HR: 0830h
AN: H11G-0931    [PDF]
TI: Multi-phase Thermohaline Convection in Porous Media
AU: * Geiger, S
EM: geiger@erdw.ethz.ch
AF: Department of Earth Sciences ETH Zurich, Sonneggstr. 5, Zurich, 8092 Switzerland
AU: Driesner, T
EM: td@erdw.ethz.ch
AF: Department of Earth Sciences ETH Zurich, Sonneggstr. 5, Zurich, 8092 Switzerland
AU: Matthai, S K
EM: s.matthai@ic.ac.uk
AF: Department of Earth Sciences & Engineering Imperial College London, Prince Consort Road, South Kensington, SW7 2AZ United Kingdom
AU: Heinrich, C A
EM: heinrich@erdw.ethz.ch
AF: Department of Earth Sciences ETH Zurich, Sonneggstr. 5, Zurich, 8092 Switzerland
AB: The simultaneous motion of heat and dissolved solutes by aqueous or magmatic fluids through porous or fractured media within the earth's crust is a key factor that drives many important geological processes, such as the formation of large ore deposits, cooling of new-formed oceanic crust along mid-ocean ridges, metamorphism, or the evolution of geothermal systems. The motion of such crustal fluids is usually dominated by convection due to density differences within the fluids that arise from pressure, temperature and compositional variations present in the fluids. Oxygen isotope data and fluid inclusion data indicate that fluids may percolate down to 15 km depth and experience temperatures exceeding 700 $^{\text{o}}$C. Although crustal fluids commonly contain various dissolved chemical components and gases, the most abundant solute is salt, i.e. NaCl. Hence, changes in the concentration of NaCl influence the density variations of crustal fluids the most. The presence of NaCl in H$_2$O has decisive effects on the thermodynamics and hydrodynamics of crustal fluids. NaCl-H$_2$O fluids can boil and separate into a high-density brine and low-salinity vapor at much higher temperatures and pressures than the critical temperature and pressure for pure H$_2$O. NaCl-H$_2$O fluids may also become saturated with respect to NaCl such that a solid NaCl phase coexists with a liquid or vapor fluid phase. Because salt advects faster than heat but diffuses slower than heat, the resulting double-diffusive and double-convective motion of salt and heat may lead to non-linear flow instabilities such as periodic or chaotic behavior. While many studies have addressed the theory of convection driven by temperature and/or salinity gradients, they were limited to a Boussinesq approximation and neglected phase separation. In this study we have numerically examined the behavior of multi-phase thermohaline convection in a porous media heated and salted from below using a novel finite element - finite volume algorithm and a new equation of state for the NaCl-H$_2$O system. Convection at various depths and and for temperatures up to 600 $^{\text{o}}$C and salinities up to 30 wt. % NaCl was studied. The simulations show that, comparable to single-phase thermohaline convection, condition exists where the flow pattern evolves towards a convective or diffusive steady state. Flow patterns always appear to exhibit periodic behavior if the fluid starts to boil. The evolution of flow patterns, however, cannot be directly related to certain ranges of the classical descriptive dimensionless numbers such as buoyancy ratio or Raleigh number because of the complexity of the NaCl-H$_2$O system that does not always allow for a direct calculation of those numbers.
DE: 3210 Modeling
DE: 3220 Nonlinear dynamics
DE: 3230 Numerical solutions
DE: 3240 Chaos
DE: 8135 Hydrothermal systems (8424)
SC: Hydrology [H]
MN: 2003 Fall Meeting