03 Novembre – Thesis defense - Vincent Le Maout

10 h15 Amphi C - Esplanade des Arts et Métiers (Talence)

Modelling of multiphase flows of viscoelastic fluids in porous media.

Viscoelastic multiphase flows in porous media are at the crossroad of many engineering sciences. Initiated with petroleum industry, their range of application is now extended to many additional areas, such as civil engineer-ing, geotechnics, composite impregnation and more recently life sciences. Mathematical formulations of these problems often rely on governing equations formulated directly at the macroscale, or are derived from micro-scopic considerations using upscaling technics. Generally, the second approach is prefered as it permits to estab-lish a clear connection between the scales of the porous media and to identify the restraining hypothesis neces-sary to the formulation of the equation system. However, when upscaling is performed, many unknown parameters remain to obtain a close set of equations, and additional closure relationships must be considered in order to find a solvable formulation. For the flows of interest, exhibiting multiphasic and viscoelastic properties, the usual macroscale empirical relations may be too inaccurate to capture relevantly the influence of underlying physics at play, and few experimental data allow characterising the missing parameters.
A solution to this problem consists in performing numerical simulations at the microscale to extract missing information about media properties through microfluidic experiments in silico. To achieve this multi-scale modelling strategy, a pore scale model has been derived in this thesis for two applications of interest:  improved oil recovery and tumor growth. The derivation of a unique model for these applications makes use of conservation equations at the microscale considered during upscaling operations. The obtained formulation allows a multiphase flow description by means of a phase-field method and the viscoelasticity of phases is introduced through the Oldroyd-B constitutive equation. The resulting mathematical model, implemented in a finite element code, permits to study in what extents the introduction of the polymer solution viscoelastic rheology during enhanced recovery process improves the mobilization of oil at pore scale. The influence of viscoelasticity on numerical solutions, as well as sweep efficiency of the medium, is compared to literature experimental results. On other hand, the mathematical model has been specialised to simulate the growth of a few hundred microns wide tumor aggregates. Since the precursor works of Steinberg the viscoelastic fluids analogy for cells aggregate is increasingly used for mathematical modelling. In this thesis, this similarity allows to study numerically the evolution of tumor aggregates in various environments. The biomechanical formulation of the problem permits to simulate cells population behaviour under mechanical load, which affects the growth rate according to the constraints in the system.  In this context, the mathematical model is used to separate mechanical from biological effects, and provide original explanations on tumor growth in confined environment. The predictive capacity of the model on in vitro experiments shows the relevance of the viscoelastic multiphase flow for the tumor growth description.

Event localization