HYDROCARBON GASES OF THE GOREVOI UTES UNDERWATER OIL-GAS SEEP (Lake Baikal, Russia)
G.V. Kalmychkov1, A.V. Egorov2, A. Hachikubo3, O.M. Khlystov4
1A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovkii pr. 36, Moscow, 117997, Russia
3Kitami Institute of Technology, 165 Koen-cho, Kitami 090-8507, Japan
4Limnological Institute, Siberian Branch, Russian Academy of Sciences, ul. Ulan-Batorskaya 3, Irkutsk, 664033, Russia
Keywords: Hydrocarbon gases, methane, oil, Lake Baikal
Abstract
We investigated the molecular and stable isotope compositions of hydrocarbon gases of the Gorevoi Utes oil-gas seep (Lake Baikal) characterized by a simultaneous discharge of oil and gas from the lake floor. It has been found that these hydrocarbon gases are mostly thermogenic methane (δ13С-С1 = -53.9 to -38.8‰; δ13С-С2 = -23.4 to -33.3‰). At the same time, the gases have a minor amount of С2+, seldom reaching 10%. The С1/С2+ value varies from 9 to 2700, with the average value being 807, which is atypical of petroleum hydrocarbons. We suggest that degassing of oil leaking to the lake floor affects the molecular composition of such gases. Some secondary processes, primarily molecular fractionation of gas during its migration into the subsurface sediments and anaerobic biodegradation of methane homologues, contribute to the decrease in С2+ content.
DOI: 10.15372/RGG2019110
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