Abstract

The Bayu-Undan gas condensate field, in the Timor Gap Zone of Cooperation Area A (ZOCA) was discovered in early 1995 by the Bayu-1 well drilled within ZOCA 91-13 by the PSC contract operator, Phillips Petroleum Company ZOC. The Bayu-1 well intersected a gross 155 m gas-condensate column within Middle Jurassic sandstones at a depth of 2954.5 mSS. Four months later, the ZOCA 91-12 joint venture, operated by BHP Petroleum (91-12) Pty. Ltd., drilled the Undan-1 well, 10 km northwest of the Bayu-1 well, on a separate culmination within the closure defined by the Bayu-1 gas-water contact. Undan-1 and five appraisal wells have intersected the top reservoir either close to or high to prognosis, resulting in a twofold increase in the mapped gross rock volume of the field since the initial mapping completed after the field was discovered. This is due to poor seismic imaging at the reservoir level and unpredicted velocity and static anomalies.

The sandstone reservoir consists of late Oxfordian to Callovian, shallow marine, deltaic to shoreface, coarsening upward parasequences, overlying Callovian to Bajocian marginal marine to coastal plain sediments. The trap is an east-west oriented horst block bounded by en-echelon normal faults to the north and south, with dip closure to the east and west. Seal is provided by Tithonian to Barremian marine claystones. A likely hydrocarbon source is contained within the Barremian to Callovian interval, which is mature for condensate and wet gas expulsion in the southern Sahul Syncline and Malita Graben.