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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. [ABSTRACT FROM AUTHOR]

The principle hydrocarbon source in West Qaidam Basin, China, is the Xiaganchaigou formation, which charges a series of Cenozoic large reservoirs. We identified a series of organic-rich intervals within a sequence of Oligocene-age Xiaganchaigou evaporites in southwest Qaidam. By analyzing 2D and 3D seismic tomography and gamma ray well logs, we defined the distribution and extent of these source rocks. We also characterized their composition with trace element analysis and carbon and oxygen isotope measurements. Our data demonstrated distinctive characteristics of these source rocks with high salinity, abundant organic material, high hydrocarbon generation efficiency, and low maturity, which are associated with relatively rapid and productive hydrocarbon generation. Using high-pressure and high temperature experiments to simulate pyrolysis in samples of the source rocks, we investigated what enabled these young salt-rich source rocks to generate such an abundance of hydrocarbons. Our results highlighted the key role of saline and radioactive minerals in catalyzing accelerated pyrolysis of hydrocarbons during diagenesis and catagenesis. Salt catalysis clearly played an important role in hydrocarbon generation within lower maturity formations and also significantly improved and redefined the source rocks distribution and the extent of probable reserves in the southwest Qaidam. [ABSTRACT FROM AUTHOR]