Fluid Flow In Fractured Porous Media:Characteristics And Modeling

For fractured rock masses commonly found in engineering,the internally developed matrix and fractures have important contributions to fluid flow.The study of fluid flow characteristics in fractured porous media is of great significance for major projects such as mining,oil and gas storage,water conservancy and hydropower,underground storage of nuclear waste,and geotechnical environmental protection.In this paper,the fractured porous media is divided into regular fractures and irregular fractures.Using a combination of laboratory tests,theoretical analysis and numerical simulation,this paper comprehensively analyzes the representation element volume(REV)and the matrix-fracture flow transfer of fractured porous media,and proposes a generalized matrix-fracture flow transfer model for fractured porous media.The major results of this study are summarized below:(1)A set of equipment that can simulate the flow in fractured porous media with regular fractures was designed and developed,and an indoor dual-medium percolation test has been carried out using this test device.Experiments of matrix-fracture flow transfer in fractured porous media under different velocities of matrix and fracture are analyzed.The experiments show that there is a strong nonlinear relationship between the matrix-fracture flow transfer term and flow rates.(2)A generalized matrix-fracture flow transfer model of fractured porous media is proposed.Studying the matrix-fracture flow transfer of fractured porous media under regular fractures and irregular fractures,comprehensively considering the influence of the matrix-fracture interface occurrence and the nonuniformity of pressure distribution,using fracture pressure correction factors to characterize the effect of pressure nonuniformity,and a generalized matrixfracture flow transfer model for fractured porous media is proposed.The generalized matrixfracture flow transfer model can be degraded into a traditional shape factor model with idealized geometry.Comparing the generalized matrix-fracture flow transfer model with the shape factor theory,it is found that the shape factor theory is only applicable to the analysis of the matrixfracture flow transfer term in the fractured porous media with regular fractures,and the generalized matrix-fracture flow transfer model can be applied to the regular fractures and irregular fractures.(3)The influence of geometric characteristics and physical properties(permeability)on REV of fractured porous media with irregularly fractures is studied,and the expression of REV value of fractured porous media considering medium geometry is established.The Monte-Carlo method was used to generate a random fracture1 network.The REV values and equivalent permeability coefficients of the permeability of a single medium(fracture)and dual medium under different media geometries were compared under the condition of unidirectional flow configuration and radial flow configuration.The REV value of the fractured porous media is smaller than that of the single media,the equivalent permeability coefficient is larger than that of the single media,and the REV value and permeability coefficient of the unidirectional flow configuration are larger than those of the radial flow configuration.The relationship between the REV values and the fracture track length and spacing,the equivalent permeability coefficient and the matrix/fracture permeability ratio relationship,and the difference between the dual media percolation characteristics under the condition of unidirectional flow configuration and radial flow configuration is study.(4)The effects of geometrical characteristics and physical properties(permeability)of the fractured porous media on the matrix-fracture flow transfer and fracture pressure correction coefficients in a two-dimensional fractured porous media with irregularly fractures were studied.On the REV scale,the matrix-fracture flow transfer term and fracture pressure correction coefficients in two-dimensional fractured porous media with different fracture trace lengths,densities,and fracture/matrix permeability ratios were analyzed,and matrix-fracture flow transfer term was found.The matrix-fracture flow transfer term increases with the increase of fracture trace length,density,and fracture/matrix permeability ratio,and the fracture pressure correction coefficient decreases with the increase of fracture trace length,density,and fracture/matrix permeability ratio.By comparing the traditional shape factor model and the generalized matrix-fracture flow transfer model,it is found that the generalized matrix-fracture flow transfer model has a wider scope of application.(5)The effects of geometrical characteristics and physical properties(permeability)of the fractured porous media on the matrix-fracture flow transfer and fracture pressure correction coefficients in a three-dimensional fractured porous media with irregularly fractures were studied.On the REV scale,the matrix-fracture flow transfer term and fracture pressure correction coefficients in two-dimensional fractured porous media with different fracture trace lengths,densities,and fracture/matrix permeability ratios were analyzed,and matrix-fracture flow transfer term was found.The effects of fracture trace lengths,densities,and fracture/matrix permeability ratios on the matrix-fracture flow transfer term and fracture pressure correction coefficient in a three-dimensional dual medium are the same as those in two-dimensional.By comparing the flow characteristics of two-dimensional and three-dimensional media,it is found that the matrix-fracture flow transfer term in three-dimensional is larger than that in twodimensional,and the correction coefficient of fracture pressure is larger than that in twodimensional.