Simulation of salt cavity healing based on a micro-macro model of pressure-solution

Abstract

CO₂ storage in salt rock is simulated with the Finite Element Method (FEM), assuming constant gas pressure. The initial state is determined by simulating cavity excavation with a Continuum Damage Mechanics (CDM) model. A micro-macro healing mechanics model is proposed to understand the time-dependent behavior of halite during the storage phase. Salt is viewed as an assembly of porous spherical inclusions that contain three orthogonal planes of discontinuity. Eshelby’s self-consistent theory is employed to homogenize the distribution of stresses and strains of the inclusions at the scale of a Representative Elementary Volume (REV). Pressure solution results in inclusion deformation, considered as eigenstrain, and in inclusion stiffness changes. The micro-macro healing model is calibrated against Spiers’ oedometer test results, with uniformly distributed contact plane orientations. FEM simulations show that independent of salt diffusion properties, healing is limited by stress redistributions that occur around the cavity during pressure solution. In standard geological storage conditions, the displacements at the cavity wall occur within the five first days of storage and the damage is reduced by only 2%. These conclusions still need to be confirmed by simulations that account for changes of gas temperature and pressure over time. For now, the proposed modeling framework can be applied to optimize crushed salt back filling materials and can be extended to other self-healing materials.