Carboniferous-Lower Permian reservoirs in the Baltic region, which could explain their origin, were carried out.…”

“…However, Silurian organic-rich facies are potential rocks for shale gas and shale oil (e.g. Poprawa 2010; Karnkowski et al 2010;Kotarba and Lewan 2013).…”