The degassing of mantle is a continuous global process. The hydrocarbon as well as other gases in the deep earth continuously inject into the crust in an area of weakness. In some suitable areas, it will form commercial natural gas pool. The reserves of abiogenic natural gas will be much more than explored reserves in the world. The upwilling of mantle matter, intensive magmatic activity, and development of deep faults in the Songliao basin provide favorable condition for the migration and accumulation of mantle volatile. Helium isotopic ratios of commercial natural gas reservoirs inlhe basin show that it is a mixture of crust and mantle source helium. Owing to the influence of lithology and age of reservoix- and the magmatic activities in the basin, the proportion of mantle helium in commercial natural gas varies in a large range, but most commercial natural gases contain significant mantle helium. The statistical analysis of methane δ~(13)C values indicate that δ~(13)C_1 of 24 % out of 107 commercial natural gas samples are much heavier than those of biogenic methane. It shows the isotope characteristics of abiogenic methane. The δ~(13)C patterns of methane and its homologous in several commercial natural gas wells are δ~(13)C_1 > δ~(13)C_2 > δ(13)C_3 > δ_(13)C_4, which are different from those of biogenic natural gases (δ~(13)C_1 < δ ~(13)C_2 < δ_(13)C_3 < δ~(13)C_4). According to the statement about abiogenic natural gas, the geological tectonic setting of the Songliao basin, the contribution of mantle helium, δ~(13) C_(CH_4) > -25‰ and the carbon isotopic distribution patterns for methane and its homologous can be acted as full proofs of the formation of abiogenic commercial natural gas pool in the Songliao basin.
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