674 research outputs found
Mechanical effect of absorption Carbon sequestration and swelling of coal
International audienceMechanical effect of absorption Carbon sequestration and swelling of coa
Comparison between classical potentials and ab initio for silicon under large shear
The homogeneous shear of the {111} planes along the <110> direction of bulk
silicon has been investigated using ab initio techniques, to better understand
the strain properties of both shuffle and glide set planes. Similar
calculations have been done with three empirical potentials, Stillinger-Weber,
Tersoff and EDIP, in order to find the one giving the best results under large
shear strains. The generalized stacking fault energies have also been
calculated with these potentials to complement this study. It turns out that
the Stillinger-Weber potential better reproduces the ab initio results, for the
smoothness and the amplitude of the energy variation as well as the
localization of shear in the shuffle set
Dislocation formation from a surface step in semiconductors: an ab initio study
The role of a simple surface defect, such as a step, for relaxing the stress
applied to a semiconductor, has been investigated by means of large scale first
principles calculations. Our results indicate that the step is the privileged
site for initiating plasticity, with the formation and glide of 60
dislocations for both tensile and compressive deformations. We have also
examined the effect of surface and step termination on the plastic mechanisms
Adsorption and strain: The CO2-induced swelling of coal
International audienceEnhanced coal bed methane recovery (ECBM) consists in injecting carbon dioxide in coal bed methane reservoirs in order to facilitate the recovery of the methane. The injected carbon dioxide gets adsorbed at the surface of the coal pores, which causes the coal to swell. This swelling in confined conditions leads to a closure of the coal reservoir cleat system, which hinders further injection. In this work we provide a comprehensive framework to calculate the macroscopic strains induced by adsorption in a porous medium from the molecular level. Using a thermodynamic approach we extend the realm of poromechanics to surface energy and surface stress. We then focus on how the surface stress is modified by adsorption and on how to estimate adsorption behavior with molecular simulations. The developed framework is here applied to the specific case of the swelling of CO2-injected coal, although it is relevant to any problem in which adsorption in a porous medium causes strains
Poromechanics of Microporous Carbons: Application to Coal Swelling during Carbon Storage
International audienceCoal seams are naturally filled with natural gas. Enhanced Coal Bed Methane recovery (ECBM) is a technique which consists in injecting carbon dioxide (CO2) in coal seams in order to enhance the recovery of the methane (CH4) present in the coal seams. A major issue for the industrial development of this technique is the loss of permeability of the reservoirs during injection. In a coal bed, most of the transport of fluids occurs in a network of natural frac- tures. The loss of permeability is attributed to the closure of the fractures induced by the swelling of the coal ma- trix during the progressive replacement of CH4 by CO2. Since both fluids are mostly adsorbed in the microporous matrix of coal, this particular problem raises the funda- mental question of how adsorption impacts the mechanics of a microporous solid. In this work, we present a porome- chanical modeling valid for microporous solids under ad- sorption and we apply this modeling to the specific case of ECBM. The first section presents the theoretical derivation of general constitutive equations of poromechanics which are valid for generic pore sizes and morphologies. In the second section, we apply this general poromechanics to the specific case of CH4 adsorption in coal. We use molecu- lar simulations to calibrate the derived constitutive laws. In the third section we validate this calibration by analyz- ing results of adsorption experiments in unjacketed condi- tions. The fourth section is dedicated to the case of CO2 adsorption in coal. Finally in the last section, we use this modeling to predict the swelling of coal in the context of ECBM
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