Stress model for Germany – Basement

The TU Darmstadt subproject focuses on the compilation of basement structures of Germany and its vicinities. Thus, data on the crustal structure from the pre-permian sediments up to the crust-mantle boundary are considered. In consequence results of geophysical investigations are consulted as main data sources.

The geometry of the entire model, consisting of the basement units and overburden, will be used as a basis for the discretization to a geomechanical-numerical model. After the definition of the material properties and the boundary conditions, the equilibrium of the acting forces will be calculated in a stress-strain analysis. The stress model will be calibrated by iterative adaptation to stress data that have been measured in-situ. The resulting “best-fit” model allows stress predictions for areas, where no measured stress data are available. Furthermore, the working schedule includes flanking generic parameter studies on the influence of basement structures on the stress field.

Scaling of rock properties

Furthermore, the scale dependent selection of mechanical rock parameters will be investigated. Existing concepts are compared, which allow a quantitative inclusion of the mechanical effect of the interface structure (faults or joints) on the basis of mechanical rock parameters which can be determined in the laboratory (e.g. Young’s modulus, Poisson ratio, friction angle, uniaxial compressive strength). Accordingly, the rock properties change with the scale or the element size of the geomechanical-numerical model. In addition to empirical methods from practice, Discrete Fracture Network (DFN) models that allow a statistically equivalent fracture network description will be investigated for up-scaling. In combination with mechanical rock properties and mechanical properties at the discontinuities, a spatially variable and anisotropic Young’s-modulus, representing a large rock volume, can be calculated.

Model structure and results