EURO-ECO 2011 Hanover 21 - 22 November 2011	Environmental, Engineering - Economic and Legal Aspects for Sustainable Living
	European Academy of Natural Sciences, Hanover European Scientific Society, Hanover University of Bremen, Bremen

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Knowledge of deep underground flow systems is important, amongst others, in the contexts of (i) geothermal energy production, (ii) nuclear waste disposal, (iii) flow dynamics in coastal aquifers, and (iv) natural gas extraction. Underground water flow is controlled by:

• density variations. Water density is known to change with depth due to increasing temperature and salinity,
• viscosity variations. Water viscosity can vary by one magnitude order in the Earth’s crust,
• open fractures. Flow velocities can be several orders of magnitude larger than within the rock matrix,
• variations in rock permeability, and
• chemical precipitations. Quartz is the most common mineral in the Earth’s crust.Precipitation/dissolution of quartz can lead to sealing/widening of fractures and of the rock matrix.

To understand coupled processes of the groundwater flow dynamics in the underground, the numerical computer-model HydroGeoSphere is being developed and used. HydroGeoSphere can simulate variable-density thermohaline flow and multi-species contaminant transport including radioactive chain reactions. Finite element method is applied to discretize differential equations of flow and transport. A Picard iteration scheme is used to linearize the coupled system of equations of variable-density flow and transport. Fractures are represented using either a discrete fracture approach or a dual continuum approach. Discretized equations are being solved through a powerful iterative matrix solver.

Processes of variable-density flow in fractured rock and in coastal aquifers are currently being investigated at the Institute of Fluid Mechanics of Leibniz Universität Hannover. Projects are funded by DFG (Deutsche Forschungsgemeinschaft), and they are carried out by the Emmy Noether Young Research Group that Prof. Graf coordinates.

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