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Summary
The Exmouth Sub-basin forms part of the intra-cratonic rift system of the Northern Carnarvon Basin, Australia. It has undergone a complex tectonic history with multiple phases of uplift, erosion, inversion, and regional tilting. Hydrocarbon exploration has resulted in discovering a variety of oil and gas accumulations; however, the distribution of hydrocarbons and charge from different petroleum systems is still poorly understood. The new basin-wide, long-offset, broadband Exmouth 3D Multiclient seismic data (MC3D) allowed for an updated understanding of the structural and depositional evolution.
We built a regional 3D basin and petroleum system model that integrates this updated structural and stratigraphic framework and results from potential field modelling to a) improve our understanding of the thermal history and petroleum charge, b) assess critical parameters and processes impacting the petroleum systems, and c) evaluate the associated exploration risks such as biodegradation. The thermal model is based on a) a short period of extension in Latest Triassic (Rhaetian) as observed in the deeper image of the recent MC3D seismic survey, and b) a Latest Jurassic to Earliest Cretaceous magmatic event documented by potential field modelling and interpreted igneous intrusions on seismic data. The 3D basin model was calibrated to data from more than 30 wells in the sub-basin. Model results predict that burial of the Early Cretaceous Barrow Group controlled hydrocarbon generation and expulsion over large areas of the sub-basin; towards the south, however, results suggest that hydrocarbon expulsion from shallower Jurassic source rocks continued into Late Cretaceous time, a period when the regional Early Cretaceous Muderong Formation is predicted to be an efficient seal rock. This implies that vertical, short-distance migration may contribute significant petroleum charge to the accumulations in the southern part of the Exmouth Sub-basin.