CO₂与原油接触时会发生传质现象直到两相组成相似，此时界面张力消失，即达到混相。最小混相 压力（MMP）是CO₂混相驱的重要参数之一，目前主要采用细管实验法来确定其大小，但该方法费时费力， 而经验公式法又存在较大的局限性。利用PR 状态方程确定了气、液达到平衡时的各组分组成，并结合混 相函数计算出了此时的MMP 值。实例表明：与经验公式法相比，由PR 状态方程计算出的MMP 值最接 近细管实验值；混相函数的迭代精度对计算出的MMP 值影响较大。

When carbon dioxide comes in contact with oil, the mass transfer phenomena occur. The compositions of two phases become similar, and the interfacial tension disappears, and then gas and oil form miscible. The minimum miscibility pressure（MMP） is an important parameter in CO₂ injection process. There are manymethods for the determination ofMMP, and the slimtube test is the most widely used one. However, the experiments are time-consuming, and the empirical formula has great limitations. Thus the PR equation of state ofMMP determined for CO₂ flooding is a good choice. The composition of each component could be determined by the PR equation of state when the gas-liquid phase achieves balance. MMP could be calculated by using the miscibility function. The result shows that the MMP determined
by PR equation of state is more accurate than that by empirical equations. The iterative precision of the miscibility function has a significant impact on the result.