| Abstract |
Within the scope of the research project "3Dmodelling of the deep geothermal potentials of Hesse" the deep geothermal potential of the Federal State of Hesse was assessed in a comprehensive approach. The heat in place has been quantified and the deep geothermal potentials were analyzed for different geothermal systems, as hydrothermal and petrothermal systems as well as fault related and closed systems like deep borehole heat exchangers. For the assessment of the deep geothermal potential, knowledge of the geological structure and the geothermal properties of the potential reservoir rocks are indispensable. Therefore, a 3D geological structural model of the Federal State of Hesse (Germany) has been developed (Arndt 2012). For the assessment of deep geothermal potentials, the reservoir temperature is the key parameter. Therefore, the temperature distribution in the subsurface was modelled to a depth of 6 km below surface using actual data measured in deep wells. This model allows the prognosis of the underground temperature with a depth dependent accuracy of ±5 K ± 5 K/km. Predictions of the geothermal properties are based on data sets of outcrop analogue studies, borehole data and core investigations as well as hydraulic test data compiled within the scope of this study. Systematic measurements of thermophysical and hydraulic rock properties such as thermal conductivity, thermal diffusivity, heat capacity, density, porosity and permeability of relevant geologic formations have been combined with in situ temperature measurements, hydrothermal upwelling zones, characteristics of geological faults in different lithologies and were added to the 3D geological structural model. Since both the hydraulic and thermophysical properties strongly depend on the in situ conditions of the reservoir, the lab and field data had to be adapted considering the temperature and pressure of the reservoir. Thus, the outcrop analogue data was compared with in situ data from deep hydrocarbon exploration wells to develop empiric algorithms for the depth and temperature dependence of the hydraulic properties. For the thermophysical properties established equations from crustal scale thermal models were used. Evaluation of the deep geothermal potentials are based on the various rock and reservoir properties stored in the 3D geothermal model which were assessed using a Analytic Hierarchy Process (AHP) based multiple criteria decision support system to identify and visualize different geopotentials cell based incorporating their relevance for different deep geothermal systems. Depending on the chosen parameters, the model is highly capable to evaluate many different geopotentials. Therefore, threshold values based on technical constraints for each parameter were defined specifying whether the potential is very high, high, medium, low or very low. The resulting geothermal model, which incorporates the quantification and the analysis of the deep geothermal potentials, is an important tool, which can be used at an early stage of the planning phase for the design of geothermal power plants. Furthermore, it allows quantification of the deep geothermal potential and is intended to be an instrument for public information. |