From the pore scale to the lab scale: 3-D lab experiment and numerical simulation of drainage in heterogeneous porous media

A well-controlled 3-D experiment with pre-defined block heterogeneities is conducted, where neutron tomography is used to map 3-D water distribution after two successive drainage steps. The material and hydraulic properties of the two sands are first measured in the laboratory with multistep outflow experiments. Additionally, the pore structure of the sands is acquired by means of image analysis of synchrotron tomography data and the structure is used for pore-scale simulation of one- and two-phase flow with Lattice-Boltzmann methods. This gives us another set of material and hydraulic parameters of the sands. The two sets of hydraulic properties (from the lab scale and from the pore scale) are then used in numerical simulations of the 3-D experiment. The paper discusses critical aspects and benchmarks for experimental measurements of 3-D water distribution in heterogeneous porous media. Additionally, we discuss possibilities as well as difficulties and limitations in the determination of hydraulic properties of materials using two conceptually different approaches (pore scale and lab scale). We then test with the numerical simulations how good can predictions on flow and water content in structured media be when using these state-of-the-art methods for the determination of hydraulic properties. Based on the numerical simulations, we discuss which parameters are more difficult to predict and which of the two approaches (lab scale or pore scale) enables better predictions.