Structural Styles and Hydrocarbon Prospectivity of the Ceduna Sub-Basin, Australia: Part One

Abstract

The Ceduna Sub-basin is the most underexplored offshore basin in Australia and one of the few remaining frontier basins in the world today. With only a few dry wells, assessing the prospectivity of the basin can be challenging. The Ceduna Sub-basin has undergone five phases of tectonic evolution. The Area of Interest (AOI) consists of a dip-aligned strip of 3D seismic survey data cropped from the regional Ceduna 3D MSS seismic survey acquired in 2012. The survey covers an area of around 2,300 km2. The objective of this study is to build a structural framework for the sub-basin. A similarity attribute was generated for the 3D seismic sub-volume at various time slices to better understand the major orientation and distribution of faults within the AOI. Two major fault trends were observed a NW-SE trend and a NNE-SSW trend. A semi-automatic fault extraction workflow was used, which consists of integrating two automatic fault extraction workflows (using two commercial software packages). These two automatic fault extractions were combined with some manual sparse fault interpretation performed on representative in-lines and cross-lines across the AOI in addition to the qualitative fault trend interpretation that was performed on the dip-steered similarity time slices. This workflow resulted in mapping 79 fault sticks that were later joined to form 28 fault planes. Two delta systems in the Ceduna sub-basin are described as having different structural styles. Therefore, at least two distinct fault systems can exist corresponding to the structural style of each delta. By closely examining thickness variations between the mapped packages and the presence of syn-depositional or syn-extensional wedges, it can be concluded that most of the major faults within the AOI have experienced rapid and continuous growth and reactivation. These findings have significant implications for the prospectivity of the Ceduna Sub-basin in general, and the timing of trap formation and fault seal analysis in particular. Two trapping styles were observed: shallow rollover anticlines that developed against the large regional listric faults within the Campanian- Maastrichtian section, and tilted-fault blocks that are associated with the highly oblique deep fault system. The latter form potential hydrocarbon traps within the deeper sediments in the AOI. A detailed geomechanical analysis is needed to understand the nature, extent, and evolution of these structural traps.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018