| Abstract |
The Permocarboniferous is the biggest hydrothermal reservoir in the northern Upper Rhine Graben and has so far been investigated in large scale studies only. To further assess the geothermal reservoir potential of the different lithostratigraphical units and facies types within this variscan intramontane basin, knowledge of their thermophysical and hydraulic properties is essential. Where the Cenozoic Upper Rhine Graben crosses the Permocarboniferous molasse basin, 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 power generation. The Permocarboniferous deposits are subdivided in different subgroups and consist lithologically of several facies types including fine-, middle- and coarse-grained sandstones, arcosic sandstones, siltstones, volcanics and subsidiary carbonates. Within the scope of this study, outcrop analogue studies west of the Graben in the Saar-Nahe Basin, and east of the Graben in the Sprendlinger Horst, Wetterau and the Wetterau-Fulda Basin are conducted. Each lithostratigraphic formation and lithofacies type is sampled at various outcrops, so that a sufficient amount of samples of the different sedimentary rock types is available in order to evaluate their petrophysical, sedimentological and geochemical characteristics statistically. The petrophysical parameters measured include porosity, permeability, density, thermal conductivity, thermal diffusivity and uniaxial compressive strength. So far, the petrophysical properties of more than 80 locations have been determined, showing a clear correlation with the facies type. Among the stratigraphical units, Glan-Subgroup´s and the Nahe-Subgroup´s porosity averages to 16.4 % and 15.4 %, permeability to 3.3·10-15 m² and 1.1·10-16 m², thermal conductivity to 2.3 W/(m·K) and 2.0 W/(m·K) and thermal diffusivity to 1.4·10-6 m²/s and 1.2·10-6 m²/s respectively. Additionally, the hydraulic conductivity of the reservoir was studied, using data of about 400 hydraulic tests conducted in 230 wells within the outcrop analogue area and were correlated to the stratigraphic units, the distance to the nearest fault and its orientation. Based on drilling and seismic data as well as geologic maps together with the compiled petrophysical and hydraulic data, it is intended to establish a 3D reservoir model of the Permocarboniferous in the northern Upper Rhine Graben and western Saar-Nahe Basin. Due to the importance of fault zones, lithostratigraphical units and facies types, detailed modeling will allow a better prediction of reservoir temperatures and production rates and will subsequently allow a better prognosis of the exploration risk. |