The paper discusses the use of porous media equivalents for networks of discontinuous fractures in fractured rock. It explores the conditions under which a fractured rock behaves like a homogeneous, anisotropic porous medium. The study uses field data and a realistic two-dimensional fracture system model to analyze the behavior of fractured rock under simulated flow tests. The results are plotted as permeability ellipses, showing that fractured rock does not always behave as a homogeneous porous medium with a symmetric permeability tensor. The study finds that fracture systems behave more like porous media when fracture density is increased, apertures are constant, orientations are distributed, and larger sample sizes are tested. The paper also discusses the theory of anisotropic permeability, the measurement of directional permeability, and the concept of homogeneity in porous media. It concludes that the size of the representative elementary volume (REV) must be small enough to have a constant gradient and large enough to contain a representative sample of heterogeneities. The study also examines the effects of fracture density, aperture distribution, and orientation distribution on the hydraulic behavior of fractured rock. The results show that as fracture density increases, the hydraulic behavior of the fracture system becomes more like that of a homogeneous, anisotropic material. The study also highlights the importance of considering the scale effect in permeability measurements and the need for larger samples to obtain accurate results. The paper concludes that the use of porous media equivalents for fractured rock systems can greatly enhance the ability to analyze field data on fractured rock systems.The paper discusses the use of porous media equivalents for networks of discontinuous fractures in fractured rock. It explores the conditions under which a fractured rock behaves like a homogeneous, anisotropic porous medium. The study uses field data and a realistic two-dimensional fracture system model to analyze the behavior of fractured rock under simulated flow tests. The results are plotted as permeability ellipses, showing that fractured rock does not always behave as a homogeneous porous medium with a symmetric permeability tensor. The study finds that fracture systems behave more like porous media when fracture density is increased, apertures are constant, orientations are distributed, and larger sample sizes are tested. The paper also discusses the theory of anisotropic permeability, the measurement of directional permeability, and the concept of homogeneity in porous media. It concludes that the size of the representative elementary volume (REV) must be small enough to have a constant gradient and large enough to contain a representative sample of heterogeneities. The study also examines the effects of fracture density, aperture distribution, and orientation distribution on the hydraulic behavior of fractured rock. The results show that as fracture density increases, the hydraulic behavior of the fracture system becomes more like that of a homogeneous, anisotropic material. The study also highlights the importance of considering the scale effect in permeability measurements and the need for larger samples to obtain accurate results. The paper concludes that the use of porous media equivalents for fractured rock systems can greatly enhance the ability to analyze field data on fractured rock systems.