InterPore2026

Mixing enhancement in porous media with impermeables inclusions

19 May 2026, 09:50

1h 30m

Poster Presentation (MS08) Mixing, dispersion and reaction processes across scales in heterogeneous and fractured media Poster

Speaker

Clément PETITJEAN (Université de Rennes)

Description

Mixing describe the process of homogenisation of solute concentration fields by the coupled action of fluid advection and diffusive processes. In flows through porous media, it is of key importance in a range of fluid-fluid and fluid-solid reactive transport processes, notably in the subsurface. At the pore scale, laminar flow through the porosity produces exponentially growing fluid deformations which strongly impact solute mixing dynamics [1].
In contrast, at larger scale, continuous and isotropic permeability fields produce helicity-free velocity fields, which impede the occurrence of exponential fluid deformations [2]. However, permeability fields with local discontinuities may still have a significant impact on mixing, which has been overlooked so far. In this communication, we investigate the impact of the presence of impermeable inclusions in a porous matrix on the transport and mixing of solutes at the Darcy scale.

We use an innovative experimental setup to image and quantify conservative mixing in bi-dispersed porous mixtures consisting of large spherical inclusions (3-20mm) surrounded by fine sand (0.1-1mm). We image with a laser sheet the spatio-temporal echo of a fluorescent dye, sequentially pushed and pulled by reverting the flow inside the porous mixture. This technique allows to quantify transverse mixing processes in opaque materials [1]. We measure the spatio-temporal distribution of concentration echo and the decay of scalar variance with time, or equivalently advection distance (Fig. 1) for multiple ratios of inclusions size versus sand size. We also measure the transverse spreading of the solute echo, thus quantifying macro-dispersive processes.

We observe that the presence of inclusions greatly enhances transverse mixing compared to homogeneous porous materials. We find that the temporal scaling of the variance decay do not obey Fickian macro-dispersive transport process, suggesting that the discontinuous Darcy flow resulting from the presence of the inclusions leads to non-negligible fluid deformation.

Our results thus demonstrate that macro-scale fluid-deformation should be taken into account in transport models.