Abstract

Reefs and reefal environments of Miocene age provide excellent reservoirs for oil and gas fields throughout the Far East. In addition, they are directly comparable to the present day systems. They can be conveniently grouped into isolated or attached platforms, or mixed siliciclastic - carbonates platforms.

For attached platforms to fully develop they require relatively stable tectonic regimes, features not typical of the Far East. Therefore the most common platform types throughout the Late Tertiary are the isolated or mixed siliciclastic-carbonate systems.

Isolated systems are generally associated with structural highs, whereas the mixed systems commonly locate on the side or distal of active distributaries.

The carbonate-siliciclastic relationship is clearly evident from outcrops (Miocene in the Piabwe embayment area of Myanmar and in the Miocene of North Sumatra - Indonesia) or from Miocene cored intervals (e.g. Apar in the Mahakam delta - Indonesia and Dai Hung in Vietnam). The same relationship is evident today in the Mahakam delta and Pater Noster Island Indonesia as well as the Irrawaddy delta in Myanmar.

From an exploration viewpoint the overiding critical factors governing large accumulations are carrier bed efficiency and migration focus. In addition seal integrity is particularly important for the mixed systems, as demonstrated by the Mahakam delta exploration results.