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Abstract
In this thesis, fluid flow in naturally fractured reservoirs with arbitrarily oriented fractures is simulated and the flow mechanism in matrix and fracture and their interactions are studied. Three different algorithms are presented to simulate single and two phase fluid flows through naturally fractured reservoirs. These are a grid based effective permeability tensor model, a single phase fluid flow simulator, and a two phase flow simulator. In order to validate the numerical work, series of laboratory experiments are designed and conducted. The grid based effective permeability is a unique tool that allows the use of the actual geometry of the fracture networks in the calculation of block permeabilities. The tensors are obtained by the boundary element method along with periodic boundary conditions. This numerical model includes multi-scale fractures and uses an appropriate methodology for each type of fracture, i.e. short, medium and long fractures. The model incorporates fluid flow in matrix, at the matrix-fracture interface and from fracture to fracture. It also assesses the effect of disconnected fractures on fluid flow. The computational efficiency of the presented model is improved in this thesis.
In the second algorithm, a simulation model based on the grid based effective permebailities is presented. This is a finite element model that calculates pressures and production rates in naturally fractured reservoirs with arbitrary oriented fractures. To demonstrate an application of this model, a slice of fracture networks from a fractured basement reservoir of the Amadeus Basin is simulated. First, the permeability tensor model is used to obtain the grid based permebailities. Then the flow simulator is fed by the grid block permeabilities to calculate pressure and velocity profiles throughout the reservoir. In one case, reservoir was depleted (depletion case), while in the second case, a five spot injection production scenario was modeled. Results show the importance of fracture networks in the fluid flow simulation, as flow is highly influenced by the connectivity of the fractures and the orientations.
A new laboratory-based glass bead model is introduced to visualize fluid flow through matrix and fractures as well as to measure absolute and relative permebailities of homogeneous and fractured porous media. In the experiments, the matrix and fracture are represented by two different sizes of glass beads. Single phase experiments are performed for single and multiple (two) fractures and the absolute permebailities are measured. These permeabilities are used to validate the permeability tensor model for single and multiple (two) fracture systems. Displacement tests for oil-water systems are conducted for homogeneous and heterogeneous systems. Pressures and productions are recorded for different realizations of fracture networks, and then the history matching technique is employed to obtain final relative permeability curves by using black oil simulator (CMG).
In the third algorithm, a two phase fluid flow (oil-water) model is presented. This model uses the finite difference method and calculates the pressure and saturations for fractured reservoirs. The IMPES method is adopted to solve pressures implicitly and saturations explicitly. The aim of this model is to simulate the laboratory based homogeneous and heterogeneous systems. Finally, laboratory obtained relative permeabilities are fed to the two phase flow model to estimate and compare the pressures and productions for homogeneous and heterogeneous systems. A reasonable agreement between the results is found which ensured the efficiency and accuracy of the numerical model as laboratory experiments provide authentic validations for numerical models.
In the final step, a new methodology is presented to upscale the laboratory-derived two-phase relative permeability relationship for different fracture systems to the reservoir scale. As an application, the proposed upscaling procedure is applied to a multi-fracture region of 1000m×1000m of the Amadeus Basin. Results reveal that the laboratory-based relative relative permeability based on simplified fracture-matrix geometries can form the benchmark data which can be upscaled for the field applications.