Exploration drilling began in Kyrgyzstan in 1962. During the years 1976-1982 it was concentrated in the southwest part of the Fergana depression, where two fields were discovered: Bashkent and Togap. Both the Bashkent and Togap folds flatten out with depth, and on the top of the Paleogene sediments they are expressed as structural noses that plunge to the west. Although these folds are identical structurally, the composition and quality of the oil are markedly different.
Bashkent field was discovered by well no. 5. A flow of oil was recovered from Oligocene Stratum III in the 1809-1920 m interval. Formation pressure is 236 atm, and density of the oil is 0.864. Yields of oil ranged from 10 to 50 bbls a day. Stratum III here consists of dense, fine-grained sandstone 15-18 m thick. Net pay is 5 m, and porosity is in the 15-25 percent range.
Togap field was discovered by well no. 1. A flow of oil at 40 bbls a day was recovered from Stratum III in the 1310-1320 m interval. Formation pressure is 115 atm, and density of the oil is 0.873. Stratum III here consists of sandy siltstone along with beds of fine-grained sandstone. Thickness is 10-15 m, and net pay is 3.5 m. Porosity is in the 13-21 percent range.
Targets for drilling other than the Fergana depression during the coming decades are the Alay, Talas, Vostochno-Chuy, Issuk-Kul, and Naryn-Chatyrkul depressions.
The Paleogene section of the Alay depression appears to be the same as in the Fergana depression. Further, this depression joins the Cis-Kun-Lun oil-gas-bearing downwarp of China. Three anticlinal structures are known, and geological studies indicate that they may prove to be productive.
The Talas depression is joined on the northwest by the Chu-Sarysuy depression of Kazakstan. Its oil-gas potential has not yet been studied. Several local structres are present, but the stratigraphic section has not yet been worked out. It is possible that this depression is similar to the Chu-Sarysuy depression, where gas fields have been discovered. In the Vostochno-Chuy depression there is interest in pinchouts of Upper Paleozoic and Cenozoic sediments.
The western part of the Issuk-Kul valley has not been drilled, although salt is known in the Neogene section, and thick Upper Paleozoic clastics are present in the mountains around the depression. Methane is found in formation waters of the Carboniferous and Paleogene-Neogene.
The Naryn-Chatyrkul depression was connected with the Fergana depression before uplift of the Fergana Range beginning in the Late Jurassic. Drilling has penetrated Jurassic and unmetamorphosed Paleozoics in the section. Their presence beneath thick Cenozoic deposits suggests that they have an oil-gas potential.
Taken from Usuvaliyev and Toktonaliyev, 1990; digested in
Petroleum Geology, vol. 28, no. 5/6, 1994.
Copyright 2001 James Clarke. You are encouraged to print out this
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