Geochemical characteristics and origins of noble gases of the Kela 2 gas field in the Tarim Basin, China

Research on noble gases is important which can provide more information on gas origins and sources due to their special chemical inertness and genesis related to nuclear processes. However, few studies have been carried out on noble gases in the largest un-compartmentalized gas field in the Tarim Basin. In this study, molecular and isotopic compositions of noble gases and hydrocarbon gases in the Kela 2 gas field were analyzed. Hydrocarbon gases are the dominant gases, accompanied by minor N2, CO2 and extremely low contents of noble gases in the Kela 2 gas field. He content is generally 1 order of magnitude higher comparing to that of air, while Ne, Ar, Kr, and Xe contents are 1-3 orders of magnitude lower than corresponding atmospheric values. The δ13C2 value indicates natural gases in the Kela 2 gas field are typical coal-derived gases. Noble gases in the Kela 2 gas field are typical crustal derived source, mainly originating from decay of crustal radioactive elements. Natural gases in the Kela 2 gas field are speculated to be derived from the coal measures source rocks of Triassic to Jurassic with major contribution from coals and secondary contribution from mudstones.