Sample preparation details
The end faces of each core plug were smoothed to parallel using a rock
saw and a lathe equipped with an angular grinder. Parallelism was
checked with a 0.01 mm resolution caliper. Each core was oven-dried at
~333 K for several days to reduce absorbed water. We
then calculated the total volume and density of each core by measuring
its mass and dimensions using a scale and a caliper to accuracies of
0.001 g and 0.02 mm, respectively. A helium pycnometer (Micromeritics
AccuPyc II 1340) was used to measure the solid volume and porosity of
each core.
To evenly distribute the saturating water or the helium gas to test
permeability across the sample end-face, we placed 3.175 mm thickness,
10 µm grain size, AISI 316 stainless steel porous frits between each
sample holder and the adjacent sample end-face.
Sample MT07 at stage S3 - i.e., fractured after being exposed to
humidity - was epoxy impregnated before removing the rubber jacket to
avoid offsetting the fracture.