Reservoir characterisation of the Flag Sandstone, Barrow Sub-basin, using an integrated, multi-parameter seismic AVO inversion technique

The Early Cretaceous Flag Sandstone within the Barrow Sub-basin is a proven hydrocarbon reservoir. The main trapping mechanism is four-way dip closed anticlines, formed by drape compaction. An integrated, multi-parameter seismic AVO inversion technique was utilised that improved the mapping of the Flag Sandstone and identified the presence of trapped hydrocarbons. The identification of the Flag Sandstone on seismic sections is complicated due to a low acoustic impedance contrast between the Flag Sandstone and the overlying shales. The same interface gives a good AVO response. Previous interpretation efforts have used the seismic AVO response to map the top of the Flag Sandstone on far-angle stacks. These efforts were very successful for mapping structure but were influenced by wavelet tuning effects and were limited for high-grading the structures based on hydrocarbon potential. To aid in characterising the fluid distribution in the reservoir rocks a simultaneous AVO inversion algorithm was used based on three partial angle stacks and conditioned well logs, inverting for acoustic and shear impedance. The results of this multi-parameter impedance inversion produced a variety of attributes. The Vp/Vs attribute was aimed at improving the TWT structural pick whereas P-impedance became the basis for discriminating water and oil saturated sands.