Abstract

The Pattani Basin is an elongated Tertiary rift system situated in the center of the Gulf of Thailand. Large quantities of gas, condensate and lesser oil have been discovered in the Miocene fluvial/deltaic sandstone reservoirs segmented by densely populated faults. Geochemical and basin modeling analyses have identified two operating petroleum systems in the basin: one relating to a Miocene fluvio-deltaic coaly source and the other an Oligocene lacustrine algal source.

The majority of the hydrocarbon accumulations in the Pattani Basin were sourced from the Miocene fluvio-deltaic coals and carbonaceous shales containing land plant debris. The source rocks are dominated by type III vitrinitic kerogen prone to generating gas condensate. A high abundance of angiosperm-indicative resin biomarkers (bicadinanes) and high pristane/phytane ratios indicative of mildly oxic swamp conditions characterize the condensate derived from this source facies. Fluid migration was prevalently vertical and likely episodic relating to fault movement. The Oligocene lacustrine algal oils are characterized by low pristane/phytane ratios, near absence of landplant resin markers and a high abundance of gammacerane. The lacustrine oils are generally waxy, and have low API gravity. They are mostly preserved in the flank areas and the relative basement highs of the basin.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah