Springboard 3-D: New Insights Into the Seismic Stratigraphy of the Western Ceduna Sub-Basin

Abstract

The Ceduna Sub-basin has the potential to be the next giant oil province in Australasia, it is one of the few remaining frontier Cretaceous deltas. Located in the Bight Basin, it comprises up to 15km of Jurassic to Tertiary sediments with only one exploration well that has tested the main depocenter. Historically it has been underexplored due to harsh operating conditions and a lack of proven petroleum system. The region has seen a renewed exploration interest following a dredge sampling survey conducted by Geoscience Australia that recovered excellent quality, oil-prone source rocks. This highlighted the potential for a working petroleum system. Santos and Murphy were awarded EPP43 in the Western Ceduna for a seismic-only primary term commitment in 2013. Over the summer of 2014–15 PGS acquired almost 8000km² of high-quality broadband 3D seismic over EPP43. Prior to the new Springboard 3D survey seismic coverage was extremely sparse in the permit. Interpretation of structural and stratigraphic trends was limited to vintage 2D, with often tens of kilometres between lines. The Ceduna Sub-Basin formed as Australia and Antarctica rifted apart during the Jurassic and Cretaceous, and records numerous phases of extension and subsidence related to the initiation of sea-floor spreading. Intracontinental extension in the late Jurassic to early Cretaceous drove an initial phase of syn-rift fill, most likely characterised by fluvial-lacustrine sediments. Following this was an early phase of post-rift thermal subsidence in the early Cretaceous dominated by sag-fill geometries and predicted to be largely non-marine. Deposition of marine shales in the mid-Albian was triggered by a significant increase in rate of subsidence, here considered a second post-rift phase. Coupled with a global sea-level rise this represents the first major marine incursion in the Ceduna. Deposition of the first major Cretaceous delta began in the Cenomanian, focused mainly in the Western and Central Ceduna. This rapid sedimentation drove significant syn-sedimentary listric faults that detached on the underlying Albian shales. Directly overlying this is a dominantly aggradational, in places progradational, package. It represents a later deltaic package of the Turonian–Santonian deposited during continued thermal subsidence. Initiation of seafloor spreading in the late Santonian coupled with local uplift in the hinterland triggered the deposition of a second delta system in the Ceduna. The base of the Santonian–Maastrichtian sequence is erosive, the overall package is dominantly progradational and where penetrated is sand-rich. This presentation will discuss some observations on the stratigraphy of the Western Ceduna Sub-Basin based on initial interpretation of the Springboard 3D. In particular it will focus on the dominantly marine-deltaic section of the Albian to Maastrichtian, the main focus of exploration interest.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015