Quaternary evaporites of biogenic methane gas in the eastern Qaidam Basin, China

Abstract

Biogenic methane is a variety of metabolites generated by methane bacteria, consuming a simple-nutrition organic substrate under anaerobic conditions. Due to the shallow depth at which it is generally produced, biogenic methane is easily released into the atmosphere, becoming a significant contributor to the greenhouse effect. However, if suitable collection methods are employed, biogenic methane can be gathered and used as a clean and efficient energy source. The Qaidam Basin is a large saline lake basin in the Tibetan Plateau, which is rich in biogenetic gas. During the Quaternary period, the area’s sedimentary center moved to the east of the Qaidam Basin. This resulted in the deposition of thick lacustrine sedimentary strata in the basin. Lacustrine mudstone is the primary source rock for biogenetic gas, and as a result, the gas is mostly found in the lacustrine strata of siltstone. In addition, evaporated lacustrine saline calcareous mudstone forms an effective covering layer for the gas. These lacustrine sedimentary strata provide both a favorable hydrocarbon accumulation environment and good preservation conditions for biogenic gas. As such, they could be converted into structural or lithologic gas reservoirs, through biogenic methane lateral migration with a suitable reservoir-cap configuration.