2D numerical modeling of naturally fractured media using finite elements with high aspect ratio
Pedro Rogério Cleto1; Osvaldo Luís Manzoli1; Heber Agnelo Antonel Fabbri1; Eduardo Alexandre Rodrigues1; José Henrique Krähenbühl Ambiel1
1 Universidade Estadual Paulista
doi:10.20906/CPS/CILAMCE2017-0934
Resumo
Many reservoirs are naturally fractured and contain several pre-existing fractures that can form complex networks. These fractures represent high permeability channels used to improve the production in oil and/or gas reservoirs. They also consist a mechanical and hydraulical discontinuity in rocky mass. When the fluid pressure decreases within the fracture, a reduction of its opening occurs due to the increase of the normal effective stresses causing its closure. In this case, compression strains will affect the fracture permeability up to a limit value which is defined by rock properties and fracture filling material. Seeking to better understand of the influence of pre-existing fractures permeability on pressure field and fluid flow, this work proposes a 2D finite element approach to model the fracture permeability change in naturally fractured reservoirs. The natural fractures are explicitly represented by finite elements with high aspect ratio [1]. A novel model based on concepts of damage mechanics and the nonlinear Barton-Bandis joint mechanical model [2] is used to treat the fracture closure. The fluid flow within the fractures is described by Darcy's law and one-way coupling (or explicitly coupled) method is used to solve the hydro-mechanical equations. Numerical examples with different fracture geometries are conducted to show the efficiency and accuracy of the employed model. The results show that the proposed model is able to reproduce the effects of changing fracture permeability on pressure field and fluid flow. [1] MANZOLI, O.; GAMINO, A.; RODRIGUES, E.; CLARO, G. Modeling of interfaces in two-dimensional problems using solid finite elements with high aspect ratio. Computers & Structures, Elsevier, v. 94, p. 70-82, 2012. [2] Barton, N.; S. Bandis; K. Bakhtar. Strength, deformation and conductivity coupling of rock joints. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, Pergamon, v. 22, No. 3, 1985.
Palavras-chave: Natural fractures; Elements with high aspect ratio; Barton-Bandis joint model; Hydro-mechanical analysis