Stress and fracture prediction in inverted half-graben structures

Abstract

Two-dimensional finite element models are used to study the temporal evolution and spatial distribution of stress and strain during half-graben inversion. Modeling is based on forward balanced cross-sections and involves various parameter studies to assess the impact of different syn- and post-rift lithologies as well as scenarios with syn-tectonic deposition or erosion, respectively. In total, 48 different scenarios were analyzed. Modeling results are presented as contour maps of total displacement, brittle plastic strain, mean stress and differential stress as well as vector diagrams showing the orientation of the principal stresses. This information can be combined to predict fracture types and fracture orientations and provide fracture intensity maps throughout the evolving inversion structure. Modeling results demonstrate quantitatively how stress and strain in inverted half-grabens critically depend on the rheology of the syn- and post-rift sediments and their mechanical interaction as well as the stress transfer through the hanging wall. Four end-member scenarios can be identified on the basis of distinct fault reactivation tendencies, deformation styles and fracture patterns. Model predictions are compared to natural examples of inverted half-graben structures using seismic as well as outcrop data. Thus, the geomechanical models can provide templates for a reservoir- (kilometer-) scale prediction of tectonic stresses and fractures for a common type of inversion structure.