Geoscience Australia has undertaken a regional seismic mapping study that extends into the frontier deep-water region of the offshore Otway Basin. This work builds on seismic mapping and petroleum systems modelling published in the 2021 Otway Basin Regional Study. Seismic interpretation spans over 18 000 line-km of new and reprocessed data collected in the 2020 Otway Basin seismic program and over 40 000 line-km of legacy 2D seismic data. Fault mapping has resulted in refinement and reinterpretation of regional structural elements, particularly in the deep-water areas. Structure surfaces and isochron maps highlight Shipwreck (Turonian–Santonian) and Sherbrook (Campanian–Maastrichtian) supersequence depocentres across the deep-water part of the basin. These observations will inform the characterisation of petroleum systems within the Upper Cretaceous succession, especially in the underexplored deep-water region. Presented at the 2022 Australian Petroleum Production & Exploration Association (APPEA)

<div>As part of the Exploring For The Future (EFTF) program, the Australia’s Future Energy Resources (AFER) project has investigated the potential of energy resource commodities in the Pedirka/western Eromanga basins region targeting conventional and unconventional hydrocarbons as well as evaluating the suitability of sedimentary sections to store carbon dioxide.</div><div>The interpretation of new biostratigraphic and reprocessed seismic data provided new insights into the regional geology of this previously explored region. The Permian, Triassic and Jurassic depositional history of the study area is largely recorded by extensive fluvial-lacustrine sediments, including changes from braided to meandering river systems and sustained periods of flood-plain environments in which thick sequences of coal-bearing strata developed. During the Cretaceous, expanding shallow marine environments were established in the western part of the Pedirka/western Eromanga region.</div><div>Age-control obtained from palynological analysis and the mapping of key seismic horizons yielded an improved understanding of the extent and character of unconformities which define breaks and changes in depositional processes. Results from new regional stratigraphic correlations initiated a comprehensive review of previously established basin definitions in the greater Pedirka/western Eromanga area. </div><div>While confirming the stacked nature of these basins which hold sedimentary records from the early Paleozoic to the Late Cretaceous, changes to stratigraphic basin boundaries have been applied to more correctly reflect the impact of unconformity related depositional breaks. As a result, the Lower and Middle Triassic Walkandi Formation is now assigned to the upper section of the Pedirka Basin, while the Upper Triassic Peera Peera Formation represents commencement of deposition in the western Eromanga Basin, thereby abandoning the recognition of the Simpson Basin as a separate Triassic depocenter.&nbsp;</div><div><br></div><div><br></div>

Geoscience Australia has undertaken a regional seismic mapping study of the offshore Otway Basin extending across the explored inner basin to the frontier deep-water region. Seismic interpretation covers over 18000 line-km of new and reprocessed data acquired in the 2020 Otway Basin seismic program and over 40000 line-km of legacy 2D seismic data. We present new basin-scale isochore maps that show the distribution of the Cretaceous depocentres. Maps for the Lower Cretaceous Crayfish and Eumeralla supersequences, together with those recently published for the Upper Cretaceous Shipwreck and Sherbrook Supersequences, completes the set of isochore maps for the main tectonostratigraphic basin intervals. Mapping of basement involved faults has revealed structural fabrics that have influenced depocentre development. The tectonostratigraphic development of depocentres and maps of deep crustal units delineate crustal thinning trends related to late Cretaceous extension phases. This work highlights the need to review and update structural elements. For example, the boundary between the Otway and Sorell basins is now geologically constrained. The refinements to the tectonostratigraphic evolution of the Otway Basin presented here have important implications for the distribution and potential maturity of petroleum systems, especially with regard to heat flow associated with crustal extension. Presented at the 2024 Australian Energy Producers Conference & Exhibition (AEP) (https://energyproducersconference.au/conference/)

Geoscience Australia has undertaken a regional seismic mapping study of the offshore Otway Basin extending across the explored inner basin to the frontier deep-water region. Seismic interpretation covers over 18,000 line-km of new and reprocessed data acquired in the 2020 Otway Basin seismic program, over 40,000 line-km of legacy 2D seismic data and GA’s new 2023 Otway 3D post-stack Mega Merge seismic dataset. This work provides a new perspective on regional structural architecture and basin evolution and has important implications for hydrocarbon prospectivity of this region. This seminar was two short talks centring on the Otway Basin. <u>Post-stack 3D merging to fast-track regional interpretation - offshore Otway Basin case study, presented by Merrie-Ellen Gunning</u> This case study was to produce a regularised and seamless 3D dataset of the highest possible quality, for the offshore Otway Basin, within two-months. The input migrated volumes varied by data extent, migration methodology, angle range and grid orientation. Fourteen input volumes totalling 8,092 km2 were post-stack merged and processed to produce a continuous and consistent volume, enabling more efficient and effective interpretation of the region. The surveys were regularised onto a common grid, optimised for structural trend, prior to survey matching. A mis-tie analysis algorithm, applied over a time window optimised for interpretation of key events, was used to derive corrections for timing, phase and amplitude, using a reference. This was followed by time-variant spectral and amplitude matching to improve continuity between volumes. Additional enhancements including noise removal and lateral amplitude scaling were also applied. The final merged volume offers significant uplift over the inputs, providing better imaging of structure and events and dramatically improving the efficiency and quality of interpretation. This enables rapid reconnaissance of the area by explorers. <u>Structural architecture of the offshore Otway Basin presented by Chris Nicholson</u> We present new basin-scale isochore maps that show the distribution of the Cretaceous depocentres. Maps for the Lower Cretaceous Crayfish and Eumeralla supersequences, together with those recently published for the Upper Cretaceous Shipwreck and Sherbrook Supersequences, completes the set of isochore maps for the main tectonostratigraphic basin intervals. Mapping of basement involved faults has revealed structural fabrics that have influenced depocentre development. The tectonostratigraphic development of depocentres and maps of deep crustal units delineate crustal thinning trends related to late Cretaceous extension phases. This work highlights the need to review and update structural elements. For example, the boundary between the Otway and Sorell basins is now geologically constrained. The refinements to the tectonostratigraphic evolution of the Otway Basin presented here have important implications for the distribution and potential maturity of petroleum systems, especially with regard to heat flow associated with crustal extension.

During 2021–2024 Geoscience Australia conducted regional seismic mapping across the offshore Otway Basin that extended into the frontier deep-water region. This work was part of a broader pre-competitive study undertaken in support of petroleum exploration. Seismic horizons and faults were interpreted on three regional data sets, including: over 18 000 line-km of new and reprocessed data compiled for the 2020 offshore Otway Basin seismic program; over 40 000 line-km of legacy 2D seismic data; and the Otway 3D Megamerge dataset. This digital dataset (publication date 5 August 2024) updates and replaces a previously released dataset (publication date 16 May 2022). This updated dataset includes 8 surface grids and 11 isochron grids generated from the following seismic horizons (in ascending stratigraphic order); MOHO (Mohorovičić discontinuity), TLLCC (top laminated lower continental crust), Base (base Crayfish Supersequence), EC2 (base Eumeralla Supersequence), LC1 (base Shipwreck Supersequence), LC1.2 (base LC1.2 Sequence), LC2 (base Sherbrook Supersequence), and T1 (base Wangerrip Supersequence). Fault polygons created for all surfaces (except for MOHO, TLLCC, and LC1.2) are also included in the dataset. Maps generated from the dataset depict deep-water Cretaceous depocentres, and trends in crustal thinning and rifting during the Cretaceous. This revised map package has underpinned updates to regional structural elements, including a revision of the boundary between the Otway and Sorell basins.