A reassessment of the petroleum systems in the offshore northern Perth Basin

Abstract

The discovery of commercial oil in the Cliff Head-1 well in 2001 set an important milestone in the exploration history of the offshore northern Perth Basin. The region had been less explored before then, partly due to the perception that the main source of onshore petroleum accumulations, the Late Permian-Early Triassic Hovea Member, had only marginal potential offshore. The typing of the Cliff Head oil to the Hovea Member provided evidence that the key onshore petroleum system extends offshore and has revitalised exploration with 13 new field wildcat wells drilled since 2002. A reassessment of the hydrocarbon generative potential in the offshore northern Perth Basin confirms the widespread occurrence of good to excellent oil-prone Hovea Member source rocks in the Beagle Ridge and Abrolhos Sub-basin. The Early Permian Irwin River Sequence and several Jurassic Sequences are also recognised as prime potential source rocks offshore, mostly for their gas-generative potential. The unique hydrocarbon assemblages exhibited by the Hovea Member extracts are shared by the oils recovered from Permian reservoirs in the offshore Cliff Head-3 and Dunsborough-1 wells, indicating the Hovea Member as the primary source charging these accumulations. Geochemical correlation of oil stains from Hadda-1 and as far north as Livet-1 provides evidence for a working Early Triassic petroleum system across much of the Abrolhos Sub-basin. In this area, the Hovea Member was shown to be both of limited quality and only marginally mature for oil generation, which suggests the occurrence of effective source kitchens in the adjacent Houtman Sub-basin.