A multi-stage 3-D stress field modelling approach exemplified in the Bavarian Molasse Basin

Abstract

Abstract. The knowledge of the contemporary in situ stress state is a key issue for safe and sustainable subsurface engineering. However, information on the orientation and magnitudes of the stress state is limited and often not available for the areas of interest. Therefore 3-D geomechanicalnumerical modelling is used to estimate the in situ stress state and the distance of faults from failure for application in subsurface engineering. The main challenge in this approach is to bridge the gap in scale between the widely scattered data used for calibration of the model and the high resolution in the target area required for the application. We present a multi-stage 3-D geomechanical-numerical approach which provides a state-of-the-art model of the stress field for a reservoir-scale area from widely scattered data records. Therefore, we first use a large-scale regional model which is calibrated by available stress data and provides the full 3-D stress tensor at discrete points in the entire model volume. The modelled stress state is used subsequently for the calibration of a smaller-scale model located within the large-scale model in an area without any observed stress data records. We exemplify this approach with two-stages for the area around Munich in the German Molasse Basin. As an example of application, we estimate the scalar values for slip tendency and fracture potential from the model results as measures for the criticality of fault reactivation in the reservoir-scale model. The modelling results show that variations due to uncertainties in the input data are mainly introduced by the uncertain material properties and missing S H max magnitude estimates needed for a more reliable model calibration. This leads to the conclusion that at this stage the model's reliability depends only on the amount and quality of available stress information rather than on the modelling technique itself or on local details of the model geometry. Any improvements in modelling and increases in model reliability can only be achieved using more high-quality data for calibration.

RETRACTED ARTICLE: Predictability and controlling factors of overpressure in the North Alpine Foreland Basin, SE Germany: an interdisciplinary post-drill analysis of the Geretsried GEN-1 deep geothermal well

“…Although the stress regime of the North Alpine Foreland Basin in SE Germany is controversially discussed (Drews et al 2018;Greiner and Lohr 1980;Lohr 1978;Megies and Wassermann 2014;Müller and Nieberding 1996;Müller et al 1988;Reinecker et al 2010;Seithel et al 2015;von Hartmann et al 2016;Ziegler et al 2016), Drews et al (2018) showed that disequilibrium compaction with the assumption of vertical stress as a proxy for mean stress is a valid model to estimate pore pressure and overpressure from shale velocities in the North Alpine Foreland Basin in SE Germany.…”

The 3D stress state from geomechanical–numerical modelling and its uncertainties: a case study in the Bavarian Molasse Basin

“…To model the initial stress state, we follow the two-step approach of applying gravity followed by lateral displacement as explained in detail in Hergert et al (2015). The model rheology is linear elastic and rock properties are the same as given in Ziegler et al (2016) and listed in Table 1. To solve the resulting 3D partial differential equation that describes the equilibrium of the volume forces (gravity) and surface forces (displacement boundary conditions), we use the finite element method.…”

“…3). This entire process is referred to as model calibration and is assisted by the FAST Calibration tool which is documented in detail in Ziegler et al (2016) and Ziegler (2018). At the end of the calibration procedure, the best-fit stress state is available at each node in the model.…”

Predictability and controlling factors of overpressure in the North Alpine Foreland Basin, SE Germany: An interdisciplinary post-drill analysis of the Geretsried GEN-1 Deep Geothermal Well

“…Although the stress regime of the North Alpine Foreland Basin in SE Germany is controversially discussed (Drews et al 2018;Drews et al 2019;Greiner and Lohr 1980;Lohr 1978;Megies and Wassermann 2014;Müller and Nieberding 1996;Müller et al 1988;Reinecker et al 2010;Seithel et al 2015;von Hartmann et al 2016;Ziegler et al 2016), Drews et al (2018) showed that disequilibrium compaction with the assumption of vertical stress as a proxy for mean stress is a valid model to estimate pore pressure and overpressure from shale velocities in the North Alpine Foreland Basin in SE Germany. This is also supported by the interpretation of leak-off tests and formation integrity tests in shale packages in the greater Munich area, which suggest the presence of a normal faulting or trans-tensional stress regime in the Cenozoic basin fill of the North Alpine Foreland Basin in the greater Munich area (Drews et al 2019).…”