Gross depositional environment (GDE) maps were made for six key intervals in the onshore portion of the Jurassic to mid-Cretaceous Otway Basin in South Australia. The Department for Energy and Mining (DEM) has undertaken this comprehensive review (including a petroleum systems model – PSM) so as to stimulate conventional oil and gas exploration but also to inform Carbon Capture and Storage and subsurface hydrogen storage plays.
The GDE maps are the culmination of geological understanding in each interval with results from whole of-basin (chrono-stratigraphic) well correlation, seismic horizon/fault mapping, seismic facies interpretation and core interpretation integrated. Also, where available, interval-specific bore hole image (BHI) derived paleo-current directions were added, along with petrology and biostratigraphic information. The mapping reveals varied GDEs including deep lacustrine affected by ice, a lacustrine turbidite system, extensive fluvial/lacustrine, fluvial/flood plain and ribbon-like alluvial fan aprons.
Well penetrations were used to control seismic horizon picking with syn-depositional faulting a key driver in understanding both the style and axes of deposition. The resulting isopachs and interval-active (growth) faults functioned as the backdrop for well signature maps. Independent core interpretation was then used as primary depositional evidence, giving spatial context and locally informing seismic facies. Subsequently seismic facies interpretations were made away from well control allowing for complete GDE map coverage for all six intervals.
These powerful integrated datasets together with the PSM are focussed at firstly stimulating renewed explorer interest in this basin and then underpinning a new phase of petroleum and subsurface gas storage exploration.

Ideally when combining different 3D seismic surveys differences in acquisition parameters warrant full pre-stack reprocessing from field data. However, there are occasions where this is not possible due to time, financial or data access constraints; a valuable alternative is post-stack merging and enhancement of existing migrations.
The offshore Otway Basin was the subject of such a project, the objective of which was to produce a regularised and seamless 3D dataset of the highest possible quality, within a two month turnaround time. The input migrated volumes varied by data extent, migration methodology, angle range and grid orientation. 14 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. DUG’s 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 the Investigator North survey as a reference. This was followed by time-variant spectral and amplitude matching, with gain corrections applied, 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 event and dramatically improving the efficiency and quality of interpretation. This enables rapid reconnaissance of the area by explorers.

Geoscience Australia has undertaken a regional seismic mapping study of the offshore Otway Basin extending across explored shelfal areas to the frontier deep-water basin. Seismic interpretation spans over 18000 line-km of new and reprocessed data collected in the 2020 Otway Basin seismic program and over 40000 line-km of legacy 2D seismic data. This study focuses on the Turonian-Santonian (Shipwreck Supersequence), Campanian-Maastrichtian (Sherbrook Supersequence), Barremian Eumeralla Supersequence, Santonian LC1.2 Sequence, basement, top lower laminated crust and reflection MOHO (Mohorovičić discontinuity). Structure surfaces and isochore maps reveal Cretaceous depocenter distribution, basin structural architecture, and crustal thinning trends between the inner basin platform and the outer margin highs. In the southeast, a dominant north-south basement grain controls faulting, basement features, and basin architecture. The Mussel Hinge Zone exhibits en échelon, northwest-oriented detachment faults, marking a zone of major crustal thinning between the inner platform and deep-water area. In the northwest, the east-northeast-oriented Trumpet Fault and outboard stepping detachment faults indicate significant crustal thinning to the south. Combined with basement-MOHO and upper crust-MOHO isochores, these structural features delineate proximal, necking, distal and outer structural domains across the margin. The highly extended nature of the outboard deep-water Otway Basin crust is indicated, which may have important implications for heatflow and therefore hydrocarbon prospectivity. The Cretaceous depocenter isochore, supported by gravity data collected as part of the 2020 Otway Basin seismic program, has led to basin boundary updates, notably expanding the Nelson Sub-basin and revising the Otway-Sorrel boundary to reflect geology rather than historic administrative boundaries.

The Gippsland Basin is a prolific hydrocarbon basin, with Gas initially discovered in the Barracouta Field in 1965 and Oil discovered by the Kingfish field in 1967. Discovered resource within the Gippsland Basin Joint Venture have been in the order of ~5.5 BBL OOIP and ~15TCF OGIP.
Historically the basin was covered with a patch work of legacy 3D seismic surveys acquired from 1980-mid 2000’s, often shot with very old technology resulting in sub optimal imaging of the subsurface. Following some initial work CGG reprocessed 10,190km2 of these legacy datasets as part of their ReGeneration project in 2018 and in 2020 acquired 8751km2 of long offset, deep tow and undershot seismic data, processed with FWI, deghosting and demultiple steps to provide a step change in the subsurface image for the basin.
With these data sets, Woodside has been able to extract images of the regional depositional systems through the basins evolution allowing an understanding of depositional environments. These observations range in scale from interpretation of individual channel and channel belts to the distribution of the major shoreface systems and marine fans.

As part of an integrated geological, geochemical, and geophysical study, conventionally cored intervals from the lower-most stratigraphic section of the onshore South Australian part of the Penola Trough, Otway Basin have been reviewed and reinterpreted.
The three cored wells; Bungaloo-1 (cores 3 and 4), Jolly-1ST1 (cores 1, 2, 3 and 4) and Sawpit-2 (cores 1, 2 and 3), were described using a ‘quick-look’ approach to determine gross lithological and sedimentological information.
Seven lithology types were observed: claystone with horizontal lamination, claystone with horizontal lamination and dropstones, clay/silt stone with massive-horizontal lamination, silt/sandstone with horizontal lamination, sandstone with ripple lamination, sandstone with parallel lamination and sandstone with massive bedding +/- rip-up clasts.
The first two lithologies are interpreted as representing deposition in a profundal lacustrine depositional environment. The first, containing interpreted varves is the most distal and the second with dropstones indicates climatic conditions and/or proximity to a seasonally frozen lake shoreline. The last five lithologies are interpreted as lacustrine turbidite depositional environments, specifically BOUMA sequences e, d, c, b and a respectively. Subsequent seismic facies interpretation has identified mound and canyon-like features and interpreted them as fan and slope-feeder channels respectively.
This rock-based turbidite interpretation provides an alternative to the current fluvial channel and/or crevasse splay model for reservoir deposition and as such presents a new exploration play. Further the reservoirs immediate lateral association with gas/oil-prone source rocks (in prep) and seals in the clay-rich lithologies potentially provide for stratigraphic trapping in addition to the previously targeted fault-controlled structural traps.