低渗透油藏 CO₂混相条件及近混相驱区域确定

Determination of CO2 Miscible Condition and Near-miscible Region Flooding in Low Permeability Reservoir

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

为了探究 CO2在低渗透油藏中与原油的混相条件及在近混相条件下的驱油效果，采用室内物理模拟方法，通过均质、非均质长方体岩心实验，在评价影响 CO2驱油效果的渗透率、岩心长度、渗透率级差和压力因素的基础上，借助采收率与各影响因素参数指标，分析非混相、近混相和混相不同阶段的曲线特征，建立了近混相驱区域的确定方法。采用该岩心实验方法，在模拟油藏条件下，CO2与原油的最小混相压力为 18.5 MPa左右，比传统细管实验确定的17.8 MPa高出0.7 MPa，同时根据驱油曲线特征，划分了CO2非混相、近混相和混相区域，并根据驱油效率确定出近混相驱的压力区域为16.5～ 18.5 MPa。建立的最小混相压力岩心测定方法和近混相驱区域划定的方法，为进一步深化 CO2近混相驱油机理的认识及 YC油田 CO2矿场驱油方案的设计提供了参考。图7参 18

Whether CO2 flooding can be mixed with crude oil under reservoir conditions directly affects the oil displacement efficiency，therefore CO2 miscible and near-miscible flooding in low permeability reservoirs was studied. By conducting CO2 flooding experiment in both homogeneous and heterogeneous rectangular cores，the oil recovery results were acquired through the various series of experiments considering permeability，migration distance，permeability differential as well as the flooding pressure under the simulated reservoir conditions. Therefore，the classification of the immiscible，near-miscible and miscible CO2 flooding in low permeability reservoir was determined by the gas flooding results，and the near-miscible area was also defined. The minimum miscible pressure（MMP）of CO2 with crude oil was 18.5 MPa in this study，which was 0.7 MPa higher than that determined by slim tube experiment（17.8 MPa），a conventional method to determine the carbon dioxide MMP. Based on the displacement curve，the CO2 flooding process was divided into three stages，immiscible，near-miscible and miscible region. The near-miscible pressure of CO2 displacement in YC oil ranges from 16.5 MPa to 18.5 MPa. The MMP measuring of CO2 flooding was determined by core flooding method and the near-miscible flooding region was defined，which offered reference to the further understanding of mechanism in CO2 near-miscible displacement and scheme design of CO2 flooding in YC oilfield.