Sources of Hydrocarbon Gases in the Mud Volcano Kedr, Southern Basin of Lake Baikal: Results of Experimental Investigations

Abstract

Outcrops of the Oligocene-Pliocene coal-bearing Tankhoi suite are traced along the southern shore of Lake Baikal and submerge under its Southern Basin, in which several hydrate-bearing zones of focused discharge of hydrocarbon fluids have been found. To test the hypothesis that coals of the Tankhoi Suite can be sources of hydrocarbon gases in these zones, we collected coal samples from the Shakhterskaya Gorka outcrop. The experiment on gas generation from the selected samples was carried out in a special autoclave at a temperature of 90°C for eight months. This paper presents the results of this study, which confirm the important role of gas generation processes from coals in the formation of fluids in the Kedr mud volcano. Further migration of gases was accompanied by biodegradation and the formation of secondary microbial methane due to CO2 reduction. This was one of the reasons for the observed carbon isotopic pattern in methane (heavier than ‒50‰ VPDB) and carbon dioxide (positive values) taken from near-surface sediments and hydrates of the Kedr mud volcano, as well as for the significant enrichment of authigenic siderites in the heavy 13C isotope.