Hdr Research Programme and Results of Drill Hole Urach 3 to Depth of 4440 M - the Key for Realisation of a HDR Programme in Southern Germany and Northern Switzerland

Abstract

The prerequisites for specific research into the use of Hot Dry Rock geothermal energy at great depths and temperatures of up to 147?C in Europe were created with the drilling and completion of the 3334 m deep research drill hole Urach 3 in its phase I (1977/78), and its subsequent extension to 3488 m in phase I1 (1982/83) within the metamorphic gneiss rock of Urach. Basic results concerning the temperature field, joint system, stress field and hydraulic behaviour of the rock were achieved. Within the scope of a feasibility study (1990-1996) local boundary conditions, infrastructure, user potential and a preliminary utilisation concept (3 MWel, 17 MWth) were evaluated. Geological parameters were determined by the extension of the already existing drill hole Urach 3 from 3488 m to 4445 m depth. The bottom hole temperature at true vertical depth of 4394.72 m was determined with 170OC. It can be proved that the temperature gradient is constant with 2.9 "W100 m depth. As main lithological units metamorphic rocks such as biotite-gneiss, anatexite and diatexite were drilled. The crystalline is effected by brittle deformation. The resulting fixture system is sealed by hydrothermal products (clays, carbonates, sulphates). The aperture of fractures is in the range of some tenth to 10 millimetres. Televiewer and FMI logs show a general northsouth orientated joint system and borehole breakouts around N 80-120" N. The orientation of maximum horizontal stress direction was determined with N 170" E. Wireline Hydro& Stress measurements at 3352 m depth yields values of Shmin between 41-50 MPa. Estimated stress magnitudes of Anelastic Strain Recovery (ASR) measurements on cores from 4425 m depth yields values of Sh=63 MPa. It is proposed that the Urach site located in a widespread tectonic horizontal strike-slip system is suitable for a HDR demonstration project. The results can be applied in southern German and northern Swiss regions.