The principal oil fields of Turkmenistan are located in the West Turkmen depression, which is the eastern part of the South Caspian oil-gas province. All the pools are in Neogene sediments.
In spite of extensive geological exploration in areas of the onshore operating oil fields of the Balkhan region, no large fields have been discovered in recent years, and exploration for Mesozoic oil has been slow in coming. Available geological information suggests, however, that oil pools will be found in carbonates and reef buildups of the Upper Jurassic and Neocomian.
One of the areas of interest for Mesozoic oil and gas is the Cheleken high in the coastal area of Western Turkmenistan.
Cheleken oil has been known since ancient times. Even before the beginning of Our Era oil from Cheleken was exported to areas that are now Iran, Afghanistan, and other countries of the East. Oil was produced from shallow pits and exported in goat skins. Production from pits was recorded in the Eighteenth Century. As of 1900 oil was produced on Cheleken Island by 23 companies including the Nobel Company. Production was discontinued in 1924 but renewed in 1955 after new discoveries.
Cheleken high is a large anticline, which measures 35 by 20 km. Present exploration targets the Pliocene Redbed Unit. Mesozoic rocks have not yet been penetrated by the drill. The oldest rocks drilled so far are are Miocene.
Some fifty years ago the suggestion was made that fragments of Cretaceous and Jurassic rocks might be present in the debris of the mud volcanoes that occur extensively in the region.
In the summer of 1990 samples were collected from the mud volcanoes of the Dagadzhik sector of Cheleken Island to provide information on the nature of the roots of these features. Various rock types were identified: clays, siltstone, sandstone, argillite, carbonates, onyx, and anhydrite. Present among the carbonates are organo-clastic, algal, bryozoan, and coral limestones, the latter occuring as pieces of recrystallized material. Fragments of gastropods, brachiopods, spicules, and foraminifera were found also.
Among several species of foraminifera identified are Triplasia poroviensis Mitjanina, which is a late Callovian form; Epistomina parastelligra Hofk, which is a transitional species of the Callovian- Oxfordian; and Epistomina stelligeraformis Miatljuk, which is an early Oxfordian species of Mangyshlak and the Middle Volga. Age of these rocks is thus dated as Callovian-Oxfordian of the Late Jurassic.
The organic limestones from the debris of the mud volcanes of the Aligul sector of the Cheleken area are very similar in lithologic and faunal composition to the Upper Jurassic carbonates of the Greater Balkhan. The Aligul massif is the highest part of an ancient buried structure, or it is part of a barrier reef, where highly porous reservoir rock should be present. Depth will not be too great. (From Amanniyazov, 1992; digested in Petroleum Geology, vol. 32, no. 3, p. 296-297)
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