Hydrocarbon migration and mixing in four recently discovered oil fields of the southwestern Eromanga Basin

Abstract

The Cooper and Eromanga Basin is located in northeastern South Australia and southwestern Queensland. Nine samples from four fields within the SA sector of the Cooper-Eromanga Province along the southwestern Patchawarra Trough (Sellicks and Christies) and western Wooloo Trough (Worrior and Arwon) were analysed. The aromatic source and maturity cross plot of 1-MP/9-MP versus 2-MP/1-MP was used to determine the ratio of mixing between Permian- and Jurassic/Cretaceous-sourced hydrocarbon in oils. These oils from the Patchawarra Formation within the Sellicks Field has ~0.9% Rc and is a Family 2 Permian end-member, which has migrated a minimum distance of 23-24 km. This same oil contributes 60-70% of the input to the Birkhead and Hutton reservoirs in the Christies Field. The Jurassic input (~0.6% Rc) came from a Birkhead source located 15-30 km to the east. The Worrior and Arwon Fields contain mixed oils within Jurassic and Cretaceous reservoirs. Here the Permian input decreases up section (Hutton 70%, Birkhead 65%, McKinlay 60%) with the Permian Toolachee Formation and Jurassic Birkhead Formation being the likely source rocks. The minimum migration distance for the oil sourced within the Birkhead Formation is 4-5 km from the west and ~24 km from the east.