Exploration Challenges in North West Java: New Carbonates Play in Upper Cibulakan Formation

Tropical climate condition in Indonesia favored the reefs carbonates to plenteously grow in many regions. A case study from the Lower-Middle Miocene carbonates reservoir of the Upper Cibulakan Formation in northwest Java Basin. A continuous change of global sea level in each era in northwest Java Basin is the origin of the local distribution carbonates in the formation. Upper Cibulakan Formation is deposited between Baturaja Formation and Parigi Formation which lithologically similar with Upper Cibulakan Formation, moreover, both of the formations have already proven in producing hydrocarbon. To =study the contribution of porosity development to the potential of the hydrocarbon and its petroleum system evaluation, we combined petrography analysis and core-plug description. The identified thin section showed that many type of porosity distributed along the formation and the average porosity is 2.5% - 37% which qualified as good – excellent reservoir. Among 450 ft accumulations of carbonates reservoir came from the source rock of lacustrine clastic deposits in Middle Eocene-Lower Oligocene of Jatibarang Formation and fluvio deltaic coal and shale Lower Oligocene-Lower Miocene of Talang Akar Formation. The hydrocarbon itself is expected to laterally migrate to anticlinal dome, structural trap, and stratigraphic trap with carbonate buildup and sealed by the composition of claystone of Cisubuh Formation. The most decisive evidence appeared in core sample of GT-23 well where the oil found within the vuggy porosity. Thus, the hydrocarbon prospectivity in Upper Cibulakan Formation is immensely high by cause of the adequate of petroleum system and it is accessible to be furtherly explored.