Experimental study of miscible displacement fronts in rough self-affine fractures - art. no. 066306

Miscible fluid displacements are studied experimentally in a radial how bet ween two complementary replica of a self-affine rough granite fracture surf ace. The displacement front between a dyed fluid and a transparent (but oth erwise identical) one is followed optically through one face of the cell. T he evolution of its geometry is studied as a function of time. flow-rate. a nd normal and lateral relative displacements between the two surfaces. For a purely normal displacement, the front is globally smooth, due to the cons tant local distance between surfaces. For a finite lateral displacement, th e front is rough due to spatial variations of this distance; its geometry i s fractal and its dimension is directly related to the Hurst exponent H app roximate to0.8 of the surface, The fractal regime is observed only above a lower cut-off scale that depends on the normal spacing of the surfaces and an upper one that increases with the injected volume and with the amplitude of the lateral displacement.