Carbon dioxide flooding is a promising tertiary oil recovery technology in respect both to technical and, if operating costs are properly controlled, to economic benefit. Moreover, the injection of this greenhouse gas also has environmental merits. Flue gas from power plants and natural CO2 gas is the main available source of the CO2 , however, CO2 sources are rarely pure. Purifying the flue gas will increase operating costs significantly. Therefore, understanding the roles of impurities in fluid phase behavior and mis-cibility characteristics is necessary for designing a cost-effective CO2 enhanced oil recovery process. This paper studies the effect of the different impurities in the CO2 stream on the phase behavior and the MMP. With the effect of impurities on the CO2 MMP, it is shown that the presence of intermediate hydrocarbon gas solvents in the CO2 gas stream can reduce the CO2 MMP, whereas, the N2 and CH4 tend to have the opposite effect. EOS simulation is demonstrated to be an effective toll to analyzing the miscibility of oil-gas systems. Core flood tests are conducted to investigate the oil recovery behavior resulting from CO2 injection. The ultimate oil recoveries of the tests show that the miscibility and near-miscibility have the same mechanism. The presence of intermediate hydrocarbon gas solvents in the CO2 gas stream can enhance the ultimate recovery, whereas, the N2 and CH4 tend to have the opposite effect.%二氧化碳驱是一种行之有效的提高采收率的技术,为设计经济可行的二氧化碳驱方案,需要对二氧化碳中的杂质气体对原油相态和驱替效果的影响进行研究.在实验基础上建立了纯二氧化碳一原油体系模型,计算不同杂质气体对该体系的相态影响；采用细管实验和状态方程方法确定最小混相压力,分析杂质气体对最小混相压力的影响；通过拟合长岩心纯二氧化碳驱替实验数据,计算了不同杂质气体对驱替过程的影响.研究结果表明,氮气和甲烷的混入不利于原油降粘和膨胀；最小混相压力随氮气和甲烷摩尔分数的增加而增加,随中间烃组分摩尔分数的增加而降低；中间烃组分能使二氧化碳的驱油效率增加,而氮气和甲烷的存在使驱油效率降低.
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