| Field and laboratory investigators have observed thin, tabular zones of localized compressional deformation in high porosity sandstone. In experiments, these 'compaction bands' form perpendicular to the maximum stress and display greatly reduced porosity. Permeability is reduced by over an order of magnitude, and may affect the withdrawal of fluids from reservoirs. Studies addressing band formation as a type of strain localization predict the onset of the bands in a range of constitutive parameters roughly consistent with experiments, but predictions are highly dependent on the constitutive relation used. Previous yield cap constitutive models employed a single deformation criterion, linking hydrostatic and shear response. In this work, we propose a pair of yield cap models employing separate inelastic deformation parameters for volumetric and shear response. The new models are able to model deformation in complex loading paths and predict compaction localization accurately. |
