沥青对CO₂驱最小混相压力影响研究

Study on the Effect of Asphaltene on the Minimum Miscibility Pressure for CO₂ Flooding

摘要: 在现有的提高采收率技术中，注气驱是在聚合物驱、热采、水驱之后，又一个重要的提高采收率的方法，我国低渗油藏较多，采用的注入气绝大多数是CO₂。我国大多数油田普遍存在最小混相压力(Minimum Miscibility Pressure, MMP)高于地层压力的问题，CO₂与原油达成混相的条件下容易造成地层破裂，无法实现CO₂混相驱。在CO₂驱中会产生沥青质沉积，沥青质沉积会严重影响油田开发效果，因此研究沥青对于CO₂驱有重要的实际意义。本文使用油–气–沥青三相闪蒸计算模型和多级混合单元算法(Multiple-Mixing-Cell Method, MMC)计算MMP。随后分别在不同温度、不同压力和不同注入气时观察沥青析出特征及对沥青析出的影响。明确CO₂驱过程中沥青析出对MMP的影响，并给出抑制沥青析出的相关建议。

Abstract: Among the existing enhanced oil recovery techniques, gas injection follows polymer flooding, thermal recovery, and water flooding as another important method for increasing recovery rates. China has a significant number of low-permeability reservoirs, and the injected gas is predominantly CO₂. However, in most oilfields across China, the minimum miscibility pressure (MMP) is higher than the formation pressure, making it difficult to achieve CO₂ miscible flooding as CO₂ and crude oil tend to cause formation fracturing under miscible conditions. During CO₂ flooding, asphaltene precipitation occurs, which severely impacts oilfield development efficiency. Therefore, studying asphaltene is of practical significance for CO₂ flooding. This paper employs an oil-gas-asphaltene three-phase equilibrium calculation model and the multiple-mixing-cell method (MMC) to calculate the MMP. Subsequently, the characteristics of asphaltene precipitation and its influencing factors are observed under varying temperatures, pressures, and injected gases. The study clarifies the effects of asphaltene precipitation on MMP during CO₂ flooding and provides recommendations for mitigating asphaltene precipitation.