Deep-water plays in the western Black Sea: insights into sediment supply within the Maykop depositional system
E. V. L. Rees, M. D. Simmons, J. W. P. Wilson, 2018. "Deep-water plays in the western Black Sea: insights into sediment supply within the Maykop depositional system", Petroleum Geology of the Black Sea, M. D. Simmons, G. C. Tari, A. I. Okay
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The Oligocene–Early Miocene Maykop depositional system of the Western Black Sea Basin is investigated in terms of sediment supply and provenance. Potential sediment source regions and conduits for sediment supply into the deep-water portion of the basin are evaluated based on the tectonic history and framework of the region, and are supported by observations from published well, reflection seismic and isopach data. The outcrop geology of the present-day land areas adjacent to the basin is used as a guide to the likely provenance and, hence, quality of potential siliciclastic reservoirs. Reservoir presence and reservoir quality are key subsurface risks for exploration in deep-water plays involving Maykop turbidite sandstones and charge from the well-known Maykop organic carbon-rich mudstones that are widespread across the basin.
Sediments sourced from the NE Moesian Platform and Dobrogea, channelled into the offshore Black Sea via the Histria Trough, are considered moderate risk in terms of primary reservoir quality, as evidenced by thick packages of fine-grained sediment. In contrast, sediments derived from the southern Strandja Massif fed into the Burgas Basin, and potentially into the deeper-water Turkish Black Sea, are relatively low risk in terms of reservoir quality, given the abundance of acidic intrusions within the massif. Sediment derived from parts of the northern Strandja Massif, especially the volcaniclastics of the Srednogornie region, are likely to have poorer reservoir quality characteristics. Sediments derived from the granitic Bolu Massif within the Pontides might be of good reservoir quality but are likely to be ponded behind the offshore Kozlu Ridge. An important sediment source-to-sink system was derived from the Balkanides and entered the deeper-water western Black Sea via the Kamchia Trough. The present-day Kamchia river is a relatively minor sediment supplier to the Black Sea, but the palaeo-Kamchia river of the Oligocene–Early Miocene would have exploited a much greater drainage area consisting of an axial trunk stream, occupying the newly formed Kamchia Foredeep to the north of the Balkanides, and transverse rivers sourcing sediment from the granitic and gneissic bodies of the Balkan Mountains and from Early Cretaceous and Palaeogene sandstones. These would provide reasonable reservoir quality, and it is estimated from reference source-to-sink relationships that offshore sediment flux via this system was probably at least eight times greater than at present. Known shelf-edge canyons in offshore Bulgaria facilitated this sediment reaching the deep water offshore, where a sedimentary fan with a length in excess of 150 km is likely to have developed. This suggests that the potential is good for encountering good-quality reservoir sands in the Maykop succession deep water of the western Black Sea, and this aspect of regional play risk could be of less concern than was previously considered.
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The Black Sea remains one of the largest underexplored rift basins in the world. Future success is dependent on a better understanding of a number of geological uncertainties. These include reservoir and source rock presence and quality, and the timing of migration of hydrocarbons relative to trap formation. An appreciation of the geological history of the Black Sea basins and the surrounding orogens is therefore key. The timing of basin formation, uplift of the margins, and of facies distribution remain issues for robust debate. This Special Publication presents the results of 15 studies that relate to the tectono-stratigraphy and petroleum geology of the Black Sea. The methodologies of these studies encompass crustal structure, geodynamic evolution, stratigraphy and its regional correlation, petroleum systems, source to sink, hydrocarbon habitat and play concepts, and reviews of past exploration. They provide insight into the many ongoing controversies concerning Black Sea regional geology and provide a better understanding of the geological risks that must be considered for future hydrocarbon exploration.