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Cretaceous Plays of the Black Sea

Abstract

The Black Sea retains an abiding fascination for petroleum geologists. Large structures, seepage, widespread sources rocks, and producing fields around its margins invite serious consideration of its exploration potential notwithstanding the challenges of drilling in deep water. A wide variety of Cretaceous play types occur with the Black Sea Basins. These include pre-rift platformal and reefal carbonates; syn-rift clastic systems including lowstand deltas and fans; post-rift carbonate platforms on localised highs. These plays relate to the geodynamic history of the Black Sea. Whilst its early (Triassic/Jurassic-Early Cretaceous) history as part of the Izanca Ocean and the passive margin of northern Tethys is reasonably clear, debate still rages on the timing of the opening of the eastern Black Sea vs. the western Black Sea and the creation of oceanic crust. Some models postulate East Black Sea opening during the mid-Cretaceous (synchronous with the western Black Sea) – others a Late Cretaceous - Eocene opening. Each model has implications for petroleum systems development and thermal history. Early Cretaceous rifting in the western Black Sea may have led to localised potential source rock deposition in syn-rift successions, but further offshore and in the Eastern Black Sea it is the Oligo-Miocene Maykop Formation and equivalents that will provide charge. Outcrop data provides insight in the richest horizons within this (at its base) which is a valuable input into petroleum systems modelling. Reservoir presence and quality remains a key risk. The Late Jurassic-Early Cretaceous platform carbonate succession provides a superficially attractive target (including much publicised reefal build-ups) but the sequence stratigraphy of these carbonates as gleaned from outcrops can identify other reservoir facies and provide clues to the karstification and diagenesis of this succession and implications for reservoir quality. Intervals within the Valanginian and Aptian all contain potential lowstands (and subsequent transgressive sand sheets) worthy of consideration. Provenance from arc-related volcanics and ophiolites is an issue around the Turkish and Georgian margin, whilst provenance from metamorphosed flysh is an issue on the Ukrainian margin. Sands derived from the Russian/Ukranian Shield or local granitic sources in the Russian Caucasus offer better prospects of good sand quality.