An overview of deepwater petroleum play types of the Black Sea

Abstract

Deepwater hydrocarbon exploration drilling only commenced in the Black Sea less than twenty years ago, mostly due to the economical/technological challenges associated with mobilizing suitable rigs through the Bosporus. However, to date about 20 deepwater wells have been drilled targeting a large variety of plays in this very large underexplored basin complex. The numerous deepwater Black Sea play types can be subdivided into pre-, syn- and post-rift plays. Post-rift play types have proven to be more successful finding either biogenic gas in Miocene to Pliocene reservoirs associated with the Paleo-Danube, or oil in Oligocene deepwater siliciclastic systems. Syn-rift or early post-rift plays, in contrast, assumed mostly shallow water carbonate reservoir targets. Just one well targeted pre-rift stratigraphy. The largest targets are syn-rift fault blocks, such as the Andrusov and Tetyaev highs are in the center of the Black Sea, respectively. Although their internal stratigraphy is still very poorly constrained (i.e. proportion of pre-rift versus syn-rift), translating to not only reservoir presence risk but also to reservoir quality risk, the trap sizes are very large. Also, the assumed lateral charge from the Miocene-Oligocene Maykop Formation and from the Middle Eocene Kuma Formation makes these structures attractive. The overall structure of the Shatsky Ridge in the Russian sector of the basin is complex as it has elements of a large Jurassic carbonate platform with reefs on top. The Polshkov High is unique in the sense that it represents a large rotated syn-rift fault block along the lower plate edge of the Western Black Sea in Bulgaria. On the conjugate upper plate margin, very large inverted syn-rift structures, such as the Kozlu Anticline, are recognized in the Turkish sector. On top of some of these syn-rift highs, various carbonate geometries were interpreted on seismic data which turned out to be associated with Cretaceous volcanism. In the post-rift basin fill several intra-Cenozoic reservoirs are being targeted in the compactional anticlines above the large syn-rift highs. Another play associated with deepwater sands of the Maykop sequence in the deepwater extension of the Subbotina discovery offshore Crimea. The Subbotina structure is just one compressional anticline among many other situated in a dominantly Miocene, south-vergent folded belt offshore Kerch Peninsula. Similar folded belts are also known in the Russian, Georgian, Turkish and Bulgarian sectors of the Black Sea. However, reservoir quality is a definite risk for the Cenozoic reservoir intervals in certain segments of the Black Sea as the function of the corresponding provenance areas. Another new element in the last few years is the recognition of widespread presence mass transport complexes (MTCs) in the paleo-deepwater segments of the Black Sea. Whereas MTCs generally represent non-reservoir units in the basin fill, they could be responsible for some unusual traps. In general, most of the deepwater exploration failures in the Black Sea to date are directly related to the lack of reservoir at the targeted stratigraphic levels. However, the recent discoveries have underlined the presence of at least two active and effective petroleum systems covering large parts of the deepwater Black Sea Basin.

AAPG Datapages/Search and Discovery Article #90325 © 2018 AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin, Lisbon, Portugal, May 2-3, 2018