Stability of Concentrated Crude Oil-In-Water En1ulsions As A Function of Shear Rate, Temperature And Oil Concentration
Authors: Mao M.L. , Marsden S.S. 
Published: March 2010

Emulsions were prepared with a California crude oil and tap water by stabilizing with a nonionic emulsifier (Triton X-114). Their rheological properties were studied as a function of composition, temperature and shear rate. Those having high concentrations of the dispersed phase behaved like pseudoplastic fluids. Apparent viscosity or consistency increased with the concentration of the dispersed phase and decreased with temperature. ASTM plots of kinematic viscosity VB temperature were linear for each emulsion. Viscosity corrections for temperature could be made for the W/O emulsions, but not the O/W ones, from a knowledge of the viscosity temperature relationship for the oil and a single value of the emulsion's apparent viscosity. The inversion of O/W emulsions to form W/O ones may be predicted by an empirical equation relating oil concentration, temperature and shear stress.

Introduction

EMULSIONS are dispersions of oil droplets in water or water droplets in oil. We are all familiar with them in our every-day life, and we are particularly aware of them in the oil industry. Many crude oils are produced as emulsions and some of the major products of our industry are sold as emulsions. They form an important area of technology as well as an interesting subject of science.

In the oil production industry, emulsions are looked on with disdain because they are often an expensive, bothersome problem. However they do have properties which can, with wisdom, be used to advantage. Simon and Poynter(1) as well as others (2,3) have shown how produced water-in-oil (W/O) emulsions can be converted to oil-in-water (O/W) ones to achieve many advantages, Emulsions or dispersions of crude oil in water or brine have been successfully used in some pipeline transportation systems (1) and have been proposed for others(5,6). In these latter cases, we take advantage of the relatively low flow resistance of the continuous aqueous phase compared to that of the oil phase, particularly at arctic temperatures. For this reason, it is very important to maintain water or brine as the continuous phase.

Under some conditions, one type of emulsion will invert or change into the other type. By chemical means, Simon and Poynter were able to invert the highly viscous, naturally produced W/O emulsions into the much more fluid O/W ones. They also noted in their paper that increased shear and1or increased temperature would cause an inversion of three O/W emulsions back to W/O ones.

This latter observation prompted us to question the stability of emulsions in pipelines where shear is very high. Evidently it has not been a problem for pipelines carrying waxy crude oil-in-water dispersions at temperatures well below the pour point of the crude oil(4), where inversion is difficult to visualize. The effect of temperature suggests that it may not be a problem at ambient arctic temperatures.

The purpose of this study was first to determine the rheological properties of emulsions containing different amounts of crude oil at different temperatures.