| Title | Fracture Mapping and Determination of Horizontal Stress Field by Borehole Measurements in HDR Drillholes Soultz & Urach |
|---|---|
| Authors | Helmut Tenzer |
| Year | 1995 |
| Conference | World Geothermal Congress |
| Keywords | borehole imagery, sonic logs, fracture mapping, HDR, Soultz, Urach |
| Abstract | Well logging with borehole imagery and sonic logs enables continuous recording of natural and artificial planar The fracture system in Soultz granite was determined to be N S with submaxima at N E and N E. The orientation of the maximum horizontal stress was determined to be N and N Results of VAL. and DSI logging (sonic tools) and the evaluation of Stoneley wave reflections enables the determination of hydraulically activated joints and fractures. Investigations on microcracks show an orthogonal strike direction of N and N E. Structural analysis of the joint system in drillhole Urach 3 between 4000 and 4444 m obtains a maximum strike of N S Hydrofrac packer tests at 3352 depth yield stress values of and of The major horizontal stress direction was determined hy different methods to be between N and N Results of ASR measurements on cores from 4424 m depth yield magnitudes of between 99 and 137 Interpretation of leak-off tests obtained magnitudes of around 65 at 4420 m depth. The stress regime in the Urach gneiss is characterized by a nearly left faulting system with the maximum principal stress having NNW-SSE direction. The classical Hot Dry Rock technology can here be followed in the wide spread tectonic, horizontal strike-slip system. In the Soultz field the natural hydrothermal convection and the of the tension field in the expanding tectonics of the Upper Rhein Graben as well as the major fault systems must be included in any closer investigation of multiple artificial fracture system that are to be used to generate a heat exchanger. |