Architecture of Middle Miocene to Pleistocene Sands using 3D Seismic in the Songkla Basin, Gulf of Thailand

Abstract

The Songkhla basin lies offshore in the Gulf of Thailand and is one of the productive basins for hydrocarbon in fluvial reservoir sands of Cenozoic age. This study aimed to investigate the development of depositional settings in shallow section of the basin and documented both sand distribution and fluvial architecture using 3D seismic data. Moreover, wireline log data was also used to analyze the depositional environment at wells. Nine seismic time-slice images from shallow to deeper section were analyzed. Different parameters associated with channels were documented and these channels were classified based on key measured parameters. It has been observed that channels just above two unconformities are having low sinuosity while as we move upward from unconformities sinuosity increases. Moreover, the dominant flow direction in Middle Miocene was SW-NE, but above Middle Miocene unconformity dominant flow direction was WE. The channels just above the two unconformities were interpreted as braided, formed due to the drop of base level. The base level drop might be related to combined effect of tectonic subsidence and sea level changes. Log interpretations along with seismic interpretation reveal fluvial environments in Middle Miocene. On the other hand no logs were available for the upper section (Middle Miocene to Recent) therefore only on the basis of results of seismic inversion it has been inferred that section above the Middle Miocene unconformity is more shaly followed by sandy section containing fluvial channels. The source of sediments changed above Middle Miocene unconformity from the southwest to the west.