Abstract

The Krisna Field, located on the western flank of the Sunda Basin, constitutes one of the most significant petroleum discoveries by PERTAMINA-IIAPCO in the Southeast Sumatra Production Sharing Contract Area. The oil accumulations found to date are associated with the “Krisna High”, an old paleotopographic basement high which in late Oligocene time acted as a source of terrigenous material and later became a favorable site for the growth/sedimentation of reefal carbonates. Deposition of the reservoir rocks took place mainly under transgressive conditions, although some regressive pulses have been recognized. As the rate of transgression of the “Krisna High” increased, reefal growth could not keep pace and ceased.

Hydrocarbon accumulations found on the “Krisna High” are mainly of a stratigraphic nature; however, the structural component in some instances plays an important role.

Geochemical data indicate that Krisna hydrocarbons were generated in the Sunda Deep. Therefore, moderate to long distance migration is postulated via the basal unconformity and major fault zones.

A preliminary interpretation of the relationship between facies distribution and porosity development is presented in the discussion to follow. Porosity in the reservoirs is mainly secondary, and is associated with low energy back-reef facies.