GeoDict offers two methods to determine a pore throat size distribution:

• Percolation Path
• Bubble Point

Percolation Path

If only a single maximal path is computed, the Percolation Path gives the diameter of the largest spherical glass bead that can pass the structure. If more paths should be found, the already found paths reduce the pore space. This means the same bottleneck cannot be used a second time. Repeatedly applied this results in a size distribution.

The found percolation path has a spherical cross section, but in this example the resolution is very coarse, so the cross section is cubic. This can be observed when looking at the percolation path from the Y-direction, which is the flow direction to determine the path. In our example the largest percolation path has a diameter of two voxels. This is the smallest diameter of the second to left pore throat.

When searching more paths, their diameters would be the diameters of the next smaller pore throats. One disadvantage of the percolation path is, that it will find the shortest diameter of a pore throat. But there might be pores that have a large expansion in one direction and in another direction they have only a few voxels diameter. Percolation path only sees the smaller diameter while the other is omitted. This is the case for the shown example.

Bubble Point

For these cases the Bubble Point method is more suitable. The bubble point method is often used for filters or metal wire meshes. It is based on a real physical experiment, where the observed media is placed in a liquid. Underneath, a gas under pressure is placed and the pressure rises during the experiment. The non-wetting gas will at some point break through the pore with the largest diameter and rise through the structure until it exits. Thus, it detects the largest pore throat in a structure. The pressure point is then converted into a pore diameter using the Young-Laplace or Washburn equation. However, it is assumed that the pore throat has a cylindrical shape, which might not be the case in reality. Moreover, a gas bubble is quite flexible and can fill the whole cross-sectional area of an arbitrarily shaped pore throat.

For metal weaves, GeoDict offers the GeoApp ASTM Calculation Factor, which determines a calculation factor to convert the pressure into a pore diameter, following the standards provided in the ASTM E3278-21 norm.

To use the bubble point method, the smallest pores in the structure need to have a resolution of at least 5 voxel. As this is not the case for our example, we use the Rescale command from ProcessGeo with strictly rescaling. Here, the number of voxels in each direction is doubled and all corners remain.

We apply Bubble Point with flow in Y-direction. The second to left pore throat is again identified as smallest pore throat.

The view from the Y-direction in the image on the left shows that now nearly the whole cross section of the pore throat belongs to the bubble point.