インドネシア第三系西ナトゥナ海堆積盆における圧縮性反転構造運動と石油地質

Abstract

The West Natuna Sea Basins are the Tertiary, inverted, intra-continental rift-basins in the Sunda Shelf, Northern Indonesia. The basins include remarkable oil producers as well as most other Indonesian Tertiary basins. Inversion-anticlinal traps in the basins have been classic examples of a positive contribution of inversion tectonics to formation of petroleum systems and plays.The Tertiary mega-sequence of the basin includes a Middle to Upper Eocene lacustrine deposit, an Oligocene fluvial to deltaic deposit, an Early Miocene muddy facies deposit, a Middle Miocene deposit of sand-dominant deposit, and a Late Miocene through Recent alternative mud-sand deposit. The West Natuna Sea stratigraphy remarkably lacks the thick Early to Middle Miocene carbonates that are normally well-developed in the most Indonesian Tertiary basins. The Oligocene and Lower Miocene sandstones are productive reservoirs, and widely deposited Oligocene and Lower Miocene mudstones provide regional and top seals, for petroleum systems in the basins.Four petroleum systems are identified in the southern West Natuna Sea based on the magnitudes of inversion tectonics and resulting thermal “kitchen” that developed. Systems (1) and (2) are based on petroleum-charging kitchens, such as the Malay Basin or the Bawal Graben. These kitchens are distinguished from each other by carbon stable isotope ratios of alkanes and aromatics of crude oils and by a biomarker. Systems A and B are by tectonic styles related to petroleum accumulations, such as basement highs or inversion anticlines. The four petroleum system are recognized from west to east and north to south in the area; such as System (1) A (Belida oil field), System (1) B (Tembang, Buntal and Bintang Laut gas pools), System (2) B (Forel oil pool, Belanak oil and gas field) and System (2) A (Udang oil field). System (1) forms much larger petroleum-accumulations than System (2). Sizes of the accumulations are clearly related to the sizes of kitchens that charged the accumulations.