| Title | Local Stress Anomaly, Their Interplay to Deep Seated Fault Structures and Geomechanical Characterization of Geothermal Reservoirs in South Germany |
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| Authors | Robin SEITHEL, Roman SCHMIDT, Thomas KOHL, Andreas HENK, Ingrid STOBER |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Local Stress anomaly,Upper Rhine Graben, fault zones, triaxial tests, 1-D hydro mechanical Model |
| Abstract | Due to an increased heat flow and the presence of several aquifers, the Upper Rhine Graben (URG) offers favorable conditions for geothermal utilization and several geothermal projects emerged in the last decade. Previous research in this tectonic setting proved that the hydraulic and geomechanical behavior of the geothermal reservoirs is mainly governed by the existence of meso-scale fractures and deep large-scale faults systems. The occurrence of induced seismicity as a result of fluid injection, however, clearly demonstrates that a better understanding on their role is still required. Especially the local stress field can be significantly influenced by the existence of fault zones, which is exemplarily shown on a case study in the Molasse Basin. There, measured image logs in three geothermal wells demonstrate that the stress field in the vicinity of these reservoir structures can be rearranged. Fracture data as well as stress indicators were interpreted using these logs and analyzed to determine the local stress field. As a result, two of the wells with the all over the molasse basin existing fracture set (E - W and N - S) point to the regional existing N - S oriented strike slip stress field. The third well with a significantly different fracture system point to a N–S oriented normal faulting regime or a 40° counter clock’ wise rotated strike slip stress regime. So, the fracture system and the stress regime demonstrate local stress changes influenced by existing fault structures. This research aims to a better characterization and parameterization of deep reaching faults and is intended to establish an improved understanding of their impact on reservoir mechanics. Our research comprises additionally geomechanical experiments (triaxial tests) with different rock types (granite and sedimentary rocks) to gain insight into fault parameterization and behavior under varying P/T conditions. Furthermore, geological field work on existing faults accessible in underground mines will be carried out to characterize these structures in the field. Besides this lab and field approach, another focus lies on the development of site-specific numerical models to predict the stress distribution and the permeability evolution of large-scale fault systems over geologic time scales. |