Flow patterns and pressure gradient correlation for oil–water core– annular flow in horizontal pipes

The water-lubricated transportation of heavy oil seems to be an attractive method for crude oil production with significant savings in pumping power. With oil surrounded by water along the pipe, oil–water core–annular flow forms. In this paper, the characteristics of oil–water core–annular flow in a horizontal acrylic pipe were investigated. Plexiglas pipes (internal diameter = 14 mm and length = 7.5 m) and two types of white oil (viscosity = 0.237 and 0.456 Pa·s) were used. Flow patterns were observed with a high-speed camera and rules of flow pattern transition were discussed. A pressure loss model was modified by changing the friction coefficient formula with empirical value added. Totally 224 groups of experimental data were used to evaluate pressure loss theoretical models. It was found the modified model has been improved significantly in terms of precision compared to the original one. With 87.4% of the data fallen within the deviation of ± 15%, the new model performed best among the five models.