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.
The present study evaluates aperture distributions and fluid flow characteristics for variously sized laboratory-scale granite fractures under confining stress. As a significant result of the laboratory investigation, the contact area in fracture plane was found to be virtually independent of scale. By combining this characteristic with the self-affine fractal nature of fracture surfaces, a novel method for predicting fracture aperture distributions beyond laboratory scale is developed. Validity of this method is revealed through reproduction of the results of laboratory investigation and the maximum aperture-fracture length relations, which are reported in the literature, for natural fractures. The present study finally predicts conceivable scale dependencies of fluid flows through joints (fractures without shear displacement) and faults (fractures with shear displacement). Both joint and fault aperture distributions are characterized by a scale-independent contact area, a scale-dependent geometric mean, and a scale-independent geometric standard deviation of aperture. The contact areas for joints and faults are approximately 60% and 40%. Changes in the geometric means of joint and fault apertures (μm), e m, joint and e m, fault , with fracture length (m), l, are approximated by e m, joint = 1 × 10 2 l 0.1 and e m, fault = 1 × 10 3 l 0.7 , whereas the geometric standard deviations of both joint and fault apertures are approximately 3. Fluid flows through both joints and faults are characterized by formations of preferential flow paths (i.e., channeling flows) with scale-independent flow areas of approximately 10%, whereas the joint and fault permeabilities (m 2 ), k joint and k fault , are scale dependent and are approximated as k joint = 1 × 10 À12 l 0.2 and k fault = 1 × 10 À8 l 1.1 .
BACKGROUND AND PURPOSE:The natural history and therapeutic management of dissecting vertebrobasilar aneurysms without ischemic or hemorrhagic stroke (nonstroke dissecting vertebrobasilar aneurysms) are not well-established. We conservatively followed patients with nonstroke dissecting vertebrobasilar aneurysms and evaluated the factors related to clinical and morphologic deterioration.
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