Specific surface area versus porosity from digital images

By computing the total porosity phi and specific surface area S for a number of segmented digital volumes of natural sandstones, carbonates, and granular samples, as well as their subvolumes, we observe fairly tight trends between those two variables. The emerging picture is different for low-to-medium porosity rocks from that for high-porosity granular samples. In the former, S increases with increasing phi, while the behavior is opposite in the particulates. We explain these trends by invoking simple theoretical derivations where the consolidated low-to-medium porosity samples are modeled as solids with inclusions, while the particulates are represented by packs of grains. While in the former S is linearly proportional to phi, it is linearly proportional to 1 - phi in the latter. The digital data are fairly accurately matched by the respective theoretical curves with the pore- and grain-size statistics extracted from the digital volumes. This fact arguably means that the trends obtained here from microscopic digital volumes are valid at a much coarser core and reservoir scale.

Automated summary

By computing total porosity and specific surface area for various natural sandstone, carbonate, and granular samples, tight correlations between these two variables were observed. Different trends were identified for low-to-medium porosity rocks compared to high-porosity granular samples, which were explained through theoretical derivations based on solid inclusions and grain packs. The accuracy of the digital data matching the theoretical curves indicates that the trends observed at a microscopic level are applicable at a much larger core and reservoir scale.