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ABSTRACT: The impact of late tilting on hydrocarbon migration, eastern Browse Basin, Western Australia

Keall, Jon M.1, and Philip M Smith2 (1) BHPP, Melbourne, Australia (2) BHPP

The recent discoveries of oil in Gwydion-1 (1995) and Cornea-1 (1996) on the eastern margin of the Browse Basin, have confirmed the presence of an oil source. The oils have been typed to Early Cretaceous and possibly Late Jurassic source rocks which are not locally mature, with migration of approximately 50 km from kitchen areas to the west being required.

Wells drilled along the eastern side of the basin have commonly intersected residual oil columns below the present day oil-water-contacts which are controlled by the structural spill points. This suggests that when the traps were charged they had greater structural closure. Modelling of hydrocarbon generation suggests that the oil-prone source rocks have been generating oil from kitchen areas since the early Tertiary. Migration of oil towards the eastern basin margin probably commenced at this time, filling traps which lay on migration pathways. Uplift and erosion in the Miocene resulted in tilting of traps along the eastern basin margin, causing a reduction in the amount of structural closure, and spilling of oil updip. Structural reconstructions of the basin prior to the Miocene-age tilting indicate that large volumes of oil were originally trapped and have subsequently remigrated updip. Much of this remigrated oil would have reached the sea floor and been lost from the system. However, some oil is likely to still be trapped in structures which lie further along the spill chains. Detailed reconstructions of the kitchen areas and migration pathways through time allow the more prospective fairways to be recognised and highgraded.

Recognition of the oil potential in the basin has resulted in an upsurge in planned exploration activity, the results of which will be known in the next few years.

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