HR: 10:35h
AN: H51H-02    [PDF]
TI: Investigation of Matrix Diffusion in Deep Hot-Dry-Rock Reservoirs Using Single-Well Injection-Withdrawal Tracer Tests
AU: * Herfort, M
EM: herfort@erdw.ethz.ch
AF: Swiss Federal Institute of Technology, Engineering Geology ETH Hoenggerberg, Zurich, 8093 Switzerland
AU: Ghergut, I
EM: Iulia.Ghergut@geo.uni-goettingen.de
AF: University of Goettingen, Geoscience Center, Applied Geology Goldschmidtstr. 3, Goettingen, 37077 Germany
AU: Sauter, M
EM: Martin.Sauter@geo.uni-goettingen.de
AF: University of Goettingen, Geoscience Center, Applied Geology Goldschmidtstr. 3, Goettingen, 37077 Germany
AB: The dimensioning of geothermal energy usage from deep hot-dry-rock reservoirs requires knowledge of the effective heat exchange surface between liquid and solid phases. Tracer tests are an appropriate technique for the investigation of this surface since matrix diffusion and hence tracer transport is a function of the effective contact area. However, investigations within such reservoirs are difficult: Usually only one borehole is available due to economic restrictions, high temperature stimulates tracer decay, and matrix diffusion is masked by hydrodynamic dispersion within the advective pore space due to heterogeneity. To overcome these difficulties, an experimental concept was developed. It is based upon the synchronous application of several non-retarding tracers with different diffusion coefficients. Using the single-well injection-withdrawal (SWIW) technique, the effect of hydrodynamic dispersion is partially reversed, while the effect of molecular matrix diffusion is enhanced. Hence the differences between the tracer breakthrough curves are due to different matrix diffusion. Knowing the diffusion coefficients of the individual tracers, an effective contact surface between liquid and solid phases can be estimated. Since each tracer is subjected to the same advection and dispersion, the formation heterogeneity is of minor importance and the different transport behavior can be attributed to the molecular diffusion only. The tracers under investigation are sulfonated naphthalene- formaldehyde condensates (SNFC) and the corresponding monomeres. These compounds are available in various chain lengths, spanning a range of aqueous diffusion coefficients. Modern HPLC methods enable their analysis down to a �g/l level. Since SNFC are environmentally benign, they could be recently applied within the unsaturated soil zone, in a shallow aquifer as multi-tracer mixture, and in geothermal systems. The experimental approach and first results are presented.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 5104 Fracture and flow
DE: 5139 Transport properties
SC: Hydrology [H]
MN: 2003 Fall Meeting