Carbon isotope characteristics of natural gas in the Sichuan Basin, China

摘要

There are over ten gas-producing beds and six main gas-generating rock intervals in the Sichuan Basin in the middle of China. In this paper, carbon isotopic data of natural gas from different regions and reservoirs were studied. The δ~13C value of most gas samples show the pattern of δ~(13)C_1<δ~(13)C_2< δ~(13)C_3<δ~(13)C_4, indicating their biogenic origin. Samples with δ~(13)C_1 δ~(13)C_2 might be a mixture of gases from different source rocks or of different maturity. The δ~(13)C value of humic gas is more negative than that of sapropelic gas. The δ~(13)C value of the analyzed CO_2 indicates it is of biogenic origin.