Carbonates: Porosity and permeability voxel to voxel

Description

We ackquired micro-CT images from two carbonate outcrops (Indiana Limestone and Silurian Dolomite), and used it to calculate porosity at each voxel (the samples are considered pure, since Indiana Limestone is 99% calcite, and Silurian Dolomite, 97% dolomite). For thus, we segmented pores (porosity=100%) and 'solid' (porosity=5%) and used the grayscale of these two points to calculate porosity directly in the image. Since there is no voxel with 100% solid at the resolutions used, we followed Arns et al. (doi:10.1051/e3sconf/20198905002) and adopted the concept of background porosity - we considered that 'solid' phase in fact corresponds to 5% porosity (this value was calculated using the same methodology as Qingyang Lin et al., doi:10.1016/j.advwatres.2016.08.002). Besides the porosity fields, we also obtained permeability fields for these samples by two methodologies: In methodology "P", the porosity file was used as input in Winland equation to calculate the permeability field; In methodology "S", we segmented the resampled micro-CT images in regions of similar permeabilities, considering that regions of similar grayscale values have similar permeabilities.