表面活性剂对超低渗透油藏渗流特征的影响

针对超低渗透岩心,通过宏观驱替实验研究不同界面张力的表面活性剂对单相启动压力、油水两相启动压力、相对渗透率曲线、降压效果及提高采收率效果的影响,分析表面活性剂对超低渗透油藏渗流规律的影响。研究结果表明,随驱替液界面张力的降低,单相启动压力明显降低。油水两相启动压力实验中,在油水两相相同流速比下,随界面张力的降低,油水两相启动压力梯度逐渐降低,含水饱和度逐渐增大。从束缚水饱和度到残余油饱和度,随含水饱和度的增加,油水两相启动压力梯度先缓慢下降,后迅速下降。相渗曲线实验中,随表面活性剂质量分数的增加,油水两相渗流区增大,油相相对渗透率增大,残余油下水相相对渗透率增加,残余油饱和度降低,油气采收率升高,水相(端点以内)渗透率基本没有变化。表面活性剂段塞驱替实验中,岩心一次水驱后,注入表面活性剂可明显降低超低渗透岩心的注入压力、提高岩心采收率,且油水界面张力越低,降压效果越好,提高采收率幅度越大。

Effect of surfactant on seepage characteristics of ultra-low permeability reservoir

Using ultra-low permeability cores, the influences of surfactants with different interfacial tension on single phase and two phase starting pressure gradient of oil/water as well as relative permeability curves were studied. The effects of the surfactants on reducing injection pressure and enhancing oil recovery were also studied. The basic mechanisms of surfactant flooding to enhance oil recovery of low permeability reservoirs were obtained. The results show that the single phase starting pressure gradient of oil or water significantly decreases while the interfacial tension of the surfactant solution used as a displacing fluid. At the same ratio of displacing velocity, starting pressure gradient of oil and water two-phase gradually decreased, and water saturation gradually increased, as the interfacial tension decreased. The relative permeability curves of core had following characteristics: while oil/water interfacial tension decreased, the two-phase region became wider and the residual oil saturation decreased, and water relative permeability at residual oil saturation increased, and ultimate oil recovery increased. The results of the core displacement experiments show that injecting surfactant slug after the first water flooding can decrease the injection pressure significantly and enhance oil recovery to some extent. And,the lower the oil-water interfacial tension, the better the effect of enhancing oil recovery. And, the lower the oil-water interfacial tension, the better the effect of reducing injection pressure.