Geochemical evidence for strong ongoing methanogenesis in Sanhu region of Qaidam Basin

Sanhu depression of Qaidam Basin is the largest biogenic gas production region in China.Headspace samples were collected from two wells in this region,and hydrogen and propylene compounds were detected in these samples with a certain concentration.The stable hydrogen isotope ratio of H 2 is relatively light (-700‰--820‰).The stable carbon isotope ratio of propylene ranges from -27‰ to -40‰,which coincides with the rule of change of the stable carbon isotope of kerogen at the corresponding horizon.The characteristic analysis of sediments,structures,and Ar and He components in the region indicates that these microelement compounds are the product of degradation of organic substances by microorganisms,rather than from the mantle source,inorganic reaction or other sources.Detection of these components provides solid evidence for the strong ongoing methanogenesis in this region.