Characteristics Of Nonhomogeneous Porous Medium On Percolation And Seepage

Theoretical and applied researches of percolation are more and more active in recent years, and great deals of successes have been achieved in each field. But in former studies and literatures, there were theoretical researches of percolation on homogeneous porous medium but not nonhomogeneous features on percolation laws and seepage characteristics.The nonhomogeneous materials in former researches were macro of micro-structure particles of them on the difference between mechanical and structure parameters, for example, permeate coefficient and strength. The nonhomogeneous porous medium in this study is heterogeneity of pores in space distribution. They are composed of multi-pores and densification particles. Because the size and number of densification particles are obeyed fractal laws, based on sierpinski carpet structure and nonhomogeneous porous medium models could be constructed. For instance of coal, multi-pore particles are represented coals and densification ones are represented the others impurities out of coals. The homogeneous porous mediums referred in the paper are homogeneous in space distribution of materials'pores.such that the paper is studied mostly in nonhomogeneous porous medium, the results will be significant on percolation laws and seepage features of realistic coal or rock mass.Based on the introduction of investigate and development on percolation theories, the application of them on seepage aspects have been illustrated and some of researches have also been conducted as follows: The high-precision micro CT experimental apparatus which model isμCT225KV FCB has been used to operate on oil shale, packsand, sandstone, coal sample and anthracite from Yangquan for CT scanning experiments, and the structure characteristics of various coal or rock samples have also been analyzed. The oil shale, coal sample and sandstone which have different structure characteristics have been selected for research objects, at last various CT figures of three-dimension reconstructive digital models for different coal or rock samples were established using CT figure analyses program by the research group from these scanning CT figures. In the foundation of two and three dimension homogeneous porous medium percolation model, the structure distribution features on percolation laws and porous connections of nonhomogeneous porous medium have been emphasisly investigated and the results showed that:(1) the homogeneous porous medium which the porous connections'size in threshold percolation and the number were belonged to fractal laws. The carpet models were also belonged to fractal law but the threshold percolation was less than homogeneous one. The porous connections of nonhomogeneous porous medium which porosity belonged to fractal law was not in threshold percolation. As porous connections distribution of two dimension were mostly affected by randomly nonhomogeneous, so the size and number of porous connections in three dimension double logarithm coordinate were belonged to leaner law and the correlation coefficients are more than two dimension ones. (2) In comparison to porous connections distribution curves of homogeneous porous medium, sierpinski carpet model and nonhomogeneous porous medium and found that, no matter two or three dimension, the curve of nonhomogeneous one was displayed epirelief at smaller connections. So there are few smaller connections in nonhomogeneous porous medium. (3) In comparison to the size and the number of porous connections distribution curves in oil shale, sandstone, coal sample, we can reach:1) In two dimension, the porous connections distribution curves of oil shale and sandstone displayed epirelief before it obeys power law, and displayed indented after it obeys power law, but the porous connections distribution curves of coal sample is not epirelief before it obeys power law.2) In there dimension, the trend of the porous connections distribution curves in coal sample is the same as oil shale and sandstone under the different porosity, displayed epirelief and indented,and will be epirelief when the porous connections is small,but the porosity as the size and the number of porous connections follows fractal law is obviously smaller then that of oil shale and sandstone,it is about 0.25%,and greatly smaller than its percolation threshold of 7.75%.(4) The number of porous connections of two or three dimension homogeneous and nonhomogeneous porous medium are increased firstly and decreased later followed by porosity increased. And when the number of porous connections is the largest, the porosity of two or three dimension nonhomogeneous porous medium are both less than the relevant homogeneous porous medium.Introduced the concept of critical porosity and based on the seepage characteristics studies of two dimension homogeneous and nonhomogeneous porous medium and found that:(1) if the porosity of two dimension homogeneous porous medium is less than 30%, the seepage region of fluid is very little. The fluid was not operated seepage even if larger pressure. If the porosity is at the range from 30% to 40%, the region of seepage gradually increased. If it is more than 40%, the seepage region of fluid expands rapidly. (2)Selected nine nodes in the middle of 200mm*200mm network and injected 1 m3/s flow, and looked into the seepage with time step 2000 minutes calculate 10 times, statisticed and analysed its curves and graphics,and founded that the critical porosity of two dimensional homogeneous porous medium is about 45%. Established a 200 mm side length cube and divided it into 2003 subnets, injected 1 m3/s flow in its center of the grid nodes, and looked into the seepage with time step 4000 minutes calculate 5 times, statisticed and analysed its curves and graphics,and founded that the critical porosity of there dimensional homogeneous porous medium is about 18%.(3)The seepage of two dimensional homogeneous porous medium is the same as homogeneous entity model,its ratio of the largest scale of y and x direction in the flow graph fluctuates near the 1,and that of nonhomogeneous porous medium fluctuates with the structure features of coal rock.(4)The relationship curve of seepage area and time in two-dimensional homogeneous porous medium follows logarithm law,and that of there-dimensional obey the power law.The curve of seepage area and time in two-dimensional, three-dimensional carpet model and nonhomogeneous porous medium follow the power law.(5) Respectively Constructed two-dimensional homogeneous porous media, rules of carpet and random carpet model,which are 243 units, selected nine nodes in the middle of each model and injected 1 m3/s flow, and looked into the seepage with time step 2000 minutes calculate 10 times, statisticed and analysed its curves and graphics,and founded that:1) The critical porosity of two dimensional homogeneous porous medium is about 45%,and that of regular and random carpet are about 40%.When the porosity is less than the critical percolation porosity, due to the presence of dense particles, regular carpet is greater than the homogeneous porous media, and because the random distribution of dense granules, and random carpet's seepage curve slope significantly greater than the other two species ideal material. When the porosity is greater than the percolation critical porosity, the slopes of flow curve in various materials are between 600 and 700.2) The trend of a,b are the same in various ideal material under different porosity,and the values of a,b mutate in its critical porosity,and the more mutation is behave the greater difference between the slope of the curve before and after its critical porosity. The Values of a,b reach the minimum value in its corresponding seepage critical porosity, and stabilized between 0.7 and 0.8.