Quantification of fluid flow: hydro-mechanical behaviour of different natural rough fractures

Fractures display high heterogeneity on their hydraulic properties. Roughness causes channeling within the fracture plane. Heterogeneity is controlled by the presence of contact points (in situ normal loads) and by the aperture distribution (residual voids). Fracture roughness and tortuosity imply that fluid-rock exchange surfaces are much more complex than those of the parallel and smooth plates models. The purpose of this work is to characterize these physical parameters using finite difference modelizations. A hydraulic model of fluid flow has been performed taking into account the elastic closure of fractures with depth. Maps of contact points and relative local loads within the fracture planes are realized. They allow to visualize different and more or less developed channeling of fluid flows. Highly altered fractures are characterized by homogeneous fluxes despite the appearance of numerous contact zones during the fracture closure. On the contrary, fresh fractures developed strongly and increasing fluid flow channels with depth. This different but gradual behaviour of fluid flows within gradually altered fracture planes seems to follow a more general law previously detected with the roughness and tortuosity studies. The rock nature and its degree of alteration strongly control the fracture permeabilities. These observations must be initially taken into account to perform more accurate models of long-lived circulation in fracture networks at the reservoir scale. (C) 2000 Elsevier Science B.V. All rights reserved.