RESTLESS

Fault zones and induced seismicity

Fault zones with their potentially increased hydraulic permeability are a preferred exploration target for deep geothermal projects, particularly in the Upper Rhine Graben. The joint project RESTLESS is investigating the influence of fault zone lithology and architecture as well as the stress state on the occurrence of induced seismicity in connection with pore pressure changes. In addition to the Universities of Mainz and Erlangen, the Institute for Geothermal Resource Management in Bingen and Deutsche Erdwärme GmbH are partners in the project.

RESTLESS Faktenbox

Facts about the project

Project manager: Dr. Tesfay Mebrahtu PhD project: Sornnalad Wittayasettakul +++ Duration: 01.9.2023 – 31.12.2025 +++ Project funding: Bundesministerium für Wirtschaft und Klimaschutz (BMWK) Projektträger Jülich (PTJ)

Rock mechanical and fault gouge investigations in the Upper Rhine Graben.
Rock mechanical and fault gouge investigations in the Upper Rhine Graben.

For the parameterization of geomechanical fault zone models, both intact and deformed rocks as well as fractures are investigated. The sample material comes from surface outcrops with faults in Muschelkalk, Buntsandstein and basement rocks. Uniaxial, triaxial and Brazilian tests as well as direct shear tests are used to determine the elastic properties and failure criteria of the various fault zone rocks. Ring shear tests are also carried out on fault gauge material.

Geomechanical model showing the Bruchsal fault.
Geomechanical model showing the Bruchsal fault.

Geometries typical for fault zones in Muschelkalk, Buntsandstein and basement rocks are transferred to hydromechanical finite element models and parameterized accordingly. The numerical simulations are used in various scenarios to investigate the effects pore pressure changes have on the effective stresses and the localization of deformation in the fault zone. Subsequently, the modeling results will be upscaled to geomechanical reservoir models, which are unable to depict the details of a fault zone due to their much larger scale. A current geothermal project from the central Upper Rhine Graben will be used for the practical implementation and testing of the approach.

In preparation.

Status Quo & Outlook

The various rock mechanical investigations are currently underway on intact sample material and fractures from fault zones with lithologies typical of the Upper Rhine Graben. In addition, a geomechanical model is being set up for the case study in the central Upper Rhine Graben.