The thermal field of the Upper Rhine Graben – Temperature predictions based on a 3D model

The Upper Rhine Graben (URG) is one of the regions in Germany with promising potentials for deep geothermal energy production. As part of the EU-funded project “IMAGE” (Integrated Methods for Advanced Geothermal Exploration), we aim to understand the processes and physical rock properties that control the temperature distribution in the deep subsurface of the URG. Typically, numerical models are developed to predict the hydrothermal conditions and to reduce the risk of drilling non-productive geothermal wells. One major problem related to such reservoir-scale models is setting appropriate boundary conditions that define, for instance, how much heat enters the reservoir from greater depths. To address this problem, we first develop a lithospheric-scale 3D structural model that differentiates the main geological units of the lithosphere including the shallow sedimentary basin fill but also the configuration of the deeper crust and lithospheric mantle. Based on this model we solve the steady-state conductive heat equation to understand the first-order controlling factors of the regional thermal field. Furthermore, this regional thermal model provides the boundary conditions for smaller and higher resolved models of the basin fill, for which coupled heat and fluid transport is simulated in a next step. We present the methodological workflow, the developed 3D structural and thermal models, and assess how heat transport mechanisms in response to lithological and structural features on different scales control subsurface temperatures

Seismic reflection data integrated in a combined 3D isostatic and gravity modelling approach – new insights into the lithospheric structure of the northern Upper Rhine Graben and Hessen (Germany)

Seismic reflection and refraction profiles reveal information on first-order heterogeneities of the crust. After application of a suitable time-to-depth conversion we have re-interpreted near-vertical migrated seismic reflection data of the DEKORP project that image the deep subsurface of the northern Upper Rhine Graben and the federal state of Hessen. The most prominent feature in the crystalline crust, visible in these profiles, is a highly reflective lower crust differentiated from a 'transparent' upper crust showing considerably less continuous reflections. We present a workflow of integrating the seismic data into a combined 3D isostatic and gravity modelling approach. Basement depth as well as the thickness and lithological variations of the sediment fill are well known in the region. 3D isostatic calculations allow predicting the average density of the sub-sedimentary crystalline crust and thus the thickness distributions of the Upper and the Lower Crust for those parts of the study area where seismic information is missing. Finally, we calculate the 3D gravity response of the entire lithosphere of Hessen and interactively adjust the crustal density configuration to the measured gravity field while keeping the seismic information. The product of our approach, i.e. a lithospheric-scale observation-constrained 3D structural model, is used to numerically simulate heat transport processes for temperature predictions in this region of high potential for geothermal utilisation

Temperature Predictions for the Northern Upper Rhine Graben and Hessen (Germany) – a lithosphere-scale 3D modelling approach

The Upper Rhine Graben and its northern prolongation, the Hessian depression, were formed as part of the European Cenozoic Rift System in a complex extensional to transtensional setting. At present-day, the Upper Rhine Graben is one of the regions in Germany that are well suitable for deep geothermal exploitation. As part of the EU-funded project “IMAGE” (Integrated Methods for Advanced Geothermal Exploration), we aim to contribute to the development of an integrated and multidisciplinary approach for the exploration of geothermal reservoirs by understanding the processes and properties controlling the spatial distribution of key parameters such as temperature in the subsurface. Typically, numerical models are developed for predictions on the hydrothermal conditions and for reducing the risk of drilling non-productive geothermal wells. One major problem related to such reservoir-scale models is setting appropriate boundary conditions that define, for instance, how much heat enters the reservoir from greater depths. To understand the deep thermal field of the northern Upper Rhine Graben in the federal state of Hessen, we first develop a 3D structural model that differentiates the main geological units of the lithosphere including the shallow sedimentary basin fill. This model allows to solve the steady-state conductive heat equation and understand the first-order controlling factors of the regional thermal field. We present the database (e.g. seismic reflection data) and the methodological workflow (involving, e.g., 3D gravity modelling) that were used to develop the lithospheric-scale 3D structural model. Furthermore, we show how certain features of the structural model such as thickness variations of the radiogenic-heat-producing crystalline crust control the temperature distribution in the subsurface

The deep thermal field of the Upper Rhine Graben

The Upper Rhine Graben has a significant socioeconomic relevance as it provides a great potential for geothermal energy production. The key for the utilisation of this energy resource is to understand the controlling factors of the thermal field in this area. We have therefore built a data-based lithospheric-scale 3D structural model of the Upper Rhine Graben and its adjacent areas. In addition, 3D gravity modelling was performed to constrain the internal structure of the crystalline crust consistent with seismic information. Based on this lithosphere scale 3D structural model the present-day conductive thermal field was calculated and compared to measured temperatures. Our results show that the regional thermal field is mainly controlled by the configuration of the upper crust, which has different thermal properties for the Variscan and Alpine domains. Temperature maxima are predicted for the Upper Rhine Graben where thick insulating Cenozoic sediments cause a thermal blanketing effect and where the underlying crustal units are characterised by high radiogenic heat production. The comparison of calculated and measured temperatures shows a reasonable fit although local misfits indicate, as expected, an additional convective influence of fluid flow on the thermal field of the Upper Rhine Graben

Heterogeneous crystalline crust controls the shallow thermal field – a case study of Hessen (Germany)

We present a seismic- and 3D-gravity-constrained lithospheric-scale 3D structural model of Hessen that differentiates 7 sedimentary units, 5 Variscan upper crustal bodies, the lower crystalline crust and the lithospheric mantle. To predict the presentday subsurface temperatures, we solve the steady-state conductive heat equation by using a 3D FE method and assigning lithology-dependent thermal properties. We show that the thermal field is mainly controlled by the varying radiogenic heat production in the crystalline crust, which results in a colder NW and a warmer SE domain. Locally, this regional trend is superimposed by thermal blanketing of low-conductive sediments leading to higher temperatures

Temperature Predictions for geothermal Exploration – a Lithospheric-scale 3D Approach applied to the Northern Upper Rhine Graben

The Upper Rhine Graben and its prolongation, the Hessian depression, were formed as part of the European Cenozoic Rift System in a complex extensional to transtensional setting. At present-day, the Upper Rhine Graben is one of Germany’s the regions in Germany that are well suitable for deep geothermal exploitation. In the framework of the EU-funded “IMAGE” project “IMAGE” (Integrated Methods for Advanced Geothermal Exploration) we aim to contribute to the development of an integrated and multidisciplinary approach for the exploration of geothermal reservoirs by understanding the processes and properties controlling the spatial distribution of key parameters such as the underground temperature. Typically, reservoir-scale numerical models are developed for predictions on the subsurface hydrothermal conditions and for reducing the risk of drilling non-productive geothermal wells. One major problem related to such models is setting appropriate boundary conditions that define, for instance, how much heat enters the reservoir from greater depths. To understand the deep thermal field of the northern Upper Rhine Graben in the federal state of Hessen, we first develop a 3D structural model that differentiates the main geological units of the lithosphere including the shallow sedimentary infill. This model allows us to solve the steady-state conductive heat equation and understand the first-order controlling factors of the regional thermal field in the region. We present the database (e.g. reflection seismic data) and the methodological workflow (involving, e.g., 3D gravity modelling) that were used to develop the lithospheric-scale 3D structural model. Furthermore, we show how certain features of the structural model such as thickness variations of the radiogenic-heat producing crystalline crust control the temperature distribution in the subsurface