Imaging past depositional environments of the North West Shelf of Australia: Lessons from 3D seismic data

Seismic surveys over the North West Shelf (NWS) of Australia have generated one of the largest 3D seismic data libraries worldwide with a coverage of ~325,000 km2 of medium- to high-quality data. A major challenge now is using the best tools and techniques to interpret these data in a cost-effective timeframe. In this context, a major breakthrough in recent years has been the introduction of full-volume and semi-automatic seismic interpretation tools that geologists can use to create 3D relative geological time models from which an unlimited number of horizons may be extracted. These workflows have been applied to improve stratigraphic understanding and to interpret past depositional environments in sedimentary basins of the NWS. Four case studies are presented in this paper: (1) Mungaroo Formation (Thebe Gas Field area); (2) Lower Barrow Group (Scarborough Gas Field area); (3) Puffin Formation; and (4) Cenozoic carbonate margin. These illustrate key lessons regarding best practice interpretation of 3D seismic data on the NWS: (1) application of quantitative analysis tools to seismic stratigraphy to better predict shallow- and deep-water reservoir distribution at various temporal and spatial scales (i.e., quantitative seismic stratigraphy); (2) application of quantitative analysis techniques to seismic geomorphology in combination with modern analogues to better predict reservoir architecture and heterogeneity, and create modelling scenarios with various scales of uncertainty (i.e., quantitative seismic geomorphology); (3) integration and interpretation of regional 3D seismic data in the vicinity of an area of interest to better understand the broader depositional system and its regional context, which ultimately may improve reservoir modelling and fluid flow prediction; and (4) integration and interpretation of local 3D seismic data in combination with regional 2D seismic data to obtain a firstorder understanding of the controls on shallow- and/or deepwater reservoir architecture and better predict their distribution. These techniques and workflows, applied to 3D seismic data of ever-increasing quality, offer new and exciting opportunities for geologists to reinterpret existing paradigms or enhance their understanding of the past depositional environments of the NWS. Although the NWS has been explored for more than 50 years, these approaches, using vintage or new 3D seismic data, can help reinvigorate exploration in basins that are considered mature and unlock potential of underexplored areas.