Geochemical features of natural gas in the Qaidam Basin, NW China

Abstract Based on the results of natural gas components, carbon isotopes, and light hydrocarbon components analyses, this paper studied geochemical features of natural gas in the Qaidam Basin. These analyses include the intersection relationships of (1) natural gas methane carbon isotopes (δ 13 C 1 ) and ethane carbon isotopes (δ 13 C 2 ); (2) natural gas ethane carbon isotopes (δ 13 C 2 ) and hydrocarbon exclusive of methane contents (C 2 + ); (3) natural gas methane carbon isotopes (δ 13 C 1 ), ethane carbon isotopes (δ 13 C 2 ) and propane carbon isotopes (δ 13 C 3 ); (4) natural gas light hydrocarbon components and carbon isotopes; and (5) natural gas light hydrocarbon carbon isotopes. Natural gas consists mainly of (1) pyrolysis gas derived from type I and type II kerogen and mixed gas in the southwestern Qaidam Basin; (2) pyrolysis gas derived from type II and III kerogen and mixed gas in the northwestern Qaidam Basin; (3) coal- derived gas in the northern Qaidam Basin; and (4) biogenic gas in the eastern Qaidam Basin.