Geochemical characteristics and play targets of gas in eastern Qaidam Basin, NW China

Abstract

Natural gas exists extensively in the Sanhu region of eastern Qaidam Basin, NW China, where five gas fields and two gas-bearing structures have been discovered and where lots of gas shows have been found. The gas was identified as typical biogenic gas with geochemical characteristics of depleted methane carbon isotope ratios and low abundance of heavy hydrocarbon gas components. The generation of methane is mainly related to the CO2 reduction pathway. The existence of C5-C8 hydrocarbons in gas samples and enriched carbon isotope values of ethane and propane in a few gas samples indicate that natural gas in this region may contain some thermogenic gas. It can be concluded that favorable source rock and conservation conditions exist for the formation of biogenic gas and its accumulation in reservoirs. Expanding this exploration domain, especially paying more attention to reservoirs of shallow and ultra shallow biogenic gas, deep biogenic gas, and deep thermogenic hydrocarbon generation has been suggested for future exploration activities. Key words: Qaidam Basin, Sanhu area, natural gas, geochemical characteristics, exploration domain, biogenic gas