| Title | Stress field rotation in the EGS well GRT-1 (Rittershoffen, France) |
|---|---|
| Authors | Hehn, R; Genter, A; Vidal, J; Baujard, C |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | Upper Rhine graben, Rittershoffen, geothermal well GRT-1, Stress field, stress orientation, drilling induced tensile fracture, Alsace |
| Abstract | The stress state in GRT-1, a recent deep geothermal well drilled in Northern Alsace (Upper Rhine Graben, France) has been investigated based on drilling-induced fractures (DIF) observed on borehole acoustic logs. Some of those fractures are compressive fractures, known as Breakouts, and others are tensile fractures, called DITFs in this study. They are used to estimate the orientation of the stress field because they occur respectively in the direction of Shmin and SHmax. At a small scale, SHmax orientation follows a cyclic profile repeating every 50 m MD along the borehole. Those small cycles participate to a more global trend, where the orientation of SHmax tend to reach the regional orientation (N145°E) in weaker layers (as clays or marls), and turn clockwise toward N50°E in hard rock layers (as dolomite and sandstone). Finally, this study shows that the entire stress state of the sedimentary layer is decoupled from the basement one: the orientation of SHmax is N155°E in the basement, but is globally N20°E in the sedimentary layer. |