Sharp transition to strongly anomalous transport in unsaturated porous media

Andrés Velásquez‐parra (1, 2) , Tomás Aquino (3) , Matthias Willmann (2) , Yves Méheust (3) , Tanguy Le Borgne (3) , Joaquín Jiménez‐martínez (2)

1 Swiss Federal Institute of Aquatic Science and5Technology
2 D-BAUG - Department of Civil, Environmental and Geomatic Engineering [ETH Zürich]
3 GR - Géosciences Rennes

The simultaneous presence of liquid and gas in porous media increases flow heterogeneity compared to saturated flows. However, the impact of saturation on flow and transport has so far remained unclear. The presence of gas in the pore space leads to flow reorganisation. We develop a theoretical framework that captures the impact of that reorganization on pore-scale fluid velocities. Preferential flow is distributed spatially through a backbone and flow recirculation occurs in flow dead-ends. We observe, and predict theoretically, that this previously-identified flow structure induces a marked change in the scaling of the velocity probability density function compared to the saturated configuration, and a sharp transition to strongly anomalous transport. We develop a transport model using the continuous time random walk theory that predicts advective transport dynamics for all saturation degrees. Our results provide a new modeling framework linking phase heterogeneity to flow heterogeneity in unsaturated media.

Domaines: Hydrologie; Mécanique des fluides [physics.class-ph]

Andrés Velásquez‐parra, Tomás Aquino, Matthias Willmann, Yves Méheust, Tanguy Le Borgne, et al.. Sharp transition to strongly anomalous transport in unsaturated porous media. Geophysical Research Letters, 2022, 49 (3), pp.e2021GL096280. ⟨10.1029/2021GL096280⟩. ⟨insu-03537085v1⟩