Energy-weighted Amplitude Variation with Offset: A new AVO attribute for low impedance gas sands

Abstract

Amplitude Variation with Offset (AVO) is a technique that has been widely used as a reliable indicator of hydrocarbon expressions in seismic data. The technique uses mathematical approximations and approaches in order to estimate variations in seismic amplitude as a function of incidence angle, and related them to lithology and pore-fluids. In this study, a new AVO attribute is presented. The Energy-weighted AVO attribute uses Zoeppritz approximations and exploits the fact that hydrocarbon-bearing sediments show anomalous seismic responses relative to their backgrounds. The new AVO attribute emphasizes this hydrocarbon-associated effect and attenuates the background signal. In addition, the fact that the attribute integrates the signatures of conventional AVO attributes (intercept×gradient) with seismic data makes the discrimination of hydrocarbon anomalies from other anomalies caused by anomalous lithologies such as coal, carbonates or salt, straightforward. More interestingly, the new attribute can be applied to both prestack and poststack data. This indeed would solve several problems and difficulties encountered with prestack data, as prestack data are generally less readily available, and have a much lower signal to noise ratio.The process has been examined using synthetic data generated from Zoeppritz equations, and then applied to real prestack and poststack data. At all stages, promising results have been derived and the hydrocarbon effect and extent could be successfully predicted, also the AVO effect of hydrocarbons could be investigated even in the poststack data.