Influence of major fault zones on 3-D coupled fluid and heat transport for the Brandenburg region (NE German Basin)
To quantify the influence of major fault zones on the groundwater and thermal field, 3-D finite-element 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.