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Source Rocks of the Paratethys Region (Central Europe to Central Asia): Regional Distribution and Implications for Hydrocarbon Exploration

Abstract

A high number of petroleum provinces with combined remaining recoverable reserves of 95 billion BOE exist in the Paratethys region stretching from Central Europe to the South Caspian Sea.

In the majority of these provinces, the most important source rocks were deposited in a semi-restricted inland sea setting in the Oligocene to Lower Miocene (Menilite Fm., Maikop Grp.). Estimates of the source potential index (SPI) greatly vary from less than 1 ton of hydrocarbons per square metre (tHC/m²; e.g. Hungarian Paleogene Basin) to more than 70 tHC/m² (Eastern Carpathians) in different sub-basins of the Paratethys. Petrographic and biomarker data suggest that these major differences are controlled by organic matter productivity, salinity and redox conditions, as well as by locally changing basin geometries. Significant vertical variations of the source potential reflect short-term palaeoceanographic changes including the “Solenovian Event”, a time of basin isolation, which resulted in brackish conditions in the entire Paratethys during Early Oligocene time.

In addition to Oligo-/Miocene source rocks, various Mesozoic, Eocene and Middle/Upper Miocene source rocks charged a significant number of fields. Compound specific isotopy of n-alkanes (CSI-A) in combination with classical biomarkers turned out to be a powerful tool for oil-source correlations and helps to distinguish oils of different provenance. For example, Oligocene source rocks deposited before the Solenovian Event and during its early stages show a characteristic V-pattern in the North Alpine Foreland Basin (NAFB) and the western Carpathians (WC), when CSI-A data are plotted versus chain length. This helps to distinguish between oils generated from Mesozoic (western part of the NAFB, Lower Oligocene (main part of the NAFB) and Upper Oligocene source rocks (WC).

The Black Sea, a remnant of the Paratethys, is one of the last frontier basins in Europe. CSI-A data shows that oils from the western margin of the Black Sea are generated by Oligo-/Miocene rocks, whereas mixtures of Eocene and Oligocene oils prevail at its eastern margin.