Uncertainty-Weighted Robust Frequency-Scanning AVO Inversion for Fluid Prediction in Marine Low-Permeability Gas-Bearing Sandstones: A Case Study from the Xihu Sag, East China Sea

Abstract

Marine low-permeability gas-bearing sandstones are commonly characterized by thin sand–mud interbeds, poor reservoir properties, limited seismic bandwidth, and heterogeneous pore structures and fluid distributions, which make stable fluid prediction from conventional prestack seismic attributes difficult. This study proposes an uncertainty-weighted robust frequency-scanning amplitude variation with offset (AVO) inversion method, termed URFS-AVO, for gas-bearing sandstone identification in the Xihu Sag, East China Sea. Under a fluid-matrix decoupled AVO framework, a frequency-dependent P-to-P (PP) reflection-coefficient equation related to the fluid bulk modulus is combined with matching-pursuit Wigner–Ville distribution (MP-WVD) spectral decomposition to obtain local time–frequency spectra from prestack angle gathers. Moving narrow frequency windows are then used to estimate local fluid-dispersion attributes within the effective seismic bandwidth. Rather than extracting the maximum response, URFS-AVO fuses multi-window estimates using local inversion uncertainty and frequency-domain consistency. Tests based on the Chapman pore–microcrack model and the generalized propagator matrix show that the proposed attribute is sensitive to gas-bearing variations. Compared with maximum-window frequency-scanning AVO (FS-AVO), URFS-AVO produces a more focused target-layer response and suppresses unstable background fluctuations, especially under noisy conditions. Application to marine prestack seismic data from the Xihu Sag shows that high URFS-AVO responses are generally consistent with gas-bearing intervals interpreted from well logs. The method provides a stable seismic constraint for fluid prediction in marine low-permeability gas-bearing sandstone reservoirs.

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