Oil-oil and oil-source rock correlations in the northern Vienna Basin and adjacent Carpathian Flysch Zone (Czech and Slovak area)

Abstract

The geochemistry of oils was studied to characterize their origin and possible relationships to the source rocks in the contact region of the Bohemian Massif, Western Carpathians, and the northern part of the Vienna Basin in the Czech Republic and Slovakia. The reservoir depths range from 700 to 6000 m and temperatures from 36 to 150{sup o}C. Their stratigraphic and structural positions comprise the Neogene of the Vienna Basin, underlying Inner Carpathian units, adjacent Carpathian Flysch and foredeep, autochthonous Palaeogene, Palaeozoic, and the crystalline basement of the Bohemian Massif. The genetic potential of the source rocks increases from the Palaeozoic through the autochthonous Palaeogene, and from the Jurassic to the Oligocene Menilite Fm. in the Flysch nappes. The Jurassic and Palaeogene enter the oil window at a depth of at least 3.5 km. Oils were expelled from the source rocks buried deeper than 4-5 km where they have reached maturation levels equivalent to 0.8 to 1.17% vitrinite reflectance. Oil families differ mainly in oleanane content and other indicators of either marine or terrestrial organic facies. Biodegradation of oils occurs in reservoirs at depths down to 1.8 km. The compositions of some of the oils may be explained as a results of evaporative fractionation and gas percolation through the deeper oil accumulations. Mixing of biodegraded oils with allochthonous gas condensates suggests two principal migration events. (Author)