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Abstract: Incised Valley Fills and Their Implications for Production and Exploration, Belida Field, Indonesia

Robert Pascoe

Belida is a 200 MMBOR field discovered in 1989 in the West Natuna Basin, Indonesia. The major oil production is from early Miocene tidal sandstones, draped over a low relief, inversion anticline. The late Oligocene through early Miocene stratigraphy of the West Natuna Basin exhibits problematic lacustrine and marginal marine affinities, and Lake Maracaibo can be invoked as an analogue system. Cyclicity is clearly evident in the stratigraphy, and climate, eustasy and tectonics can all be demonstrated as primary controls.

The productive tidal sandstones are interpreted as the fills of incised valleys located on and adjacent to early growth of the inversion anticline. During inversion fluvial drainage was constrained laterally by the initial extensional architecture and responded to reduced accommodation space by incision. Strong tidal currents during the ensuing transgression allowed winnowing and aggradation of multi-storey sandstone reservoirs with darcy permeabilities, resulting in world-class well productivites. The association of tectonic inversion and the earliest, significant relative sea level rise in the basin, produced a sandstone of reservoir quality uncharacteristic of the stratigraphic section as a whole.

Delineation of the incised valleys has been possible by extensive use of core and 3D seismic facies mapping. Implications for reservoir simulation and offset exploration are discussed.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela