Paleoenvironment study of a syn-rift stratigraphic unit in the northern Pattani Basin, Gulf of Thailand.

Abstract

The Oligocene syn-rift section associated with the Similan-Lanta structural trend on the northwest flank of the Pattani Basin, Gulf of Thailand is the focus of this study. The syn-rift section hosts the main source rock in the marginal areas of the Pattani Basin and the lack of success of some wells in this area suggests an incomplete petroleum system and the general model needs to be re-evaluated. This study is primarily based on seismic facies interpretation from a 3D seismic data set and supported by well log and geochemical data. A reconstruction of the Paleoenvironment during the syn-rift was done to analyze the relationship between the underlying basement structure and the potential source rock distribution. Three main depositional facies were identified from the study including fluvial plain, lacustrine and alluvial fan facies. The seismic facies analysis suggests that the initial stage of syn-rift development created a series of isolated lakes which developed adjacent to the rift boundary fault. During the middle syn-rift stage a fluvial system developed from the north and filled up the adjacent downstream accommodation space. This was subsequently superseded by a widespread lake which developed along the basin axis in the upper middle rift stage. The structural controls which created the various lacustrine environments controlled the depth and extent of the important source rock distribution. The source rock in this area is not widespread but the geochemical analysis suggests that it is within the generating oil window and does generate hydrocarbons. Migration pathways between syn-rift source rock deposits and potential traps need to be carefully considered when evaluating this areas hydrocarbon potential.