哈尔金混合气藏成因及气体的垂向分布规律

The origin and gas vertical distribution of the Harjin mixed-gas reservoir

松辽盆地长岭断陷哈尔金气藏(营城组)是烃类(CH4)与CO2混合气藏。对哈尔金混合气藏成因、气源特征及成藏期次研究表明,该混合气藏是烃类先于CO2注入,气藏定型于新近纪,属晚期成藏。根据天然气在气藏中浮力与毛细管力平衡的物理模型,推演出烃类气藏含气饱和度分布的数学模型,该模型反映了储层中原始含气饱和度分布的基本原理。混合气藏中各种气体垂向分布符合重力分异原理,在均匀介质储层条件下,从气藏的底部向顶部,密度较大的CO2饱和度逐渐降低,而密度相对较小的CH4饱和度逐渐增加。在构造混合气藏的多孔介质储层中,密度大的CO2气占据较大的孔隙部分,密度相对较小的CH4气占据中等孔隙部分,而束缚水占据较小的孔隙部分。哈尔金混合气藏顶部CO2含量高于底部是由于储层孔隙结构的变化所致。

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.