Characterization of main heat transport processes in the Northeast German Basin: Constraints from 3-D numerical models

Abstract

[1] To investigate and quantify main physical heat driving processes affecting the present-day subsurface thermal field, we study a complex geological setting, the Northeast German Basin (NEGB). The internal geological structure of the NEGB is characterized by the presence of a relatively thick layer of Permian Zechstein salt (up to 5000 m), which forms many salt diapirs and pillows locally reaching nearly the surface. By means of three-dimensional numerical simulations we explore the role of heat conduction, pressure, and density driven groundwater flow as well as fluid viscosity related effects. Our results suggest that the regional temperature distribution within the basin results from interactions between regional pressure forces as driven by topographic gradients and thermal diffusion locally enhanced by thermal conductivity contrasts between the different sedimentary rocks with the highly conductive salt playing a prominent role. In contrast, buoyancy forces triggered by temperature-dependent fluid density variations are demonstrated to affect only locally the internal thermal configuration. Locations, geometry, and wavelengths of convective thermal anomalies are mainly controlled by the permeability field and thickness values of the respective geological layers.Components: 9000 words, 9 figures, 2 tables.

Deep 3D thermal modelling for the city of Berlin (Germany)

“…In contrast, we do not find indications for density and buoyancy-driven free convection of the modelled fluids. This is in agreement with the results of Kaiser et al (2011) and Noack et al (2013 -this issue). They show that conditions facilitating free convection are rarely met within the NEGB and that free convection will be suppressed where the hydraulic potential is high, so that the thermal signature of the system is controlled rather by the forced convective flow components.…”

“…The relative impact of different heat transport mechanisms on the thermal field of the NEGB has been demonstrated before (e.g. Kaiser et al 2011). Also for the Perth metropolitan area, the consideration of coupled fluid and heat transport has been shown to be essential to estimate the exploitable heat in place (Schilling et al 2013).…”

“…Balling et al 2013 -this issue;Bayer et al 1997;Cacace et al 2010;Cherubini et al 2013 -this issue;Hurtig and Rockel 1992;Noack et al 2010;Norden et al 2008). Beside thermal conduction, also heat transfer coupled to flowing groundwater has been identified as an important controlling factor for subsurface temperatures in the NEGB (Cacace et al 2010;Kaiser et al 2011;Noack et al 2013 -this issue). Considering the complex interplay between crustal structure and temperatures in the NEGB and the limited availability of direct temperature observations for depths greater than 1 km in the Berlin area ( Fig.…”

“…In order to integrate into the numerical model existing discontinuities (geological holes) characterizing the Rupelian Clay unit, the geometries of these hydrogeologic windows have been forced onto the model by means of a constrained triangulation around their boundaries. A GIS-based approach has then been followed to set the correct parameterisation in these subdomains (for more details see Kaiser et al 2011). …”

The origin of deep geothermal anomalies in the German Molasse Basin: results from 3D numerical models of coupled fluid flow and heat transport

“…To enable a reliable temperature prediction for a geothermal reservoir, the significant heat transport mechanisms coupled to the fluid flow processes in the respected area have to be understood on a bigger scale. Thereby, different types of heat transport acting in a sedimentary basin should be considered (Kaiser et al 2011): (1) conductive heat transport, where the efficiency of heat transfer depends on the thermal conductivity of the lithology of the respective layer and the occurring thermal gradient; (2) advective heat transport, where heat is transported passively by pressuredriven fluid flow; and (3) convective heat transport, where heat is transported by density-driven convective fluid flow. In a fluid influenced geothermal environment, such as the Molasse Basin, a combination of all three heat-driving mechanisms can be expected, as been already shown for other sedimentary basins, e.g.…”