HR: 16:45h
AN: H24C-04    [Abstracts]
TI: Detecting and Quantifying Minute Specific Discharge With Geothermal Methods
AU: * Clauser, C
EM: c.clauser@geophysik.rwth-aachen.de
AF: Applied Geophysics, RWTH Aachen University, Lochnerstr. 4-20, Aachen, D-52056 Germany
AU: Hartmann, A
EM: a.hartmann@geophysik.rwth-aachen.de
AF: Applied Geophysics, RWTH Aachen University, Lochnerstr. 4-20, Aachen, D-52056 Germany
AU: Rath, V
EM: v.rath@geophysik.rwth-aachen.de
AF: Applied Geophysics, RWTH Aachen University, Lochnerstr. 4-20, Aachen, D-52056 Germany
AU: Ruehaak, W
EM: w.ruehaak@gga-hannover.de
AF: GGA Leibniz Institute for Applied Geosciences (GGA-Institute), Stilleweg 2 , Hannover, D-30655 Germany
AU: Schellschmidt, R
EM: ruediger.schellschmidt@gga-hannover.de
AF: GGA Leibniz Institute for Applied Geosciences (GGA-Institute), Stilleweg 2 , Hannover, D-30655 Germany
AU: Zschocke, A
EM: zschocke@gga-hannover.de
AF: GGA Leibniz Institute for Applied Geosciences (GGA-Institute), Stilleweg 2 , Hannover, D-30655 Germany
AB: Detecting and quantifying subsurface flow is important for selecting suitable host rock formations for a safe long-term deposition of hazardous material in underground repositories. The sensitivity of the thermal regime for advective heat transport associated with flow systems provides a possibility for detecting and quantifying flow by geothermal methods. However, the flow-related temperature signatures are very small and non-unique. Therefore similar thermal signatures associated with other processes need to be quantified and subtracted from the temperature data to be analysed for flow. These are primarily: (1) steady-state refraction of (predominantly vertical) terrestrial heat flow due to heterogeneous thermal rock properties; (2) transient downward diffusion of long-term variations of the Earth's mean surface temperature as a response to the changing climate in the past. We illustrate our approach for two data sets from the Molasse Basin in southern Germany and the Northern German Sedimentary Basin: First, the relevant physical rock properties are measured directly on samples in the laboratory or inferred from a suitable combination of borehole logs of related properties. Thus, the non-uniqueness inherent in inferring rock properties can be constrained, and their variation with depth can be determined at logging resolution. This way it was possible to generate from our data calibrated vertical profiles of thermal conductivity for which previously no data had been available. Based on a fractal pore space model we succeeded in calibrating a highly non-linear relation between porosity and hydraulic permeability for Molasse Basin reservoir sandstones. Based on these data, we quantified the magnitude of the signatures associated with steady-state terrestrial heat flow (including effects of refraction) and transient thermal downward diffusion using forward and inverse model simulations. These were then subtracted from the temperature data. The residual temperatures were finally interpreted with respect to vertical or horizontal specific discharge at resolutions of 1 mm/a and 1 m/a, respectively. In case of several suitably distributed boreholes,the flow direction may also be determined at a resolution of around ±15°.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1859 Rocks: physical properties
DE: 8130 Heat generation and transport
SC: Hydrology [H]
MN: Fall Meeting 2005