Résumé
The carbon capture and storage consists in injecting large quantities of CO2 in supercritical form directly into deeply located geological formations. During the geological storage, chemical reactions may induce some important and irreversible changes of the rock properties [1].The morphology of the pore network and solid skeleton defines important macroscopic properties of the rock (permeability, stiffness). The proposed micromechanical approach is based on the following morphological criteria [2]:- basic measures: volume fraction, surface areas of phases- sizing: distributions of pores or grains size- spatial distribution: estimation of characteristic length scale, geometrical dispersion, anisotropy- connectivity: which highly influence on permeability (existence of percolation)Sandstones are products of a series of complex geological and hydrodynamical processes. In simplified way it can be described by sandgrains transport, deposit, compaction and diagenesis. In this work we reconstructed the 3D sandstone geometry by simulating the way of the sandstone-forming processes. The reconstruction method consists of three main steps [3]:- sedimentation: grain deposit- compaction: bulk volume reduction and pore space extension- diagenesis: decrease of the characteristic size of the porous phase.Generated samples satisfy aforementioned morphological and statistical informations which were obtained by 3D image analysis of X-ray tomography of the natural rock sample.The chemical degradation of the material is taken into account by performing the numerical erosion of the microstructure by using 26-neighbourhood structuring element. We proposed two scenarii of numerical dissolution:- the first scenario (isotropic dissolution): consists in dissolving all the pore space- the second scenario: consists in dissolving only percolated porous network.The proposed modelling is universal in the sense that it uses non-dimensional time scale that can be adjusted to a particular time-dependent process. Some numerical upscaling techniques (linear homogenization, effective Darcy’s law) are used in order to estimate evolution of elastic effective behaviour and permeability, triggered by progressive dissolution of microstructure. A new methodology enabling imposing periodic boundary conditions, in order to estimate mechanical properties, on non-periodic geometry is proposed. A link between effective elastic moduli and permeability is proposed.