Water-lubricated oil flows in a Couette Apparatus

Abstract

Self-lubricating flow of bitumen froth occurs when water droplets dispersed in the viscous oil phase form a lubricating layer surrounding a bitumen-rich core in a commercial pipeline operated by Syncrude Canada Ltd. In this study, self-lubricating flow was modelled experimentally by shearing water-in-oil emulsions in a Couette cell device (viscometer). Bitumen and two commercially available lube oils (N-Brightstock and Shellflex 81 0) were tested. Dispersed phase water concentrations ranged from 10 to 35 wt%. The ability to produce self-lubricating flow was a function of dispersed phase water concentration, temperature, oil viscosity, spindle speed and spindle size (gap width). For tests conducted at constant temperature, the critical spindle speed required to achieve self-lubricating flow was found to decrease with increasing water concentration. The critical spindle speed at which self-lubricating flow was achieved was found to increase with increasing temperature for the emulsions tested. Flow maps showing the critical spindle speed as a function of temperature indicate a clearly delineated transition region between viscous (non-lubricating) and self-lubricating flow. The critical spindle speed required to achieve self-lubricating flow was found to be similar when the viscosities of different oils were matched by varying the operating temperature. Self-lubricating flow was achieved with small and medium diameter spindles but not with the large diameter spindle. Models of self-lubricating flow in the Couette cell were developed to predict the thickness of the water layer that forms during self-lubricating flow. The thickness of the water layer calculated from these models is less than that determined by others for pipeline flows. The results of this study indicate that the ability to produce and maintain selflubricated flow is highly dependent upon water concentration, emulsion temperature and the continuous phase viscosity. Further studies of these model emulsions using pipeline flows are required.