| Title | Facies and Diagenesis of Rotliegend Geothermal Reservoir Formations (Upper Rhine Graben, Germany): Impact on Thermophysical and Hydraulic Properties |
|---|---|
| Authors | Achim Aretz, Kristian Bär, Annette E. Götz, Ingo Sass |
| Year | 2014 |
| Conference | European Geothermal Workshop |
| Keywords | Rotliegend, Permocarboniferous, Upper Rhine Graben, outcrop analogue study, geothermal reservoir characterization, diagenesis, thermal conductivity, porosity, permeability |
| Abstract | The Permocarboniferous is the largest hydrothermal reservoir in the northern Upper Rhine Graben in SW Germany and has so far been investigated in large scale studies only. Where the Cenozoic Upper Rhine Graben crosses the Permocarboniferous molasse basin of the internal variscides, the top of the up to 2 km thick formation is located at a depth of 1 to 3 km and is overlain by Tertiary and Quaternary sediments. At this depth the reservoir temperatures exceed 150 °C, making it suitable for geothermal electricity generation. To further assess the potential of this geothermal reservoir knowledge of the different lithostratigraphical units and facies types within this former Variscan intramontane basin and their thermophysical and hydraulic properties is essential. In the present study, a combination of outcrop analogue studies and drill core investigations was conducted. In total 850 outcrop samples were analyzed, measuring porosity, permeability, thermal conductivity and thermal diffusivity. Furthermore, 60 plugs were taken from wells that encountered or intersected the Permocarboniferous in the northern Upper Rhine Graben at depths between 1,800 to 2,900 m. Petrographic analysis of 90 thin sections was conducted to quantify the mineral composition, sorting and rounding of grains, the kind of cementation to determine the type of diagenesis and its influence on porosity, permeability and the degree of compaction. |