Abstract: The changes of electrical properties of water flooded reservoirs are complex, which brings great difficulty to the identification of water flooded zone and the evaluation of remaining oil saturation. In this paper, simulated waterflooding experiments under reservoir conditions are carried out by using sealed coring samples, the variations of rock resistivity are analyzed for the situations when the water of different salinities is injected to displace oil and the influences of changes of pore structures, and formation water salinity on rock electrical parameters are discussed. The experimental results show that when high salinity water or formation water is injected to displace oil, the rock resistivity always monotonously decreases and exhibits a“L”shape, and the better the physical properties are, the larger the decrease amplitude of rock resistivity will be; when low-salinity water is injected to displace oil, the rock resistivity generally displays a“U”or“S”shape and the better the physical properties are, the resistivity will change to monotonous increase from monotonous decrease, and the higher the water saturation at the first inflection point will be. The changes of pore structure resulted from the changes of injected water volume have no significant impact on rock electrical parameter. With the increase of formation water salinity, cementation index and saturation index will gradually increase. The influence of the difference of formation water salinity at different waterflooded stage on rock electrical parameters should be considered when calculating residual oil saturation.

Key words: waterflooding development, reservoir, watered out, resistivity, salinity, rock electrical parameter, rock resistivity experiment, electrical conductivity