Mechanism Of Non-linear Seepage Flow In Low Permeability Rock And Its Variable Permeability Numerical Solution

Non-linear seepage mechanics in low permeability rock and its numerical analytical method is one leading task of seepage research, which acts as an important role to hydraulic engineering, petroleum industry, mining project, waste landfill, and so on. This doctoral dissertation is pertaining to the research subject concerning the non-linear seepage mechanism in low permeability incompetent rock, which is supported by National Science Fund of China. The task mentioned above is studied in this dissertation by delving into the result of a series of seepage experiments and trying to find out some method for numerical analysis.Based on the parameters concerning pore structure of conglomerate and sandstone gathered from the rock body of casting and mercury penetration experiments, those stones from Shimenzi Reservoir, Xinjiang province and from Changqing oil field Gansu province respectively are taken as samples in this regards. The common pore structural feature of these low permeability rock is concluded at first, which could be deemed to set up the relation between rock and its low permeability feature as well as non-linear seepage phenomena within.It is revealed by the saturated single liquid seepage experiment performed by FDES-641 triaxial system that the movement of low speed seepage in low permeability media departs from the law of Darcy, meanwhile the curve of seepage flow would not pass through the origin of coordinates. Permeability of rock changes with the pressure gradient either. Non-linear seepage formula with high fitting accuracy is achieved by the method of numerical analysis. Starting from the point of the mechanical characteristics of boundary layer, the physical meaning of the non-linear term in formula is revealed, meanwhile the mechanics towards non-linear seepage flow but caused by boundary layer is concluded.Unsaturated seepage experiments in low permeability rock present more obvious non-linear seepage characteristics. One numerical model of unsaturated seepage flow in constant diameter capillary is established based on the simplified model of capillary and the theory of boundary layer, meanwhile the analysis formulas of seepage velocity and threshold gradient of non-Darcy seepage flow are deduced accordingly. The mechanics towards non-linear seepage flow but caused by capillary pressure is analyzed by this way. When summing up the unsaturated experimental phenomena above, it can be concluded that the macroscopical movement characteristics of unsaturated seepage flow would behave much close to that of the saturated infiltration when the degree of liquid saturation in rock comes up to 85%. Similar formula used to describe the movement of saturated seepage can also be applied to characterize the unsaturated flow in this regard.It is proved by the liquid-solid coupling seepage experiment that rock owns elastoplasticity, loading would bring rock with plastic deformation beyond retrieve, and the loading history would play a significant effecting role in the change of permeability of rock. The functional relationship between the permeability and the effective confirming pressure is analyzed through experiment. Due to great complexity of the coupling factors affecting the permeability of rock, the coefficient of sensitiveness between the permeability of rock and the effective pressure is defined accordingly as to generalize those factors. Power function can be used to describe the relation between the permeability of rock and the effective pressure based on the coupling seepage experiments, and the function between the permeability of rock and the effective pressure but based on the conception of coefficient of sensitiveness is established hereafter.With the help of not only the summary of the experimental findings mentioned above, but also some further contradistinctive experiments together with some corresponding theoretical deduction as well, the mechanics towards non-linear seepage flow are delved into and totally classified into three categories, those are, the pore characteristics of rock, the feature of liquid and the interaction between liquid and rock.According to the research findings of non-linear seepage flow, one variable permeability non-linear seepage numerical model is established in this dissertation. The corresponding solution for the non-linear equation is developed either. Calculation program based on the model is developed hereby and the feasibility of the non-linear model as well as its solution is illuminated by the designed examples.