Abstract: The natural gas of western sag of Liaohe exploration area is widely distributed and the oil and gas are accompanied with each other. Hence this paper analyzes the migration, accumulation and distribution pattern of the natural gas combining with its composition and source characteristics, the exsolution features of crude oil dissolved gas and petroleum geology condition. Vertically, condensate gas reservoir, oil reservoir, gas cap reservoir, and gas reservoir are distributed from bottom to top successively at the same exploration area. Horizontally, natural gas is mainly distributed in the hydrocarbon generation sags. Dry gas is primarily distributed in the shallow part of the hydrocarbon generation sags and in the slope of neighborhood, while wet gas is distributed at different depths. Dry gas from the First Member to the Second Member of Shahejie Formation is mainly distributed in the hydrocarbon generation sags and their neighborhood, while the dry gas from the Third Member to the Fourth Member is mainly in the slope zone around the sags. The crude oil dissolved gas is the major source of natural gas accumulated in independent phase. There are four different types of natural gas reservoirforming patterns the sags with different structures. Shallow gas is rich in the effective traps over the oil reservoirs of hydrocarbon generation sags; the deep formation of the hydrocarbon generation depression and the salient around are important areas of high maturity natural gas exploration

Key words: natural gas, dissolved gas in crude oil, accumulation model, western sag, Liaohe exploration area