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ABSTRACT: What really matters when analysing lakes in SE Asia?

Sladen, Chris1, Hoang Ngoc Dang2, Nguyen Quoc Thap2
(1) BP Amoco, Irkutsk, Russia 
(2) BP/Statoil, Ho Chi Minh City, Vietnam

The importance of ancient lake basins in creating vast hydrocarbon and coal reserves in SE Asia has long been recognised, and as a consequence billions of barrels of oil, trillions of cubic feet of gas, and millions of tones of coal that originated from lake basins are produced each year. Different controls on these lake basins and the sequences that fill them have been studied, and reported on intensively during the last 25 years.

In this paper, we take a look at what really matters when analysing and predicting lacustrine facies in SE Asia, and how one can unravel the answers. Rather than repeat data and information from the much documented lacustrine basins in SE Asia, we take the opportunity to illustrate key points using some of the early Tertiary basins from the less well known areas of offshore Vietnam which have great potential for hydrocarbons.

The three factors of subsidence outpacing sedimentation rate, climate and hinterland geology consistently recur as key controls during the evolution of lake basins in SE Asia. These controls appear to have had a fundamental impact on the development of lake basins, the way in which they are infilled, and the sediment types that infilled the lakes. Lake basin evolution was frequently characterised by extensional tectonics that created prolonged phases with subsidence outpacing sedimentation enabling a lake to exist, a suitable sub-tropical to tropical climate enabling organic matter to flourish, and a widespread carbonate-rich hinterland which caused a reduced coarse clastic input into the lakes.

To understand the sediment fill of each of these basins, detailed palaotopographic analysis is the essential pre-requisite. Without such analysis, predictions are inherently less accurate.

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