EFFECT OF SHEAR DISPLACEMENT ON THE APERTURE AND PERMEABILITY OF A ROCK FRACTURE

The results of experiments ruing radial and unidirectional flow in a c arefully described single rough aperture are reported and compared wit h numerical predictions. Aperture replicas of a natural sandstone frac ture were made at 0, 1 and 2 mm shear displacements using silicone rub ber, with a reproducibility of better than 2%. The experimental arrang ement permitted shear displacement to be obtained without causing dama ge to the two displaced surfaces, which thus retained their original ( and essentially matching) geometry. Both the number of contact points and the fractional contact area decreased with increasing shear displa cement. With increasing shear displacement, mean aperture and standard deviation increased and the ratio of standard deviation to mean apert ure increased slightly. Semivariogram studies indicated that as shear displacement increased in the direction normal to the roughness ridges , the aperture distribution became more closely correlated in the dire ction par allel to the roughness ridges than in the shear direction. F low tests showed that,with increasing shear displacement, the fracture became heterogeneous and anisotropic and became more permeable in the direction perpendicular to the shear displacement than in the directi on parallel to the displacement. Simulations were made of flow through the fracture using the Reynolds equation and the actual aperture dist ribution; the measured hydraulic apertures were generally about 20% lo wer than those measured numerically. (C) 1998 Elsevier Science Ltd. Al l rights reserved.