Numerical Study of Callovo-Oxfordian Argillite Expansion due to Gas Injection

Abstract

An important aspect in an underground radioactive waste disposal project is the characterization of hydrogen production due to steel container corrosion and its migration in the initially water-saturated host rock. For the French repository project, gas injection tests into initially saturated samples of the Callovo-Oxfordian (COx) claystone were conducted to mimic these phenomena. They showed an important expansion of the tested samples. In this paper, a series of hydromechanical simulations were performed, within the framework of two-phase flow in deformable porous media, to explain both hydraulic and mechanical responses of the material in those experiments. The analysis of experimental and numerical results suggested the simultaneous advance of gas and damage fronts through the sample. The increasing gas pressure led to the decay of the material rigidity and, consequently, to the alteration of the hydraulic properties, particularly the permeability. Simultaneously, the mechanical damage caused a significant expansion of the tested COx samples. The good agreement between the experimental and numerical results supported these explanations and should lead, in future works, to a more complete hydromechanical model aiming to simulate the problem of hydrogen production and migration.