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ABSTRACT: Geochemical characteristics of Mesozoic petroleum systems in the Bonaparte Basin, northwestern Australia

Edwards, Dianne S.1, John M. Kennard1, Jim C. Preston2, Roger E. Summons1, Chris J. Boreham1, and John E. Zumberge3
(1) Australian Geological Survey Organisation, Canberra, ACT, Australia 
(2) BHP Petroleum Pty Ltd, Melbourne, Victoria, Australia 
(3) GeoMark Research Inc, Houston, TX

The Bonaparte Basin has been actively explored for over twenty years. The recent oil discovery at Tenacious in the Vulcan Sub-basin, oil production from the Laminaria-Corallina fields on the Laminaria High, as well as gas/condensate discoveries at Bayu-Undan, Sunrise and Sunset fields in the Zone of Co-operation (ZOCA), highlight the continuing prospectivity of the region.

Despite this focussed exploration, geoscientists are yet to come to an understanding of the regions petroleum systems. This study uses isotopic and biomarker analyses carried out on Mesozoic oils from the Bonaparte Basin to geochemically characterise oil families within the Westralian Petroleum Supersystem. Oil-oil correlations are made between the Vulcan Sub-basin, ZOCA and the Browse Basin, and statistical analysis indicates multiple oil families sourced from Jurassic and Early Cretaceous rocks. These oils are contrasted with those of the Palaeozoic petroleum systems in the Petrel Sub-basin.

The Upper Jurassic Lower Vulcan Formation has sourced the majority of oils produced from the Vulcan Sub-basin which are assigned to the Westralian-2 Vulcan Petroleum System. In the ZOCA region, two distinct end-member oil families/sub-families are recognised; a land-plant influenced family in the west, and a marine influenced family in the southeast. A third oil family in the north comprises condensate from Sunrise-1 that has a distinct marine carbonate biomarker signature. A fourth group of oils, reservoired in fractured Darwin Formation, has a marine geochemical signature and appears to have been expelled from the Cretaceous Echuca Shoals Formation. These oils are geochemically similar to some Browse Basins oils.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia