Geochemical effects on natural convection in porous media

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Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13209
Qualification Level
Qualification Name
Department, School or Faculty
  • We describe a model of buoyancy-driven flow in a saturated reactive porous medium, the porosity and permeability of which evolve through precipitation and dissolution as a mineral is lost or gained from the pore fluid. We consider two scenarios: convection driven solely by solutally induced buoyancy e ects with a vertically varying equilibrium solubility, and convection driven by a combination of thermally and solutally induced buoyancy effcts where the solubility of the dissolved component depends on the temperature. In both cases we characterise the onset of convection using linear stability analysis, and explore the further development of the coupled reaction-convection system numerically. For solutal convection, at low Rayleigh numbers the effect of the reaction-permeability feedback is shown to be destabilising, while at higher Rayleigh numbers the porosity evolution has a stabilising effect. Over longer timescales, reaction-permeability feedback triggers secondary instabilities in quasi-steady convective circulation, leading to rapid reversals in the direction of circulation. Over very long timescales, characteristic patterns of porosity emerge, including horizontal layering as well as the development of vertical chimneys of enhanced porosity. For thermosolutal convection we find that, when the system is solutally unstable, the behaviour of the system is qualitatively the same as for solutal convection, regardless of whether the system is thermally stable or unstable. However, new, interesting behaviour is seen when the system is solutally stable. The long-term evolution of the porous layer depends on whether the underlying thermal or solutal gradient dominates. When the solutal gradient dominates, the reaction-permeability feedback triggers a secondary instability, resulting in the lateral migration of the concentration and temperature elds and rapid reversals in the direction of circulation. However, when the thermal gradient dominates, the reaction-permeability feedback tends to suppress the circulation, although it re-emerges after a long quiescent period.
Resource Type
Date Created
  • 2012
Former identifier
  • 947896