New insights into the deep-water Otway Basin – Part 2. Tectonostratigraphic framework revealed by new seismic data

Abstract

The inboard areas of the Otway Basin, particularly the Shipwreck Trough, are well explored and a petroleum-producing province. However, outboard in water depths greater than 500m, the basin is underexplored with distant well control and sparse 2D reflection seismic data coverage. The presence of a successful petroleum province onshore and in shallow waters raises the question as to whether these plays may extend further outboard into the deep-water areas. In the deep-water area, structural complexity and poor imaging of events in the legacy seismic data have resulted in interpretation uncertainty and consequentially a high-risk profile for explorers. The 2020 Otway Basin seismic program acquired over 7000-line km of 2D reflection seismic data across the deep-water Otway Basin. In addition, over 10000km of legacy 2D seismic data were reprocessed to improve the tie between the inboard wells and the new seismic grid. This new dataset provides the first clear insight into the structural and stratigraphic framework of this frontier area, including better imaging of the sedimentary section and the lower crust, increased structural resolution and improved calibration of the outboard seismic reflectors via ties to the inboard wells. Interpretation of the new data has led to an improved assessment of the structural elements and the extension of regional supersequences into the deep-water areas. These refinements have been used as input into petroleum systems modelling work and will provide a foundation for future work to understand petroleum prospectivity, including the distribution of source, reservoir and seal facies.

Stratigraphic framework and structural architecture of the Upper Cretaceous in the deep-water Otway Basin – implications for frontier hydrocarbon prospectivity

“…The objective of this study is to extend Cretaceous supersequence and fault mapping across the offshore Otway Basin, building on the regional sequence framework of Krassay et al (2004), Romine et al (2020), Schenk et al (2021) and Karvelas et al (2021). With emphasis on the Upper Cretaceous Shipwreck and Sherbrook supersequences, mapping was refined across the 2020 Otway Basin 2D grid and across an additional ~40 000 line-km of legacy 2D seismic data.…”

“…Totterdell et al (2014) recognised that the sparse coverage and poor imaging in legacy seismic data was a limiting factor in the geological understanding of the deep-water Otway Basin. This limitation was addressed by the 2020 Otway Basin 2D seismic program (Karvelas et al 2021). The seismic data collected (Fig.…”

Potential field interpretation and modelling in the deep-water Otway Basin

“…Unlike the onshore and shallow offshore parts, with hydrocarbon discoveries, the deep-water part is underexplored with sparse 2D seismic lines and no wells. The 2020 Otway Basin Seismic Program (OBSP) (Karvelas et al 2021;Fig. 1) acquired 8200 line-km of 2D seismic, gravity and magnetic data, and had the key objective of improving the quantity and quality of data over the deep-water parts of the offshore basin for regional interpretation and basin analysis.…”