缝洞型油藏注烃气提高采收率参数优化数值模拟研究

Enhanced oil recovery and parameter optimization of hydrocarbon injection in fractured-cavity reservoirs

缝洞型油藏储集空间多样、非均质性极强、油水性质差异大且水驱非混相氮气驱流度比大,水窜气窜严重、波及范围有限,一次采油和二次采油阶段原油采收率远低于碎屑砂岩油藏。以塔河油田S91缝洞单元为对象,在地质建模、历史拟合、剩余油表征和相态实验拟合基础上,开展缝洞型油藏注烃气提高采收率数值模拟研究,评价缝洞型油藏烃气混相条件,优化注烃气提高采收率参数。结果表明:S91单元注入烃气与地层原油最小混相压力为42.5 MPa,在目前地层压力下可以实现混相,混相机理为汽化气驱,随注入气重烃组分含量增加至21%,最小混相压力为35.62 MPa,采收率增幅到最大值。注气方式为裂缝型储集体注气,溶洞型储集体采液,注气参数优选注气量168×10^(4) m^(3)、注气速度4×10^(4) m^(3)/d及注采比1∶0.9。

Fractured-cavity reservoirs have diverse storage spaces,strong heterogeneity,large differences in oil-water properties,high mobility ratio of immiscible nitrogen flooding in water flooding,serious water and gas channeling,limited sweeping range,and primary and secondary oil recovery stages.Oil recovery is much lower than that of clastic sandstone reservoirs.Taking the S91 fracture-cavity unit in Tahe Oilfield as the object,on the basis of geological modeling,history matching,remaining oil characterization and phase state experimental fitting,a numerical simulation study on enhanced oil recovery by hydrocarbon injection in fractured-cavity reservoirs is carried out,so as the evaluation of the hydrocarbon-gas miscibility conditions in fractured-cavity reservoirs,and the optimization of EOR parameters of hydrocarbon injection.The results show that the minimum miscibility pressure of injected hydrocarbon gas and formation crude oil in S91 unit is 42.5 MPa,which can be miscible under the current formation pressure.The mechanism of miscibility is vaporization gas flooding.As the content of heavy hydrocarbon components in the injected gas increases,the recovery factor increases.The gas injection method is gas injection in fractured reservoirs,and liquid recovery in caved reservoirs.The gas injection parameters are preferably 168×10^(4) m^(3),gas injection rate of 4×10^(4) m^(3)/d,and injection-production ratio of 1∶0.9.