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Characteristics of Nonhomogeneous Porous Medium on Percolation and Seepage

Author: WangJiangFang
Tutor: FengZengChao
School: Taiyuan University of Technology
Course: Engineering Mechanics
Keywords: Heterogeneous porous media Micro-CT Percolation Seepage
CLC: O357.3
Type: Master's thesis
Year: 2011
Downloads: 303
Quote: 1
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Abstract

In recent years, the percolation theory and its application study compared active percolation theory in various fields of application have also made considerable achievements, but in previous studies and literature, just for a homogeneous porous medium percolation theory aspects study, almost no literature to elaborate or study of percolation in heterogeneous porous media law and percolation characteristics. Non-homogeneous materials studied in the past literature refers to material meso, or micro particles differences on some kind of mechanical or structural parameters, such as permeability coefficient, strength; heterogeneous porous media mentioned in this article refers to the porosity of the material in the space distribution of non-uniformity. The material can be divided into porous particles and dense granules. Obey fractal law due to the size and number of dense granules, in accordance with the Sale Verbinski carpet structure, build heterogeneous porous media model, coal, for example, the particles of the porous coal particles, dense granules Unlike the coal itself other impurities. Heterogeneous porous medium mentioned herein refers to the porosity of the material is uniform in spatial distribution. So this is primarily studied from the perspective of heterogeneous porous media, the percolation law and understand the real coal-rock seepage characteristics of great practical significance. This paper first introduces the overview of the research and development of the percolation theory, percolation theory in seepage, and carried out the research work of the following aspects: the use of μCT225KV FCB High Precision Micro-CT test machine oil shale, fine sandstone, sandstone and Yangquan anthracite and coal samples CT scan experiment, analysis of various structural features of coal and rock samples, choose oil shale, sandstone and coal samples with different structural characteristics of the three coal-rock samples CT image analysis program developed by research group as a research object, based on the scan from the CT images, and various coal CT image three-dimensional reconstruction of digital models of rock samples. On the basis of two-dimensional, three-dimensional heterogeneous porous media percolation model, this paper focuses on heterogeneous porous media percolation law group structure and pore connectivity distribution characteristics of the study concluded: (1) heterogeneous porous media are to obey the percolation threshold at the pore size of the group and the number of fractal law. The carpet model also percolation at the threshold pore size of the group and the number of subject fractal law, but its percolation threshold of less than heterogeneous porous media. Rather than homogeneous porous media group distribution porosity obey fractal law is not equal to the percolation threshold; due to the two-dimensional distribution of the pore group by the larger, three-dimensional pore group size and the group of non-homogeneous randomness number of linear relationship in double logarithmic coordinates, fitting correlation coefficient greater than two-dimensional. (2) relatively homogeneous porous medium, Sale Verbinski carpet model and heterogeneous porous media pore distribution curve group can be seen, either two-dimensional or three-dimensional, heterogeneous porous medium pore group the hour curves showing convex upward trend, indicating that a small number of small groups of heterogeneous porous media. (3) more oil shale, sandstone and coal samples, the number of pore group size and group distribution curve can be drawn: 1) the two-dimensional case, oil shale, and sandstone distribution curve in its obey the power law before and after showing the relationship between the upward convex and concave trend, while the coal sample distribution curve before the power-law relationship and not convex upward trend. 2) three-dimensional case of coal and oil shale, and sandstone porosity pore distribution curve group trend is the same, and both showed a different trend of bump and upwardly convex group is very small case, but fractal law of obedience between the number of their group size and group the porosity significantly less than oil shale and sandstone, probably in at 0.25%, and the percolation transition occurs far cry from the percolation threshold of 7.75%. (4) two-dimensional, three-dimensional homogeneous and heterogeneous porous media connectivity group after the first increase with increasing porosity reduction and two-dimensional and three-dimensional heterogeneous porous media connectivity group reached the maximum pore rate is less than the corresponding homogeneous porous medium. This paper introduces the concept of the seepage critical porosity, percolation characteristics of two-dimensional homogeneous and heterogeneous porous media, concluded: (1) when the two-dimensional heterogeneous porous media porosity of less than 30% , a percolation area of ??the fluid is small, even when the pressure is large, the fluid also substantially does not occur seepage; slowly increases when the porosity is between 30% and 40% between the seepage of fluid region; When the porosity is greater than 40% fluid seepage area is expanding rapidly. (2) 200mm × 200mm grid center selected nine nodes to set the flow of 1m3 / s, and observed that the time step for 2000 minutes 10 times the seepage curve with graphics, statistical analysis, to obtain a two-dimensional heterogeneous porous media seepage critical porosity of about 45%. Establish cube with a side length of 200mm, divided into its 2003 size Subdivisions 1 m3 / s flow rate is set in the center of the cube grid nodes, observation time step for 4000 minutes 5 times seepage research and analysis of the curve and graphics, to obtain three-dimensional heterogeneous porous media seepage critical porosity of about 18%. (3) two-dimensional heterogeneous porous medium model and homogeneous entity model seepage (permeability coefficient for each direction is the same) is the same as the ratio of the largest scale of the its seepage graphics y direction and x direction in the near 1 fluctuations; rather than heterogeneous porous media seepage graphics y direction and x direction of the largest scale ratio based on the structural characteristics of the coal and rock samples show different trends. (4) the relationship of the two-dimensional heterogeneous porous media seepage area with seepage time curve is logarithmic; seepage area of ??three-dimensional heterogeneous porous media seepage time curve obeys a power law relationship. The two-dimensional, three-dimensional model of the carpet and heterogeneous porous media seepage area with seepage time curve obeys the power-law relationship. (5), respectively, to build 243 units of the size of a two-dimensional heterogeneous porous media, rules the carpets and random carpet model, 9 node to select the grid center into a flow of 1 m3 / s, and a time step of 50 minutes to calculate 100 times after seepage, statistical analysis of the curve and parameters, and concluded as follows: 1) heterogeneous porous media seepage critical porosity of about 45%, and the rules and random carpet model in the vicinity of 40%; When porosity when the porosity is less than the percolation critical, due to the presence of the dense granules, the rule carpet percolation curve slope is greater than in the homogeneous porous medium, random carpet due to a random distribution of the dense granules, the slope of the flow curve is significantly greater than the other two ideal material ; When the porosity is greater than the percolation critical porosity, the slope of the flow curve of a variety of materials are between 600 and 700. 2) under a variety ideal material with different porosity, the B value trends is the same; and A, the value of b are in its the seepage critical porosity at a mutation, the mutation more, before and after the percolation curve slope The greater the difference. A value reaches the minimum value in its corresponding the seepage critical porosity at, b values ??are first increased and then stabilized between 0.7 and 0.8.

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CLC: > Mathematical sciences and chemical > Mechanics > Fluid Mechanics > Viscous fluid > Seepage
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