OIL OIL AND OIL SOURCE-ROCK CORRELATIONS IN THE CARPATHIAN FOREDEEP AND OVERTHRUST, SOUTH-EAST POLAND

The chemical composition of 35 crude oils and the extracts of potentia l source rock samples from south-east Poland were studied in detail by geochemical methods in order to understand their genetic relationship s. Twenty-six oils, including three seep samples, were collected from Cretaceous to Oligocene reservoirs within the Carpathian Overthrust. N ine oils originated from Carboniferous to Miocene reservoirs within th e Carpathian Foredeep. The rock samples studied were selected after Ro ck-Eval pyrolysis screening of a large suite of samples and consist of one Lower Cretaceous sample and five Oligocene Menilite shale samples (from three different outcrop locations all within the Carpathian Ove rthrust). Geochemical fingerprinting indicates at least two families o f crude oils: the first, represented only by one oil, has no specific characteristics except for a light carbon isotope composition; the sec ond family is characterized by the presence of 28,30-dinor-hopane, ole anane and a highly-branched isoprenoid C25 alkane. Within this latter family four subfamilies were recognized: (A) 19 oils having the aforem entioned characteristics, (B) seven oils similar to subfamily A, but w ith a relatively high sulphur content, (C) one oil with high abundance of higher-plant derived triterpanes, and (D) seven oils with abundant 28,30-dinor-hopane. Although maturity influences the relative abundan ce of 28,30-dinor-hopane, it suggested that subfamilies A, B, and C ha d an initial low 28,30-dinor-hopane content, whereas subfamily D an in itial high 28,30-dinor-hopane content. Only one oil of subfamily A cou ld potentially be a high maturity counterpart of subfamily D. A Palaeo zoic source rock is suggested for the first family, and the second fam ily, including the majority of the oils from the Carpathian Foredeep, is most likely derived from the Oligocene Menilite Shales. An oil/sour ce rock relationship with the Menilite Shale is supported by the prese nce (although not in all samples studied) of 28,30-dinor-hopane, olean ane or its precursors, and the highly-branched isoprenoid alkane. The strong facies variations observed within this shale gave rise to the d ifferent types of crude oils in the second family.