Comparative Analysis of Angle Gather Extraction Methods for AVO Inversion Using Accurate Zoeppritz Equation

Abstract Amplitude Versus Offset (AVO) inversion plays a crucial role in exploration and development of hydrocarbon reservoirs because it enables the derivation of reservoir elastic properties from seismic data. In recent years, AVO inversion methods based on the accurate Zoeppritz equation have gained increasing attention, as they aviod the limitations of approaches that rely on approximated Zoeppritz equations-such as the restricted reflection angle ranges and the assumption of reservoir property weak contrast at the reflection boundaries. In practice, the reflection angle gathers input to AVO inversion are converted from offset gathers using approximated method, such as the straight-ray method. This study quantitatively compares the precision of angle gathers converted using the straight ray method and a Snell’s law based method and evaluates its impact on the subsequent AVO inversion with accurate Zoeppritz equation. Synthetic tests show that the Snell’s law-based method produces angle gathers that match the theoretical results closely, whileas the straight-ray method produces significant inaccuracies particularly at large reflection angles and in thin-bed structures with large vertical velocity variations. The inaccurate angle gathers noticeably degrade the precision of AVO inversion based on the accurate Zoeppritz equation. A field data example further demonstrates that the Snell’s law based method yields inverted seismic velocities and density that align more closely with well-log measurements, and produces fluid factor distributions that correlate well with production data. This study provides valuable reference for designing and implementing AVO inversion workflows aimed at achieving high precision reservoir characterization for complicated geological structures.