Effect of water salinity on flow pattern and pressure drop in oil–water flow

• Oil–water flow patterns transition lines changes with water salinity.
• Oil–water flow pressure drop increases with water salinity.
• Inversion point location starts earlier for the case of saline water.
• A stable interface between oil and saline water compared to the interface for tap water.

The effect of water salinity on flow pattern and pressure drop in oil–water flow was investigated experimentally in an acrylic 2.25-cm diameter horizontal pipe. The used oil has 781 kg/m3 density and 1.85 cP viscosity at 25 °C. Water salinity was increased to 75‰ by mixing food salt with an amount of 9% of water weight to the water tank. The addition of salt changed the density of the water from 999 kg/m3 to 1065 kg/m3, and the viscosity from 0.985 cP to 1.246 cP at 23.5 °C. This caused the oil–water density ratio to change from 0.78 to 0.732 and the viscosity ratio to change from 1.94 to 1.536. The results showed that salinity delayed the transition from dispersion of oil in water over a water layer flow pattern to the dispersion of water in oil and oil in water flow pattern. It was also noticed that the waves in the stratified with mixture at the interface flow pattern in saline water had less amplitudes than that in tap water. Results for the pressure drop showed that inversion point location was noticed to start earlier in saline water than in tap water, and the decrease rate in pressure drop as the oil fraction approaches the inversion point was reduced in saline water. This means that inversion effect was reduced. However, since saline water density is greater, higher pressure drop was produced.