Abstract

Widuri field is located on the northwest flank of the Asri basin in the Southeast Sumatra PSC area. The discovery well, Widuri-1, was drilled in April 1988 to a total depth of -3735'SS and penetrated 170' of net oil pay in upper Talang Akar Formation sandstones. The structure is a faulted anticline which formed approximately 19 mya (early Miocene), shortly after deposition of the Talang Akar Formation. The trapping mechanism combines structure and stratigraphy and oil is found in six separate reservoirs over a vertical interval of approximately 350 ft. Eight delineation wells and 40 development wells confirmed a giant oil field over an area of approximately 5000 acres. Initial production start-up was December 1990.

A study was undertaken to map and predict the reservoir distribution as a basis for the development drilling program and subsequent reservoir simulations. The study integrated the available electric logs and core data with the 250 m grid of 2-D seismic. Selected interval isochron and reflection amplitude maps proved to be important in developing the reservoir model.

The basal reservoir is a coarse grained, fluvial sandstone with multistorey and multilateral stacking, while the uppermost reservoir is a fine grained, single storey, distributary channel associated with a tide-dominated delta. The intermediate reservoirs show a complete gradation between these two extremes. This gradual change in river/channel type is accompanied by a change in reservoir quality and sandbody geometry from an essentially thick, sheet sandstone at the base to a thin, 2000 feet wide, shoestring sandstone at the top.

The reservoir model proved to be a very effective predictive tool during development drilling and will be a critical factor in future simulation studies. In addition, the model has direct application to both refining and defining exploration plays within the PSC.