The Role of Cretaceous Seal to the Hydrocarbon Potential of the Salawati and Bintuni Basins, Irian Jaya, Indonesia

SAMUEL, LUKI, and LUKMAN KARTANEGARA,* PERTAMINA, Jakarta, Indonesia

The Salawati and Bintuni basins are late Tertiary depocenters located in the westernmost part of Irian Jaya, Indonesia. The two basins are closely located and only separated by a 50-km-wide structural high known as the Ajamaru Plateau.

Petroleum exploration results in the Salawati basin are very successful. This basin has produced around 300 Mbbl of oil from the Miocene carbonates of the Kais Formation. Exploration with similar objectives in the Bintuni basin, however, gave only little success. Some oil was obtained from small Wasian and Mogoi fields, which jointly produced around 7 Mbbl of oil between 1951 and 1960. Extensive exploration campaigns between 1970 and 1980 with Miocene Kais Limestone as the objective resulted only in the discovery of the small Wiriagar field.

The big difference in petroleum potentiality of the Salawati and Bintuni basins has attracted explorationists to evaluate what significant geological factors had influenced it.

Evaluation on available exploration data of the basins had some interesting results. In terms of geologic factors controlling hydrocarbon accumulation (presence of mature source rock, migration pathway, good reservoir quality, valid trap, and effective seal), it seems that shales of Cretaceous age have played the most important role. If this regional seal is absent or noneffective, oil could migrate vertically from pre-Tertiary sources to the Tertiary reservoirs.

On the contrary, if the Cretaceous shales are present and sealing, then the underlying Mesozoic sequence is attractive and may trap hydrocarbon, if supported by the other geologic factors.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)