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Deep Oligocene Reservoirs as Potential Oil Play in Deep Waters of Western Black Sea Basin

Abstract

The Western Black Sea Basin (WBSB) is still considered as exploration frontier despite the fact that gas and oil production in the shelfal areas of Turkey, Bulgaria, Romania and Ukraine has more than 20 years of history. The reservoirs on the shelf are predominantly pre-Oligocene in age. The recent Domino-1 well with its gas discovery offshore Romania expanded the exploration frontiers into deep waters but with pre-dominantly Upper Miocene to Pliocene gas reservoir targets. The Oligocene sequence comprising the bulk of the well-known Maykop Formation is considered as the main source rock and also the reservoir in an oil play in the Eastern Black Sea Basin (EBSB). The oil tested at the Subbotina discovery (offshore Ukraine) has confirmed the Maykop as the key play element in that area. The Subbotina play is expected to extend along strike to the Tuapse foredeep, following the Great Caucasus–Crimea fold belt. The WBSB is sandwiched between the East Carpathian Belt to the NW with proven Oligocene (Menilite Formation) oil plays and to the East by the emerging Maykopian play in the EBSB. The overall Oligocene morphology and deposition environment have strongly benefited from the evaluation of a regional seismic program in the Black Sea (a long-offset and deep recording 2D multi-client survey acquired during 2012). 3D basin modeling results confirm that the Maykop section is in the early oil to wet gas window in the deeper part of the Romanian Black Sea and is getting more mature towards the central parts of the basin. The expulsion of hydrocarbons has started during the Late Miocene and is ongoing today. Two major sediment suppliers are recognized in the WBSB: Histria Trough in the NW along the prominent Peceneaga-Camena Lineament and through the Kamchia foredeep and Kaliakra Canyon in the SW. The NW sediment supply is interpreted to provide quartz-dominated reservoirs, whereas the SW sediment supply may have a higher lithic content having a different provenance area. Based on seismic facies analysis, the Lower Oligocene strata in the deepwater WBSB may have more reservoir intervals than Upper Oligocene. The expected Oligocene targets are deeply buried and tend to form combination traps. The most important targets are structural traps formed during several inversion phases, such as during the Late Oligocene and post-Miocene times.