Abstract

The Thousand Islands area of the Northwest Java Sea has recently been the site of several important oil discoveries. Two fields, Bima and Karmila, are now producing and several more are in the delineation stage, among them the AA, AVS, AU and AV-Kartini Fields. All of these fields are associated with the Thousand Islands Fault System. The Thousand Islands Fault is a major basement fault, downthrown to the west, which separates the Sunda Basin from the Seribu Platform in the Northwest Java Sea.

This paper investigates the structure and stratigraphy of the AVS Field which is characterized by multiple channel sand reservoirs of the Oligocene Talang Akar Formation. Pay zones consist of two distinct Talang Akar facies, one fluvial/upper deltaic and the other transitional/lower deltaic. These two reservoir facies are laterally correlated by well-logs. Although pay zones may have a stratigraphic control, oil is encountered on structural roll-overs confined laterally by synthetic growth faults of the Thousand Islands Fault System. The interpretation of conventional seismic reflection sections identifies the faults and structural highs of the field. Stratigraphic features, however, are better seen on non-attenuated seismic reflection sections. Oil accumulates on the structural highs after migrating from deeper zones in the Sunda Basin. There is no communication among the multiple reservoir zones because of the effective sealing provided by interbedded shales.

There are about twenty different oil bearing reservoirs in the AVS Field. Computations of net pay from these zones indicate recoverable reserves in excess of twenty million barrels.