Abstract

The Penyu Basin comprises half-grabens that are bounded by two major sets of faults: 1) NW-trending faults, which may have formed along pre-existing Mesozoic strike-slip faults and 2) ENE-trending faults, which are mainly extensional normal faults. The orientation of these faults and grabens suggests that the Basin was formed by N-S extension.

The Penyu Basin formed in the early Oligocene as a nonmarine (lacustrine) extensional basin. Marine incursions started during the early postrift stage in the late Oligocene. The synrift half-graben fill and overlying Miocene postrift strata were deformed during the early to middle Miocene as a result of basin inversion.

Vitrinite reflectance (Ro) data suggest that the penetrated section (generally Miocene postrift) is immature to early mature. Much of the mature source rock has not been penetrated but occurs in the deep synrift half-grabens. Maturity modelling studies suggest that the potential source facies in the synrift is within the oil window and may charge adjacent stratigraphic and structural traps. Besides inversion (Sunda fold) structures, basement drapes form potential plays in the postrift strata. Both these plays must be sourced from lacustrine rocks in the synrift sequence. Potential new synrift plays include hangingwall and footwall fans which could also be sourced from lacustrine rocks in the half-graben deeps.