Horizontal Stress Orientation and Fractures from Image Logs in Geothermal Boreholes in Fractured Carbonates in Switzerland

The assessment of the stress orientations is the first step for geomechanical modelling and for the understanding of the relationships between fractures, stress and fluid flow. Furthermore, an understanding of the stress regime and stress field orientation is crucial for optimizing planning of boreholes with a view to minimizing the risks. In the present publication, the results of a borehole image interpretation performed for the National Cooperative for the Disposal of Radioactive Waste (NAGRA) from a geothermal borehole in Northern Switzerland are presented. The borehole was drilled in Upper Jurassic carbonates that are partly intensively fractured and also contain vugs. It is shown that analysis and interpretation of borehole images contribute to a better understanding of reservoirs and that these data are important for efficient drilling and effective development of adjacent boreholes. The interpretation adds detail to the regional structural and present-day stress picture of the Upper Jurassic strata in the area. The main stress orientation matches results from nearby measurements. The fractures are potentially governed by local or regional structural elements, i.e. faults or folds.