Abstract

The Neogene clastic intervals, deposited in a shelf to deep-water setting, dominate the Brunei offshore area, South China Sea. Systematic mapping results based on 3D seismic and well data have been used to establish the basin framework. The Brunei offshore area is compartmentalized by faults controlled by gravitational gliding mechanism and tectonics. In general, these processes generated two types of fault systems, northwest dipping, down-to-the-basin faults and southeast dipping, counter-regional faults.

The southeast dipping, counter-regional faults are developed in the eastern offshore of Brunei where they confine a significant amount of sediment. The stratigraphy is dominated by Upper Miocene to Pleistocene, shelf to tidal deposits, known as the Champion system.

Deep faults in the offshore west dip to the southeast and younger and shallower structures dip in the opposite direction. Although the younger structures in the west are more complex compared to the eastern offshore, they are dipping down-to-the-basin and therefore do not significantly block the sediment supply to the slope area and the basin floor. The sedimentary system in the west is similar to that deposited in the east but with a thicker Pliocene interval.

The Ampa-Magpie anticline, with a significant shale injection zone as its core, occurs in the middle of offshore Brunei separating the Baram system from the Champion system. This large structure is likely related to deep NW-SE oriented basement faults.