Articles | Volume 7, issue 5
Research article
21 Sep 2016
Research article |  | 21 Sep 2016

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

Moritz O. Ziegler, Oliver Heidbach, John Reinecker, Anna M. Przybycin, and Magdalena Scheck-Wenderoth

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 geomechanical–numerical 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 SHmax 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.

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Short summary
Subsurface engineering relies on sparsely distributed data points of the stress state of the earth's crust. 3D geomechanical--numerical modelling is applied to estimate the stress state in the entire volume of a large area. We present a multi-stage approach of differently sized models which provide the stress state in an area of interest derived from few and widely scattered data records. Furthermore we demonstrate the changes in reliability of the model depending on different input parameters.