Mechanism of surfactant flooding in low-permeability oilfields

Based on the theories of decreasing threshold pressure and combined with experiments of the effect of surfactant solution on relative permeability, the mechanisms of decreasing pressure and increasing injection rate by surfactant were researched. The results show that the surfactant solution can reduce oil-water interfacial tension, increase oil flow capacity, change wettability of rock surface from oil-wet to water-wet, decrease capillary resistance of water drive, increase water-phase permeability and decrease injection pressure. The oil displacement effect is preferable when the mass fraction of surfactant solution is 0.2%, injection rate is 0.5Vp(Vp is pore volume), and the water cut is lower than 70%.