Dual-Porosity and Dual-Fracture Model for Fractured Geothermal Reservoir Simulations

The dual-porosity model is widely used in fractured geothermal reservoir simulations. However, the commonly-used dual-porosity approach does not always adapt to geothermal problems, because the matrix-fracture thermal exchange due to conduction might be inaccurately simulated. In fact, although the pressure diffusion is fast in the facture network because of high fracture permeability, the temperature diffusion is still very slow due to the low thermal conductivity. So, the fracture temperature around a matrix block cannot be considered as a constant, and we don't have a representative fracture temperature to compute the matrix-fracture conductive heat transfer. In this paper, a dual-fracture approach is proposed to improve the commonly-used dual-porosity model. The fracture medium of a dual-porosity model is split into two sets of fractures: one for the transport in x-direction, and the other for the transport in y-direction. These two fracture media have locally similar pressure, but may have very different temperature. This approach improves the matrix-fracture conductive heat exchange modeling and is suitable for the simulation of thermal problems in fractured reservoirs.