| Title | Quantification and Classification of Petrothermal Potentials: an Exploration Scheme for Mid-German Crystalline High Basement Rocks |
|---|---|
| Authors | Sebastian WEINERT, Kristian BÄR, Mohammad Javad AFSHARI MOEIN, Günter ZIMMERMANN, Ingo SASS |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | petrothermal systems, petrothermal potential, quantification, classification |
| Abstract | Temperatures above 100 °C and more are the key requirement for geothermal power production. In many geotectonic settings, as they occur in Germany, reservoir temperatures exceeding 100 °C can usually only be found in reservoir systems deeper than 3 km. Hydrothermal systems reach such temperatures only in special geotectonic settings, e.g. the Upper Rhine Graben or the Molasse basin in Germany, and usually are already under exploration and exploitation. Besides these easy to access hydrothermal systems, the majority of the geothermal potential is associated to petrothermal systems in crystalline or metamorphic basement rocks. However, to locate and quantify these petrothermal potentials is still a challenging task. We propose an exploration scheme for petrothermal potentials, which is applied to the crystalline basement of the Mid-German Crystalline High as part of the European Variscan basement. The exploration is composed by three tiers and subdivided into an outcrop analogue study, a conceptual geological 3D structural model and the estimation of petrothermal potentials based on the comprehensive geothermal 3D model composed as result of the first two tiers. Petrothermal potentials are classified based on a custom-made weighting matrix based on multi-criteria analysis. Thermophysical rock properties such as thermal conductivity and thermal diffusivity as well as petrophysical rock properties including porosity, grain and bulk density or compressional wave velocities are assessed by this weighting matrix. Reservoir geometry, rock mechanical and structural geological data are fed into the weighting matrix as additional criteria to define the potential. Petrothermal potentials will be quantified by the volumetric method and assumption of recovery factors as experienced by current EGS projects as e.g. Soultz-sous-Forêts or Rittershofen. Necessary stimulation processes during reservoir development are considered by the implementation of rock mechanical properties and the recent stress field. By interlinking the latter ones and the implementation of fracture progression models, an estimation of resulting fracture dimensions can be performed. It is further intended to validate permeability evolution during fracture growth by hydro-mechanically coupled triaxial tests of various fractured crystalline samples. |