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ABSTRACT: Petroleum exploration in the Timor Gap, 1993-1999

McIntyre, Calan , BHP Petroleum Pty Ltd, Melbourne, Australia

Since late 1993, an intensive phase of petroleum exploration has been carried out in the Northern Bonaparte Basin, in and around the Timor Gap Zone of Cooperation. A total of 56 exploration wells have now been drilled in the region, 21 of which are interpreted to have intersected live hydrocarbons. Ultimately, ten of these discoveries are likely to reach development, giving an overall commercial success rate of 18%.

Early drilling in the basin resulted in the discovery of oil at Elang, Laminaria, Corallina and Buffalo, as well as the discovery of the Bayu-Undan gas-condensate field. These early successes stimulated significant industry interest in the region, and large work programs were bid in the mid nineteen-nineties by several companies, in attempts to consolidate or develop positions in the highly successful Middle Jurassic Play Fairway.

However, as the results of further drilling were incorporated between 1995 and 1999, it became apparent that the basin's hydrocarbon habitat was significantly more complex than initially envisaged. A sharp decline in exploration success rates forced the development of revised models for reservoir distribution, structural history, hydrocarbon charge, and preservation. Of particular significance to the assessment of commercial viability was the realisation that most traps are substantially under-filled. This observation can be partially explained by a major phase of Neogene water-washing, which has preferentially removed the soluble gas-fraction.

Through the integration of these new geological models, revised play fairway maps have been developed. In the Northern Bonaparte Basin, where the conventional fairway is approaching maturity, the integration of these maps into future exploration decisions will be critical to the further discovery of hydrocarbons.

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