Modeling of natural fracture initiation and propagation in basin sedimentation context

Abstract

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.

Effect of hydro mechanical coupling on natural fracture network formation in sedimentary basins

“…In this study, the evolution of the damage parameter affects also both the joint stiffness and the fracture aperture (Ouraga et al 2017). In the ductile case ( figure 5(a)) the spacing between the fractures evolves with their length.…”

“…Fracture onset occurs when the fluid pressure in a defect reaches the limit tensile strength of the porous media (Ouraga et al 2017;Fisher et al 1995). Numerous studies have given mechanical or hydraulic explanation for fracture network spacing (Bai and Pollard 2000a;Gross 1993;Hobbs 1967;Mandl 2005).…”

“…Fracture network is studied from an equivalent model of a synthetic two layer model composed of a caprock formation with a low permeability over a highly permeable reservoir (figure 1). This equivalent model already considered for the modeling of single fracture propagation in sedimentary basins has been widely described in (Ouraga et al 2017). Thus, by considering that the permeability of the caprock formation is smaller than the permeability of the reservoir, under significant sedimentation rate, the flow from the reservoir to the sealing formation is low enough to represent a negligible part of the amount of fluid in the reservoir.…”

“…The reservoir can thus be considered as undrained, and the pore pressure in this case reads to (Ouraga et al 2017):…”

“…The Fractures are modeled with cohesive zone model undergoing damage and the flow in the fractures is described by Poiseuilles law. The damage parameter affects both the mechanical and the hydraulic opening of the fracture as discussed by Ouraga et al (2017). For the numerical simulations, the code Porofis based on finite element modeling (FEM) is used.…”