Thin-bed reservoir characterisation using high-resolution ocean-bottom-node seismic data, seismic waveform indication inversion, and a Gaussian mixture model: A case study from the Guantao Formation, Bohai Bay Basin, China

Abstract

Targeting reservoirs that fall below seismic resolution remains a primary challenge in reservoir characterisation. High-resolution ocean-bottom-node seismic data are essential for imaging oil-bearing thin-sand facies, particularly in the Guantao Formation of the Bohai Bay Basin. The basin is rich in hydrocarbon resources but underexplored due to the difficulty of identifying thin-sand bodies. This study investigated thin beds below the tuning thickness to determine reservoir quality and oil–water distribution within this formation. By applying seismic waveform indication inversion (SWII) at the reservoir level, we generated a high-frequency and high-resolution facies model validated against existing geological data. Simultaneously, a Gaussian mixture model (GMM) was utilised to detect anomalies in well-log data (gamma ray, velocity ratio [V_p/V_s], and density), leveraging inter-variable relationships to enhance geological interpretability. Results demonstrated an excellent correlation between GMM anomalies and high-resolution seismic data, significantly improving prediction accuracy in complex structural regimes. SWII effectively identified thin sand-shale layers, reflecting various stacking patterns and the effects of porosity and oil-bearing properties on sand-body velocity. Forward modelling analysis revealed the seismic-resolvable thicknesses of sand bodies, the seismic response characteristics associated with various stacking patterns, and the influence of physical properties and oil-bearing characteristics on sand-body velocity, among other factors. This integrated approach effectively resolves thin-bed distributions and identifies potential hydrocarbon traps, providing a robust foundation for future multilayer system deployment in the Bohai Bay Basin.

Keywords

Anomaly detection / Gaussian mixture model / Thin-bed reservoir characterisation / Well-log analysis / Seismic data inversion

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