Modeling of natural fracture initiation and propagation in basin sedimentation context
Résumé
During sedimentation, buried rocks are subjected to an increase in vertical stress. This increase leads to a decrease of porosity that is commonly called mechanical compaction. Indeed, the mechanical compaction depending on its rate and on the permeability of the burden rocks can induce significant overpressures. Thus, a competition is initiated between the dissipation of fluid overpressure and sedimentation rate and may result in fracture initiation. The present study deals with the initiation and propagation of natural fracture in sealing formations. A particular emphasis is put on mode I fracture propagation. An analytical solution of the pressure and stresses in a sealing formation is proposed under sedimentation by superposing two problems of poroelasticity. This analytical solution and a damage criterion are used to predict the initiation and propagation of the fracture. The damage parameter affects both the mechanical and hydraulic openings of the fracture, and the flow in the fracture is described by Poseuille's law. The fracture propagation and growth are studied by numerical simulations based on a finite element code dedicated to fractured porous media called Porofis. Interactions between hydraulic and mechanical processes are also studied, and a sensitivity study is carried out in order to find the most important parameters involved in natural fracturing under sedimentation.
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