U.S. GEOLOGICAL SURVEY Petroleum Systems of the Northwest Java Province, Java and Offshore Southeast Sumatra, Indonesia by Michele G. Bishop
Open-File Report 99-50R 2000
TERTIARY-PARIGI (382403) ASSESSMENT UNIT BIOGENIC GAS (38240301) Known biogenic gas charges upper Miocene Parigi Formation carbonate reservoirs that comprise fields in the Tertiary-Parigi petroleum system (382403) (Fig. 1 and Fig. 7) (Noble and others, 1997). Other fields that have gas reserves in these reservoirs, and are distant from known mature source rocks, are included in this petroleum system although data as to the precise source of the gas are not available. Some authors have interpreted gas in the Pre-Parigi and Parigi as thermogenic, being sourced by Talang Akar coals and having migrated to the reservoir (Fig. 4) (Yaman and others, 1991), whereas Noble and others (1997) suggested that the source sediments for the near-surface bacterial gas are fine-grained claystone and mudstone facies of the Parigi and Cisubuh Formations. The gas is reported to be dry and to contain 98% methane with minor ethane, nitrogen, and carbon dioxide (Yaman and others, 1991 The upper Parigi Formation reservoir consists of platform carbonates, developed as bioherms with enhanced solution porosity, that form good reservoirs sealed by transgressive shales of the Cisubuh Formation (Yaman and others, 1991; Noble and others, 1997). These carbonates range in thickness from a few feet to as much as 400 ft (122 m) (Yaman and others, 1997). The carbonate buildups are aligned north and south and are best developed in an east to west trend, being less well developed to the north (Yaman and others, 1997).
The
Tertiary-Parigi petroleum system contributes 15% of the energy equivalent
of the total gas and 8% of the total hydrocarbons to the reserves of the
Northwest Java Basin province (Noble and others, 1997). Shallow targets
that can be easily identified on seismic data, make this gas resource important
to the total reserves of the province (Yaman and others, 1991).
TERTIARY-CENOZOIC (382404)
BILLITON BASIN HYPOTHETICAL (38240401)
No possible source rock has been described but, based on maturation in other areas of the province, maturation might be expected between 3,300—6,600 ft (1,000—2,000 m) of burial depth. Migration presumably could occur vertically and laterally into any clastic and carbonate reservoirs that might be present.
The Pliocene to Pleistocene Cisubuh Formation is composed of claystones
that act as seals in the province. No trap style has been described.
Basement highs have been encountered during drilling, suggesting that possible
drape structures, stratigraphic pinchouts, or carbonate buildups are present
(Petroconsultants, 1996).
UNDISCOVERED PETROLEUM
There are also numerous future
exploration targets in the Ardjuna assessment unit within the Talang Akar
and Upper Cibulakan sandstones. Large deltas, shoreline deposits,
and sea-level highstand and lowstand features may provide additional opportunities
for development of reservoirs and traps. Although most of the carbonate
buildups have been identified, more subtle carbonate reservoirs and traps
may yet be found. The estimated quantities of conventional oil, gas
and condensate that have the potential to be added to reserves by 2025
are 1,380 MMBOE (U.S. Geological Survey World Energy Assessment Team, 2000).
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