Module: Microporosity Analysis ()

Description:

Introduction
This filter is used to try to interpret subresolution porosity information and is mainly used for carbonate rock samples. The main assumption is that the solid phase(s) are sufficiently monomineralic so that grayscale can actually be related to subresolution porosity.

Note: This filter can only take three-phase segmented datasets as input and is usually run in conjunction with Segmentation Three Phases Tool.

Microporosity phase assignement
As a first step in the microporosity assignment it sets two thresholds: and . It can do this in two ways depending on the parameter Auto Threshold. If this is set to true, then it sets them based on the mean intensity standard deviation of the two 'known' phases: void (0) and solid (2), and the parameter Multiplication Factor.

If Auto Threshold is false the user has to set the thresholds manually.
As a second step, the intermediate phase (1) is divided up into (given by Number Of Microporous Phases) socalled microporosity phases. They correspond to a certain fraction of subresolution porosity, or microporsity. The first microporous phase, which usually corresponds to 100% microporosity (see below) is assigned to all voxels that were labelled intermediate, but have an x-ray attenuation (intensity) value lower than the void cut-off . The last microporous phase, which usually corresponds to 0% microporosity (see below) is assigned to those voxels that were labelled intermediate, but have an intensity value larger than the solid cut-off, . All other intermediate phases are linearly divided between the two extreme values: and . A good value of n is 102, or 52.
By setting Auto Threshold to false, the user can also set the extreme microporosity values by hand. For example if a comparison with an scanning electron microscopy (SEM) image shows that the 'solid' phase actually still have a few percent microporosity, then set Solid Phase Microporosity to 0.02 and set to 100.

Porosity
The total porosity is given as the macroporosity (phase 0) plus the porosity contributed by the .

Connectivity
The filter can perform a connectivity analysis. Beware, this is a time consuming process! This option will perform two series of experiments. At first it starts with the macroporosity and checks if this phase is spanning the sample in Z-direction (connectivity given by the parameter Voxel Connectivity). Then it adds to that macropore phase the 100% microporosity phase and does the same analysis. It keeps adding the subsequent microporosity phases and analyses the connectivity.

In the output spreadsheet this series of experiments is the first table presented. The x-axis value is the microporosity value of the last phase added, the next column is the fraction of this combined phase that is in the spanning cluster (if any), and the third column is the total porosity that is associated with this spanning cluster.

The second series of experiment starts with the 1% microporous phase and does the same connectivity analysis, then it adds the next microporous phase (e.g. 2%) and check the connectivity of the combined phase and so on.

Connections:

Input
Input: tomographic data. The file must be 16-bit unsigned and contain less than 2 billion voxels.

Segmented Data
Segmented Data : three phase segmented data. Labels of different phases are supposed to be as follows: 0-Pores, 1-Microporosity, 2-Grains. The file must be 8-bit unsigned and contain less than 2 billion voxels.

Ports:

Number of Microporous Phases

Number of bins for the microporosity distribution. Note: one bin is used for 0% phase and one for 100% phase. 102 (or 52) is a good default number.

Voxel Connectivity

How the connectivity of the microporous phases is calculated. Using either the 6, 18 or 26 connected cube.

Auto Threshold

If true, thresholds are set automatically, otherwise enter different values.

Multiplication Factor

Multiplication factor. Thresholds are set through:


where is the mean of the intensities of the void or solid phase.

Set this to true if you wish to automatically set the thresholds for the 100% and 0% points in the microporosity calculation. The thresholds will then be set using the mean and standard deviation of the high and low phases.

Low Threshold

If 'Auto Threshold'=false use this value as the low_threshold for the microporosity calculation. Any voxel with a value lower than this will be set to the 'low intensity extreme value' (usually 100% microporosity.)

High Threshold

If 'Auto Threshold'=false use this value as the high_threshold for the microporosity calculation. Any voxel with a value higher than this will be set to the "high intensity extreme value" (usually 0% microporosity.)

Auto Extreme Values

Automatically or manually set the actual microporosity for the microporosity values in the dataset.

Void Phase Microporosity

If 'Auto Extreme Values'=false, then use this value to set the microporosity value for the low intensity (void) phase (which is otherwise 1.0 = 100% microporosity.)

Solid Phase Microporosity

If 'Auto Extreme Values'=false, then use this value to set the microporosity value for the high intensity (solid) phase (which is otherwise 0.0 = 0% microporosity.)

Connectivity Analysis

If set to false, only the total porosity is calculated.

Reverse Values

Reverse the order of the microporosity values (ie. 1->102...102->1). This can be useful for analysis of a tomogram wetted with high x-ray absorbent liquid.