GEOLOGY AND PETROLEUM PROSPECTS OF SERAM ISLAND, EASTERN INDONESIA

Abstract

The Island of Seram is located near the eastern end of the Indonesian Archipelago about 250 km southwest of Irian Jaya and 1000 km north of Darwin.

The two main Late Tertiary to Quaternary basins (the Bula and Wahai Basins) totalling approximately 6000 km2 occur both offshore and onshore along the northern and northeastern coasts of the island. Several smaller basins of similar age occur along the eastern, southern and northwestern coasts.

Sedimentation in the Bula and Wahai Basins began in the Early Pliocene with a marine transgression which continued into the Early Pleistocene and resulted in the deposition of bathyal facies mudstone and siltstone in the deeper parts of the basins. In the Early Pleistocene uplift occurred resulting in the formation of a regional unconformity in the sedimcn tary sequence. This uplift was followed by further transgression and deposition of neritic sediments during later Pleistocene to Recent times. The estimated maximum thickness of sediments in the Bula and Wahai Basins is 1400 and 2800 m respectively.

Although the basement rocks of Seram have been severely folded and faulted, structural deformation within the Plio-Pleistocene basins has been much more subdued, resulting in minor tilting, draping of sediments over basement highs or Pleistocene reefs, and more rarely, small, down-to-the-basin faults near the basin margins.

The Bula Basin is a proven petroliferous basin with the small stratigraphie Bula-Lemun Oilfield of Pleistocene age on its northwestern margin. In addition there are abundant surface oil seeps and good free oil shows have been recorded from wells drilled in the Belien-Kola area. Porous beach and bar sands and reefal limestones have been encountered within the onlapping Pleistocene sediments. Future exploration in Seram has good prospects of discovering further oilfields of the Bula-Lemun type.