N₂对非纯CO₂驱油效果的影响

N₂是驱油用CO₂中常见的杂质气体，N₂的存在会影响最小混相压力（MMP）和CO₂驱的效果。采用延长油田原油和岩心进行了细管实验和岩心驱替实验，注入4种摩尔分数分别为0，5%，10%，15%的N₂与CO₂混合气体，根据细管实验确定MMP；采用高于纯CO₂的MMP 20%的压力和等于MMP 50%的压力进行岩心驱替实验。细管实验结果表明，N₂的存在会显著增大MMP，CO₂中含摩尔分数5%的N₂会使MMP增大29.34%，10%会使MMP增大64.07%；岩心驱替实验表明，N₂的混入对CO₂驱产生了不利影响。对于CO₂混相驱，N2的摩尔分数越高，采收率的提高值越低，N₂的摩尔分数对非混相CO₂驱的影响较小。

N₂ is a common contamination in CO₂ resources and it can influence the minimum miscibility pressure(MMP) and displacement efficiency of CO₂ flooding. In this paper, the crude oils and cores from Yanchang Oilfield in China are used to carry out slim tube experiment and core displacement experiment. The mol concentration of N₂ in CO₂ vaires from 0 to 15%. A pressure of 20% higher than pure CO₂ MMP is used to ensure miscible condition and a pressure of 50% equal to pure CO₂ MMP is used for immiscible condition in core flooding experiments. Slim tube experiment results show that the existence of N₂ increases MMP. The mol concentration of 5% of N₂ in CO₂ increases its MMP by 29.43%; the mol concentration of 10% of N2 in CO₂ increases its MMP by 64.07%. Core flooding results show that the existence of N₂ in CO₂ gas makes the CO₂ flooding performance worse. For miscible CO₂ flooding, the higher the CO₂ content is, the lower the incremental recovery is and the less the effect of the mol concentration of N2 on immiscible CO₂ flooding is.