Study on flow pattern maps in hilly-terrain air–water–oil three-phase flows

Although three-phase flows are often encountered in offshore petroleum engineering, but there have been only a few comprehensive studies on flow pattern maps. In the present study, an experimental program was carried out to obtain flow pattern maps in hilly-terrain air–water–oil three-phase flows. Two elbows, including two symmetrical inclined pipes, were used at the peak and the valley respectively, with an inclination angle of 0–30°. The test section was made of transparent acrylic resin, with a total length of 10 m and an inner diameter of 40 mm. The superficial velocities were 0.01–15 m/s, 0.01–2 m/s, and 0.01–2 m/s for air, water and oil, respectively.By using a high-speed camera and a single-wire capacitance probe, we recorded the flow processes and measured the water layer height in the pipe, and further identified different flow patterns. Similar to the flow patterns in horizontal pipes, eleven typical flow patterns were observed in the present study. However, the ranges in the flow pattern maps were extended for intermittent flow in uphill pipes, and also for stratified flow in downhill pipes. When each superficial velocity was low enough, elbows, causing accumulation at the peak and the valley of the hilly-terrain system, determined the flow pattern in the downstream pipes, and resulted in different flow patterns in the uphill and downhill pipes. Nevertheless, when superficial gas velocity was high enough, exceeding 10 m/s, all the flows tended to be annular along the whole hilly-terrain pipes. It may be appropriate to simplify the air–water–oil three-phase flow into gas–liquid two-phase flow, where water fraction had an effect on oil–water distribution and changes the viscosity of the liquid mixture. As a result, water fraction was considered as a secondary factor to determine flow patterns when compared with pipe structures and superficial velocities.

► Three-phase flow patterns can be simplified as gas–liquid two-phase flows.
► Eleven flow patterns were obtained experimentally in hilly-terrain air–water–oil three-phase flows.
► Elbows enhance the mixing of oil and water, and the separation of gas and liquid.
► Water fraction is a secondary factor to affect flow patterns compared with phase superficial velocities.