Modeling Hydraulic Fracture in Finite Difference Reservoir Simulator

Hydraulic fracturing is essential for the development of low-permeability reservoirs (especially gas). A successful fracturation increases several folds the well productivity. Numerical simulations are necessary to predict post-fracturing performances, but fracture representation in a reservoir model leads to some difficulties. If the fracture is modeled by cells of the exact fracture thickness (a few millimetres), an implicit scheme and many cells are required, so the computation cost is high. If the fracture is included in much larger reservoir cells, a methodology has to be defined to get similar results to the first approach. This paper presents a low-cost simulation method tested for single phase, gas-water and oil-water flow in vertical fractures. The fracture is included in cells 1 to 10-meter thick. Pseudo absolute permeabilities are computed from the reservoir and fracture permeabilities and from the geometrical characteristics. Simulation results show that formation relative permeabilities and capillary pressure data may be kept unchanged for these cells. The single phase flow results agree with analytical results. All the 2-phase simulations were performed first with the real scale of the fracture then with the fracture successively included in 1 and 10 m thick blocks. The fluid productions of these comparative simulations are close. The method applies to oil and gas reservoirs over a large pressure and permeability range. The method easily predicts the time dependency of the well productivity index.