Abstract

Compared to the western part of NorthWest Java Basin, i.e., Arjuna Sub-basin and its associated graben systems onshore West Java, the eastern part of the basin is thought to have less hydrocarbon potential. During the 1970's and 1980's the area was explored by several operators with disappointing results.

The western and eastern parts of the basin can be distinctly delineated by the N-S bounding fault north of Cirebon: the west-facing normal fault, which is a splay of the NW-SE trending OO fault, and the east-facing Cirebon fault onshore. Some hydrocarbon accumulations have been proven (e.g. the OO, X, Jatibarang and Cemara Fields) adjacent to this boundary. Most of the hydrocarbons in the area are found within Paleogene clastic reservoirs.

The existence of Paleogene deposits are considered to be a critical factor for the petroleum system in the basin since they provide both good reservoir quality and potential source rock, notably from the deltaic and lacustrine systems of the Talang Akar and upper part of the Jatibarang Formations. The unsuccessful exploration in the eastern portion of the North West Java Basin (known as Eastern Carbonate Shelf) is considered to be due to the lack of these deposits.

Structural analysis applied to basement-involved faults in the study area (in the vicinity of the bounding fault, i.e., Jatibarang-Brebes and adjacent offshore areas) reveals that the N-S trending faults act as a releasing double-bend structure of the NW-SE right-stepping strike-slip fault system. This fault system (the OO and Brebes Faults) was generated by the N-S compressive stress during the Miocene and is originally thought to be an extensional regime of the Cretaceous-Oligocene Meratus System that was rejuvenated during the Miocene. From the analysis it can be observed that a depocentre developed to the east of the bounding fault. The occurrence of the Paleogene graben system (depocentre) in the eastern part of the North West Java Basin is the critical factor to meet the requirements for hydrocarbon accumulation in the area.