Deepwater Otway Basin

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Current work includes:

Developing a regional gross depositional environment model for the Sherbrook Supersequence; through the integration of our diverse geoscientific expertise and utilising the valuable resource that is the legacy core and cuttings from the National Offshore Petroleum Data and Core Repository.
Analysis and interpretation of wells across the south-eastern parts of the Otway Basin, building on Volume 1 of the Well Folio (Nguyen et al., 2022).
Potential field modelling to assess depth to basement and crustal thickness, to improve our understanding of basin architecture, both onshore and offshore, and enhance our Petroleum Systems Models.

2022 Products:

Updated surfaces and isochrones from interpretation of the 2020 and 2021 data, providing a regional overview of major sequence boundaries.
Well Folio of Western Otway Offshore Wells including composites and well data, an exploration ready resource.
Magnetics and Gravity enhancement grids from the 2020 data merged with legacy data, demonstrating regional features such as depocentres and the extent of volcanics.
Western Offshore Otway Seismic Reprocessing—a number of seismic surveys from mostly offshore South Australia (red lines—Figure 1) were reprocessed to improve understanding of the area. The data will be available for download shortly from NOPIMS.

Previous releases:

New seismic data acquired in 2020, along with legacy and some reprocessed data, were interpreted (grey and blue lines—Figure 1) to enhance our understanding of the petroleum prospectivity of the deep-water Otway Basin (Karvelas et al., 2021). This included the development of a regional Petroleum Systems Model (Schenk et al., 2021).

See below for links to products and publication listings.

Basin Overview

The Otway Basin is a passive margin basin located in southeastern Australia (Figure 1)—it covers the onshore, but extends mostly offshore. The basin hosts Late Jurassic–Cenozoic sediments. In the offshore water depths range from shelfal to over 5000 m. Basement is expected to comprise rocks largely of the Neoproterozoic–Cambrian Ross-Delamerian Orogeny. As of 2022, there are commercial gas fields on the offshore shelf, around the Shipwreck Trough (Figure 1), but no oil discoveries. Offshore producing gas fields are: Casino-Henry, Geographe, Halladale, Speculant and Thylacine. Gas fields under development include: Artisan, Enterprise, Hercules and La Bella. The Minerva gas field has been decommissioned.

Due to the limited audience of this diagram and its complexity, no alternative description has been provided. Please email clientservices@ga.gov.au

Otway Basin showing 2D seismic coverage, tectonic elements, petroleum wells and fields for the offshore.

In the Otway Basin unconformity-bound seismic supersequences are associated with multi-stage rifting and thermal subsidence basin phases related to the separation of Gondwana and Antarctica from the Late Jurassic to the Eocene (Krassay et al., 2004). 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 deepwater Otway Basin. This limitation was addressed by the 2020 Otway Basin 2D seismic program (OBSP), which included the acquisition of a new 2D seismic grid and the reprocessing of several key legacy seismic lines extending up onto the shelf (Figure 1; Karvelas et al., 2021). This new and reprocessed seismic data totals 18 000 line-km, provides a comprehensive coverage across the deepwater region and is tied to inboard wells via the reprocessed lines.

The primary objective of the Deepwater Otway Basin Study is to extend Late Cretaceous supersequence and fault mapping across the offshore Otway Basin (Nicholson et al., 2022), building on initial mapping on the new 2D seismic grid by Karvelas et al. (2021) and on the shelf, in the southeast of the basin, by Romine et al. (2020). Mapped horizons are based on the sequence framework of Krassay et al. (2004). Seismic mapping of Cretaceous supersequence boundaries, with emphasis on the Upper Cretaceous Shipwreck and Sherbrook supersequences, is refined across the OBSP grid and extended over an additional ~40,000 line-km of legacy 2D seismic data. The supersequences are tied to eighteen wells with reference to updated well biozonations (MGPalaeo, 2020). In addition, the acquisition of new gravity and magnetic line data during the OBSP enables the generation of more accurate gravity and magnetic maps for the offshore Otway Basin (PoudjomDjomani and Gunning, 2022).

Another objective of this study is to investigate the hydrocarbon prospectivity in the deeper outboard domain. Given there are no deepwater petroleum wells this relies largely on the presence of postulated Turonian-Santonian source rocks. Schenk et al. (2021) provide an overview of hydrocarbon generation and entrapment potential for the deepwater province using several basin transect models from the new OBSP grid, mapped sequences and extrapolated petroleum well maturation parameters from the inboard shelfal areas.

Otway Basin showing image of 150 km high-pass filter of the merged gravity grid.

Otway Basin showing image of the tilt-derivative of the merged magnetic grid.

