Fluid factor of fracture and seismic velocity response in anisotropic coal beds

The storage and transport of gas and water in coal seam are related to the density, strike and filler of cracks. Research on the identification and prediction of coal seam cracks will be helpful to prevent and control disastrous accidents in coal mines, such as water inrush and gas outburst. It plays an important role in the safety evaluation of coal mining. Based on the theory of fracture equivalent model, the variation characteristics of fluid factor in coal seam crevices with different fillings and fracture weaknesses parameters(fracture density, aspect ratio, volume modulus, shear modulus, Lamé parameters) are analyzed by combining Schoenberg linear sliding model with dry, gas-bearing and saturated cracks in coal seam. Through calculating seismic wave group and phase velocity of coal bed with vertical cracks, the response characteristics of seismic wave anisotropic velocity are obtained when the density and filler of cracks in HTI coal bed change. From the forward simulation results of the HTI coal bed theoretical model, it can be seen that the fracture fluid factor in the model has a positive correlation with the fracture density and geometric shape, but a negative correlation with the volume modulus of filling fluid. HTI coal bed P wave group and phase velocity are sensitive to gas and water in the fracture, SV wave group and phase velocity are not sensitive to dry fracture(gas filling), and SV wave group velocity is very sensitive to water in fracture. The feasibility of coal seam fracture fluid prediction is realized through the response analysis of crack fluid factor and anisotropic velocity parameters in HTI coal bed. It lays a foundation for analyzing seismic wave propagation characteristics of coal seam with cracks and provides theoretical support for crack prediction of coal seam.