Emissions from oil sands tailings ponds

In oil sands tailings ponds, the upper strata (FFT & MFT) are colloidal suspensions containing fines and clay particles, with significant yield stress. Depending on the diluents used in processing the bitumen, various residual hydrocarbons remain in the ponds and are broken down by bacteria. Typically this is CO₂ and/or CH₄ that is formed, which are targets for emission reduction related to climate change.

Our work here focuses at the behaviour of bubbles in yield stress fluids: trapping, release and migration of bubbles, transport across interfaces, multiple bubbles, stability, etc. We are interested to understand all aspects of the dynamics of gas generation, release and entrapment in oil sands tailings ponds. The research here covers different facets of bubble dynamics.

• We have clearly defined the concept of a critical yield number, which relates to trapping and release of bubbles.
• We have made variational estimates of the critical yield stresses (yield number) necessary to prevent bubbles from rising and have computed these yield limits for a wide range of bubble shapes. Our computations include the effects of surface tension.
• We have performed numerous experiments on bubble rising in yield stress fluids. These agree with similar experiments of other authors using similar lab fluids. These have clarified the role of viscoelasticity on bubble shape: specifically the tail region and wake, as bubbles rise through elasto-visco-plastic (EVP) fluids
• We have clearly defined the concept of a critical yield number, which relates to trapping and release of bubbles.
• We have made variational estimates of the critical yield stresses (yield number) necessary to prevent bubbles from rising and have computed these yield limits for a wide range of bubble shapes. Our computations include the effects of surface tension.
• We have devised experiments to study the growth and release of single bubbles trapped in a gel. These have been calibrated and show that for real (EVP) fluids there can be considerable elastic creep before the bubble is rises.
• We have compared 2D planar bubble flows and axisymmetric 2D bubble flows, using regularised constitutive models
• We have explored the yield limit of pairs of bubbles and randomised bubbly liquids, in 2D planar geometries
• We have devised experiments for the onset of motion of clouds of bubbles. These show a range of behaviours ranging from isolated bubble release, through mobilization of bubble chains/arrays to a bursting phenomenon.
• We have performed experiments with 2-3 bubbles to explore coalescence, effects on bubble release, etc
• When we inject/release multiple bubbles, they tend to follow the path of previous bubbles, but are smaller and move faster. This indicates that the pathway of the first bubble also creates some form of “damage” to the gel.
• Other experiments have purposefully damaged the gel of introduced e.g. a water layer. Bubbles released appear to be attracted towards the rheologically weaker layer of fluid. We are studying this phenomena more closely, using experiments and computation.
• We have performed both simulations and experiments to study the passage of bubbles through different layers of fluid. This leads to a change in bubble shape typically and interesting transients crossing the interface.
• The above studies reveal an interesting tunneling phenomena.
• Passage through the interface also reveals different patterns of entrainment, e.g. of the lower fluid into the upper in the wake of the bubble.
• We are studying entrainment in yield stress fluids more deeply

Our sponsors

• UBC
• NSERC
• IOSI
• COSIA
• KFAS