International audienceIn this study, we present the design of a purpose-built test cell, capable of closely mimicking boundary conditions which can be routinely imposed in fluid flow simulators. The test cell permits conducting systematic studies on the influence of unresolved pore-scale wall-roughness and pore space morphology on the hydraulic conductivity: it is therefore an ideal instrument for the generation of validation datasets for the next generation numerical flow models

Guerton, F.

Hume, L

Moonen, Peter

Poncet, P

English

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HAL Id: hal-02175583
https://hal.archives-ouvertes.fr/hal-02175583
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Experimental and numerical cross-validation of flow in
real porous media. Part 1: Experimental framework
F. Guerton, L Hume, P Poncet, Peter Moonen
To cite this version:
F. Guerton, L Hume, P Poncet, Peter Moonen. Experimental and numerical cross-validation of flow
in real porous media. Part 1: Experimental framework. 3rd International Conference on Tomography
of Materials and Structures (ICTMS 2017), Jun 2017, Lund, Sweden. ￿hal-02175583￿
 
EXPERIMENTAL AND NUMERICAL CROSS-VALIDATION OF FLOW IN 
REAL POROUS MEDIA. PART 1: EXPERIMENTAL FRAMEWORK 
F. Guerton*1, L. Hume†2, P. Poncet‡2 & P. Moonen§1,3 
1Univ Pau & Pays Adour, CNRS, DMEX-IPRA, UMS 3360, 64000, Pau, France 
2Univ Pau & Pays Adour, CNRS, LMAP-IPRA, UMR 2952, 64000, Pau, France 
3Univ Pau & Pays Adour, CNRS, TOTAL, LFCR-IPRA, UMR 5150, 64000, Pau, France 
 
Keywords: experimental design, test cell design, reference data, synthetic porous media. 
 
Summary: In this study, we present the design of a purpose-built test cell, capable of closely mimicking boundary 
conditions which can be routinely imposed in fluid flow simulators. The test cell permits conducting systematic studies 
on the influence of unresolved pore-scale wall-roughness and pore space morphology on the hydraulic conductivity: it is 
therefore an ideal instrument for the generation of validation datasets for the next generation numerical flow models. 
 
1. INTRODUCTION 
Many simulators claim to be capable of calculating fluid flow at the pore scale, based on X-ray scans of a porous 
medium of interest. However, as demonstrated by [1], the predictive power of these simulators remains to be 
demonstrated. Model validation is challenging, as direct observation of the flow field inside real porous media is generally 
not possible, and as model and experiment generally exhibit differences in geometry, boundary conditions and/or physics. 
In this study, we present the design of a purpose-built test-cell dedicated to the generation of reference data for 
validating a next-generation flow simulator. The test cell design accounts for typical constraints of simulators, such as the 
difficulty to treat large datasets (billions of voxels). The design furthermore aims to limit differences between the 
experimental and numerical setup (precise control of the boundary conditions) and permits conducting systematic studies 
on key-parameters of models (such as the impact of pore wall roughness).  
2. A DEDICATED TEST CELL 
An experimental setup has been devised to conduct systematic flow studies (Figure 1). It mainly consists of a pump, 
driving fluid through synthetic or real porous materials confined in a dedicated Hassler cell. Key-parameters like the 
pressure drop over the medium and the traversing mass flux can be precisely controlled via the pump operating parameters 
set by the user, and measured by a sensor recording the differential pressure between the cell’s inlet and outlet.  
The corner stone of the experiment is the design of the Hassler cell capable of handling the constraints of typical 
numerical models. Furthermore, the cell has to be versatile so that it could handle a wide range of samples with a different 
degree of complexity. To accommodate both non-consolidated and consolidated cylindrical samples, the Hassler cell is 
essentially an axisymmetric cylindrical tube made out of polycarbonate. This material was selected as it could handle 
moderate inner pressure without dramatically attenuating the X-ray beam. The cell’s dimensions (Figure 2) are 
determined based on the characteristics of the tomograph used in this study (a Bruker Skyscan 1172). This tomograph is 
capable to generate datasets with a voxel resolution around 3µm. If no binning is used, this would correspond to a field 
of view of around 12x8mm. This defines the maximum height of the inner volume of the test cell. The inner diameter can 
be reduced without compromising the representativeness of the envisaged samples. A diameter of 6 mm was selected as 
a compromise between representativeness and scan time.  
A key design constraint was the need to be able to ensure an isotropic flow through the entrance and exit surfaces of 
the sample. To that extent, small reservoirs were created at top and bottom (to ensure a uniform pressure distribution) and 
they are separated from the sample by metal sintered filters (to equalize pressure variations along the surface) with a 
known pressure drop. The filters are threaded, permitting to impose a slight confinement pressure on non-consolidated 
samples. The differential pressure inside the top and bottom reservoirs is measured by an adapted probe.  
                                                          
