Influence of major fault zones on 3-D coupled fluid and heat transport for the Brandenburg region (NE German Basin)

Abstract

Abstract.To quantify the influence of major fault zones on the groundwater and thermal field, 3-D finiteelement simulations are carried out. Two fault zones -the Gardelegen and Lausitz escarpments -have been integrated into an existing 3-D structure of the Brandenburg region in northeastern Germany. Different geological scenarios in terms of modelled fault permeability have been considered, of which two end-member models are discussed in detail. In addition, results from these end-member simulations are compared to a reference case in which no faults are considered.The study provides interesting results with respect to the interaction between faults and surrounding sediments and how it affects the regional groundwater circulation system and thermal field.Impermeable fault zones seem to induce no remarkable effects on the temperature distribution; that is, the thermal field is similar to the no-fault model. In addition, tight faults have only a local impact on the fluid circulation within a domain of limited spatial extent centred on the fault zone. Fluid flow from the surrounding aquifers is deviated in close proximity of the fault zones acting as hydraulic barriers that prevent lateral fluid inflow into the fault zones.Permeable fault zones induce a pronounced thermal signature with alternating up-and downward flow along the same structures. Fluid flow along the plane of the faults is principally driven by existing hydraulic head gradients, but may be further enhanced by buoyancy forces. Within recharge domains, fluid advection induces a strong cooling in the fault zones. Discharge domains at shallow depth levels (∼ < −450 m) are instead characterized by the presence of rising warm fluids, which results in a local increase of temperatures which are up to 15• C higher than in the no-fault case. This study is the first attempt to investigate the impact of major fault zones on a 3-D basin scale for the coupled fluid and heat transport in the Brandenburg region. The approach enables a quantification of mechanisms controlling fluid flow and temperature distribution both within surrounding sediments and fault zones as well as how they dynamically interact. Therefore, the results from the modelling provide useful indications for geothermal energy exploration.

The 3D conductive thermal field of the North Alpine Foreland Basin: influence of the deep structure and the adjacent European Alps

“…Such phenomena have already been described for other basins in different tectonic settings (Bayer et al 1997;Allen and Allen 2005;Stephenson et al 2009;Noack et al 2010;Cherubini et al 2014) and are laterally influencing each other. For the Alps and the Molasse Basin this implies that the heat coming from the asthenosphere together with the heat generated in the crystalline crust arrives at the base of the insulating sediments of the Alpine Body and the Molasse Basin, is stored within the sediments and causes higher temperatures within the latter.…”

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

“…Ascending warmer fluid in the area of the positive thermal anomalies and descending colder fluid in the area of the negative thermal anomalies driven by density gradients within the faults caused insignificant (1-5 K) local cooling which did not lead to changes in the general temperature trend. Such a limited spatial influence of permeable fault zones on the regional thermal field has been already described by Cherubini et al (2014). However, an implementation of permeable fault zones into reservoir-scale models might still be of high importance for the local temperature.…”

“…3) as described before. Accordingly, high hydraulic conductivities prevail in the northern and eastern-most model parts, and Like the layers, all faults have been characterized with hydraulic properties following Schulz and Thomas (2012) and Cherubini et al (2014). Thereby, a hydraulic conductivity much higher than of any other layer of the model was assumed for the faults to open permeable fluid flow paths.…”

“…Such influence of hydraulically conductive major fault zones on the thermal field has also been studied by Cherubini et al (2014) for the area of Brandenburg in north-eastern Germany using a basin-scale 3D numerical model of coupled fluid flow and heat transport. Their results, however, indicate only a limited lateral influence of permeable fault zones on the regional thermal field.…”

Regional hydraulic model of the Upper Rhine Graben

“…With respect to the regional hydrodynamics, previous studies have identified the URG as a regional discharge valley. The main recharge is thought to occur along the graben flanks (Black Forest, Vosges Mountains and Odenwald) with groundwater discharging preferentially within the graben itself (Clauser and Villinger, 1990;Freymark et al, 2019;Guillou-Frottier et al, 2013;Lampe and Person, 2002;Pribnow and Clauser, 2000). Indeed, the deepest topographic point (also the lowest elevation of the hydraulic head) is found in the northern domain within the federal state of Hesse.…”