Study On Hydraulic Characteristics Of Fractured Media Under Hydraulic Fracturing

Now exploitation of hydraulic electricity is at the height of power and splendour in China, and many larger-scale water power stations will be built up. The foundations of these high dams are crack rocks, after big reservoirs impounding, high hydraulic pressure will be put on the crack rocks, and can they bear the high pressure? The stability and permeability of dam foundation rock cracks determine the project's safety. In order to meet water power stations' need, the author applies hydraulic fracturing to this field and research into these problems. But, applying hydraulic fracturing to evaluation the stability and permeability of dam foundation rock cracks is a vacancy in our knowledge. So, the selected topic of thesis has important value in theory and practice.On the basis of previous hydraulic fracturing theory, according to hydraulic fracturing field experiments and with natural cracks in gorges as initial conditions, using the theories of Tectonics, Rock mechanics, Dynamics of groundwater and Fracture mechanics, the paper researches laws of the fracture initiation, fracture growth & crack stability, its permeability in the process of hydraulic fracturing, and analyzes the mechanism of hydraulic fracturing. At last, applying the theories to a project.Analyzing of the results of hydraulic fracturing field experiments, determination pressure of rock fracture initiation is the crack size. According to the injection rate and pressure in the process of hydraulic fracturing, the representative modeling of hydraulic fracturing process is designed as a process with three stages: crack initiation, fracture growth and fracture stability. The flow reduce is the symbol of fracture growth stage. Using dimensionless method, the paper concludes that at the stage of crack initiation, the relation of aperture & hydraulic pressure is log law and the relation of fracture's permeability & hydraulic pressure is log law too, and that at the stage of fracture stability, the relation of aperture & hydraulic pressure is linear law and the relation of fracture's permeability & hydraulic pressure is linear law too. The paper analyzes the process of hydraulic fracturing on mechanism, realizing the processes of hydraulic fracturing and crack initiation under normal stress have difference on deformation mechanism. There are only elastic deformation and brittle deformation on the process of hydraulic fracturing, and not compaction. At the stage of fracture initiation, the groundwater is turbulent flow, and the relation of J - v is an exponential expression. At the stage of crack stability, the groundwater is approximately laminar flow. In the paper, the seepage under stress shows the obliquity effect. Finally, because the characteristic of water power stations: the significantly difference of the principle stresses before and after reservoirs impounding, and the non-perfectly hydraulic fracturing field experiment, the paper approximately applies conclusions into a water power station. But the results still have the important value to this project and similar projects.