Abstract: In response to poor understanding of formation damage mechanism in the process of water flooding development of Chang₄₊₅ low permeability reservoirs, Nanliang Area, experimental methods such as electron microscopy scanning, casting slice, confocal imaging and XRD were utilized to analyze the pore structure and rock composition of reservoir cores before and after water flooding, determine the effect of water flooding development on reservoir pore characteristics, analyze the potential damage, real-time variation pattern of core permeability in water flooding process by comparison of the salinity and material contents between injected water and formation water, and summarize the mechanism of formation fouling and blockage. The results concluded that the damage of water flooding to Chang₄₊₅ low permeability reservoir, Nanliang Area mainly included salt sensitivity and scaling caused by the incompatibility among injected water, formation water and reservoir, as well as the blockage of mechanical impurities in the reservoir caused by the poor quality of injected water. The study results provide methodological and theoretical support for understanding the damage mechanism of water flooding to low permeability reservoirs.

Key words: low permeability reservoir, water flooding, compatibility, formation damage, scaling