Characterization Of Coal Pore Fracture Structure Based On CT Technology And Fractal Theory

Coal is a porous medium with obvious stratification characteristics.The microstructure of coal affects the physical and chemical properties of coal itself.Engineering problems such as coalbed methane mining and downhole flood control all involve the microstructure of coal.Due to the diversity and heterogeneity of coal and the limitations of various research methods,it is difficult to accurately clarify the pore fracture structure of coal.With the continuous development of computer technology,CT scanning technology has been more and more widely used in the field of mining,and the research content has been studied from two-dimensional CT scanning image to study coal damage defect to CT three-dimensional reconstruction to study coal structure and realize coal body.Extraction of internal pore fracture structures.At the same time,the digital model of CT three-dimensional reconstruction can realize the microscopic scale seepage simulation,and the fractal dimension can quantitatively characterize the internal pore fissure structure of coal.This is the development and utilization of coalbed methane under the current energy transformation situation in China.In order to obtain the real physical model which can characterize the microporous fracture structure of coal,the internal gas seepage law is discussed by numerical simulation.Based on CT scanning experiment,fractal theory of three-dimensional reconstruction technology and finite element analysis method,qualitative and quantitative characterization of coal structure is proposed.The method and the application of three-dimensional fractal dimension to characterize the complexity of pore-fracture structure,and gradually carried out the research on the topic of "characteristics and application of coal-hole fracture structure based on CT technology and fractal theory".The main research contents and conclusions are as follows:1)High-resolution CT scan images of six coal samples were obtained by conducting CT scanning experiments on six coal samples with different degrees of metamorphism.The median filtering algorithm is selected to denoise the CT image of the coal sample,so as to preserve the detail features and edge information of the image.The image is segmented by selecting a threshold based on the porosity method,thereby obtaining a binarized image of the region of interest of the image.The characterization unit of the reconstructed coal sample is calculated by the constraint of coal porosity,so that the most suitable model size is selected to characterize the coal structure.The processed CT image is reconstructed by AVIZO for the three-dimensional reconstruction of the coal pore fracture structure.The three-dimensional pore fracture structure of the coal.2)A method for qualitative and quantitative characterization of pore fracture structure of coal is proposed by obtaining a three-dimensional pore fracture structure based on reconstruction.Firstly,the qualitative characterization of the coal structure is carried out,and the gray value of the two-dimensional CT image is detected,and then the gray histogram of each coal sample is obtained,and the internal structure of each coal sample is preliminarily analyzed;then the three-dimensional reconstruction of the coal structure is observed,qualitative Analytical pore fracture structure.Secondly,quantitatively and statistically analyze the pore micro-parameters of six coal samples—pore size,pore volume,porosity,coordination number,throat length,etc.,study the probability distribution of pore size and volume of each coal sample,and characterize the pore structure of coal sample.The complexity.The heterogeneity of pore fracture structure was quantitatively characterized by the statistical mean deviation of coal surface porosity.The gas seepage simulation was carried out based on the three-dimensional coal pore fracture structure,and the velocity streamline diagram and pressure cloud diagram of each coal sample were obtained.Finally,a simplified model of the pore network with topology is established to further characterize its connectivity.3)Through the research on the fractal theory,the three-dimensional coal pore fracture structure combined with the three-dimensional fractal theory is used to quantitatively analyze the complexity of the pore fracture structure of the coal sample and the porosity and permeability.First,the concept of fractal geometry and the calculation of fractal dimension are introduced in detail.The Matlab program based on 3D fractal theory is programmed and then the 3D pore fracture structure data volume is introduced into it to calculate the volume fractal dimension of each coal sample.The complexity of the fracture structure of each coal sample is quantitatively characterized and the pore structure parameters and pores are analyzed.Based on the fracture structure parameters of CT three-dimensional reconstruction combined with the fractal fractal mathematical model,the fractal dimension of tortuosity is obtained.The relationship between volume fractal dimension and tortuosity fractal dimension and porosity and permeability is studied respectively.The effect of different pore fracture structures on the porosity and permeability of coal.In order to verify the accuracy of the simulated data,the mercury intrusion experiment was carried out,and the obtained data was compared with the simulated data.The results show that the simulation results are within a reasonable error range and the accuracy of the data is verified.