Abstract

The Pattani Basin is the largest of a series of elongate N-S trending Tertiary rifts formed in the Gulf of Thailand.

In the Pattani, large quantities of gas and lesser oil are trapped in Miocene fluvial sandstone reservoirs within densely faulted graben systems. Geochemical and basin modeling studies show that two separate petroleum systems control the occurrence of hydrocarbons in the basin. Critical exploration risk factors for both include source rock quality and thermal maturity.

The dominant petroleum system in the Pattani Basin is made up of Miocene gas-generating terrestrial coals and shales currently mature in the deeper central portions of the basin. Migration pathways are relatively short to charge interbedded sandstone reservoirs. Leaky fault traps require active recharge to sustain gas accumulations. The second system consists of Oligocene oil-prone lacustrine shales mature in basin flank areas but overmature in the central trough. Oil is found on basin slopes where it has migrated into overlying Miocene reservoirs via basement onlap and fault conduits. Additionally, early oil generated in basin axial regions may be trapped in older, stable structural highs. The dual hydrocarbon systems active in the Pattani combine to create a prolific, world-class petroleum basin.