Source: Journal of Geophysical Research: Solid Earth
Clays are often considered bad news for permeability, and faults containing clay are often thought as barriers to fluid flow. New data and analysis presented in Farrell et al.  highlights that clay type, not just clay content, is important in dictating the permeability of a fault zone.
The authors measured the permeability of faulted authigenic clay-bearing (i.e. clay formed in-situ) sandstones in the laboratory, and performed detailed microstructural analysis to look at clay morphologies. Based on these data, and data collected that characterizes the size of the pore throats within the sandstones, they concluded that the faulting of authigenic clays can increase pore connectivity relative to the unfaulted host rock, thereby increasing permeability and creating a permeability anisotropy. Future researchers are urged to incorporate information about different clay types into fault seal models.
Citation: Farrell, N. J. C., Debenham, N., Wilson, L., Wilson, M. J., Healy, D., King, R. C., et al. . The effect of authigenic clays on fault zone permeability. Journal of Geophysical Research: Solid Earth, 126, e2021JB022615. https://doi.org/10.1029/2021JB022615
―Michael Heap, Associate Editor, JGR: Solid Earth