Geology and Hydrocarbon Systems in the Western Black Sea

Authors: GEORGI GEORGIEV

Abstract: This paper presents the author's integrated regional studies during the last decade. The main purpose is to present an overall understanding of the geological structure, sedimentary basins and hydrocarbon systems of the whole Western Black Sea Zone (WBSZ). This study is based on original data from boreholes, seismic and gravity-magnetic surveys and hydrocarbon accumulations. Many geophysical borehole data obtained for WBSZ during the last 3-4 decades were interpreted mostly at a national level using different approaches, terminology and nomenclature for the same or similar lithostratigraphic and tectonic units. Therefore, a unified approach to interpretation of borehole-seismic data and correlation of stratigraphic, sedimentological and tectonic units has a key importance for overall clarification of the deep geological structure and the hydrocarbon challenges. A set of regional geological cross-sections along good quality basic seismic lines and basic boreholes was constructed. A detailed tectonic map of the WBSZ has been compiled by integrated interpretation of seismic borehole and gravity-magnetic data. The definition of hydrocarbon systems and promising exploration trends is made by source rock assessment, Oil-Oil and Oil-Source rock correlations, analyses of the reservoir/seal pairs and the hydrocarbon migration and accumulation. Genetic correlations are based on many Rock-Eval, Gas Chromatography/Mass Spectrometry (GC-MS) and carbon isotope analyses. The complex geological structure of the WBSZ is defined by four groups of tectonic units: (1) Western Black Sea basin (WBSB) - its western zone with the Kamchia and the Histria westward wedging branches (sub-basins); (2) portions of the Moesian, Scythian and East European platforms; (3) fragments of the North Dobrogea, Eastern Balkan, Eastern Srednogorie and Strandzha orogens; (4) Burgas and Babadag basins. Four different oil genetic types have been identified. Three main hydrocarbon systems with economic potential are defined, they relate to: WBSB and its Histria and Kamchia branches, the East-Varna trough and the Bourgas basin. Conceptual models for hydrocarbon systems and their prospect exploration trends are constructed.

Keywords: Western Black Sea Zone, tectonic structure, hydrocarbon systems

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