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Beyond‐laboratory‐scale prediction for channeling flows through subsurface rock fractures with heterogeneous aperture distributions revealed by laboratory evaluation
Author(s) -
Ishibashi Takuya,
Watanabe Noriaki,
Hirano Nobuo,
Okamoto Atsushi,
Tsuchiya Noriyoshi
Publication year - 2015
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb011555
Subject(s) - joint (building) , geology , fracture (geology) , fault (geology) , standard deviation , shear (geology) , scale (ratio) , displacement (psychology) , aperture (computer memory) , flow (mathematics) , geometry , mechanics , geotechnical engineering , structural engineering , mathematics , seismology , engineering , physics , petrology , statistics , psychology , quantum mechanics , psychotherapist
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 −12 l 0.2 and k fault = 1 × 10 −8 l 1.1 .