* e-mail: fabrice.guerton@univ-pau.fr 
† e-mail: laurene.hume@univ-pau.fr 
‡ e-mail: philippe.poncet@univ-pau.fr 
§ e-mail: peter.moonen@univ-pau.fr 
3. METHODOLOGY 
A wide range of configurations, having different levels of complexity, can be investigated. For each studied case a 
two-step approach is followed. Firstly, the Hassler cell containing the sample is fixed on the tomograph’s sample holder 
and a 3D tomographic scan is started. At this step, the Hassler cell is disconnected from the hydraulic circuit and the 
sample is in a dry state. Then, the acquired projections are processed, via the reconstruction software supplied with the 
tomograph, and the beam hardening and ring artifacts are corrected. The resulting image stack is then denoised by a 
median filter and manually segmented. The binarized cylindrical region of interest, corresponding to the sample, is 
provided as input for flow and permeability simulations. Depending on the simulator, this geometry can either be meshed, 
or simulations can be run directly on the voxel data. 
In a second step, the Hassler cell is connected to the hydraulic circuit and the pressure drop over the sample is measured 
experimentally for a given flow rate and gauge pressure. This permits the direct determination of the permeability at a 
given pressure level (average between inlet and outlet pressure). Numerically calculated and experimentally acquired 
permeabilities are then compared. By systematically increasing the complexity of the configuration of interest, model 
deficiencies can be detected and corrected.  
4. RESULTS AND OUTLOOK 
The first and simplest configuration of interest consists of a pack of smooth micro-spheres (dry soda lime glass, Duke 
Standards) whose nominal diameter of 553 ± 11 µm is certified. This diameter was selected to have around 10 spheres 
across the diameter of the test cell. When using binning 4, the region of interest will be around 500
3
 voxels, which can be 
handled by a typical numerical solver, and each sphere is described by around 50 voxels across its diameter, which is 
sufficient to have an accurate geometrical representation. A voxel size of 15µm has been selected to ensure that the entire 
sphere pack is within the field of view. Figure 3 depicts a rendering of the reconstructed 3D sphere pack. Spheres at the 
top and bottom part of the sample are truncated as both metal inlet/outlet filters induce an image artefact. Replacing them 
by synthetic filters will enable imaging the entire sample, and therefore remove a key uncertainty when comparing to 
simulations on the same geometry.  
Afterwards, a test series on a similar sphere pack will be conducted, whereby the roughness of the spheres is 
chemically altered. The roughness change will not be visible at the resolution of the scan, yet it will be large enough to 
affect the differential pressure measurements and hence the permeability. This test therefore allows assessing the impact 
of unresolved geometrical features on the permeability.  
Measurements using different fluids, using multi-modal sphere-packs and at higher spatial resolutions are foreseen as 
well, and it is anticipated to make the reference data available to the scientific community. 
 
 
 
 
Figure 1: instrumented device 
 
Figure 2: designed Hassler Cell  Figure 3: image rendering of a 
reconstructed 3D volume of 
spheres stacked inside the cell 
 
References 
[1] I. Bondino, G. Hamon, W. Kallel and D. Kac, Relative Permeabilities From Simulation in 3D Rock Models and 
Equivalent Pore Networks: Critical Review and Way Forward. Petrophysics, Vol 54:6, 2013. 
Acknowledgement 
The authors kindly acknowledge financial support from the Carnot Institute ISIFoR (project PRESS-RX) and UPPA 
(project HR-flow). 


Experimental and numerical cross-validation of flow in real porous media. Part 1: Experimental framework

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Experimental and numerical cross-validation of flow in real porous media. Part 1: Experimental framework

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