P-wave reflection coefficients have been a valuable tool to quantify the shale/sand system. The reflection coefficient is a complex function of P-wave velocity, density and other elastic factors. For shale/sand system, the reflection coefficients can be further complicated by the HTI anisotropy induced by fractures. Fracture density can affect the induced HTI property directly, and can have an impact on the calculated reflection coefficients. While exact numerical simulation is more accurate than simple approximations, the approximations are much more physically intuitive for AVO interpretation. To investigate the effects of fracture density on the P-wave reflection coefficients, shale/sand models are created that represent class 1, 2, 3 sand systems in this study. The reflections coefficients for different share/sand model and different fracture densities are calculated. Azimuthal responses to the fracture densities are investigated. From the synthetic tests, it is conclusive that the fracture density not only changes the AVO slope, but also impacts the azimuth response gradient for all three types of shale/sand systems. In general, the reflectivity response due to fracture is more obvious in the azimuthal observation.
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