Fractal Analysis Of Seepage Characteristics Of Fractured Porous Media

Fractured porous media are generally composed of porous matrix and fracture networks, and micro pores in matrixes and fractures are randomly and disorderedly distributed. The most widely used models for fractured porous media are considered as dual-porosity and dual-permeability models. Such media widely exist in nature such as the cracked soil, fractured rock, biological tissue and water/oil/gas reservoirs etc. The seepage characteristics of the fractured porous media have the significant influence on nuclear waste disposal, oil or gas exploitation, geothermal energy extraction and tumor therapies. However, due to the disordered and complicated micro-structures of fractured media such as irregular orientation and size of fractures and pores, and the tortuosity of flow path etc, it is very difficult to analytically study the seepage characteristics in fractured porous media. So far, the microscopic transport mechanisms of fluid in fractured porous media are still not well understood. Fortunately, in the1980s, the fractal geometry theory, which is one of nonlinear sciences, has been shown to be powerful in characterization of porous media. The sizes of fractures and pores have been shown to have the self-similarity and fractal characteristics. Based on fractal porous media, the fractal model of fracture networks is proposed, and then the seepage properties in fracture networks, porous media and fractured porous media have been also investigated. The work in this thesis is one of the mostly interested hotspots in the cross field of theoretical physics, geophysics, and complexity science. The specific research conclusions obtained in this thesis are as follows:First, the fractal theory for porous media is extended to fracture networks. Then, the models for area density, fractal fracture networks and permeabilities for Newtonian fluids and gas shale of fracture networks are proposed based on fractal fractured network theory. The proposed permeabilities and the predicted fracture density are compared with the numerical simulations and experimental data.Second, the permeability model for the Newtonian fluid flow in the fractured porous media is derived based on the fractal geometry theory for porous media and fracture networks and basic seepage law (cubic law). The validity of the proposed model is verified by the comparisons between the model predictions and experimental data, and the parametric study is also performed in this section. It has been found that the ratio of the maximum pore/capillary diameter of a porous matrix to the maximum fracture aperture of a fracture network has the significant influences on permeability.Third, the charactristic of spherical/radial seepage in porous media have attracted steadily attention in many sciences and technologies. Considering the effects of capillary pressure, the effective radial permeability and relative permeability for spherical seepage in porous media are studied by the fractal theory for porous media. The parametrical effects on the radial permeability are also studied. The validity of the proposed model is verified by comparing the model predictions with the available model and the existing experimental data.Finaly, slug flow, which is one of the mostly interested topics of two-phase flow in porous media, is studied. The slug flow widely exists in oil and gas pipelines, underground water reservoirs, and nuclear reactor cooling systems and in fuel cells, etc. The analytical models for seepage characters, both permeabilities and relative permeabilities, for slug flow in a capillary are proposed. Then, we extend the methodology to analyze the seepage characters of slug flow in fractal porous media. The validity of the proposed slug flow model is verified by comparing the model predictions with the available experimental data. The parametrical effects on the relative permeabilities are also investigated.