Study on characteristics of seismic wave velocity response in orthotropic fractured coal seams

In coal seams,nearly orthogonal fractures are often developed,and the orthogonal fractures can be approximately used as orthotropic media.The analysis of the relationship between the anisotropic response characteristics of seismic waves and the fracture media is the basis for fracture prediction by seismic waves.In order to study the seismic wave velocity in coal seam to the influence of the fracture medium,selection of orthogonal anisotropic coal seam as the research object,according to the orthogonal anisotropic medium elastic matrix,combining Schoenberg Linear Slippery Theory and Hudson Theory,using the orthogonal anisotropic coal seam crack equivalent method,and through the orthogonal anisotropic medium group,phase velocity formula,orthogonal anisotropic coal seam group and phase velocity analysis,under the influence of fracture parameter was further studied the seismic anisotropy parameters of coal seam and the speed of response are studied.The results show that: in a given theoretical model,if the coal seam fracture is filled with different fluids,when the fracture aspect ratio or fracture density are constant,the anisotropic parameters will also change with the change of the volume modulus of the filling fluid.The longitudinal waves in the dry fracture (gas filling) and saturated water fracture models of OA coal seam show strong anisotropy.P wave is sensitive to the dry fracture (gas filling) and full water in OA coal seam,while SV wave is more sensitive to the water-bearing fracture of OA coal seam,but not to the gas.