The Amu-Dar'ya gas-oil province extends over an area of 360,000 sq km in central and eastern Turkmenistan and western Uzbekistan. The province extends to the southeast into Afghanistan, where it covers an additional 45,000 sq km. This province coincides with the eastern half of the Turan platform. Exploration began in the region in 1929. The period from 1935 to 1952 was a time of various geological and geophysical surveys. The first discovery was Setalantepe gas field in 1953. The province is gas-prone. See also News Letters 22, 25, 42, and 89, and also U.S.G.S Open-File Report 88-272.
Five reservoirs and five seals are recognized from the top downward in the stratigraphic section of the sedimentary cover in Turkmenistan.
The lower Turonian seal is at relatively shallow depths on the Central Kara Kum high in the western part of the province to -1600 m to its south on the Bakhardok monocline. Then in the middle of the basin it is at -2400 m in places. The rock consists largely of clay and is generally 300-400 m thick. Where absent, Senonian sediments act as a seal.
The Albian-Cenomanian reservoir complex ranges in depth from -500 to -800 m on the Central Kara Kum hhigh to -2400 m in the Murgab depression in the southeast part of the province. Maximum thickness is about 700 m. It is largely siltstone and sandstone and is commercially gas-bearing in several areas.
The upper Aptian-lower Albian seal is at depths of -800 to -1200 m; it is deepest at -2900 m in the Murgab depression, where it is 300-400 m thick. Elsewhere it is thinner. It has a clay and clay-sand composition.
The Aptian reservoir complex dips regionally to the southeast. Thickness is not persistent, being absent in some places, 100 m thick in the Murgab depression, and 300-400 m in the Cis-Kopet Dag foredeep on the southwest border of the province. It consists of dolomite, marl, and sandstone in the Murgab depression, whereas sand-silt varieties predominate on the Central Kara Kum high and to its east. The main pools of the Central Kara Kum high are in Aptian reservoirs.
The Barremian seal underlies the Aptian reservoir complex. Its is at -1600 to -2000 m depth on the Central Kaara Kum high to -3000 m in the Murgab depression. Thickness is not more than 40-70 m, and the rock is largely clay.
The Neocomian reservoir complex is at depth of -1600 m on the Central Kara Kum high to -2800 m in the Murgab depression. Thickness is 200-400 m. The section is largely carbonate in the Murgab depression and clastic on the Central Kara Kum high. The Shatlyk formation contains the main gas reserves of this complex. Some oil has also been recovered.
The Kimmeridgian-Tithonoan seal contains a thick salt unit up to 1200 m thick, pinching out to the southwest. It is at -2800 to -3200 m depth.
The Callovian-Oxfordian reservoir complex is at depth of -4000 m and more. Thickness ranges from 200 to 1000 m. Limestone and dolomite make up the section. A whole series of gas fields are present in this play.
At the base of the Callovian is the lower Callovian seal, a clay unit 100-150 m thick. It appears to be at depth of -5000 to -7000 m.
The Lower-Middle Jurassic reservoir complex consists of limy sandstone, siltstone, clay, and argillite. Commercial gas pools have been found in several areas.
Taken from Khodzhakuliyev and Abukova, 1985; digested in Petroleum
Geology, vol. 25, no. 3/4, 1991, two maps showing distribution of
reservoirs.
Copyright 2001 James Clarke. You are encouraged to print out this
News Letter and to forward it to others. Earlier News Letters are
available at: http://geocities.com/internetgeology/
This News Letter is distributed wirhout charge in the interest of our
science of petroleum geology. To be added to the distribution list,
please send your e-mail address to: jamesclarke@erols.com
For information of the journal Petroleum Geology, please telephone
703-759-4487 or FAX at 703 759-3754.