Effect of Carrier Fluid Properties on the Self-Lubricated Flow of Bitumen Froth
Creators: Gbadamosi, Mubarak A
Publisher: name: University of Alberta Library
Year: 2023

<p>Bitumen froth is produced from mined oil sands using the water-based extraction process. The froth is very viscous and contains roughly 60% bitumen, 30% water, and 10% fine solids (by mass). The mixture of water, fine solids, and dissolved ions in the froth is usually called carrier fluid. The carrier fluid properties vary significantly depending on the process water chemistry and the concentration of fines in the bitumen froth. After extraction, the bitumen froth is transported to treatment and upgrading facilities using the self-lubricated flow technique. The self-lubricated flow occurs due to the migration of some of the carrier fluid in the froth to the high-shear region near the pipe wall. This results in the formation of a thin lubricating water layer around the bitumen-continuous core, thereby lowering the pump energy required to transport the bitumen froth. Despite the strong dependence of self-lubricated flow on the lubricating layer produced by the carrier fluid, there is no information in the literature on how the properties of the carrier fluid impact the flow. Therefore, the objective of this work is to investigate the effect of carrier fluid properties, specifically pH, salt concentration, and fines concentration, on the self-lubricated froth flow.<br>
Previous studies have shown that the parameters affecting self-lubricated froth flow in pipeline transport can be studied using a Couette cell device. Using the Couette cell device to study the self-lubricated flow mechanism has numerous advantages; these includes cost-effectiveness, simpler experimental design, and the requirement of smaller froth quantities for conducting experiments. Hence, the parameters affecting the self-lubricated flow mechanism were studied in this work using a Couette cell device. Preliminary experiments were conducted to investigate the effects of water concentration on self-lubricated flow using a water-in-oil emulsion as a bitumen froth analog. The concentration of the dispersed phase was varied between 10 to 30 wt.%. The results showed that increased water concentration reduces the spindle speed required to produce a  self-lubricated flow. <br>
The main experiments were conducted using bitumen froth samples. The first phase of the experiments examined the effect of temperature on self-lubricated flow. The tests were conducted at 50, 55, and 60 \degc. The results showed that the increase in temperature increases the shear rate required to maintain a stable self-lubricated flow. This observation can be attributed to the reduction in the viscosity ratio of the continuous phase to the dispersed phase. The result agrees with the experiments conducted by Bello using water-in-oil emulsions as a bitumen froth analog.  The second phase of the project was designed to examine the effect of carrier fluid pH, salts concentration, and fines concentration on self-lubricated flow. The salts concentration refers to the concentration of sodium chloride in the carrier fluid. Studies on the effect of carrier fluid pH on self-lubricated flow were performed at pH values of 8.5, 9, 9.5, and 10. Notably, above the pH 9, the shear rate required to produce the self-lubricated flow increased. Further experiments were conducted to examine the effect of carrier fluid NaCl concentration on the self-lubricated froth flow. The tests were performed at 1205 ppm, 2000 ppm, and 3000 ppm. It was observed that above 2000 ppm, a higher spindle speed was required to produce a self-lubricated flow. The increase in the shear rate required to produce a self-lubricated flow with an increase in pH and salt concentration is due to the reduction in bitumen-water interfacial tension. As the interfacial tension decreases, the dispersed droplets in the froth will have lesser resistance to deformation. Consequently, a high shear rate will be required to facilitate the droplet migration to produce a lubricating layer. The final phase of this project investigated the effects of carrier fluid fines concentration on the self-lubricated flow. The concentration of fines in the carrier fluid was varied between 0 to 6.3 vol.% by adding kaolinite clay. The result shows that the increase in the yield stress of the carrier fluid increases the stability of the self-lubricated flow. This observation can be attributed to the increased resistance of the lubricating water layer against deformation, allowing it to remain stable within the annulus.</p>