TauFactor48 three-dimensional tortuosity factor analyses. Detailed results are provided in the supplementary material (Table S1). (a) Section of binary volume (black = porous volume; white = non-porous volume) in a schematic of tortuosity factor analysis with constant base axes and increasing the unit length of the test axis at 10% proportions. (b) Plot of average tortuosity factors for nano- and micro-CT volumes. (c) Porous phase volume percent comparison from 3 to 20% using the nano-CT volume along the bedding-parallel axes. Red star at the end of 3 and 5% tests is the point at which the computation failed. (d–g) Stacked 3D image of modelled interconnected pathways through clay-rich layer at micro- and nano-scale.