The characteristics of ultralow permeability reservoirs changed after waterflooding.Thin-section analysis and scanning electron microscopy(SEM) of core samples from inspection wells indicated that calcite and barite were formed in ultralow permeability reservoirs during waterflooding operations.Some asphaltene precipitates on the surface of formation rock would influence the reservoir porosity,permeability,wettability,and electrical properties.In this paper,the changes of physical,electrical,and fluid properties of ultralow permeability reservoirs during waterflooding operations were analyzed.This provides important information to improve waterflooding performance in ultralow permeability reservoirs. The characteristics of ultralow permeability reservoirs changed after waterflooding. Thin-section analysis and scanning electron microscopy (SEM) of core samples from inspection wells indicated that calcite and barite were formed in ultralow permeability reservoirs during waterflooding operations. Home asphaltene precipitates on the surface of formation rock would influence the reservoir porosity, permeability, wettability, and electrical properties.In this paper, the changes of physical, electrical, and fluid properties of ultralow permeability reservoirs during waterflooding operations were analyzed. This provides important information to improve waterflooding performance in ultralow permeability reservoirs.