A new enriched method for extended finite element modeling of fluid flow in fractured reservoirs

Fractured porous media are always characterized by complex fractures on multiple scales. Conventional reservoirs simulation methods always fail to capture the flow dynamics of multiscale fracture networks without mesh refinement. In this work, the fluid flux is approximated using the extended finite element method (XFEM) to accurately represent discontinuities and singularities that develop as a result of the much larger permeability within the fractures than in the matrix. We consider two individual cases: infinite-conductivity fractures (pressure gradient is neglected along the fracture) and finite-conductivity fractures (pressure gradient is present along the fracture). Benchmark problems describing fluid flow around a single fracture for the two cases are both solved to demonstrate optimal convergence of the method and the improved accuracy compared to a traditional finite element approximation. The new method provides a far more accurate representation of the pressuregradient singularity near the fracture tip. To demonstrate the robustness of the method, the pressure fields surrounding an arbitrary network of intersecting fractures for the two cases are modeled, illustrating those enrichments representing multiple fractures can be superposed in a straightforward matter to simulate fluid flow in complex fracture networks. Finally, an engineering case for transient oil production from a horizontal well in a fractured reservoir is presented to demonstrate promising prospects of the proposed method.