Products and Publications

Data products

Otway Basin MC 2D MSS 2020—7011.675 km of deep (12s) broadband 2D seismic data acquired in 2020 and processed to PreSDM. Available from NOPIMS and on request from ausgeodata@ga.gov.au.
- Figure 1 shows the newly acquired seismic data across the offshore Otway Basin
Otway Basin Regional 2D Reprocessing 2020 PreSTM & PreSDM—selected lines from surveys AGSO MS137 and DS01 Sorell processed to PreSDM, while selected lines from surveys Chevron EPP22, OP80, Trocopa, Copacabana, OTOX06 Christine, OS02 and OEP04 processed to PreSTM. Available from NOPIMS and on request from ausgeodata@ga.gov.au.
- Figure 1 shows the reprocessed legacy data across the offshore Otway Basin
Otway Basin Regional 2D Reprocessing 2021 PreSTM & PreSDM—selected lines from surveys AGSO MS137, KMG04 and OH91. Available from NOPIMS and on request from ausgeodata@ga.gov.au.
- Figure 1 shows the reprocessed legacy data across the offshore Otway Basin
Otway Basin MC 2D MSS2020—Magnetics and Gravity Data (ENO0603786). Available from NOPIMS.
- Figures 2 and 3 show the latest updated gravity and magnetics grids, respectively, incorporating the newly acquired 2020 along ship track data.
The Northwest Offshore Otway Basin Well Folio—Data package.
Gravity and magnetic enhancement grids and images for the Otway Basin Seismic Program 2020—Data package.
Surface Grids, Isochron Grids and Fault Maps, Offshore Otway Basin—Data package.
Compositional Kinetics for the Lower Cretaceous Eumeralla Formation, Otway Group, Otway Basin, Australia—Data package.

Reports and news articles

Schenk O., Karvelas A., West T. and Kornpihl D., 2021. Otway Basin Regional Study Report. Available at https://www.ga.gov.au/nopims/releases/otway-basin-regional-study-report

Conference proceedings

Karvelas A., West T., Gunning M-E., Borissova I., Nguyen D., Nicholson C., Abbott S., Bernardel G., Mitchell C. and Schenk O., 2021. New insights into the deep-water Otway Basin – Part 2. Tectonostratigraphic framework revealed by new seismic data. The APPEA Journal 61(2), 657–664. doi:10.1071/AJ20092
Lee S.Y., Lim B.J., Anantan A. and Karvelas A., 2021. New insights into the deep-water Otway Basin – Part 1. Integrated depth imaging workflows unravelling the subsurface. The APPEA Journal 61(2), 652–656. doi:10.1071/AJ20100
Nguyen D., Edwards D.S., Gunning M-E. and Bernardel G., 2022. The Northwest Offshore Otway Basin Well Folio. The APPEA Journal 62(1), 461–466. doi:10.1071/AJ21124
Nicholson C., Abbott S., Bernardel G. and Gunning M-E., 2022. Stratigraphic framework and structural architecture of the Upper Cretaceous in the deep-water Otway Basin—implications for frontier hydrocarbon prospectivity. The APPEA Journal 62(1), 467–473. doi:10.1071/AJ21072
PoudjomDjomani Y. and Gunning M., 2022. Potential field interpretation in the Deep-water Otway Basin. The APPEA Journal 62(1), 487–491. doi:10.1071/AJ21209
Schenk O., Grosjean E., Edwards D.S., Boreham C.J., West T. and Karvelas, A., 2021. New insights into the deep-water Otway Basin – Part 3. Petroleum system modelling. The APPEA Journal 61(2), 665–672. doi:10.1071/AJ20078.

References

Krassay A.A., Cathro D.L. and Ryan D.J., 2004. A regional tectonostratigraphic framework for the Otway Basin. In ‘Eastern Australasian Basins Symposium II’. (Eds Boult P.J., Johns D.R., and Lang S.C.) pp. 97–116. Petroleum Exploration Society of Australia, Special Publication.
MGPalaeo (2020), Palynological summary sheets. Available at https://www.mgpalaeo.com.au/otway-basin/, viewed on Feb 16, 2022.
Moore A.M.G., Stagg H.M.J. and Norvick M.S., 2000. Deep-water Otway Basin: A new assessment of the tectonics and hydrocarbon prospectivity. The APPEA Journal 40, 66–84.
Romine K., Vizy J., Nelson G., Lee J.D., Baird J. and Boyd M., 2020. Regional 3D geological framework model: Otway Basin, Victoria. Victorian Gas Program Technical Report 35, Melbourne.
Totterdell J.M., Hall L., Hashimoto T., Owen K. and Bradshaw M.T., 2014. Petroleum geology inventory of Australia’s offshore frontier basins. Record 2014/09. Geoscience Australia, Canberra.