A Fracture-Only Reservoir Simulator

We present a fracture-only reservoir simulator for multiphase flow: the fracture geometry is modeled explicitly, while fluid movement between fracture and matrix is accommodated using empirical transfer functions. This is a hybrid between discrete fracture modeling where both the fracture and matrix are gridded, and dual porosity or dual permeability simulation where both fracture and matrix continua are upscaled. The advantage of this approach is that the complex fracture geometry that controls the main flow paths is retained. The use of transfer functions, however, makes the simulation method considerably more efficient than conventional discrete fracture models. The transfer functions used accommodate capillary and gravity-mediated flow between fracture and matrix and have shown to be accurate for simple fracture geometries, capturing both the early and late-time average behavior. We validate our simulator by comparing our predictions with simulation results where the fracture and matrix are explicitly modeled. We then show the utility of the approach by simulating multiphase flow in a geologically realistic fracture network. We demonstrate that both the fracture geometry and capillary forces in the matrix govern the overall transport.