Flow Properties of Alaskan Heavy-Oil Emulsions

Abstract

Abstract Technical investigation to economically produce heavy oil in Alaska began in the 1980's. Since then a significant progress has been made in the production technology (multilateral drilling, artificial lift such as Electrical Submersible Pumps (ESP) and hydrolift Jet Pumps, etc.) to facilitate the production of the heavy oil. Still, a major challenge in the heavy oil production in the Alaskan arctic region is the formation of strong emulsions. The viscosity of these stable emulsions can be 2–3 orders of magnitude higher than the dry oil viscosity at the low ambient temperatures. The viscosities of these emulsions in the surface facilities are needed to predict the hydraulics in the fluid handling systems. Oil wet solid fines tend to further stabilize the emulsion and lower the separation efficiency. The stability of the emulsion can be gauged from the fact that oil external emulsion exists even up to 90% brine fraction and has the consistency of the peanut butter (highly viscous >2×104 cP at room temperature). Laboratory titration experiments with alkanes indicate that the asphaltenes are stable in the crude oil. A Haake RS150 rheometer and a Brookfield DV-III viscometer were used to measure the viscosity of the live and dead emulsions containing various brine fractions at different temperature. The viscosity estimation by matching the pressure drop data from the field pipeline correlated well with the laboratory results. The viscosity of the emulsion decreases with temperature as predicted by the Arrhenius law. Heating the emulsion above 60oC causes partial destabilization of the emulsion resulting in slight deviation from the Arrhenius predictions. Emulsion breakers were found to be effective in reducing the viscosity of the emulsion even though they did not cause any physical separation of the brine. Based on these results, viscosity correlations have been developed to predict the viscosity of both live and dead oil-brine emulsions as a function of brine fraction, temperature, and shear rate. Viscosity correlations for emulsions presented by Barnea and Mizrahi showed excellent fit to the measured data. It was proposed to incorporate these correlations in the Pipesim, steady-state multiphase flow simulator for oil and gas production. Introduction An emulsion is a system in which one liquid phase is dispersed in the other liquid phase in the form of very small droplets. Brine phase dispersed in a continuous crude oil phase is a common type of emulsion encountered in the oil fields. In this paper, emulsion will generally mean the brine-in-oil emulsion. These emulsions are thermodynamically unstable and separate into two phases if allowed to sit for a long time. The rate of separation depends on many factors such as density difference between the two phases, interfacial tension, temperature, presence of de-emulsifier chemicals, etc. Heavy oil emulsions usually are more stable than light and medium oils. One obvious reason is that the density of heavy oil is close to that of water. Researchers1,2 have investigated other reasons for the stability of the heavy oil emulsions. The results show that the polar fractions in the heavy oil such as asphaltenes and resins can form stable film on the brine/oil interface. Thus properties of these polar fractions play an important role in the stability of the emulsions.