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.