Chemical degradation of a numerical material - Application to a Fontainbleau sandstoneReport as inadecuate

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* Corresponding author 1 LMGC - Laboratoire de Mécanique et Génie Civil 2 M3 - Mathématiques et Modélisations en Mécanique LMGC - Laboratoire de Mécanique et Génie Civil 3 MIST - Laboratoire de micromécanique et intégrité des structures 4 ThM2 - ThermoMécanique des Matériaux LMGC - Laboratoire de Mécanique et Génie Civil

Abstract : The carbon capture and storage consists in injecting large quantities of CO2 in supercritical formdirectly into deeply located geological formations. During the geological storage, chemical reactionsmay induce some important and irreversible changes of the rock properties 1.The morphology of the pore network and solid skeleton defines important macroscopic properties ofthe rock permeability, stiffness. The proposed micromechanical approach is based on the followingmorphological 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 percolationSandstones are products of a series of complex geological and hydrodynamical processes. Insimplified way it can be described by sandgrains transport, deposit, compaction and diagenesis. Inthis work we reconstructed the 3D sandstone geometry by simulating the way of the sandstoneformingprocesses. 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 wereobtained 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 erosionof the microstructure by using 26-neighbourhood structuring element. We proposed two scenarii ofnumerical 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 beadjusted to a particular time-dependent process.Some numerical upscaling techniques linear homogenization, effective Darcy-s law are used inorder to estimate evolution of elastic effective behaviour and permeability, triggered by progressivedissolution of microstructure. A new methodology enabling imposing periodic boundary conditions,in order to estimate mechanical properties, on non-periodic geometry is proposed. A link betweeneffective elastic moduli and permeability is proposed.

Author: Kajetan Wojtacki - Loïc Daridon - Yann Monerie -



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