The commercial significance of gas hydrates (clathrates) arises from their unique capacity to contain in one volume up to 220 volumes of free gas, suggesting the possibility of exceptionally high concentrations of gas resources at shallow depths.
Total area of occurrence of zones of possible gas hydrate formation in the onshore regions of Russia is 1,700,000 sq km. They are present over an area of 170,000 sq km in the northeast half of Timan-Pechora oil-gas province, 590,000 sq km in the north half of the West Siberian oil-gas province, 326,000 sq km extending over the entire Yenisey-Anabar gas-oil province, 285,000 sq km in the north of the East Siberian oil-gas province, and 374,000 sq km over the entire Lena-Vilyuy gas-oil province.
Thickness of the zones of possible gas hydrate formation ranges from 300 to 1000 m. Rocks of various age are involved, ranging from Cambrian in East Siberia to Upper Cretaceous in the Timan-Pechora province and Paleogene-Quaternary in the north of West Siberia. The rocks involved are sandy-clayey clastics and carbonates.
The most probable sources of the gas of the hydrate zones are accumulations at greater depths from which he gas has migrated upward.
The Greater Urengoy region of the north of West Siberia appears to be a very favorable area for experimental exploration for commercial gas hydrate. Within the region the thickness of the thermodynamically stable zone for hydrates is as much as 300-400 m. The top of this zone is at depths of 200-250 m, and the base is at a depth of 500-600 m. Thickness of the permafrost seal in the region is 200-250 m. The zone of possible gas hydrate formation is in a section that consists largely of clay. Large Cenomanian gas pools are present at 600-700 m below the base of this zone of possible hydrate formation.
Gas hydrates may be present in the permeable sandy rocks of the Tibeysalin Formation of the Paleogene. These rocks are present throughout the Greater Urengoy region. They have porosity of 25-35 percent and are saturated by weakly mineralized formation water. Depth to top of the prospective part of the section ranges from 240 to 380 m. Probable thickness of the possible hydrate-saturated part of the section 100-140 m. Caliper logs show significant cavities. Areas that are of interest for exploration are Samburg, Yuzhno-Samburg, Purov, Yaro-Yakhin, Vostochno-Urengoy, and Ust'-Yamsovey. (Taken from Chelyshev, Kudryavtseva, and Kraychik, 1991; digested in Petroleum Geology, vol. 30, no. 1, 1996, two maps)
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