Emergence of non-Fickian transport in truncated pluri-Gaussian permeability fields

We present a numerical simulation study of advective-diffusive scalar transport in three-dimensional high-contrast discontinuous permeability fields, generated with a truncated pluri-Gaussian geostatistical approach. The numerical experiments are run with an Eulerian approach using a novel unified numerical framework based on the finite-volume library OpenFOAM (R)(Weller et al. in Comput Phys 12(6):620-631, 1998), for (1) generating random pluri-Gaussian porous media, (2) solving the steady state Darcy-scale flow, (3) solving the advection diffusion equation, (4) computing post-processing quantities such as first order statistics, spatial probability density functions and breakthrough curves. A range of permeability contrasts, correlation lengths, and Peclet numbers are tested to assess their relative weight on transport control and for the first time, the deviation of a calibrated macrodispersive model from the Fickian transport is quantified. We identify a hierarchy of non-Fickian transport triggering factors. From the tested scenarios, permeability contrast is themain controlling parameter for the anomalous transport behaviour as it enhances the generation of preferential flow paths which are characterised by high advective flow velocities. The Peclet number and the characteristic length at which facies transitions are observed as secondary factors.