Study On Micro-seepage Law Of Coal Gas/Water Based On Micro CT-CFD Technology

Coal is a kind of extremely complex porous structure material,its internal size varies,the shape of the pore cracks,directly affect the porosity of coal,permeability and other macroscopic physical characteristics,but also affect the coal fluid storage capacity and seepage characteristics.Therefore,it is of great significance to analyze the microscopic pore structure of coal body,establish a three-dimensional pore model of coal and rock body,and use numerical simulation to analyze the seepage characteristics of gas,water and other fluids in the pore,in order to improve the coal mine production conditions,reduce the coal dust content and prevent gas outburst disasters.In this paper,the experimental operation,theoretical analysis and numerical simulation are combined.At first,that anthracite is scan by an X-ray three-dimensional microscope,Build 3D Data Volume.Then the model is processed by image processing,based on the maximum sphere method,The fractal distribution of pore,volume and surface area is analyzed,and the fractal permeability is predicted.Finally,based on the scanning model,the gas and water seepage flow under different pressure gradient is simulated,and the pressure,velocity and mass flow rate of gas and water are obtained.The results show that the anthracite model has good pore homogeneity,large pore throat size,good pore connectivity,self-similarity of pore distribution and simple structure.Under the same pressure gradient,the seepage pressure of gas and water has the same trend,and the seepage pressure decreases gradually along the direction of seepage.Gas seepage velocity is much faster than water seepage velocity,and velocity streamline diagram is more plump than water streamline diagram,some small pores have gas flowing through,but there is no water flowing through pores at the same position.The mass flow of water is greater than that of gas.Although the types of fluids are different,the distribution of gas and water mass flow is similar in the same pore model,and the maximum mass flow is concentrated in the same location.With the increase of pressure gradient,the change of pressure field is more obvious,the whole velocity increases with the increase of pressure gradient,and the maximum mass flow rate of the same section also increases gradually.The average seepage velocity of gas and water under different seepage pressures was extracted by CFD-POST software.The relationship between seepage velocity and pressure gradient was analyzed.The permeability was calculated by fitting curves and non-Darcy seepage formula.The permeability of methane and water is 6.15×10-13m2 and 3.36×10-13m2,respectively.which are slightly lower than the predicted permeability,and the permeability of water is lower than that of methane.