低渗油藏CO_2驱油混相条件的探讨

CO2与地层油能否达到混相状态对CO2驱油技术的应用效果有重要影响,界面张力法和细管实验法测量的最小混相压力(MMP)存在较大差异。岩心孔隙结构对原油相对体积及CO2密度的影响实验均说明,多孔介质的孔隙特征对流体物性参数产生较大影响,用细管实验MMP值作为油藏条件下CO2-原油体系MMP值的做法也需要理论完善。对影响CO2驱油混相条件的主要因素进行分析,认为岩石孔隙特征、地层压力以及注入流量对多孔介质中CO2-原油体系MMP有明显影响。渗透率下降,测量的MMP值也不同程度地降低;相对而言,平均地层压力较低的油藏,测量的MMP值也较低;对注入流量的研究认为优化流量可获得较低的MMP值。综合分析以上3个因素,初步建立计算多孔介质中CO2-原油体系MMP的方程。该研究将压力分布曲线进一步细化,补充了对不同压力间流体状态的描述。图7表1参11

Miscible conditions of CO2 flooding technology used in low permeability reserviors

Whether CO2 and crude oil in reservoirs are able to be in a miscible state is important in CO2 flooding. Minimum miscibility pressure (MMP) measured by the interfacial tension method is greatly different from that measured by slim tube experiment. The effects of pore structure on crude oil relative volume and density of CO2 show that the pore structure of porous media can affect liquid physical characteristics. Using the MMP measured by slim tube experiments as a MMP in reservoirs need to be proved and improved. Analysis of some major factors affecting miscible conditions reveals that pore structure, formation pressure and injection flow rate affect the MMP of CO2-crude oil in porous media. MMP in porous media decreases with core permeability decrease. A reservoir with low average formation pressures has a relatively low measurement MMP. Lower measurement MMP can be obtained by optimizing flow rate. According to the three factors analyzed above, a equation is formed to calculate MMP in porous media, which makes the pressure curve more precise. Fluid state can be described between different pressures.