Noble gas constraints on hydrocarbon accumulation and groundwater flow in the central area of Western sichuan basin

摘要

The noble gas concentrations and isotope ratios of seven natural gas samples from the central area of the Western Sichuan Basin were measured. The samples all have 40_Ar/36_Ar ratios greater than the atmospheric values, and the 3_he/4_he ratios (R/Ra) are entirely consistent with the crustal radiogenic He values. The vertical variation of the calculated CH_4/36Ar ratios with depth clearly indicates that the Ch_4 and 36Ar are intimately associated, indicating a common reservoir intermediate to the sampled reservoirs, where they are well mixed and stored together prior to en- trapment into gas reservoirs.