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Abstract: Sequence Stratigraphic Applications to Deep-Water Exploration in the Makassar Strait, Offshore East Kalimantan, Indonesia

Steven J. Malecek, Christopher M. Reaves, Wirjawan Soeria Atmadja, Komang O. Widiantara

A sequence stratigraphic study was conducted to help evaluate the exploration potential of the Makassar PSC, offshore East Kalimantan, Indonesia. The PSC is on the present-day slope in water depths of 500-3000 ft and borders the large oil and gas fields of the Mahakam delta. The study provided important insights on reservoir distribution, trapping style, and seismic hydrocarbon indicators.

Lowstand deposition on a slope modified by growth faulting and shale diapirism controlled reservoir distribution within the prospective late Miocene section. Three major lowstand intervals can be seismically defined and tied to deep-water sands in nearby wells where log character and biostratigraphic data support the seismic system tract interpretation. The three intervals appear to correlate with third-order global lowstand events and are consistent with existing sequence stratigraphic schemes for the shelf and upper slope in the Makassar area. Seismic mapping delineated lowstand features, including incised valleys and intraslope to basin-floor thicks. Regional information on positions of middle-late Miocene delta lobes and shelf edges, helped complete the picture for sand sources, t ansport routes, and depocenters.

Hydrocarbon traps formed in response to sediment loading on the slope during lowstands and show two distinct map trends. Growth faults and rollover features along the shelf edge represent the extensional component of a process that is complemented by shale mobilization and diapirism in a basinward direction. Seismic amplitude analysis using amplitude versus offset (AVO) technology showed seismic hydrocarbon indicators coincident with both types of structures. Such indicators, and the possibility of stacked lowstand reservoirs, has significantly enhanced the prospectivity of the Makassar PSC.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994