Abstract

The Tomori PSC, Located on the eastern arm of Sulawesi, is comprised of two distinct tectonostrati-graphic units, The first unit is the Banggai-Sula microcontinental block, which has been interpreted as a fragment of the Australia New Guinea Plate. The second unit is the East Sulawesi Ophiolite Belt, an ophiolite complex which was thrust over the Banggai-Sula microcontinental block in Lower Pliocene Times.

The microcontinental block is interesting from an exploration standpoint because it has developed across it two distinct structural styles, two contrasting sedimentary sequences, and two reservoir units. The structural styles were developed, firstly, as Banggai Sula moved westward towards its present position, and secondly, as it entered the collision zone with the East Sulawesi Ophiolite Belt. These tectonic processes result in the majority of the northern area of the PSC being characterized by normal and wrench faults, and the southern area of the PSC by imbricate thrusts.

The pre-collision Miocene sequence is characterized by two carbonate units, and the post collisional Pilocene-Pleistocene sequence by a thick clastic section of claystones, conglomerates, sandstones, and limestones.

The reservoir units occur within the Miocene carbonates. In the lower unit, which is composed of a sequence of platform limestones, a small oil field has been discovered. This is the Tiaka Field, and it is located in the complex thrust zone in the southern portion of the PSC. In the upper carbonate unit, which is characterized by a mixed platform reefal assemblage, two gas fields have been discovered, the Minahaki and Matindok Fields. Both carbonate units have experienced a similar diagenetic history. Source rocks for the hydrocarbons discovered on the PSC have been identified in the Miocene section. Generation and migration of the hydrocarbons took place in Pliocene/Pleistocene times, as prior to this, insufficient overburden existed to create mature source sections.