Frictional stability‐permeability relationships for fractures in shales

• Published in: Journal of geophysical research. Solid earth 2017-03, Vol.122 (3), p.1760-1776
• Main Authors: Fang, Yi, Elsworth, Derek, Wang, Chaoyi, Ishibashi, Takuya, Fitts, Jeffrey P.
• Format: Article
• Language: English
• Subjects: Activation; Biological competition; Carbon dioxide; Carbon dioxide fixation; Carbon sequestration; Carbonates; Competition; Control stability; Evolution; Flow stability; Fluid infiltration; Fluid injection; Fracture mechanics; Fracture permeability; Fractures; Friction; Geophysics; GEOSCIENCES; Hydraulic properties; Induced Seismicity; Infiltration; Measurement; Mechanical properties; Mineral composition; Mineralogy; Minerals; Modes; Oil shale; Permeability; Reduction; Reservoirs; Rivers; Sedimentary rocks; Seismicity; Seismology; Shale; Shales; Shearing; Stability; Velocity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2016JB013435

There is wide concern that fluid injection in the subsurface, such as for the stimulation of shale reservoirs or for geological CO2 sequestration (GCS), has the potential to induce seismicity that may change reservoir permeability due to fault slip. However, the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation (e.g., stable versus unstable). As seismicity is controlled by the frictional response of fractures, we explore friction‐stability‐permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in Green River shale (GRS) and Opalinus shale (OPS). We observe that carbonate‐rich GRS shows higher frictional strength but weak neutral frictional stability. The GRS fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline. By comparison, the phyllosilicate‐rich OPS has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction. Hence, we conclude that the friction‐stability‐permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration. Key Points Lab observation of friction‐stability‐permeability relationships Two shales with distinct mechanical and flow behaviors Mineralogy controls competition between wear products and dilation