Abstract

Deepwater sedimentation occurred in Java during Miocene and Pliocene time in trough/basinal areas called the Bogor-North Serayu-Kendeng Zone located in the middle of the island. These depressions were formed by isostatic subsidence compensating for the uplifted volcanic arcs located just to the south. In Plio-Pleistocene time, the trough/basins were themselves significantly uplifted and deformed, and they currently form an anticlinorium of fold and thrust belts.

Field geology and examination of seismic and well data in the Bogor-North Serayu-Kendeng Zone show that deepwater plays are viable in Java. Redeposited reservoir-quality sediments sourced from the NW Java Basin occur in the Bogor Trough/Basin. A number of oil seeps and oil fields occur in the North Serayu Trough/Basin in reservoirs of turbiditic volcaniclastic sandstones. A toe-thrust system, similar to proven productive traps in the deepwater Lower Kutei Basin, developed in the North Serayu Trough/Basin as the response to northward subsidence. A number of oil fields in the East Java area have reservoirs of Ngrayong sands, considered as deepwater deposits in the slope of the Rembang Zone. A number of gas and oil fields in Pliocene-Pleistocene volcaniclastic turbidites of the eastern Kendeng Zone also show the prospectivity of deepwater plays in Java.

Risks for deepwater plays in Java are related to the tectonic-volcanic setting of the island. Limited provenance for re-deposited reservoirs and sources, limited space of accommodation due to northward migration of thrust fronts, and complex deformation add risk to the petroleum system. Abundant volcanic materials also place some difficulties on operations and reduce the resolution of seismic data. However, opportunities for deepwater plays in Java are worth considering. The presence of existing oil and gas fields in the Bogor-North Serayu-Kendeng Zone shows the prospectivity of this play. Its potential is promising and should not be overlooked any longer.