Flows in Discrete Fracture Networks: from Fine Scale Explicit Simulations to Network Models and Reservoir Simulators

Modelling flows in fractured reservoirs is becoming essential, due to the increasing number of fractured reservoirs to be exploited. Building fluid flow simulations keeping explicit Discrete Fracture Network (DFN) models that capture well the highly localized nature of flow in fractured reservoirs is a challenging issue. A successful solution will be of considerable help for setting up EOR schemes. A rigorous workflow handling 3D DFN simulations to standard large scale simulations must be set up. We show that it is possible to build an exact approximation scheme using an original Galerkin projection technique and a quasi steady state approximation (simulation time greater that a typical diffusion time over one fracture). At the lowest order, the resulting set of equations to be solved has the structure of a resistor/capacitor network The associated mass and transmissibility matrices can be computed explicitly solving steady state boundary value Laplace equations over each fracture. Considering millions fracture models remains impossible in this context. Using geometrical considerations, we have developed accelerated algorithms allowing to treat such cases in an acceptable time on a standard computer. Validations were done with high resolution reference calculations. The theoretical aspects and validation tests will be adressed during the presentation.