Experimental Study on The Influence of Different Concentrations of Impurity Gas on The Effect of CO₂ Enhanced Oil Recovery

CO 2 injection technology is an effective enhanced oil recovery (EOR) method and also helps mitigate the greenhouse effect. However, CO 2 from different sources often contains impurities such as N 2 , CH 4 , C 2 H 6 , CO, and SO 2 , which can impact its oil displacement efficiency. This study investigates the effect of various impurities on CO 2 -driven oil recovery by conducting core flooding experiments with CO 2 gas mixtures of varying impurity concentrations. The results show that, compared to pure CO 2 , the oil displacement efficiency of N2 and CH 4 is approximately 40% lower. As the concentrations of CH 4 and N 2 increase in the gas mixture, the oil displacement efficiency continuously declines, although the time to observe oil production significantly increases. Of these, for every 10% increase in CH 4 concentration, the oil displacement efficiency decreases by about 2.6%, with N 2 having a greater impact on oil displacement efficiency than CH 4 . Furthermore, N 2 has a more significant negative impact on oil displacement efficiency than CH 4 . The addition of C 2 H 6 to CO 2 improves the oil displacement efficiency, and when the C 2 H 6 concentration reaches 15%, the efficiency surpasses that of pure CO 2 injection. Additionally, small amounts of SO 2 and CO have minimal effects on CO 2 injection efficiency, but caution should be exercised during injection to prevent potential physicochemical damage to the reservoir. This study enhances the understanding of how CO 2 containing impurities affects oil displacement efficiency and offers practical guidance for optimizing CO 2 injection composition in industrial applications.