P-wave AVAZ analysis of anisotropic thin coal bed

By build the propagator matrix of HTI thin coal bed,we deduced the exact P-wave reflectivity equation of anisotropic thin coal bed with horizontal layers. AVAZ Analysis was made to study the reflectivity response of the HTI thin coal bed. The variations of P-wave reflectivity with incidence and azimuth angle were made for HTI thin coal bed case (layer thickness less than a quarter of seismic wavelength) and thick coal seam case (layer thickness larger than seismic wavelength). The tendency was similar but the values were different. The reflection coefficients of P wave are depending not only on physical property of the upper and lower layers,but also on the layer thickness. This indicated that applying classical equations to perform inversion for thin coal bed case was not accurate. Our study showed that layer thickness (of the thin coal bed),effective Thomsen’s anisotropic parameters for HTI and crack density had great influence on the P-wave reflectivity,while the aspect ratio of cracks changed the reflectivity tiny. When the azimuth angle was 90 degrees,the reflectivity seemed no longer affected by anisotropic parameters. This was mainly because the incidence wave was parallel to the isotropic plane of the HTI media.