Influence of the Main Border Faults on the 3D Hydraulic Field of the Central Upper Rhine Graben

Abstract

The Upper Rhine Graben (URG) is an active rift with a high geothermal potential. Despite being a well-studied area, the three-dimensional interaction of the main controlling factors of the thermal and hydraulic regime is still not fully understood. Therefore, we have used a data-based 3D structural model of the lithological configuration of the central URG for some conceptual numerical experiments of 3D coupled simulations of fluid and heat transport. To assess the influence of the main faults bordering the graben on the hydraulic and the deep thermal field, we carried out a sensitivity analysis on fault width and permeability. Depending on the assigned width and permeability of the main border faults, fluid velocity and temperatures are affected only in the direct proximity of the respective border faults. Hence, the hydraulic characteristics of these major faults do not significantly influence the graben-wide groundwater flow patterns. Instead, the different scenarios tested provide a consistent image of the main characteristics of fluid and heat transport as they have in common: (1) a topography-driven basin-wide fluid flow perpendicular to the rift axis from the graben shoulders to the rift center, (2) a N/NE-directed flow parallel to the rift axis in the center of the rift and, (3) a pronounced upflow of hot fluids along the rift central axis, where the streams from both sides of the rift merge. This upflow axis is predicted to occur predominantly in the center of the URG (northern and southern model area) and shifted towards the eastern boundary fault (central model area).

Global Sensitivity Analysis to Optimize Basin-Scale Conductive Model Calibration – A Case Study From the Upper Rhine Graben

“…Due to the high dimensionality of the model, a hydrothermal simulation becomes computationally very costly, making global sensitivity analyses as investigated here prohibitively expensive. Furthermore, the number of parameters that need to be calibrated increases, making a calibration of the individual parameters increasingly difficult, due to the data sparsity (Freymark et al, 2019).…”

“…This region has gained significant interest for deep geothermal exploration due to its increased geothermal gradient, for example around Soultz-sous-Forêts, Landau, and Bruchsal (Agemar et al, 2013(Agemar et al, , 2014Illies, 1972;Pauwels et al, 1993;Geothermie, 2007;Vidal et al, 2015). However, obtaining reliable spatial temperature distributions is a major challenge as seen in the ongoing discussion in literature (Agemar et al, 2013(Agemar et al, , 2014Freymark et al, 2017Freymark et al, , 2019GeORG-Projektteam, 2013;Stober & Bucher, 2015), also because of the unclear influence of advection on the temperature distribution within the Upper Rhine Graben. So far, only "trial-and-error" model calibrations have been performed in basin-scale models of this region (Freymark et al, 2017).…”

Analyzing the influence of correlation length in permeability on convective systems in heterogeneous aquifers using entropy production

“…Additionally to permeability of a reservoir, its structure, i.e., abrupt changes in reservoir thickness, has a strong influence on the convective system. Such changes are usually caused by fault zones which not only influence reservoir structure, but normally also the spatial permeability distribution, and can thus influence groundwater flow paths (Freymark et al 2019;Inbar et al 2019). In terms of their permeability relative to that of the surrounding rock, fault zones may be more permeable, similarly permeable, or less permeable.…”

THM modeling of gravity anomalies related to deep hydrothermal circulation at Soultz-sous-Forêts (France)

“…The validation of this main hypothesis in our modeling has been discussed and supported in Vallier et al (2018). The recent work of Freymark et al (2019) highlights a weaker role than expected of the major border faults on the hydrothermal circulation at the Central URG scale.…”