A new AVO fluid indicator using the fluid line: Theory and application

A number of seismic fluid indicators are derived from seismic amplitude variations with offset. The fluid indictors typically measure the anomalous behavior of the seismic response related to hydrocarbon's saturation. This anomalous behavior can be observed in different domains such as P-wave velocity vs. S-wave velocity, P-wave reflectivity vs. S-wave reflectivity, and intercept vs. gradient, among others. In this paper, we introduce a new AVO attribute for fluid detection. The attribute is expressed as a linear combination of AVO's intercept and gradient and measures the deviation caused by pore fluid from the background fluid line defined in the Intercept-Gradient domain. The attribute can be calibrated to local geology for better performance. We test the attribute on data collected from different basins. We compare the fluid detection ability of the attribute against existing fluid indicators commonly used in AVO analysis and interpretation. The new fluid indicator shows promising performance and success in fluid detection. Next, we apply the attribute on synthetic data calculated from well data, and seismic field data from North Western Australia. The target formation is Mid-Jurassic fluvial-deltaic sandstone and is comprised of three reservoir units interbedded in shale. The attribute could help detect the gas-saturated reservoirs and distinguish them from the overall background reflectivity.