INTRODUCTION
     The Northwest Java Basin Province #3824 consists of sediment-filled, half-graben basins formed on the southern edge of the Sunda Shelf plate or craton during the Tertiary.  Two important petroleum systems are identified: (1) Banuwati-Oligocene/Miocene (382401) with assessment unit Sunda/Asri (38240101); and (2) Jatibarang/Talang Akar-Oligocene/Miocene (382402) with assessment unit Ardjuna (38240201).  There are also two other proposed petroleum systems, Tertiary-Parigi (382403) with a Biogenic Gas assessment unit (38240301) and Tertiary-Cenozoic (382404) with the Billiton Basin Hypothetical assessment unit (38240401) (Fig. 1).

     The U.S. Geological Survey assessment of the estimated quantities of conventional oil, gas and condensate that have the potential to be added to reserves by the year 2025 for this province is 2.008 billion barrels of oil equivalent (BBOE); 658 million barrels of oil (MMBO), 7,453 billion cubic feet of gas (BCFG), and 108 million barrels of natural gas liquids (MMBNGL) (U.S. Geological Survey World Energy Assessment Team, 2000).  The combined known reserves, grown reserves, and assessed new resources are more than 12 BBOE for this province (U.S. Geological Survey World Energy Assessment Team, 2000).  Other estimates for the region are 4 BBOE recoverable with approximately 14 BBOE in place (Noble and others, 1997).

     The Banuwati-Oligocene/Miocene petroleum system is located offshore Sumatra.  The source-rock facies consists of, lacustrine, oil-prone Banuwati shales of Eocene to Oligocene age, that were deposited as the initial fill in half-graben rift basins.

     The second petroleum system, Jatibarang/Talang Akar-Oligocene/Miocene, is located onshore and offshore northwest Java.  It is sourced from lacustrine shales interbedded with volcanics of the Eocene to lower Oligocene Jatibarang Formation combined with thick, oil- and gas-prone coals of the upper Oligocene to Miocene upper Talang Akar Formation.  These coal-bearing, fluvial deltaic sediments were deposited in a late rift and post-rift sag phase.  Lower Talang Akar Formation oil-prone shales that formed in shallow lakes may also have contributed hydrocarbons to this petroleum system.

     Reservoir facies for both the Banuwati-Oligocene/Miocene, and Jatibarang/Talang Akar-Oligocene/Miocene systems include Oligocene through Miocene synrift lacustrine fans and fluvial clastics, late and post-rift sag-phase fluvial, shoreline, deltaic clastics and marine carbonate reefs and bioherms.

     A third petroleum system, Tertiary-Parigi, is located in an area north of Jakarta to onshore and offshore near Semarang (Haposan and others, 1997; Noble and others, 1997).  This system consists of carbonate-sourced and bacterial gas primarily in carbonate reservoirs of late Miocene to Pliocene age.  Offshore north of the Seribu Platform, reservoir rocks are marine shelf deposits of the late Miocene to Pliocene Parigi and Cisubuh Formations and are carbonates of the Parigi Formation near Semarang (Fig. 1).  A fourth hypothetical petroleum system, Tertiary-Cenozoic, is comprised of the Vera and Billiton Basins and extends northeast into the Java Sea where sediments reach a reported thickness of about 6,500 ft (2,000 m) (Fig. 1) (Hamilton, 1974).  A few structures have been drilled with no reported shows (Petroconsultants, 1996).  The possibility of source rock and maturity are not well known although the section is sufficiently thick for source rocks to be mature.