ABSTRACT: Tropical carbonate evolution during the Cenozoic in SE Asia: implications for hydrocarbon exploration

Wilson, Moyra E. J. , Dept. of Geological Sciences, Durham University, Durham, United Kingdom

Extensive Cenozoic tropical carbonates form important reservoirs in SE Asia. An understanding of the carbonate depositional environments, spatial facies relationships, controls on deposition and diagenesis is essential in order to characterise carbonate development and reservoir potential. Diverse tropical carbonates in SE Asia differ from sub-tropical counterparts in being dominated by bioclasts, associations with evaporites or dolomites are rare, and because they were often affected by coeval tectonism or volcanism.

Eocene-Oligocene carbonates in SE Asia are commonly dominated by larger benthic foraminifera. These carbonates developed around the margins of, or on highs within, subsiding basins, and typically form large-scale platforms or isolated shoals. The margins of the platforms may be gently sloping ramp-type margins, or steeper escarpment margins. Pre-existing faults often controlled the location of the platforms and some of the platforms had syntectonic faulted margins during deposition. Good poroperms can be preserved in foraminiferal shoals or redeposited carbonates which lack micrite. Secondary porosities may develop due to fracturing, chemical dissolution resulting from compaction, or as karstic cavities. However, the lack of aragonitic bioclasts and deposition in a generally subsiding environment reduces the potential for vadose or meteoric leaching. In comparison, Neogene carbonates often contain abundant aragonitic bioclasts, such as corals or Halimeda. Neogene carbonates typically develop as reefal buildups, shelfal deposits or as isolated platforms. Active Neogene compression in SE Asia resulted in an increasing emergence of land areas, and many of the platforms were affected by tectonics or eustacy. Compared with Paleogene limestones, poroperms are generally better developed in Neogene carbonates and interparticle, biomouldic, vuggy, cavernous and fracture porosities all occur. This study stresses the importance of detailed depositional and diagenetic evaluation of carbonates and provides analogue models for subsurface reservoirs.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia