Carbonate rocks are recognized as one of the main hydrocarbon bearing reservoirs in Eastern Indonesia. The objective of this paper is to describe the potential of carbonate reservoirs in the Banggai-Sula Microcontinent. There are three phases of carbonate development in the area : (a) the rift graben-filled carbonates, (b) the pre-collisional carbonates and (c) the post collisional carbonates. The Upper Cretaceous carbonates of Tanamu Formation develop restricted in the eastern portion of the study area are interpreted as a bathyal limestones, filling the graben which was formed during the Mesozoic rifting. From exploration standpoint this bathyal carbonates which consist of tight limestones and marls have minor reservoir potential but provide good seal for elastic reservoir of the Bobong Formation underneath. A widespread development of the pre-collisional carbonates occurred during the Miocene transgression phase. This carbonate formed shallow platform limestone of the Salodik Group which conformably overlying the basal transgressive clastics. Overmost of the Banggai-Sula region covered by thick calcareous facies. To the west, the carbonate sequence was interrupted by local regressive pulse that deposited clastics and coal interbeds, where in the east, carbonate deposition remain continued. A major tectonic event at the end of Miocene, the collision of the Banggai-Sula Microcontinent against the East Sulawesi, terminated this limestone depositional cycle. In the Plio-Pleistocene, after collision period the study area became a foreland basin where the Celebes molasse was covered by the Peleng reefal limestone formation in the emerging basin condition which still continues to develop even today. The best hydrocarbon potential among the three phases of carbonate development is the upper part of the Tertiary pre-collisional carbonates. Hydrocarbon occurred in the fractured and thrusted elas-tic limestones or stratigraphically in the reefal limestones as well as in combination of both.
Authors : Rudy Ryacudu, Teguh Wibowo & Y.E Handiwiria