f Petroleum Systems of the North Malay Basin

The North Malay Basin comprises a 100 km-wide centrallbasinal gas-prone area, flanked on both sides and to the south by mixed oillgas zones. Non-associated gas fields in the central zone (Cakerawala to Bujang Trend) are reservoired mainly in groups D and E, in anticlinal traps formed by basin inversion during late Miocene times. This distribution may be biased by the depth of well penetrations in the basin centre due to the onset of overpressure. Oil occurs in faulted traps along the Western Hinge Fault Zone (Kapal to Beranang Trend), and is especially abundant on the NE ramp margin (Bunga Pakma-Raya Trend) where a separate kitchen may be present. Oil geochemistry reveals three main sources for the oils: lower coastal plain, fluvial marine and lacustrmne source rocks. Most of the oils and condensates in the basin centre and on the Western Hinge Fault Zone are lower coastal plain oils, indicating charge from the basin centre. Lacustrine oils are restricted to the Bunga Pakma-Raya Trend on the NE flank, <br>indicating charge from the basin centre as well as input from a small sub-basin to the northeast. Marine influence was found in oils from the most central position in the basin (Cakerawala-Bumi area). Vitrinite reflectance and basin modelling indicate that hydrocarbons were generated from source rocks within two main stratigraphic intervals: Group H and Group I, which are presently in the peak oil generation and gas generation stages, respectively. Figure 1 shows the distribution of oil and gas fields in relation to present-day groups H and I maturity.