Numerical investigation of dual-porosity model with transient transfer function based on discrete-fracture model

Based on the characteristics of fractures in naturally fractured reservoir and a discrete-fracture model, a fracture network numerical well test model is developed. Bottom hole pressure response curves and the pressure field are obtained by solving the model equations with the finite-element method. By analyzing bottom hole pressure curves and the fluid flow in the pressure field, seven flow stages can be recognized on the curves. An upscaling method is developed to compare with the dual-porosity model （DPM）. The comparisons results show that the DPM overestimates the inter-porosity coefficient ）, and the storage factor w. The analysis results show that fracture conductivity plays a leading role in the fluid flow. Matrix permeability influences the beginning time of flow from the matrix to fractures. Fractures density is another important parameter controlling the flow. The fracture linear flow is hidden under the large fracture density. The pressure propagation is slower in the direction of larger fracture density.

A Two-Phase Flow Simulation of Discrete-Fractured Media using Mimetic Finite Difference Method

Various conceptual models exist for numerical simulation of fluid flow in fractured porous media,such as dual-porosity model and equivalent continuum model.As a promising model,the discrete-fracture model has been received more attention in the past decade.It can be used both as a stand-alone tool as well as for the evaluation of effective parameters for the continuum models.Various numerical methods have been applied to the discrete-fracture model,including control volume finite difference,Galerkin and mixed finite element methods.All these methods have inherent limitations in accuracy and applicabilities.In this work,we developed a new numerical scheme for the discrete-fracture model by using mimetic finite difference method.The proposed numerical model is applicable in arbitrary unstructured gridcells with full-tensor permeabilities.The matrix-fracture and fracture-fracture fluxes are calculated based on powerful features of the mimetic finite difference method,while the upstream finite volume scheme is used for the approximation of the saturation equation.Several numerical tests in 2D and 3D are carried out to demonstrate the efficiency and robustness of the proposed numerical model.