Abstract

The Tarakan sub-basin is one of several sub-basins located in the northeast Kalimantan Basin. This sub-basin is located between the Tidung sub-basin to the north and the Berau sub-basin to the south. To the west, the Tarakan basin is bordered by Sekatak Ridge, and to the east by the present day deep water area of the Makassar Strait.

Geologically, the Tarakan sub-basin is subdivided into 5 geological provinces: (1) Daino-Sebuku Platform, (2) Sembakung-Bangkudulis Graben, (3) Dasin-Fanny Ridge, (4) Mintut-Tibi Slope, and (5) Bunyu-Tarakan Main Depocenter. Tectonically, these provinces are separated by normal faults controlled by Oligocene to Pliocene growth fault systems. 35 exploration wells have been drilled in the sub-basin, with only nine discoveries. The discovery wells are located in Sembakung-Bangkudulis Graben, Mintut-Tibi Slope, and Bunyu-Tarakan Main Depocenter.

Fault development occurred during three periods: Late Oligocene-Early Miocene rift faulting, Middle-Late Miocene growth faulting, and Mio-Pliocene growth faulting. The Middle-Late Miocene faults are rejuvenation of previous faults, coinciding with a change in sedimentary pattern from transgression to regression. Hydrocarbons were trapped by the Middle-Late Miocene and Mio-Pliocene growth faults. The geometry of structural traps are described as four way dip, roll-over against fault, fault traps, and unconformity closures.

An evaluation of the faulting mechanism concluded that structural traps formed by faults depend on their sealing/non-sealing condition, distance from the kitchen area, timing of migration, and the age of the faults themselves. The faults could be acting as migration path-way or seal. This paper tries to investigate and display the relationship between faults and hydrocarbon accumulations, and to predict which closures have a high probability of being traps.