Using AVO to map Cooper Basin Permian sands in the presence of coal

Abstract

Cooper basin Toolachee and Patchawarra sands are difficult to map due to strong seismic reflections from Permian coals. Seismic amplitudes are mainly driven by coal thickness instead of lithology (sand vs shale). We proposed a method for obtaining better sand prediction. This method uses AVO intercept (I) and gradient (G) and the Extended Elastic Impedance (EEI) to highlight the subtle differences between coal-shale and coal-sand interfaces. We test this method by creating several wedge models to understand the effect of coal thickness and lithology on seismic amplitudes. Results are compared with a more traditional method that recognizes a 'channel' pattern on stacked seismic and uses a geologic facies model to locate sand with respect to that channel. For the 3D survey used here, our EEI-AVO method 'finds' sand in locations predicted by the traditional facies model method as well as in new locations.