Experiments on Surfactant Stabilized Oil-Water Dispersed Flow

Abstract

This thesis is a study on the behaviour of surfactant stabilized oil-water dispersed flow in horizontal pipes. Water in oil dispersions is a common phenomenon in the oil industry, where oil and water often are produced and transported together. Crude oils have the ability to form water-in-oil (w/o) dispersions were the effective viscosity is much higher than the single oil viscosity. The formation of such dispersions in oil production systems can cause a significant reduction of the production rates due to the much higher effective viscosities of the mixture. The effective viscosity increases with the amount of dispersed water until it reaches the inversion point. The accurate prediction of the effective viscosity of emulsions in pipe flow is a crucial part of the process to the appropriate design of the systems. %The purpose of this work is to study the influence of the pipe diameter in the flow of water in oil dispersions. The first part of the report is theoretical, involving the necessary theory needed to interpret the experimental results. It also contains a description of the experimental set-up used, and the experiments conducted. An experimental investigation was carried out on the behaviour of horizontal oil-water dispersed pipe flow under atmospheric conditions. The laboratory pipe flow measurements were conducted in a medium scale multiphase flow loop with surfactant stabilized water-in-oil (w/o) dispersions. The formation of the emulsion was induced by the flow shearing itself and consisted of oil (Marcol 52) mixed with 0.25 % vol. of a lipophilic surfactant (Span 80) and salt water (3.5 % wt.). The water phase was increased with increments of 10 %. Two acrylic pipes with an inner diameter of 60 millimeter and 90 millimeter were used and mixture velocities ranged from 0.5 to 2.5 meterpersecond. Pressure drop measurements were performed in both pipes and were used to calculate the effective viscosity of the mixture. Results show that at high water cuts significantly higher effective viscosities occurred in the larger pipe diameter for the same shear rate conditions. This difference was observed to increase with water cut. In addition, a pseudo-plastic (non-Newtonian) behaviour of the emulsion was observed at high water cuts. This was verified by measuring the velocity profile using a Pitot tube. However, pressure drop measurements as a function of the mixture velocity, do not completely follow the shear thinning behaviour. In-situ droplet sizes were measured using the focused beam reflectance measurement technique. Measurements indicated that droplet sizes decreased as the mixture velocity increased for constant water cut and that droplet sizes increase with increasing water cut. A single-beam gamma densitometer is utilized to measure the distribution of the dispersed water phase across the pipe section in the 60 mm i.d. pipe. The results indicated that the flow was homogeneous throughout the whole pipe cross section.