超低渗透油藏CO2驱最小混相压力实验

利用常规方法测量超低渗透油藏CO₂-原油最小混相压力时，存在测量周期长、工作量大等问题，且不能直接观察到CO₂与原油的混相状态。为了确定杏河超低渗透油藏CO₂-原油的最小混相压力，采用界面张力法对杏河油藏CO₂和原油进行室内实验。结果表明：随着平衡压力的升高，原油中溶解CO₂的量增多， CO₂-原油之间界面张力的变化可分为2个阶段，且均呈逐渐减小的线性关系；当平衡压力从4 MPa增大到28 MPa时， CO₂-原油之间的界面张力由17.72 mN/m降到1.56 mN/m。界面张力法测得杏河油藏最小混相压力值为22.5 MPa，略大于细管实验测得的最小混相压力值22.3 MPa，由于二者数值相差仅0.9%，表明界面张力法测量超低渗透油藏最小混相压力具有较好的准确性。通过上述研究，确定了杏河油藏最小混相压力，为杏河油藏注CO₂增产开发方案的制定提供了理论支持，但是由于最小混相压力高于油藏目前压力（17.5 MPa），在目前油藏条件下CO₂与原油不能实现混相。

Experiment of minimum miscible pressure of CO2 flooding in ultra-low permeability reservoir

When measuring the minimum miscibility pressure(MMP)of CO2-crude in ultra-low permeability reservoirs,the conventional method has the problems of long measurement period and large workload,and the miscible state of CO2 and crude oil cannot be directly observed.To determine the MMP of CO2-crude oil in Xinghe ultra-low permeability reservoir quickly and accurately,the interfacial tension(IFT)method was used to conduct indoor experiments on CO2 and crude oil in Xinghe reservoir.The results show that with the increase of equilibrium pressure,the amount of CO2 dissolved in crude oil increases,and the IFT between CO2 and crude oil can be divided into two stages,and both decrease linearly.When the equilibrium pressure increases from 4 MPa to28 MPa,the IFT between CO2 and crude oil decreases from 17.72 mN/m to 1.56 mN/m.The MMP of Xinghe reservoir measured by IFT method is 22.5 MPa,which is slightly higher than that of 22.3 MPa measured by thin tube experiment.The difference between the two values is only 0.9%,indicating that the IFT method has good accuracy in measuring the MMP of ultra-low permeability reservoir.Through the above research,the MMP of Xinghe reservoir was determined,which provides theoretical support for the development of the CO2 stimulation production plan for the Xin he reservoir.However,since the MMP is higher than the current reservoir pressure of17.5 MPa,CO2 and crude oil can’t achieve miscibility under current reservoir conditions.