NUMERICAL MODELING OF HYDRO-MECHANICAL FRACTURE BEHAVIOR

A numerical approach for modeling coupled Hydro-Mechanical fracture behavior is proposed.

The movement of fluids through rock fractures is important in many engineering areas of practical interest such as those in petroleum and mining engineering. In that context, one of the most investigated and complex of subjects are the effects of stress on well productivity due to changes in hydraulic conductivity in both rock matrix rock and fractures. It is well known, that these flow characteristics are strongly controlled by fracture apertures and stress-related changes in aperture.

Recent investigations on the distribution of the apertures in natural fractures suggest that the cubic law can, better than the Darcy law, predict the fluid flux through rough walled fractures as long as the appropriate average fracture aperture is used.

A finite element code is developed to predict the influence that the variation that stress induces on a heterogeneous hydraulic conductivity field. The proposed model combines the stochastic cubic law with a non linear deformation function (hyperbolic) that is suggested to describe the stress-closure/opening curves of fractures and that allows the coupling of hydraulic and mechanical fracture behavior.

The relationships used and the validity of the present model are tested through comparison between experimental data and numerical predictions (Bart, 2000) in various boundary and loading conditions. Comparisons between the modified cubic law model, the Darcy model, and a linear stress-closure/opening relation has been performed. This shows the differences between these two models and the resulting better description given by the proposed new model.