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Poromechanics extended to microporous materials Extension des approches poromécaniques aux matériaux microporeux

le 10 octobre 2013

Gilles PIJAUDIER-CABOT, Professeur à l'Université de Pau et des Pays de l'Adour, Laboratoire des Fluides Complexes et leurs Réservoirs, Anglet, France

Résumé de l'exposé:

Poromechanics offers a consistent theoretical framework for describing the mechanical response of porous solids saturated with a fluid phase. We consider here the case of fully saturated porous solids and focus on microporous materials, e.g. solids with pores down to the nanometer size. Hardened cement paste, tight rocks, activated carbon or coal are among those materials. For these materials, a deviation from standard poromechanics is expected. For instance, when subjected to hydrostatic stresses, they may swell instead of shrinking. In very small pores, the molecules of fluid are confined and interactions are modified. This effect, denoted as molecular packing, includes fluid-fluid and fluid-solid interactions. The present work investigates how poromechanics may be refined in order to capture adsorption and molecular packing induced effects in nanoporous solids. First, the basic phenomena are illustrated with the help of molecular simulation. Then, it is interesting to investigate the results of simple upscaling techniques: taking into account the pore size distribution, adsorption isotherms reconstructed from molecular simulation results are very consistent with measurements at the continuum - macroscopic - level. On the other side, the resulting macroscopic swelling cannot be explained easily from the increase of pore pressure due to confinement of the fluid.

A revisited - macroscopic - formulation of poromechanics is then introduced. An effective pore pressure is defined as a thermodynamic variable related to the mechanical work of the fluid at the pore scale (nanoscale). Accounting for thermodynamic equilibrium, this effective pore pressure is obtained as a function of the bulk fluid pressure, the temperature and the total and excess adsorbed masses of fluid. The approach is also extended in order to account for the effect of swelling on the increase of pore surface and on the adsorbed quantities. A nonlinear poroelastic model is implemented. A good agreement in the comparison with experimental data dealing with the swelling of coal due to methane and carbon dioxide sorption is achieved.
Type :
Séminaires - conférences
Lieu(x) :
Campus de Cachan
Amphi e-média
Bâtiment Léonard De Vinci de - ENS Cachan
61, avenue du Président Wilson 94230 Cachan
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