Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland

Abstract

The stress field at depth is a relevant parameter the design of subsurface constructions and reservoir management. Yet the distortion of the regional stress field due to features such as sedimentary and tectonic structures or topography is often poorly constrained. We conduct stress sensitivity analysis using 3-D numerical geomechanical modelling with an elasto-plastic material law to explore impact of such site-specific features on the stress field in sedimentary sequence of the Swiss Alpine foreland. The dimensions are 14 × 14 × 3 km 3 and it contains 10 with different mechanical properties, intersected by two fault zones. An initial stress state is established involving a semi-empirical relationship between the ratio of to vertical stress and the overconsolidation ratio of sediments. The model results indicate that local can affect the stress field significantly to depths than the relief contrasts at the surface, especially in with horizontal tectonic loading. The complexity frictional properties of faults are also relevant. The greatest variability of the stress field arises across the different units. Stress magnitudes and stress anisotropy much larger in stiffer formations such as massive limestones than in softer argillaceous formations. The stiffer formations essentially carry the load of the far-field forces and therefore more sensitive to changes of the boundary conditions. This general characteristic of stress distribution in stiff and soft formations is broadly maintained also with loading towards the plastic limit. The stress field argillaceous sediments within a stack of formations with contrasting mechanical properties like in the Alpine appears to be relatively insensitive to changes in the boundary conditions and is largely controlled by the stiffness contrast with respect to the load-bearing formation.