Structural Evolution of Ubadari Field, Bird's Head, Papua

Yudhanto, Erick V.; Pasaribu, Dumex
Exploration & Renewal, BP Indonesia, Jakarta, Indonesia.

The Ubadari field is located in the Berau PSC, about 50 km southwest of Tangguh LNG area in Bird's Head, Papua. Ubadari-1 well was drilled in 1997, a commercial gas discovery in the Middle Jurassic "Lower Roabiba" sandstone and Paleocene sandstone reservoirs. The Lower Roabiba sandstone is deposited in a fluvial influenced estuarine channels setting. Following the first discovery, in 1998, Ubadari-2 was drilled to test a structure down dip of the Ubadari-1 well, but no commercial accumulation was found.

Why was Ubadari-2 wet? A key question that has been an issue for further exploration in the Western Berau region. In order to unravel this puzzle a Paleo-reconstruction study was undertaken to understand the structural evolution through time.

Bird's Head has three main erosional events : Permo-Triassic erosion, Oligocene erosion, and Pliocene erosion. The Oligocene & Pliocene erosional events are the main events that effect the Ubadari field, both happening post deposition. Therefore, understanding the amount of missing section in these two events becomes important to differentiate between Ubadari-1 and Ubadari-2 structural timing.

Results from this study suggests that Ubadari field was a low relief structure before Pliocene time while the Ubadari-2 was a syncline. Both structures were then inverted after Pliocene time. That is why at present day there are two separate structures.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012