Abstract:CO2-enhanced oil recovery (CO2-EOR) improves oil displacement efficiency and facilitates effective CO2 sequestration. However, in practice, the minimum miscibility pressure (MMP) between CO2 and crude oil often exceeds the formation's fracture pressure. Thus, reducing the MMP is critical for enhancing oil recovery efficiency. This study experimentally investigates how alcohol-treated CO2 affects the interfacial tension (IFT) and MMP in CO2-alkane systems. Initially, the effects of pressure and temperature on the IFT of the CO2-n-hexadecane system were systematically examined. Results show that, at constant temperature, IFT decreases with increasing pressure due to the enhanced solubility of CO2 in n-hexadecane. Below 3 MPa, IFT decreases with rising temperature, whereas above 3 MPa, it increases—highlighting that IFT is influenced by both temperature and CO2 solubility. Comparative analysis reveals that CO2-n-hexadecane systems exhibit consistently higher IFT than CO2-n-dodecane systems. This is attributed to the longer carbon chain and stronger intermolecular forces of n-hexadecane, which reduce its miscibility with CO2. Subsequently, the effect of alcohol-treated CO2 on IFT was assessed. In the high-pressure region (>6 MPa), CO2 treated with ethanol or isopropanol significantly reduces IFT, while the effect is negligible at lower pressures. This behavior stems from increased CO2-alcohol solubility at high pressure, enhancing alcohol interaction at the interface and reducing IFT. The CO2-n-dodecane system treated with ethanol also demonstrated notable IFT reduction, with a progressive decrease as pressure increased. The absence of abrupt changes suggests a steady interface modification, facilitated by ethanol’s high solubility in n-dodecane and the shorter carbon chain of n-dodecane, which promotes alcohol adsorption and alignment at the interface. Finally, MMPs of the CO2-n-hexadecane system under different treatments were determined via linear extrapolation. Alcohol-treated CO2 notably reduced MMP, especially at elevated temperatures. At 70 ℃, ethanol and isopropanol treatments reduced MMP by 20.16% and 24.28%, respectively. At 100 ℃, reductions were 13.74% and 22.67%. Isopropanol was more effective than ethanol, likely due to its longer hydrocarbon chain and stronger interfacial adsorption capacity. This study elucidates the mechanisms by which alcohol-treated CO2 interacts with alkane systems to reduce IFT and MMP, offering valuable experimental insights for optimizing CO2-EOR applications. Close-