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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.
•The exact Graebner equation is used for prestack seismic inversion of VTI medium.•The method is stable if estimating the anisotropies by using PP and PS waves.•The computational cost is reduced by adopting a Fréchet-derivative-based linear inversion.