International Geologiical Congress - Oslo 2008

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STN-03 Morphotectonics of lowland areas

 

Double diffusive convection modelling of deep thermohaline cirulation

 

Ekkehard Holzbecher, Weierstrass Institute for Applied Analysis and Stochastic (Germany)
Claus Kohfahl, Freie Universitšt Berlin (Germany)
Aneta Bacik, Polish Geological Institute (Poland)
Magdalena Dobies, Polish Geological Institute (Poland)
Michael Schneider, Freie Universitšt (Germany)
Marcin Mazurowski, Polish Geological Institute (Poland)
 

 

In the paper we explore double diffusive convective fluid motion of deep thermohaline circulation. Aside from the ambient regional flow regime the hydraulic conditions in an aquifer is determined by salt and temperature distributions, as there is a connection with a salt dome cap. Density-driven flow patterns are induced by the effect of salt and temperatures on density. Using numerical modeling with COMSOL Multiphysics (2006), we set up a reference model in a vertical cross-section with parameter values that are characteristic not only for the lowlands in Germany and Poland. It is explored under which conditions favour or disfavour thermohaline circulation.
A test-case from the international verification and validation project HYDROCOIN, organized by the Swedish SKI, examined flow patterns around a salt dome. The model region in the test-case concerns density driven flow in the aquifer overlying the upper edge of the salt-dome. A schematic view is depicted Figure 1. In the HYDROCOIN model (1989, 1990) the salt dissolution at the base of the aquifer adds another moment to the flow regime. In this exemplary situation we consider the influence of increased temperature at the salt-dome cap, in addition.
We shows results for the HYDROCOIN set-up without feedback of temperature on the fluid and the HYDROCOIN set-up, extended for heat transport (the fluid flow is (via density) influenced by both salinity and temperature). For the chosen parameter set the influence of the thermal regime is significant. Eddies are quite different in the pure saline and in the saline/thermal regime. They are stronger and more extended, when the heat regime is considered in addition to the salt regime.
In the contribution we present the geological setting, the characteristic parameters, the mathematical description (Holzbecher 1998) and its solution method by Finite Elements. Finally the results, concerning the flow regime, are given and discussed.

 

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