Numerical modeling of gas injection induced cracking with unsaturated hydromechanical process in the context of radioactive waste disposal

Abstract

This study is part of numerical simulations performed on an in-situ heating test conducted by the French National Radioactive Waste Management Agency (Andra) at the Meuse/Haute-Marne Underground Research Laboratory (URL) to study the hydromechanical behavior of the host Callovo-Oxfordian COx claystone in quasi real conditions through the international research project DECOVALEX. In this study, we present a numerical analysis of damage and cracking behavior due to gas effects on hydromechanical processes in unsaturated claystone, while considering the distribution of material heterogeneity. The proposed model is implemented in a finite element code designed to solve hydromechanical coupling problems under unsaturated conditions. The nucleation and propagation of cracks are described using an extended phase-field method, which takes into account the effects of gas and liquid pressure on the evolution of the phase-field. In particular, a macroscopic elastic model is determined using two steps of homogenization, which considers the effects of porosity and mineral inclusions. The spatial variability of these factors is modeled using the Weibull distribution function. Thus, the nucleation of cracks is directly influenced by the spatial distribution of material heterogeneity. The proposed model is applied to 3D benchmarks of gas injection in the context of radioactive waste disposal. The process, in which the overpressure-induced damage zone affects the behavior of the two-phase flow during gas injection, is well reproduced.