Petroleum systems analysis of the onshore Otway Basin, South Australia

Abstract

An updated Petroleum Systems Model was built for the South Australian onshore Otway Basin, incorporating new seismic interpretation, seismic stratigraphy, core interpretations and a recent chemostratigraphy study. The Otway Basin is a divergent passive continental margin, with the Penola Trough the most significant hydrocarbon province discovered to date. Revision of the existing geochemistry database and seismic stratigraphy along with source rock model indicates potential good quality, liquids prone lacustrine source rocks are present in the Jurassic Casterton Formation (S0-P5) and the Early Cretaceous Basal Shale (McEachern Sand equivalent)/Lower Sawpit Shale (S1-P1/S1-P2). Gas prone source rocks are modelled in the Valanginian Upper Sawpit Shale (S1-P4/S1-P5) and Hauterivian Laira Formation (S1-P6–S1-P10). Modelling suggests liquid hydrocarbons were expelled from the Lower Sawpit Shale between 126 and 70 Ma, with the majority sourced from the Penola and Robe Troughs. Gas/condensate expulsion also took place up to 30 Ma from the Upper and Lower Sawpit Shale in the Penola and Robe Troughs. Gas is modelled to have been expelled from the Laira Formation in the Tantanoola Trough, between 100 Ma and present day.