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Tectonic evolution of the Drava depression and its impact on source rock distribution, hydrocarbon generation and migration

Drava depression is located in the south-western margin of the Pannonian Basin. According to MALVIĆ & VELIĆ (2011) and MATOŠ (2014), Neogene and Quaternary tectonics in the Drava 24 7th International Workshop | Neogene of Central and South-Eastern Europe depression are very complex, due to two phases of transtension (Badenian and Late Pannonian-Early Pontian) and two of transpression (Sarmatian-Early Pannonian and Late Pontian-recent). These tectonic events had huge impact on lithology causing heterogeneities, laterally and vertically, that are particularly important in source rock distribution. There are 20 oil, gas and condensate fields in Drava depression which are according to geochemistry data genetically correlated to source rocks - marls, siltstones and mudstones of Badenian to Panonnian and Lower Miocene age (BARIĆ et al., 1998). The aim of this paper is to assess the impact of different tectonic manifestation on source rock distribution and main processes that caused hydrocarbon accumulation - maturation, generation and migration. Basin modelling can address key questions related to timing of maturation and migration by considering geologically plausible range of kerogen or organic facies in different thermal history scenarios and tectonic models. Source rocks are modelled in clusters according to affiliation to certain tectonic blocks. Quantitative information about thermal subsidence and tectonic vertical movements, heat flow (HF), paleo-water depth (PWD) and sediment water interface temperature (SWIT) changes are decisive because they vary either in time or laterally, having a great impact on source rock maturation (CSIZMEG et al., 2011 ; HORVATH et al., 1986 ; LENKEY et al., 2002). As a result, transformation ratio and maturity maps were compiled for Lower Miocene, Badenian and Pannonian source rocks, revealing large differences in present-day thermal maturity within the Drava depression, also showing differences in time of generation and expulsion up to 4 Ma. 1D models indicate the influence of kerogen type, heat flow history, subsidence and uplift variations on source rock maturation, hydrocarbon generation, timing of expulsion and migration. Based on stable carbon isotope analysis (CHUNG et al., 1988 ; SCHOELL, 1983) hydrocarbons are positively correlated to source rock, suggesting both upward and sidelong migrations from all effective depocenters. Timeline of events is an important factor in hydrocarbon exploration process. For a petroleum system to function formation of traps and seals must precede hydrocarbon expulsion and migration routes should be established (CORVER et al., 2009). Results confirm that basin models contribute to the synthesis of geological, seismic and geochemical data consistently. By defining time of parameters for petroleum occurrence, these models increase exploration efficiency.

Drava depression, tectonic evaluation, source rock

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