Geochemical Study of Oils and Oil Source Rock from the Eastern Drava and Slavonija-Srijem Depressions, Pannonian Basin, Croatia

Abstract

A Middle Miocene oil source rock has been identified by geochemicallogging of exploration wells in the Eastern Drava depression (EDD) and in the Slavonija-Srijem depression (SSD) at the south-east margin of the Pannonian Basin, Croatia. The source rock contains Type II to II/III kerogen and reaches early maturity stage at depths of about 2400 m. The Mesozoic sequences were found either to be absent or to be poor in organic matter within the analysed wells.According to C27-C28-C29 sterane and C27-C28-C29 monoaromaticsteroid distributions, gamacerane indices, C35 homohopane indicesand presence of C30 steranrs, the EDD and SSD oils wrre generatedfrom the same marine source rock. The distribution of homohopanesand high Ni/(Ni + V) porphyrin ratios indicates that the related sourcerock was deposited under suboxic conditions. The oils appear to havebeen generated from the source rock during the early to middle stagesof maturity. The oils are waxy, with pour points up to 30°C and sulphurcontents not exceeding 0.7%.