Tuapse

Tuapse Downwarp, Black Sea, Russia

Internet Geology News Letter, No. 15, October 18, 1999

The Tuapse downwarp lies offshore in the Black Sea parallel to the coast from Novorossiysk past Tuapse to Sochi. It is about 60 km wide and 250 km long, and water depth is in general 2,000 m. It is located immediately south of the Caucasus Range. Thickness of the Cenozoic section here has been estimated at 6-14 km. Parallel on the south of the Tuapse downwarp is the Shatsky Ridge, an anticlinal structure expressed in the sea-floor topography by a small area where water depth is less than 2000 m. Tugolesov and others (1985) gave a rather high appraisal for the Jurassic, Cretaceous, Paleocene, and Eocene of the Shatsky structure. For the Tuapse downwarp, however, they allocated only small pools in Miocene and Pliocene sediments - this because of absence of suitable folds and the predominance of stratigraphic traps.

A study by Glumov and Viginskiy (1999) assesses the potential of the Tuapse downwarp using the volume-genetic method. The West Kuban downwarp just north of the Caucasus Range is taken as an analog. Clays of the Oligocene-Miocene Maykop Series are the source beds. The ratio of volume of Maykop sediments of the Tuapse downwarp to that of the West Kuban downwarp is placed at 3.8 (53,500 to 14,100 cu km). On this basis the total hydrocarbon resources of the Tuapse downwarp are assessed as 6.5 billion tons (45 BBOE). This figure, however, is probably much too optimistic because the Maykop source beds of the downwarp are largely immature due to a very low geothermal gradient.

More than 50 local highs have been recorded by seismic surveys in the Tuapse downwarp. Many are caused by clay diapirs. They range in length from a few kilometers to 20-25 km. These are grouped in zones that have a general Caucasus trend. Bright spots on the seismic records indicate presence of gas pools. The Miocene-Pliocene section is regarded as the most favorable for discovery (Petroleum Geology, vol. 34 no. 1, p. 67-73, 2000, in press).

Lateral migration in the Black Sea is extremely important such that there is considerable potential for oil and gas along its margins. The Tuapse downwarp, however, is in the migration shadow of the Shatsky Ridge. This in addition to immaturity of the Maykop source beds detracts from the potential of this downwarp; however, the possibility of charge from a source rock deeper than the Maykop in the Tuapse downwarp cannot be discounted. (Eugene Iwaniw, personal communication). See also Robinson and others, Marine and Petroleum Geology, vol. 13, no. 2, p. 195-225, 1996.

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