Oil/Water Pipe-Flow Dispersions: From Traditional Flow Loops to Real Industrial-Transport Conditions

Abstract

Summary In this paper we present a study on oil/water pipe-flow dispersions. There are two main objectives of this work: The first objective is to gain more knowledge on the behavior of oil/water dispersions in pipe flow; the second objective is to validate a new methodology to characterize dispersion properties at realistic industrial conditions. The characteristics of oil/water flows such as the development of the phase-fraction profiles, droplet-chord lengths, and pressure gradient were studied in a 0.069-m-diameter and 50-m-length horizontal pipe at the Multiphase Flow Laboratory of SINTEF in Norway. The fluid system consisted of a model oil (Exxsol® D80) with and without surfactants, and tap water. A comparison of the experiments with and without a mixing valve was performed. The experiments were conducted at different superficial liquid velocities (Usl) and five different water-cut (WC) values (with WC defined as the ratio of the water superficial velocity to the liquid superficial velocity). In addition, experiments on a wheel-shaped flow loop were conducted at selected conditions. The wheel mimics realistic pipe-flow conditions for the oil/water dispersions. This methodology allows us to identify flow-developing time scales and long-term behavior, which cannot be studied in a shorter test section. Furthermore, it is possible to have an indication of the viscosity increment when dispersions form. The results from the pipe-flow experiments show that the effective viscosity of the mixed flow increases by the dispersion formation promoted by the valve. As a result, the pressure gradient in the downstream pipe increases dramatically compared with the same conditions without premixing. For the studied cases, the surfactant concentration did not have any significant effect on the pressure drop in the pipe. However, differences in the phase-fraction profiles were observed, especially with respect to flow development along the pipe. A possible explanation is that the effective viscosity of the created dispersion is not high enough to produce an increase in the pressure drop. Flow development along the pipeline (oil/water separation) is observed only for selected cases without surfactant. For the rest of the experiments, especially with surfactant, the test section was not long enough to observe flow development. With the wheel, it is simple and fast to study both the formation and the stability of dispersions with real fluids at realistic conditions. There are indications that the energy-dissipation rate could be used as a scaling parameter between pipe-flow experiments and the wheel experiments. Wheel experiments can be used cost-efficiently to investigate dispersion characteristics and long-term flow development, which cannot be observed in traditional pipe-flow loops because of their restrictions.