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

Abstract

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-hydrochemical coupling loop via a linkage of frictional properties, mineralogy, and permeability. FANG ET AL.3549

Friction‐Stability‐Permeability Evolution of a Fracture in Granite

“…Considering that the fracture permeabilities after the velocity step are mostly higher than those before the velocity step (Figure ), it is clear that fracture permeability is enhanced due to the velocity step. Such response in fracture permeability to the velocity step is preliminarily confirmed in Ishibashi, Asanuma, et al () and is consistent with the experimental observation in Fang et al (). Moreover, Im et al () has reported that permeability response switches from net reduction to net increase following fracture reactivation (i.e., upon reactivating an instantaneous slide following holding) that is consistent with the present study.…”

Contrasting Mechanical and Hydraulic Properties of Wet and Dry Fault Zones in a Proposed Shale‐Hosted Nuclear Waste Repository

“…Permeability might decrease thank to shear-enhanced compaction (Crawford et al, 2008), swelling of clays (Cuss et al, 2011;Fang et al, 2017Fang et al, , 2018, and clay-fabric development (Ikari et al, 2009). Permeability might decrease thank to shear-enhanced compaction (Crawford et al, 2008), swelling of clays (Cuss et al, 2011;Fang et al, 2017Fang et al, , 2018, and clay-fabric development (Ikari et al, 2009).…”

“…Laboratory tests have shown that once fault slip on preexisting faults in shales occurs, fault permeability can be either depleted or enhanced. Permeability might decrease thank to shear-enhanced compaction (Crawford et al, 2008), swelling of clays (Cuss et al, 2011;Fang et al, 2017Fang et al, , 2018, and clay-fabric development (Ikari et al, 2009). Conversely, permeability might increase due to deformation-induced dilatancy when sheared at low to moderate effective stresses (Im et al, 2018;Lefèvre et al, 2016;Wu et al, 2017;Zhang & Cox, 2000).…”

Collapse of Reacted Fracture Surface Decreases Permeability and Frictional Strength

“…Permeability, k (m 2 ), was evaluated assuming the cubic law of a single fracture (Witherspoon et al, ; Fang, Elsworth, Wang, et al, ; Ishibashi et al, ), and using the measured fluid flow rate for a given pressure differential: …”

“…Velocity strengthening behavior results in aseismic (stable) slip while velocity-weakening behavior is a necessary condition for seismic (unstable) slip. In general, experimental observations have shown that frictional strength and stability follow a reverse relationship: when strength is high, stability is low, as summarized in Fang, Elsworth, Wang, et al (2018). Microphysical models have shown that this results from the mechanics of surface contact and microstructure deformation of individual crystalline phases (Niemeijer & Collettini, 2013;Niemeijer & Spiers, 2007).…”