Print this pagePetroleum Geology and Exploration in Tarakan Sub-basin, Indonesia: Contribution of Growth Faults on Hydrocarbon Entrapment
BIANTORO, ELAN, LINDY F. ROTINSULU, M. INDRA KUSUMA, and TATANG SOETISNA
The Tarakan sub-basin in eastern Kalimantan is a producing sub-basin with 8 developing fields. Tectonic history of this sub-basin started with rifting interspersed with periods of upliftings ending in Late Eocene, Middle Oligocene, and Middle Miocene. These upliftings were controlled by volcanic activities during the same periods. The interaction of these processes produced the five geological blocks recognized today: (1) platform, (2) half-graben/sub-depocenter, (3) ridge, (4) slope, and (5) main depocenter.
Vulcanism intensified and reached the peak in Middle Miocene causing a change in pattern of sedimentation from transgressive to regressive. The immense supply of sediments during the regressive phase re-activated old block faults that were formed during rifting period. The re-juvenation process was followed by the development of growth faults. Vulcanism also raised the geothermal gradient and the most recent vulcanism, which ended in Late Miocene, became the heat source for hydrocarbon maturation of the Mio-Pliocene sediments. Based on shale thickness, vitrinite reflectance, and paleogeothermal gradient, the kitchen area was found to be localized in the half graben and main depocenter blocks.
The growth fault system and the limited lateral distribution of deltaic environment produced a more dominant vertical migration compared to lateral migration. This condition influenced the lack of hydrocarbons in the platform, ridge, and slope blocks. Not surprisingly, the hydrocarbons discoveries are concentrated in the half-graben and main depocenter blocks.