Petroleum System of the Paleozoic and Mesozoic Intervals in the Northern Arafura Sea, Papua, Indonesia

Eddy A. Subroto* and Dardji Noeradi
Bandung Institute of Technology, Indonesia
*[email protected]

The Arafura Sea is situated in the eastern region of Indonesia. This region is tectonically unique since it has been formed by complicated interaction between three converging plates: the Eurasian and the Indo-Australian (continental) and the Pacific (oceanic). The tectonic regime around the area started during the early breakaway phase of the Australian Plate from Gondwana during mid Mesozoic time. Some outcrop and well samples have been collected during this study. A standard geochemical analyses and a 1-D modeling have been applied to the samples. Two oil and gas source rocks have been identified in this area. The first one is the Permian Aiduna Formation. It has relatively good quality source rocks (TOC=1.28–6.55% and Ro=„b0.55%) with a coaly and calcareous character. The second source rock is the Jurassic to Cretaceous Kembelangan Group. This group comprises four formations, i.e. Kopai, Woniwogi, Piniya, and Ekmai formations. The Lower Kembelangan (Woniwogi and Kopai) source rocks are generally shaly with interbedded minor sandstone and has shown organically fair to good quality oil and gas source. Thermal maturity modeling has indicated that the lowermost sediments in the Lower Kembelangan had entered late maturity for hydrocarbon generation (Ro = 1.2%) about two million years ago. Furthermore, it was concluded that the lower unit of the Kembelangan Group had reached the level of maturity to generate hydrocarbons some 5 to 10 million years ago. The Paleozoic formations reached their maturation during Mesozoic at approximately 3.6 seconds two-way seismic time. The possible reservoirs are in some of the Mesozoic formations, such as Tipuma, Woniwogi, and Ekmai. Scanning electron microscope analysis on these formations provides an estimated porosity ranging from 5–15% and permeability of 10–20 mD.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain