PARTITION AND CONTRAST ON GENETIC TYPE OF CONTINENTAL NATURAL GAS IN THE SICHUAN BASIN

The paper studies systematically the light hydrocarbon fingerprint, carbon isotope, hydrogen isotope and noble gas isotope of natural gas in the Sichuan Basin. The natural gas carbon isotope C₁-C₂ relationship from different areas and formations show that the natural gas in the Sichuan Basin were affected by parent types of sources rock, maturity, migration and other factors. The light hydrocarbon fingerprint indicates the major source of natural gas in the Western Sichuan Depression is humus-type, the sources in southern Sichuan Basin, eastern Sichuan Basin and the central region of Sichuan Basin are both humus-type and sapropel type, and the natural gas are mainly oil-type gas. The C₁ isotope of natural gas from T₃x₂ in the middle area of the Western Sichuan Depression are higher than other areas and C₂ isotope are less than -28‰, which shows oil-type gas and higher maturity feature. The natural gases of other formations in study area are concentrating distribution relatively and display the typical feature of coal-related gas. The marine and continental natural gas in the Sichuan Basin could be distinguished by carbon isotope δ¹³C₂=-28‰ and hydrogen isotope δD₁=-140‰ of the natural gas. The noble gas isotope shows that the natural gas are shell source without the addition of mantle noble gases.