Permeability anisotropy in faulted sandstone - Implications for fault seal

Quantifying the permeability of fault zones and fault rocks is critical to the success of exploration and production. Directional variations in permeability have previously been reported from clay-rich fault rocks, but here we describe significant permeability anisotropy in fault rocks produced from two different sandstones, an arenite and a sub-arkose. In both cases, the maximum permeability of the fault rock is aligned with the fault slip vector in these normal faults, and the minimum permeability is oriented in the fault normal direction. Permeability anisotropy spans 3-5 orders of magnitude in both cases, and has major implications for the prediction of sealing behaviour in the subsurface. While the across fault permeability in our samples is low and the faults might be predicted as sealing, the along fault (up-dip) permeability is so high that leakage along the fault is a real possibility. Our results highlight the need for careful analysis of directional variations in permeability, especially in fault zones and fault rocks.