关键词:  松辽盆地南部, 长岭断陷, 营城组, 哈尔金气藏, 混合气藏成因, 含气饱和度分布, 混合气垂向分布

Abstract:

The Harjin gas reservoir (Yingcheng Formation) of the Changling fault depression in the southern Songliao Basin is a mixed gas reservoir of hydrocarbons (CH₄) and carbon dioxide. The present paper discussed the origin of the mixed gas reservoir, characteristics of the gas source and accumulation stage, and showed that the hydrocarbon charging for the Harjin mixed gas reservoir occurred earlier than carbon dioxide, forming a gas reservoir in Neogene as a late-stage accumulation. Based on a physical model of the balance between buoyancy and capillary force in gas reservoirs, a mathematical model on gas saturation distribution of hydrocarbon accumulations，was proposed, which reflects the fundamental principle on the initial gas saturation distribution of the reservoir. Meanwhile, the paper indicated that vertical distributions of different gases in this mixed gas reservoir conformed to the principle of gravitational differentiation, and under homogeneous-medium reservoir conditions, the saturation of carbon dioxide with higher density reduced by degrees from the base to top while that of methane with lower density increased gradually. In porous media of this structural mixed gas reservoir, carbon dioxide occupied bigger pores due to higher density, methane occupied medium ones because of lower density, and the bound water occupied smaller ones. Because of pore geometry variety, CO₂ content at the top is more than that at the bottom in Harjin mixed-gas reservoir.

Key words: southern Songliao Basin, Changling fault depression;Yingcheng Formation, Harjin gas reservoir, origin of a mix gas reservoir;gas saturation distribution, vertical distribution of mixed gases