Outcrops as one of the keys in reconstruction of petroleum system of the Polish Outer Carpathians

Abstract

A petroleum system was recognized in the Gorlice-Bóbrka region of the Outer Carpathians in Poland. Three tectonic units (Dukla, Silesian and Magura) in the area of study are most important for petroleum industry. Several types of sandstone with reservoir potential belong to these units, but only the Istebna and Ciężkowice sandstones from the Silesian Unit were investigated in boreholes. Carefully chosen outcrop sandstones as well as some samples from available boreholes were gathered in the database. Porosity, permeability, capillary pressure investigations, petrography and computer analyses of microscopic images were performed for outcrops and borehole samples. Artificial Neural Net simulation using the whole database gave very good permeability fit for all kinds of sandstones (also from outcrops). It means that all types of sandstones are petrophysically very similar. Detailed investigations show only an insignificant porosity increase for outcrop samples. Petrography investigation provides an explanation for this fact. Circulations of meteoric waters dissolve sand grains, whereas pore throat is not changed. Correlation matrix method was applied to share factors steering petrophysical properties in sandstones from the investigated region. Source rocks responsible for generation of hydrocarbons in the area of study have been identified. Outcrop samples (157) were taken from deposits of the Dukla and Silesian units. Generally, outcrop samples were taken from the Menilite beds located along anticlines in the analysed area. Finally, hydrocarbon potential of the region was evaluated. The weathering effect was taken into consideration.