Mercury Porosimetry¶

Mercury Porosimetry simulates a mercury intrusion test on your image: mercury is pushed in at rising pressure, then the pressure is lowered again. Use it to compare an image with a lab porosimetry curve, or to read the sizes of the pore entries (throats) that control access to the pore space.

Find it Tools › Multiphase › Mercury Porosimetry
Needs a segmented 3D image, up to 900³ voxels
Returns intrusion and extrusion curves of capillary pressure against mercury saturation, the pressure at half saturation, and maps of where and when mercury entered
Runs on CPU, with PoreSpy
Science Mercury Porosimetry

Run it¶

Open Tools, then Multiphase, and select Mercury Porosimetry. You can also start from an image's page, which fills in the image for you.
Under Source, choose the Image, or a batch to run every image in it.
Under Settings, set the number of Pressure steps. The suggested 25 gives a smooth curve for most samples.
Under Compute, leave the Backend on PoreSpy.
Select Run. The job page opens and follows the job until it finishes.

The Mercury Porosimetry launch form, with an image selected and 25 pressure steps. — Choose an image or batch and the number of pressure steps.

Settings¶

Setting	Default	Range	What it does
Image		your team's images and batches	The image to analyse, or a batch to run one job per image.
Pressure steps	25	2 or more	How many pressures each curve is computed at. Only steps that push mercury into new pores add a point, so a curve can have fewer points than this.
Backend	PoreSpy	PoreSpy	The software that runs the simulation.

Mercury's surface tension (0.465 N/m) and contact angle (140°) are the standard values for the test and can't be changed.

Results¶

The Jobs list and the report sum the result up as the pressure at half saturation, \(P_{c50}\): the intrusion pressure at which mercury fills half the pore space. The job page shows:

Chart: Capillary pressure against Non-wetting phase saturation, with an Intrusion curve as the pressure rises and an Extrusion curve as it falls.
Data: the Mercury Intrusion/Extrusion Curves table, with Pc Intrusion, Snwp Intrusion, Pc Extrusion and Snwp Extrusion at every step.
Fields: a slice viewer with two maps of the intrusion, Invasion sequence (intrusion step), the step at which mercury first reached each voxel, and Invasion pressure (N/m per voxel), the pressure at which it did.

Pressures are in pascals once the image has a voxel size, and in N/m per voxel until then. See Images to set the voxel size; the result updates without a rerun.

A small example: a 120³ synthetic sample with porosity 0.55. Left: the invasion sequence on one slice; mercury enters from every face, and large pores deep inside fill late because they sit behind smaller throats. Right: the intrusion and extrusion curves, in N/m per voxel because the sample has no voxel size.

A completed Mercury Porosimetry job showing the pressure at half saturation, the intrusion and extrusion curves and the invasion sequence on one slice. — The intrusion and extrusion curves and the invasion sequence. The data table is left out here.

From the job page you can Download Report as PDF or HTML, Download scalar fields to keep the two invasion maps, and Run Again with the same settings.

Common problems¶

The extrusion curve doesn't return to zero. That's expected: mercury cut off from every face stays trapped, as in the lab.
The curve stops at a lower saturation or higher pressure than a lab test. The simulation sees only the pores in the image; pores smaller than a voxel, and compression of the sample, aren't in it.
Fewer points than Pressure steps. Steps that push no mercury into new pores are left out. Raise Pressure steps for a finer curve.
Pressures look far too small. The image has no voxel size, so pressures are in N/m per voxel. Set the voxel size on the image's page.
The image is too large. The largest image is 900³ voxels. Trim or downsample it first.

Science¶

The Washburn equation, how the morphological method builds intrusion and extrusion, and how to read entry sizes from the curve: Mercury Porosimetry in the Scientific reference.