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ABSTRACT: Tertiary Reservoirs of Offshore Northwest Java, Indonesia: Examples of Hydrocarbon Accumulations in a Mixed Carbonate-Clastic Environment

Christopher D. Atkinson, John G. Kaldi

The Tertiary deposits of the offshore northwest Java hydrocarbon province lie within a series of northeast-southwest-trending, fault-bounded, basement lows (subbasins) and on top of intervening basement highs (platforms). This structural configuration was established at the end of the Cretaceous following collision of the Sunda and Kangean microplates, and modified by fault reactivation throughout the early Tertiary. Distribution of seal and reservoir lithologies is controlled by the

complex interplay between regional tectonics, changes in global sea level, and variations in clastic sediment supply and carbonate accumulation rates. Basement lows comprise thick sequences (up to 17000 ft) of interbedded sandstones, siltstones, shales, and limestones of continental, deltaic, and shelfal origin. Basement highs consist mainly of condensed platformal carbonate sequences and relatively thin clastic deposits. Syndepositional faulting, differential subsidence, and relative sea level change resulted in thick interfingering clastic and carbonate sediments on the flanks of the major structures. The deep subbasins are the sites of hydrocarbon generation. Hydrocarbons migrated upward from these kitchens along the bounding faults and into reservoirs on the flanks and crests of a jacent basement highs. Hydrocarbon accumulations occur in fault traps, anticlinal folds over uplifted blocks, and stratigraphic pinch-outs. Reservoir quality in the clastic plays depends primarily on the relative amounts of shale and/or carbonate cement in the sandstones, whereas in the carbonate objectives, reservoir properties are controlled largely by the degree of diagenetic porosity enhancement.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990