This experimental investigation was conducted in horizontal and inclined acrylic pipe of 30.6-mm ID. The pressure gradients were determined in the dispersed flow regions with flow conditions of 0.8 – 1.6 m/s mixture velocities and 0.05 – 0.9 input oil volume fractions. The investigation showed that the addition of the 40 ppm drag-reducing polymer substantially decreased the frictional pressure gradients with drag reductions at the upward inclinations higher than those at downward inclination. The upward inclinations also increased the drag reductions at water-continuous dispersed flow regions while the reverse was the case at downward inclination in the same flow regions.


Oil-water flows are often encountered in chemical industries, and even more so in petroleum industries because of the simultaneous production of oil and water from aging oil wells in recent years. Free water has now substantially increased due to the recent focus on horizontal and near horizontal wells which are accompanied with high water cut in old wells or from the water injected for reservoir pressure maintenance. High watercut wells remain economical to operate even with water cuts as high as 0.9. Therefore, long-distance transportation of the produced oil-water mixtures in pipelines from the production sites to processing sites becomes inevitable. This necessitates the consideration of the water phase in the determination pressure gradient, which is a critical component of optimisation for pipeline operations, especially for oil fields operating at high water cuts and low wellhead pressures.

The study of oil-water flows with respect to pressure gradients actually commenced in the 1950s (1, 2) after discovering that pumping requirements during viscous oil transportation could be reduced by introducing water in the pipelines. Although this field of study subsequently received very little interest for some years, the simultaneous production of oil and water from many currently operating oil fields has revived the interest of researchers in this area. The behaviour of pressure gradients in oil-water flows from reported studies has shown to vary considerably due to the dependence of the pressure gradients on many factors which include oil properties, pipe geometry, pipe orientation, and oil-water flow patterns. (3) observed that the properties of pipe wall such as roughness and wettability can also affect the pressure gradients. According to the study of dispersed oil-water flow by (4), increasing the fraction of the dispersed phase increases the relative viscosity of the continuous phase. This results to the increase in the pressure gradient towards the phase inversion points for an oil continuous dispersion. Once past the phase inversion point, the pressure gradient decreases to that of single-phase water flow.

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