ABSTRACT:
A key point to perform realistic geomechanical modeling of fractured reservoirs consists of building a homogenized poromechanical behavior of the fractured rock. At the scale of the reservoir grid, the fractured rock appears as a homogeneous medium, whose poromechanical averaged properties have to be estimated from the geometry and properties of the phases (fracture/matrix). This work deals with the development of homogenized constitutive poromechanical laws for fractured rocks. We show how to account for a nonlinear fracture behavior in order to reproduce irreversible opening and sliding or dilatancy in an homogenization process.
1 INTRODUCTION
The conventional modeling of fractured reservoir concerns the numerical modeling of flows in the reservoir. The main steps of the fluid flow study are the characterization of the fracture networks, the integration of the data in a realistic geological models and the up-scaling of the fractured model at the scale of the reservoir grid. Then the assessment of the main drive mechanisms and the simulation of the reservoir exploitation are performed to choose the best recovery strategy. However, changes in stress during the production may lead fractures to close, open or slide depending on the fracture orientation, the matrix and fracture behaviors (Hermansson & Gudmundsson 1990, Hanks et al. 1990, Teufel 1987). During injection also, pressure variations induce an increase of the normal effective stress on the fracture (traction on the fracture plane increases). At the scale of the reservoir grid, the fractured rock appears as an homogeneous medium, whose poromechanical properties will be estimated from the geometry of the fractures and phase properties (fracture/matrix). We have shown in a previous paper (Marmier et al. 2005) how to build an homogenized behavior which can be used for geomechanical reservoir simulation in the case of elastic fractures.
