Overpressure development in rift basins: an example from the Malay Basin, offshore Peninsular Malaysia

摘要

The Malay Basin is a Tertiary transtensional rift basin located in offshore Peninsular Malaysia. A study of the subsurface pressure data has revealed at least two major overpressure compartments that are sealed by regional shale units. The main, basin-centre overpressure compartment has a domal shape and, in profile, shows a convex-up top-of-overpressure surface. In the basin centre, the top of overpressure is generally between 1900 m and 2000 m depth, and is confined mainly to a particular stratigraphic unit, the Middle Miocene unit E. It appears that the top of overpressure is influenced by the underlying regional shale seal in unit F, and that the mild overpressure encountered in unit E represents the overpressure transition zone. Due to the convex-upward top-of-overpressure surface, overpressure is generally encountered at shallower depths in the basin centre compared to the basin flanks. A smaller overpressure compartment is also identified on the northeastern flank of the basin. This compartment is sealed by the onlapping, transgressive shale of unit L (Lower Miocene) and occurs at a depth of 2600–3000 m. Hence, regional shale seals have a strong influence on overpressure distribution.