Abstract

Emily Flicos CCS & permeability: thinking about uncertainty through a perturbation analysis

One of the challenges with modelling subsurface flows is the uncertainty in measurements of geological properties, mostly due to limited resolution in observation methods. These properties can be highly heterogeneous and this heterogeneity can have a large effect on plume migration. Many subsurface flows can be modelled as a gravity current, which, for uniform material properties, has a well characterised similarity solution. The similarity solution forms the mean about which we perform a perturbation analysis, treating the uncertainty in permeability as deviations from a mean.

We restrict our focus to permeability fields which vary laterally, or across the flow, starting with the simple case of a sinusoidal perturbation to a uniform mean. At early times, the height and nose position of the current are determined by the local permeability and deviations to the height and nose grow at the same rate as the mean, proportional to the amplitude of the permeability variation. The transition between the early and late time regimes is governed by the wavelength of the permeability. At late times, lateral spreading is dominant; the height deviations decay and the nose deviations approach a steady state. The magnitude of both depend on the product of permeability wavelength and amplitude.

The single mode sets the groundwork for looking at more complex, multimodal permeabilities, with more complex results.

James Morris Bubble growth in alkaline electrolysis

In the production of hydrogen via electrolysis, bubbles of hydrogen and oxygen must grow and detach from the electrode. Discussion of factors effecting rate of bubble growth and final detachment volume, and their contribution to overall efficiency.