CO2驱最小混相压力及其动态变化研究

Study on Minimum Miscibility Pressure and Its Dynamic Variation in CO2 Flooding

针对某低渗油藏,分别采用不同方法计算CO2与原油最小混相压力(MMP),最后给出了一种简单而快捷的MMP计算方法。在CO2驱过程中,MMP不是一个定值,而是动态变化的,针对目标油藏建立CO2驱机理模型,研究CO2驱过程中降压生产、注气量、温度、压力等参数对MMP的影响。结果表明,在降压生产时原油中CH4、N2等挥发性组分的脱出能够使MMP降低,油藏压力每下降1 MPa,MMP降低0.5 MPa;累积注气量越多,驱替压力越大、油藏温度越低,CO2对原油中轻质组分的抽提越严重,剩余油中重组分含量越高,MMP越大。气驱后,原油物性变差,MMP由最初的23.56 MPa增加到278 MPa,地下原油与注入气很难再次达到混相状态,对于CO2驱后油藏的提高采收率措施应该将重点放在提高波及系数方面。

For a low permeability reservoir,different methods were used to calculate the minimum miscible pressure(MMP)of CO2 and crude oil.Finally,a simple and fast MMP calculation method was presented.In the CO2 flooding,MMP is not a fixed value,there is dynamic change for MMP.In view of the target reservoir,the CO2 flooding mechanism model is established to study the effect of the parameters such as pressure decline,gas injection,temperature and pressure on MMP during CO2 flooding.The results show that removal of CH4,N2 and other volatile components in crude oil can reduce MMP.The more gas injected,the greater the displacement pressure is,the lower the reservoir temperature is,the more light components extracted by CO2,and the larger the MMP is.Therefore,the physical properties of crude oil will become worse after gas flooding,MMP increases from 23.56 MPa to 278 MPa after gas flooding and it is very difficult to reach miscibility again.The measures to improve oil recovery after CO2 flooding should focus on increasing sweep efficiency.