Abstract: In Northeast Sichuan Basin, the accumulation elements of different areas of Feixianguan-Changxing Formations are the same, but the enriched degrees of the nature gas vary from region to region. In order to disclosure the enriched mechanism of the nature gas, this paper analyzed the origin of the nature gas in Feixianguan-Changxing Formations, the hydrocarbon generating density of main resource rocks, the characteristics and the scales of the reservoirs, the conservation condition of the natural gas, the history of hydrocarbon generation and the adjusting process of the oil and gas reservoirs with the analyzed and examined data of resource rocks, the data of the cores and lamellas, and the data of the well logging and cutting logging, etc. Results show that: (1)the Northeast Sichuan Basin is in the center of hydrocarbon generation or its vicinity , and the primary migration distances of the oil and gas are short; (2)the lithologic gas reservoirs of reefs and sands are independent, and the distribution of the reservoirs controls the scales of the oil and gas reservoirs; (3)several gypsum mantles cover the natural gas reservoirs and the conservation condition of the natural gas is good; (4)the high temperature made the early oil reservoirs cracked to the present gas reservoirs; (5)with the tectonic movement, the accumulating processes of gas are separated into three steps, the formation of the early oil reservoirs, the cracking of the early oil reservoirs with the formation of the gas reservoirs and the formation of the present gas reservoirs. Discussing the enrichment mechanism of natural gas is useful for finding the beneficial target areas in the Northeast Sichuan Basin when natural gas is explored.

Key words: enriched mechanism, natural gas, Feixianguan Formation, Changxing Formation, Northeastern Sichuan Basin