Naturally Fractured Reservoir Simulation With Effective Permeability Tensor

The development of Naturally Fractured Reservoirs (NFR) provides opportunities for progress in reservoir numerical simulation techniques. Due to the complexity of reservoirs, NFR simulation is always considered the most challengeable work for reservoir engineers. There is still no determined method for NFR simulation. This thesis is aimed to calculate the effective permeability tensor and to simulate the fluid flow in NFRs. There are three kinds of mathematical models for NFR simulation: the Equivalent Continuum Model (ECM), the Discrete Fracture Network Model (DFNM) and the Hybrid Model, all of which can be divided into deterministic model and stochastic model according to the inputs. The ECM is appropriate to filed-scale reservoir simulation while the DFNM is well known for its ability to describe heterogeneity of local-scale regions. The equivalent medium model presented in this work is a hybrid model who takes advantages of both the ECM and DFNM. The paper includes three major parts. First a discrete fracture network is realized to capture the features of the target NFR. Second, the discrete fracture network is discretized into a limited number of grids whose effective permeabilities are calculated. Finally, a MultiPoint Flux Approximation Method is developed in order to handle the tensor permeability. Programs are developed and several examples are analyzed in all three parts. It is shown that the boundary element method is an effective tool for calculating the effective permeability tensor which is sensitive to matrix permeability, fracture density and orientation but the fracture aperture. The multipoint flux approximation simulator can give accurate pressure predictions when the tensor permeabilities obtained in the second part are inputted, though with the disadvantage of high calculation cost.