Plasticity Model for Stress-Release Induced Damage

Stress-release damage in rocks may result in a permanent alteration of the rock properties, which has to be quantified and modeled in order to describe the in situ behavior of the rock based on tests from core specimens. A dual yield surface elastoplastic model is introduced to describe stress-release damage in a synthetic sandstone manufactured as an analogue to a reservoir sandstone. The synthetic sandstone, composed of sand and quartz cement, is cemented under in situ stress conditions. This process allows the quantification of damage during a stress-release that simulates the coring process. In the model, one yield surface describes the behavior of the sand matrix and the other the behavior of the cement, while the total stresses are given as in mixtures theories. The model is calibrated on synthetic sandstone test results and used for back analysis of the experiments.