Joint PP and PS pre-stack AVA inversion for VTI medium based on the exact Graebner equation

Abstract

Unconventional hydrocarbon reservoirs, such as shale rocks, are generally transversely isotropic with a vertical axis of symmetry (VTI). The identification of sweet spots in these reservoirs, which must take into account this anisotropic character, can be performed with amplitude variations with offset/angle (AVO/AVA) inversion. However, most approaches use the Rüger reflection approximate equation as forward modeling, which has low accuracy at moderate to large angles, where the seismic gathers contain most of useful information on anisotropy parameters. In this paper, we propose an exact-equation-based seismic pre-stack AVA inversion for stable estimations of anisotropy parameters in VTI media. A linear inversion scheme is adopted to save computational time and the Fréchet derivatives, the key factors of the scheme, are derived here. To improve the stability and accuracy, the PP data inversion is extended to joint PP and PS inversion, termed joint exact-Graebner-based prestack inversion (JEGI). It is applied to both synthetic and field multi-component seismic data, showing its feasibility and effectiveness.