Stress State at Soultz-Sous-ForÍts to 5 km Depth from Wellbore Failure and Hydraulic Observations

Abstract

Observations of breakouts and drilling-induced tension fractures (DITFs) in two 5 km deep boreholes of the European Enhanced Geothermal Project of Soultz-sous-ForÍts, France have been combined with the analysis of pressure data from stimulation tests in all 3 deep wells to obtained a description of the state of stress in the granite down to 5 km depth. The orientation of the maximum horizontal stress, SHmax, in the 5 km deep reservoir is found to be N169?E±14?, in accord with previous results from the 3.5 km reservoir. Analysis of pressure at the casing shoe of the deep boreholes during stimulation permits the profile of Shmin magnitude to be extended down to 5 km depth. Finally, by combining all available information, bounds were set on the magnitude of SHmax. The result is a linear characterisation for the stress state at Soultz that is valid between depths of 1.5-5.0 km (excluding the effects of local stress heterogeneity).