Breaking the Limit of Seismic Resolution to Enhance Channel Sand Delineation from Seismic Data for Deep Gas Development

Abstract

Characterising channel gas sands in the Chua field of the Central Swamp, Niger Delta, is constrained by the limited vertical resolution of seismic data and by overlapping P-impedance values between gas sands and gas shales. This study integrates long-cable anisotropic 3D seismic data with well-log information to improve subsurface layer resolution, delineate channel-sand reservoirs, and discriminate lithology and fluid content. Amplitude-versus-offset analysis of pre-stack seismic data was combined with layer-based inversion, rock-physics constraints, spectral decomposition, coherence, and curvature attributes. The results show that S-impedance inversion provided better separation of gas sands and gas shales than P-impedance inversion. The observed amplitude anomalies were associated with hard sands having higher Vp/Vs ratios than the fluid-line Vp/Vs ratio in intercept-gradient space. Shale interference caused seismic amplitudes to reflect gross reservoir thickness more strongly than direct net-pay thickness. Interpretation of the integrated data also delineated extensive braided fluvial channel systems, with interpreted sand thicknesses ranging from approximately 85 to 120 m. The combined workflow improved characterisation of channel geometry and reservoir distribution where conventional impedance interpretation alone was insufficient. The findings indicate that integrating pre-stack seismic analysis, elastic inversion, well information, and complementary seismic attributes can support more reliable delineation of deep gas channel sands in the Chua field.