Tectono-Stratigraphic Framework and Petroleum Systems of Tertiary Rift Basins in Southeast Asia

Scott Sumner¹ and Harry Doust^2
1 Shell International E&P Inc, Houston, TX
² Vrije Universiteit, Amsterdam, Netherlands

The Tertiary rift basins of Southeast Asia are situated on a stable Pre-Late Cretaceous tectonic core, “Sundaland”, which underlies much of present-day Indochina, Thailand, and western Indonesia. During the Cenozoic Sundaland was surrounded by subduction zones and was wedged between the Eocene-age India/Asia collisional domain in the northwest and the Miocene to Recent-age Australia/Asia collisional domain in the southeast. The polygenetic character of the Tertiary rift basins superimposed upon Sundaland is largely a product of the interaction of these two collisional domains.

The resultant tectonic evolution of the basins can broadly be divided into three stages: 1)Eocene-Oligocene transtensional rifting caused by the India/Asia collision; 2)Late Oligocene-Early Miocene early postrift thermal subsidence; 3)Middle Miocene-Recent late postrift compression caused by the collision of Australia with the southeast margin of Sundaland and the Reed Bank Block with northwest Borneo. During this stage many basins in the south experienced inversion, superimposed forelands, and hinterland uplift.

Each of the three stages of regional basin development has a predictable association of stratigraphic megasequences and related petroleum systems. The rift stage is generally associated with fluvial-lacustrine megasequences and oil-prone petroleum systems overlain by transgressive deltaic megasequences and oil/gas-prone petroleum systems. The early postrift thermal subsidence stage is associated with marine megasequences and gas-prone petroleum systems. The compressional late postrift stage is associated with regressive deltaic megasequences and gas/oil-prone petroleum systems. Statistical analysis of hydrocarbon production data demonstrates the strong impact basin development and paleogeographic position have on stratigraphic megasequences, petroleum systems, and hydrocarbon volumes and mix.