岩心驱替实验法测定低渗透油藏 CO₂近混相最小混相压力

Determination of Minimum Miscible Pressure in Carbon Dioxide Near-miscible Region in Low Permeability Reservoirs by Core Displacement Experiment

赵凤兰 张 蒙 侯吉瑞 侯利斌 郝宏达 王 鹏 鲁国用

ZHAO Fenglan ZHANG Meng HOU Jirui HOU Libin HAO Hongda WANG Peng LU Guoyong

CO2在驱油过程中能否与原油达到混相，直接影响驱油效果和最终采收率。因此需对 CO2在低渗透油藏中与原油的混相条件及近混相区域中最小混相压力进行系统研究。选取 YC油田低渗目标区块，以室内油藏物理模拟为基础，通过均质和非均质长方形岩心实验，在评价影响 CO2驱油效果的渗透率、采收率、驱替速度、气油比和渗透率级差的基础上，建立了测定最小混相压力的岩心驱替实验法。结果表明，该方法重复性好，可模拟低渗超低渗孔隙介质以及油藏非均质等性质，在模拟 YC目标区块油藏非均质条件下测得 CO2与原油的最小混相压力为 18.5 MPa，与数值模拟软件计算结果相同，比传统细管实验测值 17.8 MPa高出 0.7 MPa。两种方法所测结果基本一致。用岩心驱替实验法可以探究渗透率及其非均质性和驱替速度等不同因素对最小混相压力的影响规律。该岩心驱替实验方法可用于确定 CO2近混相驱最小混相压力，为深化 CO2近混相驱油机理的认识及矿场应 用提供技术基础和理论指导。图 11表 1参22

Whether CO2 flooding could mix with crude oil under reservoir conditions directly affected the oil displacement efficiency. Therefore the miscible conditions between CO2with crude oil and the minimum miscible pressure in miscible region were studied systematically in low permeability reservoirs. Selecting the low permeability target block in YC oilfield and under the simulated reservoir conditions，CO2 flooding effects were acquired through the various series of experiments considering permeability，recovery，displacement velocity，gas-oil ratio，permeability differential as well as flooding pressure by flooding experiment in both homogeneous and heterogeneous rectangular cores. The method to determine the minimum miscible pressure by core experiment was established. The results showed that the method had good repeatability and could simulate low permeability or ultra-low permeability porous media and reservoir heterogeneity. The minimum miscible pressure was 18.5 MPa under the simulated reservoir conditions，which was the same as the calculation result of numerical simulation software and was 0.7 MPa higher than that of the traditional slim tube experiment. It reflected the consistency with two methods for the minimum miscible pressure. The effect of different factors，such as permeability，heterogeneity and displacement velocity on the minimum miscible pressure by core displacement experiment were studied. The core displacement experiment method could be used to determine the minimum miscible pressure in near-miscible region，which could deepen the mechanism realization of CO2 near-miscible flooding and offer technological base and theoretical guidance for field application