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

Abstract

This paper is focused on studying oil-water pipe flow dispersions. There are two main objectives of this work: First is to gain more knowledge on the behaviour of oil-water dispersions in pipe flow. Second is to provide validation of 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 long 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 and five different watercut values (The water cut is defined as the ratio between the superficial water 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 identifying flow developing time scales and long-term behaviour, which are not possible to study in a shorter test sections. 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 mixture increases by the dispersion formation promoted by the valve. As a result, the pressure gradient increases dramatically in comparison to the same conditions without premixing. For the studied cases, the surfactant concentration did not have any significant effect on 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 the pressure drop. Flow development along the pipeline (oil-water separation) is observed just for selected cases without surfactant. For the rest of the experiments, especially with surfactant, the length of the test section was not long enough to observe flow development. With the wheel, it is simple and fast to study both formation, and stability of dispersions with real fluids at realistic conditions. There are indications that the energy dissipation rate could be used as scaling parameter between pipe flow experiments and the wheel experiments. Wheel experiments can be used to cost-efficient investigate dispersion characteristics and long-term flow development, which cannot be observed in traditional pipe flow loops due to their restrictions.