Amplitude Versus Offset and Frequency (AVO-AVF) Integration to Mitigate Fizz Gas Risk in Clastic Reservoir

Summary Direct Hydrocarbon Indicators (DHIs) like bright spots and flat spots are prone to false positives from fizz gas, lithological contrasts, and high-porosity sands. Integrated AVO and AVF analysis resolves fizz gas ambiguity in Prospect A (Sarawak Basin). Rock physics modelling (nine wells) confirmed AVO Class II/III responses. The AVO workflow used three attributes: (1) (Far–Near)×Far amplifying anomalies, (2) intercept-gradient (A×B) highlighting fluid sensitivity, and (3) Extended Elastic Impedance (EEI) rotated at χ = 10° isolating fluid effects. However, AVO alone could not resolve saturation ambiguities between fizz gas and commercial hydrocarbons. AVF complemented AVO by analyzing frequency-dependent attenuation via spectral decomposition of full-stack seismic data (5–65 Hz). Continuous Wavelet Transform generated frequency gathers, enabling intercept (I) and gradient (G) attribute extraction through amplitude-frequency regression. Elevated I×G values correlated with hydrocarbon-induced attenuation, validated by a logarithmic relationship to water saturation (Sw) logs (R2 = 0.92). Prospect A exhibited a pronounced AVF I×G anomaly, constraining Sw to 30–40. This integrated workflow mitigated fizz gas risk, confirming Prospect A’s commercial viability. The study establishes AVO-AVF synergy as a robust tool for saturation discrimination in clastic reservoirs, reducing exploration uncertainty.