Beyond‐laboratory‐scale prediction for channeling flows through subsurface rock fractures with heterogeneous aperture distributions revealed by laboratory evaluation

Abstract

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 .

Fluid Pocket Generation in Response to Heterogeneous Reactivity of a Rock Fracture Under Hydrothermal Conditions

“…The permeability of the fractured granite at room temperature (2.0 × 10 −12 to 2.1 × 10 −11 m 2 during A‐1 and B‐1; Table S1) in this study is consistent with the values of previous experimental studies, which used rubber‐sleeved fractured granite samples (10 −12 to 10 −11 m 2 ) at the same effective confining pressure (Ishibashi et al, ; Watanabe et al, ). Dissolution did not occur at the boundary between the granite sample and stainless steel jacket (Figures and ).…”

Linking microearthquakes to fracture permeability change: The role of surface roughness

“…Following Ishibashi et al [], for the rough fracture surfaces (hanging wall and footwall), a fractal dimension, a standard deviation for a referential length of 200 mm, and a mismatch length were set as 2.3 mm, 1.3 mm, and 0.7 mm. The proportion of the power spectral density (PSD) of the initial aperture with a single contact point to the PSD of the footwall surface geometry, R ( f ), was expressed as , where f is the spatial frequency.…”

Hydrologic issues associated with nuclear waste repositories

“…There are many direct observations that flow in fractures is channelized. This has been observed in laboratory‐scale fractures [ Neretnieks et al ., ; Moreno et al ., ; Brown et al ., ; Huber et al ., ; Ishibashi et al ., ; Develi and Babadagli , ]. There are also observations at larger scales that show distinct channeling [ Abelin et al ., , ].…”