AVO Attribute Analysis and Rock Property Modeling for Hydrocarbon Saturation Detection in Complex Reservoirs: BC Field, Offshore Niger Delta

Abstract Use of intercept (A) and gradient (B) attributes, remains an essential approach for seismic-based reservoir characterization in Amplitude Variation with Offset (AVO) cross plotting. This study integrates AVO cross plotting with rock property modelling to enhance reservoir and fluid characterization in the complex geological setting of the BC Field, offshore Niger Delta. A detailed cross plot analysis was performed using data from Well B-3, where four reservoirs (R-1000, R-2000, R-3000, and R-4000) were correlated and evaluated. These reservoirs were identified within depth intervals ranging from 3245.76 m to 3614.71 m, and lithological boundaries were delineated based on Volume of Shale (Vshale). A background trend of brine-saturated lithologies was established in the A–B cross plot domain, enabling the identification of hydrocarbon-bearing anomalies through systematic deviations. The analysis incorporated multiple elastic attributes Vp, Vs, Vp/Vs, impedance, porosity, bulk density, water saturation, and rock property-derived LambdaRho and MuRho to distinguish lithology and fluid types. Statistically, hydrocarbon-bearing gas sands were found to cluster in the third quadrant of the AVO cross plot, exhibiting negative A and B values indicative of Class III AVO responses. Class IIP AVO responses were also observed, showing positive near-offset and negative far-offset reflectivity. Cross plot of LambdaRho versus MuRho clearly delineated brine sands, oil sands, and gas sands. This integrated workflow successfully delineated fluid contacts and facies variations, with the AVO Class IIP sands confirmed to be oil saturated. The study combined the application of AVO cross plotting and rock property modelling in a deep offshore setting of the Niger Delta, underlining its potential to improve prospect identification and reduce interpretation uncertainty in structurally complex domains.