| Abstract |
The European Hot Dry Rock programme is located in the Rhine Graben at Soultz-sous-ForÍts. Two deep boreholes (GPK1and GPK2) were drilled in fractured granite to depths of 3590 and 3876 m, respectively, reaching temperatures between 150 and 170?C. Separated from each other by a horizontal distance of 450 m, the two wells were tested in 1997. A four-month circulation test with a permanent flowrate up to 25 kg/s provided thermal, hydraulic and geochemical data from the Soultz system. Since this test, one of the wells (GPK2) was deepened to 5,000m. In order to model water-rock interactions, the following processes have to be defined, measured or analysed: minerals assemblages in contact with water, fluid composition, temperature evolution, pressure and flow rate in the different interaction zones, such as the porous matrix, small and large fractures. Another goal of this work is to develop a geochemical model that will handle highly saline solutions (brines up to 100 g/l) at temperatures up to 200?C, and to include reactions. A new geochemical code is under development, based on CHEMTOUGH. To acquire a better understanding of the geochemical processes taking place between the fluids and the fractured hot rocks, geochemical data from six different Hot Dry Rock reservoirs are reviewed. Saturation indexes are computed with the code PHREEQC. Using data from the Soultz reservoir, a thermodynamic model is developed based on a simplified Pitzer approach. The goal of the work is to use realistic assumptions to better constrain the model and to mitigate the lack of Pitzer parameters for the Soultz brine. Later, kinetic laws will be included in the model in order to couple reactions with transport. |