AbstractRecent developments in nanotechnology illustrates that addition of nanoparticles in the polymer flooding process can improve the oil recovery factor. But there exists few researches about the polymer performance in the presence of nanoparticles. Also there is no information about the effect of silica nanoparticles on the heavy oil recovery during the polymer flooding by anionic hydrolyzed polyacrylamide (HPAM). Therefore, for the first time in this study the effect of nanosilica (NS) in the polymer flooding in the presence of salt on the oil recovery factor has been investigated in a strongly oil wet five-spot glass micromodel saturated with the heavy oil and the image processing technique was applied to analyze the displacement mechanisms and also for calculation of the efficiency in each flooding test. The oil recovery factor after one pore volume of the injected fluid has been obtained and results indicate that in the presence of NS an improvement about 10% in the ultimate oil recovery can be achieved and this is due to the viscosity enhancement of the injected fluid. Also it has been understood that nanoparticles have ability to change the wettability to water-wet in some portions of the micromodel.