Mineralogical Controls on Frictional Strength, Stability, and Shear Permeability Evolution of Fractures

Massive fluid injection into the subsurface can induce microearthquakes by reactivating preexisting faults or fractures as seismic or aseismic slip. Such seismic or aseismic shear deformations may result in different modes of permeability evolution. Previous experimental studies have explored frictional stability-permeability relationships of carbonate-rich and phyllosilicate-rich samples under shear, suggesting that friction-permeability relationship may be primarily controlled by fracture minerals. We examine this relationship and identify the role of mineralogy (i.e., tectosilicate, carbonate, and phyllosilicate content) using direct-shear experiments on smooth saw-cut fractures of natural rocks and sintered fractures with distinct mineralogical compositions. These results indicate that the friction-permeability relationship is controlled by mineralogy. Frictional strength and permeability change upon reactivation decrease with phyllosilicate content but increase with tectosilicate content. In contrast, the reverse trend is observed for frictional stability (a-b). However, the permeability change decreases with carbonate content while both frictional strength and stability increase. The permeability change always decreases with an increase in frictional stability. This relationship implies a new mechanical-hydro-chemical coupling loop via a linkage of frictional properties, mineralogy, and permeability.