A zone of possible hydrate formation is understood as a part of a sedimentary section in which thermo-barometric conditions have led to formation and stable preservation of natural gas in a solid state. Favoring this phenomenon are low formation temperature (not greater than 10-15 degrees C), elevated formation pressure, low mineralization of the formation water, and high concentrations in the gas of components that easily form hydrates (carbon dioxide, ethane, propane, iso-butane, and hydrogen sulfide). See News Letter No. 5, August 9, 1999
. Zones of possible hydrate formation are present in Timan-Pechora, West Siberia, Lena-Tunguska, and practically the entire area of Yenisey- Khatanga and Lena-Vilyuy provinces. These zones are trans-regional in character and correspond in general with regions of permafrost. Rocks of various age are involved: Cambrian in Lena-Tunguska province, Upper Cretaceous in Timan-Pechora, and Paleogene in northern West Siberia. The rocks are sandstone, shale, carbonates, and in Lena-Tunguska - tuff.
The tops of the zones of hydrate formation are almost everywhere within permafrost at depths of 200-400 m, and the base is at depth of about 1000 m. Thickness ranges from 300 to 1000 m.
The gas resources of the hydrate zone have been assessed by some as very high. This was attributed to gas dissolved in formation water in connection with repeated vertical migration of the base of the zone during Quaternary glaciation. These gases have been estimated as accounting for 90-95 percent of total resources.
According to some the mechanism for hydrate formation during glacial stages was precipitation of dissolved gas into the solid state; then during warm stages the gas hydrates melted and the gas migrated upward to collect in pools. There are problems with this model, however.
There is a low level - three fold and more - in the amount of gas dissolved in water in connection with hydrate formation. Consequently, there is little probability of substantial gas migration in a significantly undersaturated medium. Gas set free from hydrate will dissolve in water. Experiments have shown that a condition for gas dissolved in formation water to pass into hydrate is an excess of the saturation pressure of water by gas over the equilibrium pressure of hydrate formation in a water-gas solution. The observed gas saturation of the formation waters in the upper parts of the geologic sections in all the oil-gas provinces examined is not high, measured in tens to a few hundred milliliters of gas in one liter of water. The observed gas saturation of the formation water and the thermo-barometric conditions are not sufficient for conversion of dissolved gas into hydrate. The corresponding kinetics to drive this reaction are also lacking - the rate of migration of fluids in sedimentary rocks is extremely slow. The most probably source is catagenic gas that has been introduced by streaming migration.
The most favorable areas for hydrates are the Middle Yamal arch
and Chasel, Nizhne-Pur, and Nizhne-Mesoyakha mega-arches of the
north of West Siberia, the Tanam arch in Yenisey-Khatanga province,
and Khapchagay mega-arch in Lena-Vilyuy province. (Taken from
Kraychil and Chel'shev, 1990; digested in Petroleum Geology,
vol. 30, no. 4, 1996, one map showing favorable zones)
Copyright 2001 James Clarke. You are encouraged to print out this
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