Reconstruction Of Coal’s Microstructure And Simulation Of Coal Bed Methane Migration Using LBM

Coal is one of the most widely used energy in the world from eighteenth century. There is a large number of coal bed methane in it, which is so-called gas, new clean energy accepted in the recent 30 years. However, the gas collected and processed not in time will cause coal mine gas outburst, gas poisoning and gas explosion disasters in the industrial of coal, such as to the state and the people caused heavy loss of property and life. Gas extraction marched before or during coal mining can get clean and cheap resources and prevent disasters. Therefore, understanding microstructure of coal has great significance to coal bed methane mining.At present, use CT imaging technology for coal’s microstructure mostly, which is extremely expensive. Three-dimensional coal’s microstructure can be established though the numerical simulation method. We can simulate coal bed methane micro-seepage in coal using Lattice Boltzmann method (LBM), with the advantage of dealing with complex geometry boundary, which is based on molecular dynamics and statistical mechanics. Combining simulation method with LBM can solve the simulation of coal bed methane migration process in coal.Based on learning simulation method and Lattice Boltzmann method, this paper constructs the microstructure of porous media and coal using the method of quartet structure generation set (QSGS) and sphere random packing algorithm. Then gas seepage has been simulated by LBM and permeability of models has been calculated with Darcy’s law. The main research contents are shown as below.(1) Based on two-dimensional quartet structure generation set, which is introduced into three-dimensional space, we analyze influence of the parameters to porous media’s microstructure construction in 3-d QSGS. And we have established several different models in experiments considering some factors, such as the probability of initial growth cores, anisotropic factor of growth and porosity. At the same time, the gas seepage has been simulated and calculated by LBM under the condition of unlike anisotropic factor and different porosity. The results of experiments show that the great the probability, the more and smaller the pores are. On the contrary, the less and bigger the pores are. Thus the probability of initial growth cores can control the size and number of pore. At the same time, the greater anisotropic factor of growth, the more asymmetrically the pores distribute, and the pores have directionality. The length of pores increase, while the diameter of pores decrease. The porosity of pore can control the proportion of pore directly. When the microstructures with great anisotropic factor are great, their permeability is also great, which indicates the increase of anisotropic factor will improve the connectivity of pores.(2) Construct the simple three-dimensional coal’s microstructure using improved sphere random packing algorithm and built the seepage model of coal bed methane in coal with hole. And then we analyze the influence of holes to seepage of coal under this model. Several models in the same coal have been established, for example, different width of holes, different locations of holes and different directions of hole. Meanwhile, some models with the same hole in different porosity coals also have been constructed. For all those models, we calculate the permeability and the rate of lattice gas. The results tell us that the permeability shows exponential relationship with the width of holes, locations of holes also have some affect to permeability, directions of holes have a great influence to seepage and holes are more significant influence on coals having low porosity. So the holes and fractures along the flow direction should be obtained more attention in actual project.(3) Combining quartet structure generation set with sphere randomly packing, an algorithm of sphere randomly packing and pore randomly growing is proposed to reconstruct three-dimensional microstructure of coal rock. Several different porosity microstructures have been reconstructed, then single-phase migrating procedure of coal bed methane is simulated and the permeability is calculated using lattice Boltzmann method. And the velocity field of gas has been displayed. The results indicate that the algorithm of sphere random packing and pore random growing can efficiently represent microstructure of coal, and the porosity and pore width gained by random growing algorithm show good relation with coal’s permeability. With the same porosity of coal rock, its permeability shows linear relationship with the width of it spore. The simulation of the velocity field can display the behavior of coal bed methane migrating intuitively.