Effect of Water Salinity on Crude Oil Viscosity in Porous Media at Varying Temperatures

Viscosity is one major property of crude oil that is highly dependent on temperature and affects production operations. But temperature is not the only factor that affects oil viscosity; other factors include oil composition, pressure and dissolved gas. However, it has been observed that water salinity can also affect crude oil viscosity. It is therefore imperative that the effect of water salinity on crude oil viscosity be studied since water injection schemes using produced water or sea water is a common practice because it is economical and efficient in oil displacement from porous media. This paper studies the effect of water salinity on crude oil viscosity at temperatures of 30°C, 70°C and 110°C. Sand samples were flooded with crude oil of known viscosity and brine of different salinity values ranging from 30g/l to 70g/l, after which the oil viscosities were determined again as well as the brine density. The flooding experiments were conducted like relative permeability experiments under steady state with an overburden pressure of 3000psi, using a standard core flooding equipment at a flow rate of 2ml/min. The experimental results show that water salinity can increase crude oil viscosity. It was observed that the viscosity of the oil varied from 0.5cp to 2.3cp at different water salinity levels which could have been as a result of the chemical interaction between the two fluids. The effect of water salinity on the oil viscosity was more obvious at 30°C than at 70°C and 110°C, indicating that temperature could have played a vital role in the interaction process. On the other hand, the variation in water density after the oil-water interaction was more significant at higher temperatures than at 30°C. It was also observed that the maximum oil viscosity at 30°C was 2.26cp at 50g/l water salinity while 30g/l salinity gave the highest viscosity values of 1.29cp and 1.06cp for 70°C and 110°C respectively. This stresses the importance of conducting such studies with water samples intended to be used for water injection. It is therefore recommended that the effect of water salinity on crude oil viscosity be studied before embarking on any water injection scheme since high oil viscosity is not desired during oil production operations.