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Russian Geology and Geophysics

2002 year, number 7

NATURAL GASES OF BAIKAL

V. P. Isaev, N. G. Konovalova, and P. V. Mikheev
Keywords: Baikal, Selenga delta, Ust'-Selenga depression, gas shows, openings in ice, mud volcanoes, gas hydrate layer, gas-bearing basin
Pages: 638-643

Abstract

Natural gases emanating from the bottom of Baikal occur nearly ubiquitously along the shore, but their maximum concentration is observed at the front of the Selenga delta. In spring, the gas outputs are visible in the form of openings in the Baikal ice. Study was given to 54 openings. The gases are represented mainly by methane (75 vol.% on average), but highly nitrogenous types also occur (80 vol.% on average).
In addition to the explicit discharge of gases in the form of openings, the implicit discharge of gases exists throughout the Ust'-Selenga depression (USD). The chemical types of gases show areal zoning: from nitrogen on the piedmont periphery of the depression to methane in the near-shore band of the modern delta.
Joint analysis of geological, geophysical, and geochemical information proves that the USD sediment is a powerful source of generation of hydrocarbon gases and the similarity of its geologic structure with the South Caspian depression suggests the presence of "mud" volcanoes in Baikal.
A total of Cenozoic depressions of Baikal joint with its sedimentary bed is a potentially gas-bearing basin. Hydrocarbons are generated chiefly at the Baikal bottom, whereas the Selenga delta and other depressions are zones of their transit and accumulation. A regional cap for the natural reservoirs beneath the Baikal bottom may be a gas hydrate layer. Oil fields are hardly possible there, because all the studied gases are extremely dry and the bitumen contents in the USD sediments and grounds are very low. The reported facts and arguments permit the Baikal geology to be considered anew.