The paper by Bakkers and de Bresser presents new experimental data on the influence of pressure and slip on permeability (and permeability anisotropy) of clay-rich gouge. The new data are certainly valuable, and those experiments are not easy to conduct. The paper is framed heavily around CO2 storage problems, which is just one of the many possible applications of the work; this is somewhat distracting, since a lot of space is devoted (in the introduction and discussion) on the link with CO2

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... rage, which can only be addressed very generically here, at the expense of more physical/microstructural discussions about the processes that generate changes in permeability.